Nutritional Components of Amaranth Seeds and Vegetables: A Review on Composition, Properties, and Uses


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 A few decades ago Amaranthus was rediscovered as a most promising plant genus that may provide high-quality protein, unsaturated oil, and various other valuable constituents. Since then research has focused on various Amaranthus spp. and has been rapidly expanding, and a large number of reports have been published. Several review articles focusing on different aspects, such as botanical, agrotechnological, compositional, biological, chemical, and technological properties, as well as applications and health effects, have also been published since then. This comprehensive review is focused on amaranth composition, antioxidant properties, applications, and processing. The composition includes macrocomponets (lipids, proteins, carbohydrates, and dietary fiber) and other important constituents, such as squalene, tocopherols, phenolic compounds, phytates, and vitamins. These aspects of amaranth studies have not been comprehensively reviewed for a long time.


Rational and effective exploration of sustainable plant resources is an important task for ensuring global food security in the future. Humankind has been using more than 10000 edible species; however, today only 150 plant species are commercialized on a significant global scale, 12 of which provide approximately 80% of dietary energy from plants, and over 60% of the global requirement for proteins and calories are met by just 4 species: rice, wheat, maize, and potato (FAO 2005). Therefore, valorization of valuable, however, sometimes forgotten, crops has been in the focus of many researchers all over the world during the last several decades. Amaranthus (family Amaranthaceae), collectively known as amaranth, is a cosmopolitan genus of annual or short-lived perennial plants, consisting of approximately 60 species, which according to the uses for human consumption can be divided into grain and vegetable amaranths (Mlakar and others 2010).  Amaranth was important food crop in the Aztec, Mayan, and Incan civilizations; however, its production has declined remarkably, after collapsing of the Central American cultures (Bressani 2003; Schoenlechner and others 2008; Alvarez-Jubete and others 2010b). In the study of U.S. National Academy of Sciences entitled Underexploited Tropical Plants with Promising Economic Value, performed in 1975, amaranth was elected from among 36 of the world's most promising crops and identified as a major potential crop; since then, extensive research has been carried out (National Academy of Sciences 1985). Amaranth compared to other grains has the highest amount of protein, twice the content of essential amino acid lysine, more dietary fiber, and 5 to 20 times the content of calcium and iron. The mixture of rice and amaranth (1 : 1) was reported to approach the specifications of FAO/WHO protein (Singhal and Kulkarni 1988).

The number of publications on various aspects of Amaranthus spp., such as cultivation, composition, applications, and health effects, has been steadily increasing; several review articles have summarized the output of expanding research. Teutonico and Knorr (1985) reviewed the results on amaranth composition, properties, and applications, while Stallknecht and Schulz-Schaeffer (1993) focused their review mainly on botany and agronomy of Amaranthus crops. Previously published review articles also discussed the history and uses of amaranth and revealed its potential; however, a lack of sufficient experimental data was indicated as a problem in commercialization of amaranth (Teutonico and Knorr 1985). Therefore, currently amaranth cultivation remains relatively low: A. cruentus in Guatemala, A. hypochondriacus in Mexico, and A. caudatus in Peru and other Andean countries are the main species being cultivated for their seeds (Bressani 2003).

Amaranth is a multipurpose crop supplying high nutritional quality grains and leafy vegetables for food and animal feed; as possessing attractive inflorescence coloration, it also may be cultivated as an ornamental plant (Mlakar and others 2009). Nowadays amaranth could be classified as a new, forgotten, neglected, and alternative crop of great nutritional value; in fact, amaranth has gained increased attention only since the 1970s (Lehmann 1996). Crop importance, botany, and chemical composition were recently briefly reviewed focusing mainly on rheological properties of flours containing amaranth and their suitability for making bread (Mlakar and others 2009).

The studies of  amaranth composition, processing, uses, properties, and health effects have been rapidly expanding during the last decades and much new scientific and technological information has been published. Amaranth, containing fiber, protein, tocols, squalene, and the substances possessing cholesterol-lowering function, is a particularly important crop for developing countries (Johns and Eyzaguirre 2007). For instance, grain amaranth was intensively investigated as a viable crop for marginal areas of Kenya, and it was concluded that A. hypochondriacus, maturing within 60 d of planting, is a preferable species compared to A. caudatus, producing a high-quality grain in too many more days, and A. cruentus that has been shown to be of little use (Gupta and Thimba 1992).

Several review articles have been published, on different aspects of amaranth processing and utilization in Guatemala, Mexico, and Peru (Bressani and others 1992), on germplasm development and agronomic investigations in Mexico (Espitia 1992), and on the nutritional and antinutritional composition of grain and vegetable amaranth leaves in India (Prakash and Pal 1991). A. hypochondriacus was recently very briefly reviewed together with other traditional plant species as a source of functional components (Rivera and others 2010). Nutritive value of pseudocereals and their use as functional gluten-free ingredients, including amaranth, was briefly reviewed by Alvarez-Jubete and others (2010a). The latter review presented recent results on the application of such pseudocereals as amaranth, quinoa, and buckwheat, all possessing excellent nutrient profiles; however, it was noted that commercialization of these products is still rather limited. Good sensory quality gluten-free foods produced from pseudocereals would be important for consumers with celiac disease in order to ensure an adequate intake of nutrients. A wider use of ancient grains in a modern Indian/Asian diet to reduce the occurrence of chronic disease was reviewed by Dixit and others (2011). Physicochemical and digestibility characteristics of starch present in A. hypochondriacus were reviewed by emphasizing the starch after the storage of starchy products, their cooking, and the potential of starch from unconventional sources in the production of resistant starch-rich goods using various treatments (Bello-Pérez and Paredes-López 2009). Health-promoting attributes of A. cruentus were briefly reviewed by Prokopowicz (2001). Most recently, a comprehensive review was published, which is focusing mainly on health effects, such as hypocholesterolemic activity, influence on the immune system, antitumor effect, action on blood glucose levels, effects on liver functions, hypertension, antienemic effect, antioxidant activity, celiac disease, and antiallergic action (Caselato-Sousa and Amaya-Farfán 2012).

The present review is aimed at providing a comprehensive survey of the published results on the following Amaranthus spp. aspects: composition, antioxidant properties, applications, and processing. These aspects of amaranth studies have not been comprehensively reviewed for a long time. The review is mainly based on articles published during the last 2 decades; however, some important reports of earlier times are also included in order to provide results for a longer time perspective.

Oil and Other Lipophilic Constituents

Total content of extractable lipids

Lipids are very important nutritive constituents of Amaranthus seeds, with triacylglycerols (TAGs), phospholipids, squalene, and lipid-soluble vitamins such as tocopherols being the main components in the lipophilic fraction. Various minor components, such as phytosterols, waxes, and terpene alcohols have also been reported in different Amaranthus species. The content of all these components in amaranth seeds primarily depends on plant species and cultivar, whereas the extractable amount of lipids also depends on their isolation procedure and the applied solvent. Processing of amaranth seeds, such as air classification and heat treatments, also influences the content of lipids and their composition. It has been reported that TAGs in the lipid fractions of A. caudatus and A. cruentus seeds isolated with petroleum ether constituted 80.3% and 82.3%. Phospholipids represented 10.2% and 9.1%, diacylglycerols 6.5% and 5.1%, monoacylglycerols 3.0% and 3.5%, and the content of squalene was 4.8% and 4.9% of the oil, respectively (Gamel and others 2007). The lipophilic fraction may be extracted from amaranth seeds with nonpolar organic solvents, such as hexane and petroleum ether using standard procedures, or with dense gases, mainly sub- or supercritical carbon dioxide (SC-CO2). The oil may also be isolated from amaranth seeds by pressing; however, in this case, the recoveries are remarkably lower.

Some earlier performed studies reported the content of lipids in amaranth seeds between 4.8% and 8.1% (Saunders and Becker 1984). However, later investigations showed that it varies in a wider range depending on the species, cultivar, agrotechnological practices, and growing location and may be present at remarkably higher concentrations. For instance, crude fat percentages in 21 accessions of 8 amaranth species varied from 5.2% to 7.7% on the dry basis of the seeds (Budin and others 1996), whereas in another study, which analyzed 14 selections from 4 species (A. caudatus, A. hybridus, A. cruentus, and A. hypochondriacus), it was from 7.7% to 12.8% (Bressani and others 1987b) and from 10.6% to 16.7% (12 accessions) (Kraujalis and Venskutonis 2013a).  The content of lipids in amaranth seeds may be as high as 17.0% and 19.3%, as it was reported for A. spinosus and A. tenuifolius, respectively (Opute 1979; Singhal and Kulkarni 1988). Comparison of 48 A. hypochondriacus and 11 A. caudatus lines demonstrated that the A. caudatus lines had a higher fat content as compared to A. hypochondriacus lines, whereas the lines with higher color a*-values and lower 1000-kernel weight and L*- and b*-values had higher fat contents (Kaur and others 2010). Crude fat content in adapted grain amaranth genotypes “Neuer Typ” and “Mittlerer Typ” (A. hypochondriacus) and “Amar” (A. cruentus) in the Pannonian region of eastern Austria was 5.4% to 8.6%; however, crop density affected neither grain yield nor grain quality (Gimplinger and others 2007).

The accumulation of oil in “Rawa” and “Aztek” A. cruentus varieties was affected by fertilization; the highest content was determined when the plants were treated with the highest level of nitrogen/phosphorus/potassium (NPK) fertilizer. In addition, Aztec variety had a higher content of fat than “Rawa” (Skwaryło-Bednarz 2012). Some effects of NPK fertilizers on the content of fat were also observed earlier in 4 Amaranthus samples of 3 species, although the increasing NPK application level did not have any clear effect, since for both A. cruentus samples, a decrease was observed, while for A. caudatus, there was an increase (Bressani and others 1987a).

For analytical purposes, the lipid fraction is usually isolated from amaranth seeds in a Soxhlet apparatus with nonpolar organic solvents by applying standard extraction procedures. However, the yield of the oil in Soxhlet extraction may also depend on various factors, primarily particle size and process time or the number of extraction cycles. For instance, Lyon and Becker (1987) evaluated the effect of milling on the yield of oil extracted with hexane on a pilot plant scale from the seeds of A. cruentus and determined that it varied from 6.35 (Wiley mill, 20 mesh, 0.841 mm screen) to 7.01% (abrasion mill, 0.36 mm gap). In another study, A. hypochondriacus seeds were milled to obtain the flour able to pass through a 100-mesh (0.149 mm) screen and in this case, lipid yield was from 7.9% to 8.9% (Barba de la Rosa and others 2009). Particle size distribution was not measured in the majority of the previously performed studies, whereas most recently, it was shown that particle size and the milling fraction play a crucial role in the amaranth extraction procedure (Kraujalis and Venskutonis 2013a). High-protein flour fraction that was prepared by milling the seeds of A. caudatus and A. cruentus to fine granule size and subjected to air classification contained more lipids by 42% and 25%, respectively, than the raw material (Gamel and others 2007). Amaranth seeds are protected by a rigid hull that is difficult to remove; therefore, low extraction yield is obtained when the whole seeds are treated. In order to facilitate the extraction process, some special pretreatment procedures, such as instantaneous controlled pressure-prop have been applied. However, it is assumed that very fine grinding, which disintegrates the rigid seeds is an effective method to liberate most of the oil from the seeds, would not require any special pretreatment. The oil contents of A. caudatus var. “Oscar blanco” and var. “Victor” red were reported as only 1.06% and 1.08%, respectively; however, in this case, the extracts were prepared using a polar solvent (methanol) of advantage for other analysis purposes (Conforti and others 2005).

Supercritical fluid extraction using carbon dioxide as a solvent (SCE-CO2) is an alternative technique for the isolation of the lipophilic fraction from oily seeds. It has also been applied for the extraction of amaranth seeds (Bruni and others 2001; He and others 2003; Westerman and others 2006; Ikonnikov and others 2010; Kraujalis and Venskutonis 2013a, b). This method possesses several advantages (nontoxic and nonflammable solvent, inexpensive, and yields high-purity oil) compared with conventional extraction with organic solvents; however, in order to obtain high oil yields, extraction parameters must be carefully selected and optimized. It was shown that the rate of extraction is a function of the solvent flow rate, while the extract yield depends on the flow rate, material pretreatment, process temperature, and pressure. The solubility of amaranth oil was reported to increase with increasing temperature at high pressures, whereas at lower pressures, temperature increase had negative effect on the solubility (Westerman and others 2006; Kraujalis and Venskutonis 2013a). For instance, oil yield from A. cruentus was 4.98 (solvent extraction), 5.25 (30 MPa/70 °C), 4.77 (25 MPa/40 °C), 2.07 (20 MPa/50 °C), and 0.38 g/100 g (15 MPa/70 °C) (He and others 2003). It was also shown that very small amounts of oil could be extracted by SCE-CO2 from undisrupted grains, although SC-CO2 as a solvent possesses high diffusivity. In general, fine grinding increases the extraction rate and oil yield, and smaller particle size usually results in a higher extraction rate. Considering that many factors are involved in SCE-CO2, mathematical optimization methods were used to establish optimal conditions; for instance, application of response surface methodology (RSM) enabled to determine SCE-CO2 parameters for obtaining the highest extract yield from ground amaranth seeds at the optimal conditions of 35.8 MPa pressure, 40 °C temperature, 2.9 SL/min flow rate, and 110 min extraction time; however, extraction time and pressure were the most important factors on extract yield (Kraujalis and Venskutonis 2013a). It is important to note that the moisture content within 0% to 10% had little influence on oil yields at 40 °C and 25 MPa (He and others 2003).

Amaranth seeds may be processed for consumption in different ways and processing parameters may affect the oil. For instance, it was determined that the content of fat in selected varieties of A. cruentus, A. hypochondriacus, A. caudatus, and A. hybridus raw seeds was from 73.0 to 81.1 g/kg, whereas after popping, it slightly decreased and was 67.1 to 77.1 g/kg (Písaříková and others 2005a). Bressani and others (1987c) observed a 3.9% reduction in the lipid content in A. caudatus seeds due to dry heating; however, possible reasons of such findings were not determined.

Fatty acids

The composition of fatty acids in edible oils determines their nutritional, technological, and stability properties. Fatty acid composition of amaranth TAGs was determined in many studies; the percentage variations in individual fatty acids are presented in Table 1. It is obvious that the main fatty acids in all studied amaranth oils were palmitic, oleic, and linoleic. However, their percentage variations in different species and cultivars were quite remarkable. The content of stearic acid was in the range of traces-4.62%, while other minor fatty acids were present in amounts lower than 1%, except for cis-10-heptadecanoic and linolenic acids, which were found in higher levels in some analyzed oils. Thus, the major fatty acids in the oil from 11 genotypes of 4 grain amaranth species were palmitic (19.1% to 23.4%), oleic (18.7% to 38.9%), and linoleic (36.7% to 55.9%) with the degree of unsaturation (S/U ratio) in the range of 0.26 to 0.32 (He and others 2002). Together with palmitic (19.4%), stearic (3.9%), oleic (21.9%), and linoleic (43.9%) acids some epoxy and cyclopropenoid fatty-acids were reported in A. paniculatus seed oil, such as vernolic (epoxy-cis-9-octadecenoic, 7.8%), malvalic [7-(2-octyl-1-cyclopropenyl)heptanoic, 1.5%], and sterculic (2-octyl-1-cyclo-propene-octanoic acid, 1.6%) (Daulatabad and Hosamani 1992). The contents of palmitic, stearic, oleic, and linoleic acids in oils of 14 selections of A. caudatus, A. hybridus, A. cruentus, and A. hypochondriacus were 16.83% to 23.83%, 1.86% to 4.11%, 20.29% to 35.46%, and 38.25% to 57.86%, respectively (Bressani and others 1987b). The effect of A. cruentus variety (5 varieties) and location (3 locations) on the fatty acid content was also studied and it was determined that the percentage of palmitic acid was in the range of 17.06 to 21.35, stearic 3.05 to 3.80, oleic 20.26 to 32.01, and linoleic 33.56% to 43.88 g%. However, statistical evaluation of average contents did not reveal any significant differences neither between the varieties nor between the localities (Berganza and others 2003). The content of essential fatty acids in amaranth was shown to increase by presowing electromagnetic stimulation with laser light or/and magnetic field applied to seeds (Sujak and Dziwulska-Hunek 2010).

Table 1. Fatty acid composition of Amaranthus spp
     A. cru-Mean: 21A. hypo-A. cru-A. cru- 11A. cru-
 AmaranthA. cru-A. cru-Amaranthentusaccessionschon-entusentus12 A. spp.genotypes, 4entus
Fatty acid (%)[1]entus [2]entus [3][4][5][6]driacus [7][7][8]accesions [9]species [10][11]
  1. 1 Alvarez-Jubete and others (2009); 2 Sujak and Dziwulska-Hunek (2010); 3 Berganza and others (2003); 4 Bartkowiak and others (2007); 5 Yánez and others (1994); 6 Budin and others (1996); 7 Jahaniaval and others (2000); 8 Escudero and others (2004); 9 Kraujalis and Venskutonis (2013a); 10 He and others (2002); 11 León-Camacho and others (2001).

Lauric, C12:0 0.49         0.7
Myristic, C14:0 0.24 0.12  0.21 to 0.290.27 0.13 to 0.28Tr-0.30.2
Palmitic, C16:020.9 ± 0.317.0217.1 to 21.320.891918.521.4 to 23.822.220.7514.04 to 25.9119.1 to 23.420.4
Palmitoleic, C16:1 0.09 0.29  0.10 to 0.190.1116.570.33 to 0.60 0.4
Heptadecanoic, C17:0   0.08     0.07 to 0.15 0.1
cis-10-Heptadecanoic, C17:1         0.59 to 1.25 0.7
Stearic, C18:04.1 ± to 3.84.473.43.23.11 to 3.983.573.793.17 to 4.62Tr-1.13.9
Oleic, C18:123.7 ± 0.119.1320.3 to 32.021.74342222.8 to 31.530.123.5720.18 to 36.2218.7 to 38.932.1
C18:1 w7           1.2
Linoleic, C18:2c47.8 ± 0.224.8433.5 to 43.943.133344.839.4 to to 46.9536.7 to 55.938.2
Linolelaidic, C18:2t         0.17 to 0.34  
Linolenic, C18:30.9 ± 0.01.29 0.76 0.20.65 to 0.930.69 0.51 to 1.21 0.7
Arachidic, C20:00.8 ± 0.0tr 0.76  0.56 to 0.890.68 0.53 to 0.92 0.8
cis-11-Eicosenoic, C20:1 tr 0.18  0 to 0.24  0.15 to 0.65 0.3
cis-11,14-Eicosadienoic, C20:20.3 ± 0.00.1          
Arachidonic, C20:4 tr       0.09 to 0.29  
Behenic, C22:00.4 ± 0.0tr    0.14 to 0.320.24 0.11 to 0.35 0.3
Lignoceric, C24:00.4 ± 0.0nd 0.26     0.11 to 0.24  
All others          0.5 to 2.3 
Saturated26.9 ± 0.219.8720.1 to 25.126.322.421.726.8 to 28.626.9624.5420.1 to 30.9 26.1
Monounsaturated23.9 ± 0.119.2220.3 to to 23.930.2140.1420.8 to 38.1 34.7
Polyunsaturated49.1 ± 0.226.3333.5 to 43.943.933.04547.0 to 50.042.8935.3140.2 to 49.2 38.9

The oils of amaranth were compared with many other edible oils. It was reported that the yellow oil obtained with hexane from the seeds of A. cruentus was similar in appearance and composition to corn oil (Lyon and Becker 1987). Later, fatty acid profiles of amaranth TAGs isolated from 21 Amaranthus accessions (8 species) were compared to those of barley, corn, buckwheat, oat, lupin, and wheat and it was concluded that amaranth oil was most similar to buckwheat and corn oils (Budin and others 1996). Cluster analysis, which was performed for the major fatty acids of 19 edible oils, including the oil isolated from A. cruentus, indicated that amaranth was placed in 1 of the 4 groups, close to wheat and barley; the profile of fatty acids at the sn-2 position in amaranth was also very similar to that of cereals and with some similarity to cottonseed and sesame (León-Camacho and others 2001).

Amaranth oil contains a high degree of unsaturation. Therefore, the content of fatty acids may change during processing. For instance, it was reported that during puffing or popping of A. cruentus seeds, the percentage of unsaturation decreased from 75.5% to 62.3%, the quantity of linoleic acid decreased from 46.8% to 27.0%; however, the percentage of squalene increased by 15.5% (Singhal and Kulkarni 1990). Popping and cooking reduced the lipid contents in A. caudatus and A. cruentus seeds by 5.6% and 7.7%, and by 1.7% and 3.7%, respectively. However, the main TAGs, POO and PLO, did not change during air classification and heat treatments, and regardless of a high degree of unsaturation A. caudatus oil showed good oxidation stability, which was even better than that of sunflower oil (Gamel and others 2007). The A. cruentus flour and the concentrate obtained by extraction at pH 11 and precipitation at pH 4.5 contained 75.44% and 56.95% unsaturated fatty acids, respectively (Escudero and others 2004).

SCE-CO2 of A. caudatus seeds and ultrasound as a coadjuvant in the extraction process did not have significant effects on the profile of the fatty acids as compared with traditional methods (Bruni and others 2002). The data obtained on wild A. caudatus from Ecuador were compared with seed oil of Italian A. caudatus using SCE-CO2 and ultrasound-enhanced extractions. SCE-CO2 at 40 MPa was the most efficient extraction method in terms of total extract yield; however, fatty acid compositions were similar (Bruni and others 2001).

The percentage distribution of fatty acids in TAGs is important for the physical and technological properties of oil; however, the composition of amaranth TAGs has been rarely studied, probably because of the difficulties in obtaining good separations due to the formation of the so-called “critical pairs” having the same equivalent carbon number (ECN) (León-Camacho and others 2001). PLL, POL, OLL, OOL, POO, and LLL were identified as the main TAGs in 3 amaranth species by Jahaniaval and others (2000). Later, it was shown that for amaranth with high amounts of oleic and linoleic acids, the highest ECN corresponds to ECN46, followed by ECN48 and ECH44, while the values of major carbon numbers (C50-C54) are near to or within the ranges of cottonseed oil. The percentages of TAGs in A. cruentus oil were reported as follows: ECN42: LLL (4.0%), LnLO (0.6%), LnLP (0.5%); ECN44: OLL (12.1%), PLL (13.8%); ECN46: OLO (11.8%), PLO + SLL (20.0%), PPL (7.5%); ECN48: OOO (7.9%), POO + SOL (12.5%), PLS (2.1%), POP (3.8%), SOO (2.2%), SOS (1.3%) (León-Camacho and others 2001). The main TAG in A. caudatus was PLO (26.7%) followed by POO (21.1%), PPL (16.3%), PLL + PLnO (11.8%), POP (7.7%), OOO (6.2%), OLO (5.4%), POS (2.2%), SOO (1.6%), and OLL + OLLn (1.0%); whereas the quantitative composition of TAGs in A. cruentus was different, consisting of PLO (25.4%), POO (16.7%), PPL (22.6%), PLL + PLnO (16.7%), POP (6.5%), OOO (3.6%), OLO (2.6%), POS (2.7%), SOO (0.8%), and OLL + OLLn (2.4%) (Gamel and others 2007).

To improve functional properties, amaranth oil was enzymatically interesterified as a structured lipid, first by increasing its palmitic acid content at the sn-2 position by using Novozyme 435 lipase and afterward incorporating docosahexaenoic acid (DHA), mainly at the sn-1,3 positions, by using Lipozyme RM IM (Pina-Rodriguez and Akoh 2009). The DHA-containing customized amaranth oil was successfully used as a partial fat substitute or complement for milk-based infant formula; however, measurement of the oxidative stability index of the extracted fats from prototype, control, and commercial infant formulas showed that amaranth SL was the least stable compared to other fat analogs (Pina-Rodriguez and Akoh 2010).

Leafy parts of amaranth, as of many other vegetables, contain low amounts of lipids and therefore were rarely analyzed for their composition. It was reported that in the lipophilic fraction of A. retroflexus vegetables isolated with hexane from the crude aqueous alcoholic extract yielding 15%, linoleic and linolenic acids constituted 4.19 ± 0.35% and 3.71 ± 0.29% (Conforti and others 2012).


Squalene is an intermediate triterpene in the cholesterol biosynthesis pathway; its biological and pharmacological activities as well as potential uses in cosmetic dermatology were comprehensively reviewed by Huang and others (2009). Shark liver oil is considered as the richest squalene source; however, reasonable amounts are also found in olive, wheat-germ, palm, amaranth, and rice bran oils. Squalene, as the main component of skin surface polyunsaturated lipids, shows some advantages for the skin as an emollient, antioxidant, hydrating, and antitumor agent. It is also used as a material in topically applied formulations such as lipid emulsions and nanostructured lipid carriers (Huang and others 2009). Amaranth is a rich source of squalene; therefore, many studies were focused on the isolation and determination of this component in various plant species and cultivars.

The content of squalene in A. cruentus of 5 varieties and 3 locations was in the range of 2.26% to 5.67% (Berganza and others 2003); its concentrations in total lipids of 11 genotypes of 4 grain amaranth species ranged from 3.6% in A. hypochondriacus to 6.1% in A. tricolor (He and others 2002). It was demonstrated that the variation in the squalene content may be remarkable even for the same species: the seeds of “Oscar blanco” and “Victor red” varieties of A. caudatus contained 2.2% and 7.5% of squalene, respectively (Conforti and others 2005). However, it should be noted that in this case, squalene was determined in the unsaponifiable fraction of the hexane extract, which was obtained by partitioning crude methanolic extract; the total amounts of squalene measured in this study were very low, only 59 and 203 mg; most likely, the lipophilic compounds were not exhaustively isolated with the polar solvent methanol (Conforti and others 2005).

SCE-CO2 was also used for the isolation of squalene and it was reported that the effects of solvent temperature and pressure on squalene yield were different from those on oil yield. For instance, the highest squalene yield (0.31 g/100 g grain) and concentration in the SC-CO2 extract (15.3% compared with 6% in extract obtained by solvent extraction) was obtained at 50 °C and 20 MPa, although the oil yield under these conditions was only 2.07 g/100 g. (He and others 2003). The yield of squalene from A. paniculatus grains isolated by SCE-CO2 was dependent on particle diameter, extraction pressure, temperature, and time; maximal yield of 1.36 mg/g was achieved at the highest 55 MPa pressure and 100 °C during 90 min of extraction (Bhattacharjee and others 2012). Selection of extraction parameters by using RSM enabled to obtain squalene-enriched extracts containing up to 12.3% of squalene (0.71 to 1.81 g/100 g seeds) (Kraujalis and Venskutonis 2013a). In the same study, it was also observed that at 40 °C, 35.8 MPa, and CO2 flow rate of 2.9 SL/min in 30 min squalene concentration was the highest (14.43%) and oil yielded up to 6.5 g of oil/100 g, whereas continuing the same extraction the total amount of isolated squalene did not change, while oil content increased up to 15.5 g/100 g after 110 min, thus resulting in a decrease of squalene concentration in the final extract by its dilution with TAGs. The squalene-enriched fraction may also be obtained by gradual decrease of solvent pressure in the extraction system separators (Kraujalis and Venskutonis 2013b). These findings conclude that squalene solubility in SC-CO2 is better than that of oil and squalene-enriched fraction may be obtained by interrupting the extraction process at some point. However, to obtain purified fractions of squalene, multistep procedures are required. In one of the studies, it was preconcentrated by saponification of crude oil and further purified by silica gel column chromatography of unsaponifiables; using this procedure squalene content increased from 4.2% in the crude oil to 43.3% in the unsaponifiables, and, after chromatographic separation, the purity of certain fractions was as high as 98%. Finally, combining the fractions rich in squalene gave a 94% squalene concentrate, with 90% yield (He and others 2002).

Processing of amaranth seeds may have some influence on the distribution and content of squalene; for instance, it was shown that squalene tends to distribute between the fine and the coarse fractions during air classification (Gamel and others 2007). In the same study, cooking caused a slight increase in the squalene content of A. caudatus and A. cruentus, while popping increased the squalene content by 26.5% and 14.5%, respectively. The processing stability of squalene in amaranth and the antioxidant capacity of the oil-rich fraction of amaranth were studied and it was reported that squalene was stable during all of the continuous puffing up to 290 °C and roasting up to 150 °C for 20 min with a maximum loss of 12% during roasting (150 °C, 20 min) and no loss during puffing (Tikekar and others 2008). The very low lipophilic oxygen radical-scavenging capacity (L-ORAC) values determined in the same study for pure squalene showed it to be a weak antioxidant, whereas the lipophilic extract of amaranth showed higher antioxidant activity as compared to pure squalene at the same concentration, suggesting that tocotrienols and other minor ingredients played an important role as antioxidants. Squalene was detected both in the flour (6.23%) and the concentrate (9.53%) oils obtained from A. cruentus by extraction at pH 11 and precipitation at pH 4.5 (Escudero and others 2004).

Tocopherols and tocotrienols

A group of lipid-soluble compounds with the common name “tocols” and possessing vitamin E and antioxidant activities are present in all oil-containing seeds; however, their content and composition are quite different in different plant species and varieties. So far as the biological effectiveness of tocopherol and tocotrienol isomers may differ in the range of 2 orders, it is important to know both the total amount of tocols and the percentage distribution of individual isomers (Table 2). The first reports on tocotrienols in amaranth seeds were published in the 1990s, using normal-phase HPLC with fluorescence detection. The most common tocols in the seeds of 13 A. cruentus and A. hypochondriacus accessions were α-tocopherol, β-tocotrienol, and γ-tocotrienol, while some A. cruentus accessions also contained δ-tocotrienol (Lehmann and others 1994). Later, it was reported that β-tocopherol was present at remarkably higher concentrations in A. cruentus grown in Austria (León-Camacho and others 2001). It was observed that the content of tocols was different in the seeds of different origin: A. cruentus grain-types of Mesoamerican origin had significantly greater levels of 4 tocols than did A. cruentus of African vegetable-types. Comparing with many cereal grains, amaranths accumulate significant amounts of both β- and γ-tocotrienols, whereas β-tocopherol in the early studies has not been reported. Fresh amaranth samples of both species tended to have higher levels of tocotrienols than samples stored for 2 y (Lehmann and others 1994). Later, vitamin E profiles of 21 amaranth accessions belonging to 7 species were compared to those of barley, buckwheat, corn, lupin, oat, and wheat oils (Budin and others 1996). In this study, the contents of α, β, δ-tocopherols, α, γ, δ-tocotrienols, and the sum of γ-tocopherol and β-tocotrienol were in the ranges of 0.78 to 2.95, 0.71 to 6.74, 0.11 to 2.05, 0.00 to 0.11, 0.00 to 0.06, 0.00 to 0.03, and 0.06 to 0.68 mg/100 g seed (wet basis), respectively. Compared to other grains, the mean values of α, β, and δ-tocopherols in amaranths were remarkably higher. It is also interesting to note that β-tocopherol that was not found in the previous study of A. cruentus (Lehmann and others 1994) was determined in the seeds analyzed by Budin and others (1996) in the same species (1.01 to 2.14 mg/100 g) at slightly lower amounts than α-tocopherol (1.81 to 2.95 mg/100 g). Most recently, it was shown that the use of fertilizers (90 N, 60 P2O5, 60 K2O; 130 N, 70 P2O5, 70 K2O kg/ha) increased the total amount of tocopherols in “Aztek” variety of A. cruentus (Table 2). The differences in the content of tocopherols between the same species from different locations were shown for seed oil of wild A. caudatus from Ecuador and A. caudatus of Italian origin: SCE-CO2 at 40 MPa was the most efficient extraction method in terms of tocopherol yield, and the seeds of Ecuadorian genotype contained higher levels of tocopherols than Italian samples (Bruni and others 2001).

Table 2. The content of tocopherols and tocotrienols in Amaranthus
  1. 1 Skwaryło-Bednarz (2012); 2 Bruni and others (2002); 3 Ozsoy and others (2009); 4 León-Camacho and others (2001); 5 Lehmann and others (1994); 6 Kraujalis and Venskutonis (2013b).

α-TocopherolA. cruentus, A. hypochondriacus seeds2.97 to 15.65 mg/kg5
β-TocotrienolA. cruentus, A. hypochondriacus seeds5.92 to 11.47 mg/kg5
γ-TocotrienolA. cruentus, A. hypochondriacus seeds0.95 to 8.69 mg/kg5
δ-TocotrienolA. cruentus seeds0.01 to 0.42 mg/kg5
α-TocopherolA. cruentus, var. Rawa seeds (depending on NPK)10.2 to 17.4 mg/kg dw1
β-TocotrienolA. cruentus, var. Rawa seeds (depending on NPK)38.4 to 48.5 mg/kg dw1
α-TocopherolA. cruentus, var. Aztec seeds (depending on NPK)17.8 to 20.6 mg/kg dw1
β-TocotrienolA. cruentus, var. Aztec seeds (depending on NPK)35.4 to 39.8 mg/kg dw1
γ-TocotrienolA. cruentus, var. Aztec seeds (depending on NPK)2.0 to 4.0 mg/kg dw1
δ-TocotrienolA. cruentus, var. Aztec seeds (depending on NPK)15.5 to 18.4 mg/kg dw1
α-TocopherolA. caudatus seeds MeOH/Hex, ultrasound and SCE-CO212.5 to 34.81 mg/kg2
β-TocopherolA. caudatus seeds MeOH/Hex, ultrasound and SCE-CO219.55 to 43.86 mg/kg2
γ-TocopherolA. caudatus seeds MeOH/Hex, ultrasound and SCE-CO20.6 to 2.2 mg/kg2
δ-TocopherolA. caudatus seeds MeOH/Hex, ultrasound and SCE-CO221.7 to 48.79 mg/kg2
TotalA. caudatus seeds MeOH/Hex, ultrasound and SCE-CO263.7 to 129.27 mg/kg2
α-TocopherolA. cruentus seeds from Austria248 ppm4
β-TocopherolA. cruentus seeds from Austria546 ppm4
δ-TocopherolA. cruentus seeds from Austria8 ppm4
α-TocopherolA. lividus: stems/leaves/flowers: W-End3
α-TocopherolA. lividus: stems/leaves/flowers: MeOH-E31.43 ± 0.92 mg/g dw3
α-TocopherolA. lividus: Stems/leaves/flowers: EtAc-E7.12 ± 0.15 mg/g dw3
α-TocopherolAmaranth seeds, depending on SFE-CO2 parameters2.37 ± 0.06 to 9.79 ± 0.09 mg/kg6
β-TocopherolAmaranth seeds, depending on SFE-CO2 parameters82.42 ± 5.77 to 211.8 ± 1.79 mg/kg6
γ-TocopherolAmaranth seeds, depending on SFE-CO2 parameters12.36 ± 0.18 to 57.07 ± 0.67 mg/kg6
δ-TocopherolAmaranth seeds, depending on SFE-CO2 parameters14.89 ± 0.44 to 38.59 ± 0.15 mg/kg6

Traditional methods were compared with SCE-CO2 and the use of ultrasound as a coadjuvant in the extraction process; qualitatively acceptable results in the extraction of tocols were obtained in the case of using ultrasound equipment more rapidly and more economically (Bruni and others 2002). SCE-CO2 produced solvent-free extracts, reduced the risk of degradation of thermolabile components, and gave quantitatively better yields in shorter times. The highest yield of tocopherols (317.3 mg/kg seeds) was obtained at 55 MPa by adding 5% of cosolvent ethanol; however, fractionation of extracts by pressure decrease in the separators was not very effective; the highest concentration of tocopherols in the richest fraction was 7.62 mg/g, which was only by 23% higher than in the nonfractionated extract (Kraujalis and Venskutonis 2013b).

Sterols and other lipophilic constituents

Sterols are commonly present in oils and fats; however, the data on sterol composition in Amaranthus spp. are rather scarce. Fifteen sterols were quantified in A. cruentus from Austria; cholesterol, brassicasterol, campestanol, Δ5,23-stigmastadienol, sistostanol, and Δ5,24-stigmastadienol being in trace levels, whereas the others 24-methylen-cholesterol, campesterol, stigmasterol, Δ7-campesterol, clerosterol, β-sitosterol, Δ5-avenasterol, Δ7-stigmastenol, and Δ5-avenasterol constituted 0.3, 1.6, 0.9, 24.8, 42.0, 1.3, 2.0, 15.2, and 11.9%, respectively (León-Camacho and others 2001). Taraxerol (348.7 ppm), dammaradienol (189.0 ppm), β-amyrin (213.8 ppm), gramisterol 9499.0, cycloartenol (401.8 ppm), 24-methylene-cycloartanol (446.7 ppm), citrostadienol (320.5 ppm), and 4 unidentified terpenic alcohols and methyl sterols at the total concentrations of 34.9, 35.6, 49.2, and 24.6 ppm were also found in A. cruentus (León-Camacho and others 2001). A number of saturated (13) and unsaturated (10) with 1 double bond hydrocarbons (C21-C33) were reported in A. cruentus crude oil by high-resolution GC-MS at the concentrations ranging from 1.91 to 64.99 ppm in the same study. The total content of polycyclic aromatic hydrocarbons (PAHs) in cold pressed amaranth oil was reported 101.60 ± 3.22 mg/kg, with dominating light PAHs (phenanthrene, anthracene, fluoranthene, and pyrene) which constituted 81.55 ± 1.93 mg/kg (Ciecierska and Obiedziński 2013).

Proteins, Peptides, and Amino Acids

General characterization

Ingestion of gluten from wheat, rye, barley, and other closely related cereal grains triggers the immune-mediated celiac disease in genetically susceptible individuals, and therefore such individuals need gluten-free diet (Zannini and others 2012). The quality of baked goods highly depends on gluten, an essential structure-building protein; therefore, its replacement is a complicated technological task. Easily digestible albumins and globulins are the main components of highly nutritive amaranth seed proteins, which have been considered as an important candidate for such replacement. Chemical composition and nutritional properties of amaranth, quinoa, and buckwheat proteins, as well as their evaluation from the allergenicity point of view, were reviewed by comparing them with other protein sources (Schoenlechner and others 2008). The contents of proteins and their derivatives have been widely studied and these studies revealed the variations in protein content between different plant species and varieties, for example, as it was shown in the case of 25 A. caudatus cultivars (Imeri and others 1987). Protein content in 14 selections of 4 amaranth species (A. caudatus, A. hybridus, A. cruentus, and A. hypochondriacus) varied from 12.5% to 16.0% (Bressani and others 1987b), a 13% to 21% variation was observed in wild and cultivated forms of amaranth; besides albumins and globulins, the proteins were also composed of 20.8% alkali-soluble glutelins with similar nutritive value and 12% alcohol-soluble prolamins that are lacking in essential amino acids (Zheleznov and others 1997). Among the miscellaneous foods analyzed, A. paniculatus seeds had a protein content of 22 g/100 g (Rajyalakshmi and Geervani 1994). A. molerosa grains were studied in biochemical experiments with various cultivars of 12 cereal species, one buckwheat and one amaranth, and it was determined that amaranth had 15.4% protein of a favorable amino acid composition with the highest content of Met, Lys, and Arg. It was suggested that adding whole meal of amaranth and naked oat could supplement the poor Met and Lys contents in common wheat (Matuz and others 2000a). In addition, protein electrophoretic patterns and immunoblot analysis of 30 cereal and noncereal grain samples showed that no reactivity against the rabbit antigliadin (wheat) antibodies was observed against the buckwheat and amaranth samples (Matuz and others 2000b). Two commercial (“Tulyehualco” and “Nutrisol”) and 2 new (DGETA and “Gabriela”) varieties of A. hypochondriacus were grown in the Mexican Highlands zone: “Gabriela” contained the highest protein content (17.3%), but all varieties had an adequate balance of essential amino acids (Barba de la Rosa and others 2009). The analysis of 48 A. hypochondriacus and 11 A. caudatus lines revealed that A. caudatus lines had a higher protein content than A. hypochondriacus lines, while the Amaranthus lines with higher color a*-values and lower 1000-kernel weight, L*- and b*-values had a higher protein content (Kaur and others 2010). Eight groups of A. cruentus and A. hypochondriacus grain samples grown in Hungary and Austria were studied and it was found that a difference between the lowest (14.23%) and highest (17.40%) protein content was relatively large, suggesting that breeding might be a potential mean for increasing the protein content (Tömösközi and others 2009). Cooking and popping of A. caudatus and A. cruentus seeds decreased the fraction of albumins + globulins (water-soluble) and the fraction of prolamins (alcohol-soluble) in both species, while germination significantly reduced the levels of all fractions except the albumins + globulins (Gamel and others 2005). The in vitro digestibility of protein was improved after the extrusion process in “Centenario” and “Oscar Blanco” varieties of Andean native grain, called kiwicha (A. caudatus) (Repo-Carrasco-Valencia and others 2009).

Proteins of amaranth leafy parts were not studied so intensively, although their nutritional value was shown to be also quite high: the chemical score of the essential amino acids from proteins of the leaves of A. dubius flour consisting of albumins (73.42%), globulins (6.60%), prolamins (6.47%), and glutelins (6.41%) was 92.83% (Rodríguez and others 2011). Protein contents were evaluated in the foliage of 61 accessions of grain and vegetable types Amaranthus (10 species in total): variation for leaf protein was 14 to 30 and 15 to 43 g/kg (fresh weight) in vegetable and grain types, respectively. Leaf protein of some high-carotenoid lines had a well-balanced amino acid composition with high content of Lys (40 to 56 g/kg) (Prakash and Pal 1991).

Amaranth protein profiles were studied using gel filtration chromatography and various types of electrophoresis. PAGE of amaranth seed proteins gave 38 bands (buffer pH 3.2), which by their mobility were tentatively assigned to A, B, C, and D zones, whereas by protein patterns, all Amaranthus species were assigned to 7 biotypes (Zheleznov and others 1997). Furthermore, the cytogenetic and electrophoretic comparison enabled to determine the degree of diversity among amaranth forms; the phylogenetic relationship between A. paniculatus and A. hybridus was confirmed. A relationship was also supposed between these 2 species and A. lividus, and between A. powellis and A. deflexus, which by their electrophoretic patterns were assigned to the same biotype (Zheleznov and others 1997). The studies of physicochemical properties of 11S globulin (one of the most important and abundant storage proteins of the amaranth seed) suggested that the cumulative effects of many factors are responsible for its high thermal stability, whereas the balance between surface hydrophobicity and hydrophilicity is important for good emulsifying property (Tandang-Silvas and others 2012).

The protein profile and the amino acid composition of 11 species (A. viridis, A. powellii, A. muricatus, A. deftexus, A. blitoides, A. graecizans, A. retroflexus, A. albus, A. blitum, A. cruentus, and A. hypochondriacus) from wild populations (southwest of Spain) were studied by gel filtration chromatography and denaturing electrophoresis, and it was found that the profiles were similar in all species, with small variations in the molecular weights and amounts of the main seed proteins (Juan and others 2007). In this study, 6 main fractions of around 300, 180, and 120 kDa, between 40 and 50 kDa, 20 and 30 kDa, and below 10 kDa were observed, while the electrophoretic analysis showed peptides grouped into 3 main fractions, between 50 and 64 kDa, 33 and 37 kDa, and 18 and 25 kDa. The most balanced amino acid compositions were observed in A. muricatus, A. blitum, and A. powellii, while A. hypochondriacus and A. graecizans showed the most deficient amino acid composition with limitations in 5 essential amino acids (Juan and others 2007).

The application of NPK fertilizers increased protein content in A. caudatus (Peru) from 12.35% to 14.50% but not in other tested amaranth species. The fertilizers did not affect protein quality either in raw or processed grain (Bressani and others 1987a). With increasing N fertilization rate (120, 180, and 240 kg N/ha), crude protein and true protein increased in A. hypochondriacus forage (Abbasi and others 2012). The Pacesetter Grade B organic fertilizer and organic manures kola pod husk, alone or combined with reduced level of NPK, generally increased crude protein significantly on immediate and residual basis; however, the organic fertilizers had more residual effect than NPK. For instance, the organic manures kola pod husk applied with NPK at the ratio of 75 : 25 resulted in higher crude protein content by 19.8% and 14.9% in A. cruentus grown on 2 soil types in Lagos, Nigeria (Makinde and others 2010a, b). The possibilities of improving the composition and amino acid content of amaranth seeds were demonstrated using the electromagnetic stimulating methods; thus, presowing stimulation by He–Ne laser light and magnetic field resulted in increase of dry matter, crude protein, crude fiber, and crude ash in the seeds of amaranth (Sujak and others 2009).

Amino acids and peptides

As it was already mentioned, amaranth proteins contain high amounts of some essential amino acids; however, their contents depend on plant species and cultivar (Table 3). For instance, the content of Lys in proteins of 14 selections of A. caudatus, A. hybridus, A. cruentus, and A. hypochondriacus varied from 0.73% to 0.84%, with Trp values ranging from 0.18% to 0.28% (Bressani and others 1987b). Amaranth amino acid composition profile was shown to be generally closer to Leguminosae than to cereal grains, except for sulfur-containing amino acids being present in higher amounts in amaranth than in legumes. The available Lys content might be reduced by heating amaranth seeds (as with popping); however, differences in initial sugar and moisture contents of grain influencing the rate of potential Maillard reaction may be the reason of some contradictory data published in the literature on this matter (Tömösközi and others 2009).

Table 3. Amino acid composition of Amaranthus spp
        A.  A.A.
 FAOA.A.A. A.A.hypochonA.A.hypochonhypochon
 FAO/OMS/caudatuscruentuscruentusA. sppcruentuscruentusdriacuscaudatushybridusdriacusdriacus*
 mg AA/gg/100 g mg AA/g        
Amino acidproteinproteinmg/g Nproteing/kgg 16/g Ng 16/g Ng 16/g Ng 16/g Ng 16/g Ng 16/g Nμg/g
  1. *free amino acids; 1 Del Valle and others (1993); 2 Bressani and others (1989); 3 Escudero and others (2004); 4 Písaříková and others (2005b); 5 Sujak and others (2009); 6 Písaříková and others (2005a); 7 Dodok and others (1997); 8 Nimbalkar and others (2012).

Isoleucine283.6, 4.2226305.23.43.6,, 3.22.71 ± 0.693.20 ± 0.16
Leucine665.7, 6.4356587.95.46.2,, 5.84.20 ± 0.573.23 ± 0.16
Lysine584.8, 5.2351829., 7.85.95 ± 0.103.33 ± 0.17
Sulfur amino acids254.5, 4.7248366.44.55.1,, 5.9  
Cysteine    4.2 3.1,, 3.6 4.6 ± 0.23
Methionine    2.2, 2.30.64 ± 0.384.09 ± 0.20
Aromatic amino acids637.2, 7.0490630.37.1      
Phenylalanine          4.70 ± 0.304.17 ± 0.21
Tyrosine          3.72 ± 0.172.3 ± 0.12
Threonine343.3, 3.42372763., 5.03.25 ± 0.5710.7 ± 0.54
Tryptophan111.1, 1.87618ndnd    1.82 ± 0.047.79 ± 0.39
Valine354.5, 4.6256326.84.24.8,, 4.93.85 ± 0.823.78 ± 0.19
Histidine19  252.832.0,, 1.63.80 ± 0.021.89 ± 0.09
Arginine  8312.810.812.7, 13.214.513.515.6, 13.99.49 ± 0.313.19 ± 0.16
Alanine  348., 5.83.30 ± 0.47 
Aspartic acid  7113.28.510.0, 10.410.79.610.2, 10.58.20 ± 1.637.28 ± 0.36
Glutamic acid  1432514.415.5, 16.617.715.816.1, 16.814.55 ± 0.629.2 ± 0.46
Glycine  67206.814.3, 14.715.213.213.2, 15.06.77 ± 0.49nd
Proline  374.14.24.6, ± 0.211.23 ± 0.06
Serine  54115.78.8,, 8.84.85 ± 0.761.03 ± 0.05

The effects of heat treatment on amino acid content were evaluated in grain of A. cruentus, A. hypochondriacus, A. caudatus, and A. hybridus (6 varieties in total), cultivated in the Czech Republic. The differences in amino acid composition were more evident between 2 A. hybridus varieties, while for 2 studied A. cruentus varieties, it was quite similar, except for Pro (Písaříková and others 2005a). However, comparing A. hyprochondriacus grown in the Czech Republic with earlier analyzed same species from Slovakia (Dodok and others 1997), remarkable differences in the content of amino acids were observed (Table 3). Heat-treated and untreated grains contained high contents of Lys and Arg, a satisfactory content of Cys and lower levels of Met, Val, Ile, and Leu (the latter 3 appeared as limiting). An essential amino acid index of amaranth protein (90.4%), which is almost comparable with egg protein decreased to 85.4% after heat treatment by popping at 170 to 190 °C for 30 s; the significant decrease of the essential amino acid (Val and Leu) contents was also observed.

The relatively high content of essential amino acids in amaranth grain is favorable for its use as a substitution for meat-and-bone food/feed (Písaříková and others 2005a). In comparison with fine wheat flour, whole amaranth flour from A. hypochondriacus contains high Lys content (5.95 compared with 2.90 g/16 g N) and a higher amount of some other essential amino acids (Dodok and others 1997). The average protein efficiency ratios (PERs) of 14 selections of amaranth seeds processed by hot-water soaking for 20 min followed by drum-drying were 2.45 for A. caudatus selections, 2.34 for A. hybridus, 2.36 for A. cruentus, and 2.33 for A. hypochondriacus; however, these differences were not statistically significant (Bressani and others 1987b). Protein quality was highest in the popped sample of A. caudatus (net protein ration, NPR 3.19), followed by the flaked (NPR 2.78), the roasted (NPR 2.24), and the raw (NPR 1.73) samples; these values were related to available Lys (Bressani and others 1987c). Extruded amaranth grains were shown to have better PER and NPR indexes than raw or toasted samples (Ferreira and Arêas 2004).  After popping A. caudatus and A. cruentus seeds, the true protein content decreased by 9% and 13%, respectively, while among the amino acids, the loss of Tyr was the highest, followed by Phe and Met; in addition, Leu was the first limiting amino acid in the raw samples, followed by Lys, on the contrary to the popped samples (Gamel and others 2004). During germination, the amounts of Asp acid, Ser, and Ala in A. caudatus and A. cruentus seeds increased, while those of Thr, Arg, and Tyr decreased; however, the treatments did not affect the polypeptide bands of the high protein flour compared with the raw seed flours (Gamel and others 2005).

Comparison with the FAO pattern protein revealed that the concentrate isolated from A. cruentus by extraction at pH 11 and precipitation at pH 4.5 did not have a deficiency in the limiting amino acids, while the flour had Leu, Thr, and Val, with chemical scores of 78, 87, and 90, respectively; the flour and the concentrate had high content of Lys, and therefore these products may be valuable complements for cereal flour (Escudero and others 2004).

Free amino acids that may play some role in the Maillard reaction during thermal treatment of amaranth or other products with amaranth addition were also studied by LC–MS/MS (Table 3) and it was determined that their content in A. hypochondriacus was from 0.61 ± 0.03 for ornithine to 10.7 μg/g for Thr (Nimbalkar and others 2012).

The crude water-soluble extract of amaranth seeds, containing 4 novel antifungal peptides, had minimal inhibitory concentration of 5 mg peptides/mL and inhibited a large number of fungal species isolated from bakeries. The inhibitory activity was confirmed during long-term storage of gluten-free and wheat flour breads under pilot plant conditions (Rizzello and others 2009). Generally, increase in the level of Leu, Lys, Val, and Phe + Tyr was observed by presowing stimulation of amaranth seeds by He-Ne laser light and magnetic field, while the levels of Arg, Glu, and Ala decreased, and the levels of Cys, Thr, Ile, His, and Pro were not affected (Sujak and others 2009).

Amaranth protein concentrates, their fractionation, and properties

Amaranth seeds as a good source for high-quality proteins are a valuable raw material for the preparation of protein concentrates (APCs). High-protein amaranth flour yielding 38% to 39% and containing 26% to 28% protein, 10% to 16% fat, and 40% to 52% starch was produced by enzymatic process with commercial preparations of α-amylase and glucoamylase (Paredes-López and others 1990). High-protein flour may be obtained by a simple air classification: for instance, at 23 °C, filter pressure 2 mbar, centrifugation at 8000 × g, and airflow rate 80 m3/h, the high-protein flour, passing through a 115-mesh sieve, from A. cruentus and A. caudatus contained 1.45 and 1.71 times higher amounts of crude protein than the raw material (Gamel and others 2005). A high-protein (>40% protein) and the amaranth high-starch fractions (about 79% starch) were separated by differential milling, operated in a continuous stream (González and others 2007b). Bejosano and Corke (1999) demonstrated that isoelectric precipitation of the proteinaceous liquor from wet-milling the grains of 5 Amaranthus genotypes (a by-product of starch extraction) may provide the functional APCs composed mainly of glutelins, albumins, and globulins, and possessing better solubility, foaming, and emulsification than commercial soy proteins. Partial pepsin hydrolysis further improved their solubility and altered their foaming property. In another study, the isoelectrically precipitated protein isolate contained mainly globulins and a considerable amount of polysaccharides, while the isolate obtained by the dialysis contained all the albumin and globulin fractions; both amaranth protein isolates were effective stabilizing and foaming agents and it was suggested that the protein-polysaccharide complexes enhance emulsion stability due to steric repulsion effects (Fidantsi and Doxastakis 2001).

Conventional standard process and the methods including an acid washing prior to protein extraction, and heating (50 °C) during the alkaline extraction step (thermal process) were compared for the preparation of APCs; and it was found that the conventional process, when compared with another 2 processes, adversely affected product properties (Bejarano-Luján and Netto 2010). The protein yields in this study were 17.8% and 25.6% for the acid washing and thermal processes, respectively; the acid washing process had positive effects on the composition, color parameters, protein solubility, and thermal stability of the APCs, whereas the thermal process resulted in positive effects on the characteristics of the proteins and color parameters, although it negatively affected solubility. APC of A. cruentus was obtained by extraction at pH 11 and precipitation at pH 4.5; protein content in the flour increased from 16.6% to 52.56 g% in the concentrate (Escudero and others 2004). Acid pretreatment combined with isoelectric precipitation or with ultrafiltration was applied as alternative processes for obtaining higher protein concentration from A. mantegazzianus; however, protein yield was lower than in the conventional process, whereas SDS–PAGE and size-exclusion chromatography showed high-molecular-weight fractions only for isoelectric precipitation concentrates obtained by conventional and alternative processes. The product obtained by ultrafiltration was particularly rich in Phe and Lys, and it was concluded that the process is a promising method for obtaining APCs (Castel and others 2012).

Polypeptidic compositions and reactivity against an anti-Gp polyclonal antibody of 2 amaranth glutelin preparations, extracted with borate buffer at pH 10 (Gt-bo) and with 0.1 M NaOH (Gt-na), were similar, although lower than those of amaranth 11 S globulin (Gp, globulin-P) (Abugoch and others 2003). It was demonstrated that the size, polypeptidic composition, thermal stability, and denaturation enthalpy of Gt-bo molecules were similar to those of Gp subjected to a borate treatment at pH 10. The results suggested that, like Gp, amaranth Gt molecules may be hexameric oligomers of approximately 300 kDa and they would be partially unfolded during the alkaline extraction (Abugoch and others 2003).

Various agents were used for isolating proteins from A. hypochondriacus; Na2HPO4 at pH 7 was the best for albumins and globulins, whereas Na2B4O7 + 1% (w/v) SDS + 0.6% (v/v) 2-mercaptoethanol at pH 10 was preferable for glutelins; however, defatting remarkably affected the distribution of protein solubility classes (Barba de la Rosa and others 1992). Most alcohol-soluble proteins of amaranth were extracted with 55% water/2-propanol and 5% 2-mercaptoethanol; they contained 80% to 85% polypeptides of 10 to 14 kDa and 7% 20-kDa polypeptides, the rest being minor fractions (Gorinstein and others 1991a). Amaranth alcohol-soluble fractions and total proteins did not show any electrophoretic relationship with prolamins and total proteins extracted from oats, rice, maize, and sorghum. In the other study Gorinstein and others (1991b) fractionated amaranth seed proteins of 4 species (A. cruentus, A. flavus, A. caudatus, and A. hypochondriacus) into albumins and globulins (61.3), alcohol-soluble proteins A1 and A2 (1.4) and glutelins G2 and G3 (24.1). They found that the main protein subunits have molecular masses of between 10 and 45 kDa; albumins, globulins, and glutelin G3 had much higher Lys content than the alcohol-soluble and glutelin G2 fractions. Globulins were only intermediate in comparative contents of Met and Cys. Later, A. hybridum, A. cruentus, and A. hypochondriacus were shown as having very similar seed protein electrophoretic profiles examined by SDS-PAGE, seed protein markers, fluorescence, circular dichroism spectra, and Fourier transform infrared measurements. According to UPGMA (Unweighted Pair Group Method with Arithmetic Mean) algorithm, soybean, quinoa, buckwheat, and Amaranthus as a genus can be considered as phylogenic distant taxa; however, the similarities, which were found between these plants, could make them a substitution of each other as well as for cereals (Gorinstein and others 2005).

The percentage concentrations of albumins, globulins, prolamins, and glutelins in amaranth proteins isolated by sequential extractions were 51.0%, 15.9%, 2.0%, and 31.1%, respectively, of total protein isolated, the insoluble fraction being quantitatively negligible (Seguranieto and others 1992). Albumins were the richest in sulfur amino acids (4.4%), globulins in Lys (7.0%), and prolamins in Leu (10%) and Thr (7.2%), whereas glutelins were the poorest in Lys (4.2%). In the other study, albumins and globulins were reported to be rich in Lys and Val, whereas prolamins had high contents of sulfur amino acids and Phe; glutelins were rich in Leu, Thr, and His (Barba de la Rosa and others 1992). Upon electrophoresis, albumins were the most polymorphous, while prolamins were made up of fewer and less abundant components. Two-dimensional gel electrophoresis revealed the occurrence of some glutelins as the major proteins in the seed; in sucrose gradients, the albumins sedimented in a major component ranging between 1.4S and 2.OS and a minor one of 4.6S, whereas globulins sedimented in 3 components of 1.9S, 8S, and 13S (Seguranieto and others 1992). Due to excellent foaming capacity and foaming stability at pH 5 as well as maximum water and oil absorption capacities at acidic pH albumins extracted from 2 Mexican amaranth varieties could be used as a whipping agent, and in the preparation of acidic foods (Silva-Sánchez and others 2004).

The peptides present in the phosphate buffer-soluble fractions of protein isolates, protein fractions, and alcalase hydrolysates of isolates and protein fractions were shown to possess antioxidant activity (Tironi and Añón 2010). In another study, it was shown that the protein isolate and the alcalase hydrolysate of A. mantegazzianus scavenged free radicals after gastrointestinal digestion, making them promising functional food ingredients (Delgado and others 2011).

High pressure (HP) provoked denaturation of amaranth proteins, studied at 1%, 5%, and 10% w/v concentrations, which were very sensitive to the treatment (200, 400, and 600 MPa); almost complete denaturation (93%) was achieved at 400 MPa (Condés and others 2012). Thermal stability of the resistant structures from glutenins, globulin-11S, and globulin-P increased after HP, while that of albumins and globulin-7S decreased. The authors concluded that the effects of HP may be useful in the use of these proteins as food ingredients or in the novel foods.

Starch and Other Carbohydrates

Properties of amaranth starch

Polysaccharides constitute the main compositional part of amaranth seeds, starch being the main component in this fraction. Starch of various Amaranthus species was studied mainly in the 1980s and these studies were reviewed by Teutonico and Knorr (1985). Later, starch properties were characterized and compared with wheat and other starches by Schoenlechner and others (2008); therefore, in this section, only a limited number of studies, which have been performed more recently, will be reviewed. In general, amaranth seeds contain 65% to 75% starch, 4% to 5% dietary fibers, 2 to 3 times higher content of sucrose in comparison to wheat grain, and nonstarch polysaccharide components (Burisová and others 2001b and references herein). Sucrose was the major sugar followed by raffinose, whereas inositol, stachyose, and maltose were found in small amounts in most of the analyzed amaranth seed samples (Becker and others 1981). However, these figures reported in various articles on different Amaranthus species may be in a wider range (Teutonico and Knorr 1985). Later, the contents of low-molecular-weight carbohydrates in A. cruentus and A. caudatus were reported in the following ranges (g/100 g): sucrose (0.58 to 0.75), glucose (0.34 to 0.42), fructose (012 to 017), maltose (0.24 to 0.28), raffinose (0.39 to 0.48), stachyose (0.15 to 0.130, and inositol (0.02 to 0.04) (Gamel and others 2006a).

Starch physicochemical and rheological properties, playing an important role in technological processing and bioavailability, are different between various grains and seeds. Moreover, these properties undergo changes during thermal treatment and other processing. First of all, the size of a starch granule and its geometrical characteristics vary between plant species and affect many functional and physicochemical properties of the starch, and hence its potential uses (Wilherm and others 2002; Lindeboom and others 2004; Choi and others 2004). The majority of commercially available starches have a medium (10 to 25 μm) or large (>25 μm) granule size, while amaranth seed is one of the few sources of small-granule starch, typically 1 to 3 μm in diameter, and having regular granule size (Hoseney 1994). The physicochemical and digestibility characteristics of starch present in diverse food crops, including A. hypochondriacus, were reviewed by emphasizing the starch after cooking, the storage of starchy products, and the potential of starch isolated from unconventional sources to produce resistant starch-rich products using different treatments (Bello-Pérez and Paredes-López 2009).

Some studies on the effects of agrotechnological practices and treatments on amaranth composition were also carried out. Presowing stimulation by He–Ne laser light and magnetic field of amaranth seeds resulted in a decrease in the level of carbohydrates (Sujak and others 2009). The optimum crop density of adapted grain amaranth genotypes “Neuer Typ” and “Mittlerer Typ” (A. hypochondriacus) and “Amar” (A. cruentus) in eastern Austria was studied and it was found that the contents of crude fiber and carbohydrates were in the ranges of 3.5% to 4.2% and 66.7% to 72.7%, respectively; however, crop density affected neither grain yield nor grain quality (Gimplinger and others 2007).

Various technological properties of amaranth starch, which was amylopectin-type short-chain branched glucans with weight average molar masses MW = 17 × 106 and 12 × 106 g/mol, respectively, were reported to correlate with molecular features, such as branching characteristics, molar mass, occupied glucan-coil volume, packing density of glucan coils, and rheological properties (Praznik and others 1999). A viscosity of 122 mPa·s at 95 °C, low resistance to acid, but high stability to applied shearing and even high freeze/thaw stability, was determined for amaranth starch, whereas wheat starch, with a viscosity of 107 mPa·s, showed low stability under acidic conditions, but high stability to shearing (Praznik and others 1999). The studies of flour characteristics of 48 A. hypochondriacus and 11 A. caudatus lines showed that A. hypochondriacus had higher pasting temperature, and lower peak viscosity, breakdown, and setback, as compared to the A. caudatus; in addition, the lines with higher α-amylase activity showed lower peak viscosity, breakdown, final viscosity, and gel hardness, and a higher pasting temperature (Kaur and others 2010).

Amaranth starch products and fractions were obtained by various processes and treatments. Thus, a high-starch fraction (about 79% starch), which is constituted by the entire amaranth grain endosperm, or the degermed and dehulled grain together with the high-protein fraction, were obtained by differential milling (González and others 2007b). A solid character at low temperature, with high consistency when cooked, and low water solubility make amaranth high-starch flours suitable for industrial applications; precooked flours were produced by popping and extrusion processes applied to the starchy fraction of A. cruentus (González and others 2002). A partial loss of starch crystalline structure was observed after heating at 190, 200, and 210 °C but most of their granular integrity was preserved, and as temperature and moisture increased, loss of crystalline structure and degree of gelatinization also increased (González and others 2007b). Extrusion-heating resulted in a very high solubility of flours in water; however, aqueous dispersions had lower consistency when cooked, and complete loss of the crystalline and granular structure (González and others 2007a).

In another study, treatment of amaranth starches containing different amylose contents with HCl showed that gelatinization temperatures and enthalpy change of gelatinization (ΔH) decreased steeply initially, and had a slight increase with further treatment up to 12 h and then decreased indicating a distinct resistance to acid with various amylose contents: the effects of acid hydrolysis on gelatinization temperatures became less pronounced when amylose content increased (Kong and others 2012). Air classification did not affect the thermal properties of the starch flour, while gelatinization energy was decreased by 52.0% and 90.0% and by 70.0% and 95.0% in cooked and popped A caudatus and A cruentus flours, respectively (Gamel and others 2005). The studies of the effects of soaking conditions during acid wet-milling of amaranth grain showed that viscoelastic modulus and thermal properties of amaranth starch were affected by temperature (40 to 60 °C) and SO2 concentration (0.1 to 1.0 g/L), with significant interaction effect (Loubes and others 2012).

Rapidly digestible starch content (RDS, 30.7% dw) and predicted glycemic index (87.2) in raw amaranth seeds was lower than those of white bread starch; however, starch digestibility of cooked, extruded, and popped amaranth seeds was similar to that of white bread, while flaked and roasted seeds resulted in a slightly increased glycemic response (Capriles and others 2008b). The authors suggested that small starch granule size, low resistant starch content, and tendency to lose its crystalline and granular structure during heating most likely are responsible for high-glycemic properties of amaranth seed. The in vitro digestibility of starch was improved after the extrusion process in “Centenario” and “Oscar Blanco” varieties of A. caudatus (Repo-Carrasco-Valencia and others 2009).

Starch and proteins may be isolated from grains and seeds by various methods; however, the starch of amaranth is difficult to extract by wet milling due to the strong association between starch and protein, the high protein content, and the small granule size. Improved or different functional characteristics of novel starches from unconventional sources may be explored in development of new ingredients, particularly for new food products (Bello-Pérez and Paredes-López 2009). The studies on the development of commercial amaranth starch extraction methods were reported only recently; a pilot-scale Al-Hakkak process was successfully used to extract amaranth starch on a laboratory scale (Middlewood and Carson 2012a). In this study, a tangential filtration system was tested for microfiltration of amaranth starch milk into a starch-rich concentrate and an aqueous stream, containing the soluble proteins and carbohydrates: protein retention was 67% and the starch-rich concentrate had 12% of proteins on a dry basis. The disadvantage of this process is membrane-fouling, which requires a multistep cleaning cycle consisting of a cold water rinse, a protease wash, an NaOH wash, an amylase wash, and a final NaOH wash (Middlewood and Carson 2012b).

The yields of the separated starch, protein, water-soluble polysaccharides, and the insoluble cell wall material from A. hybridus were 32.9%, 29.3%, 1.6%, and 8.0%, respectively. Highly branched arabinoxylan and arabinogalactan were present in the isolated polysaccharide fractions, in addition to the prevailing nonseparated protein and starch. Glucuronoarabinoxylan was evidenced in the polysaccharide fraction obtained by freeze-drying the nondialyzable portion, but not in the water-soluble polysaccharide fractions (Burisová and others 2001b).

Bacterial extracellular cyclodextrin glycosyltransferase (CGTase, EC was applied for the synthesis of cyclodextrins from A. cruentus starch: all the commercially important α-, β-, and γ-cyclodextrins were detected chromatographically after the hydrolysis of the starch and it was concluded that amaranth starch is an excellent substrate for producing cyclodextrins because of the high dispersibility, high starch-granule susceptibility to amylases, and the exceptionally high amylopectin content (Urban and others 2012).

Dietary fiber

The definition of dietary fiber underwent various changes in the past. However, resistance to human digestive enzymes has always been the main factor in this group of nutrients. Usually dietary fiber is presented as total (TDF), insoluble (IDF), and soluble (SDF). Amaranth seeds are a good source of dietary fiber, which primarily depends on plant species and variety. For instance, the study of 48 A. hypochondriacus and 11 A. caudatus lines showed that the lines with higher a*-values and lower 1000-kernel weight, L*-, and b*-values had a higher crude fiber content (Kaur and others 2010). Another study showed that dietary fiber content in the “Centenario” variety of A. caudatus was higher (16.4%) than in the “Oscar Blanco” variety (13.8%) (Repo-Carrasco-Valencia and others 2009). Organic materials alone or combined with NPK reduced crude fiber especially on a residual basis (Makinde and others 2010b). For instance, the organic manures kola pod husk applied with NPK at the ratio 75 : 25 resulted in lower crude fiber content by 9.5% and 10.8% in A. cruentus grown on 2 soil types (Makinde and others 2010b). Amaranth contained more than 25% water-insoluble β-(1,3)-D-glucan (lichenan), which was less than in oats but higher than in the other 41 analyzed samples of cereals and pseudocereals (Hozová and others 2007). The content of resistant starch in amaranth was determined to be 0.65% (González and others 2007b), and it increased after extrusion-cooking and fluidized heating (González and others 2007a), whereas during cooking and popping, it decreased (Gamel and others 2005). The average resistant starch content in 25 Amaranthus cultivars was 12.4 ± 2.2 g/kg dw, which was remarkably lower than in other pseudocereals such as buckwheat and millet, while resistant starch/total starch proportion was 1.98% (Mikulíková and Kraic 2006). The content of these components was affected by extrusion: TDF and IDF decreased in “Centenario” and “Oscar Blanco” varieties of A. caudatus, while in “Centenario” the content of SDF increased from 2.5% to 3.1% (Repo-Carrasco-Valencia and others 2009).

Green leafy vegetables, including amaranth, were also analyzed for TDF, IDF, and SDF by the gravimetric and enzymatic methods and it was observed that significant variations exist interspecies and intraspecies for all the vegetables. The TDF and IDF contents of amaranth, hibiscus, basella, rumex, and spinach significantly increased during leaf maturation, whereas the SDF increased from tender to mature stage, but there was no further increase from mature to coarse stage, except in rumex. Processing/cooking had no significant effect on the TDF, IDF, and SDF contents in vegetables (Punna and Paruchuri 2004).

The content of SDF was notably higher in the APC (12.9%), which was extracted from A. cruentus at pH 11 and precipitated at pH 4.5, than in the seed flour (4.29%); the APC also exhibited a higher content of IDF (Escudero and others 2004). The grain from 12 amaranth accessions (4 species) did not contain (1→3), (1→4) β-glucans, whereas trypsin inhibitor activity was ≤4.3 TUI/mg. It was concluded that (1→3), (1→4) β-glucans or tocotrienols are not responsible for any hypocholesterolemic effects of dietary amaranth (Budin and others 1996).

Other Constituents

Besides proteins, carbohydrates, and lipids amaranth seeds and leafy parts contain various other constituents (Table 4  and  5), which may have various effects on the quality of plant raw material, processing properties, and human health. Earlier nutraceutical effects for amaranth were associated with fiber (Danz and Lupton 1992), squalene, tocols, or the lectin biomarker called amaranthin (Rinderle and others 1989). During the last 2 decades, much more information has been obtained on amaranth microcomponents, which are usually varying in composition and are secondary metabolites, depending on plant species and/or variety, growing conditions, and other factors.

Table 4. Phenolic constituents in various Amaranthus spp
Constituent, materialContentRef
  1. dw, dry weight; fw, fresh weight; W, water; MeOH, methanol; E, extract; t/r from R, total/released from rutin; CGE, cyanidine-3-glucoside equivalents; CE, catechin equivalents; RE, rutin equivalents; QE, quercetin equivalents; TAE, tannic acid equivalents; *measured from the bars in the provided figures.

  2. 1 Gamel and others (2006b); 2 Adebooye and others (2008); 3 Paśko and others (2008); 4 Mošovska and others (2010); 5 Klimczak and others (2002); 6 Barba de la Rosa and others (2009); 7 Ogrodowska and others (2012); 8 Steffensen and others (2011); 9 Gorinstein and others (2008); 10 Bunzel and others (2005); 11 Alvarez-Jubete and others (2010c); 12 Stintzing and others (2004; 13 Adefegha and Oboh (2011); 14 Chlopicka and others (2012); 15 Mošovská and others (2010); 16 Oboh and others (2008); 17 López and others (2011); 18 Kalinova and Dadakova (2009); 19 Suryavanshi and others (2007); 20 Ferreira and Arêas (2010); 21 Lorenz and Wright (1984); 22 Bressani (1994); 23 Becker and others (1981); 24 Breene (1991); 25 Bejosano and Corke (1998a); 26 Paśko and others (2009); 27 Milán-Carrillo and others (2012).

Phenolic compounds  
A. cruentus seed: raw flours/high-protein flour fraction/cooked/popped/germinated (dried at 30, 60, and 90 °C)5.16/5.89/3.53/4.46/3.04 to 3.68 g TAE/kg1
A. caudatus seed: raw flours/high-protein flour fraction/cooked/popped/germinated (dried at 30, 60, and 90 °C)5.24/6.86/3.96/4.28/3.41 to 4.20 g TAE/kg1
A. cruentus: treated vegetables27.4 to 61.8 GAE/100 g fw2
A. hypondriacus grain: raw/extruded flour56.60/69.50 mg GAE/100 g dw27
Total phenolic acids  
A. cruentus var. Aztec seeds/sprouts light/darkness464/380.7/370.3 mg/kg dw3
A. cruentus var. Rawa seeds/sprouts light/darkness424.6/392.6/396.1 mg/kg dw3
Gallic acid  
Methanol extract of hydrolised defatted flour0.55 ± 0.065 mg/100 g dw4
A. paniculatus seeds40.64 ± 1.1 μg/g5
A. cruentus var. Aztec seeds/sprouts light/darkness440/370/360 mg/kg dw3
A. cruentus var. Rawa seeds/sprouts light/darkness400/360/350 mg/kg dw3
Vanilic acid  
Methanol extract of hydrolised defatted flour0.33 ± 0.002 mg/100 g dw4
A. cruentus var. Aztec seeds13.5 mg/kg dw3
A. hypochondriacus seed flour: var. Tulyehualco/DGETA/Gabriela/Nutrisol1.8/1.7/1.8/1.5 μg/g flour6
A. cruentus seeds: 7 accessions109.69-158.43 mg/kg7
A. seeds: 18 different genotypesup to 5.2 μg/g*8
Syringic acid  
Methanol extract of hydrolised defatted flour0.49 ± 0.028 mg/100 g dw4
A. cruentus var. Aztec sprouts light/darkness6.3/4.2 mg/kg dw3
A. cruentus var. Rawa sprouts light/darkness4.3/3.7 mg/kg dw3
A. hypochondriacus seed flour: var. Tulyehualco/DGETA0.8/0.7 μg/g flour6
p-Coumaric acid  
Methanol extract of hydrolised defatted flour0.27 ± 0.002 mg/100 g dw3
A. paniculatus/A. caudatus seeds43.57 ± 0.9/5.2 ± 0.5 μg/g5
A. cruentus var. Rawa seeds/sprouts light/darkness3.9/28.3/42.4 mg/kg dw3
A. cruentus var. Aztec sprouts light/darkness4.4/6.1 mg/kg dw3
A. hybridus/A. hypondriacus/A. cruentus seeds: methanol extract1.2 ± 0.1/1.2 ± 0.1/1.4 ± 0.1 μg/g dw9
A. cruentus seeds: 7 accessions8.33 to 11.48 mg/kg7
A. seeds: 18 different genotypesup to 3.3 μg/g*8
Ferulic acid  
Methanol extract of hydrolised defatted flour0.56 ± 0.054 mg/100 g dw4
A. paniculatus/caudatus seeds40.05 ± 1.3/18.41 ± 0.8 μg/g5
A. hybridus/A. hypondriacus/A. cruentus seeds: methanol extract309.8 ± 26.1/288.5 ± 23.2/345.0 ± 27.2 μg/g dw9
A. cruentus seeds: 7 accessions54.30 to 85.80 mg/kg7
A. caudatus insoluble fiber (cis/trans-ferulic acids)203/620 μg/g10
Protocatechuic acid  
A. paniculatus/A. caudatus seeds100.92 ± 8.7/4.65 ± 0.4 μg/g5
A. caudatus seeds/sprouts13.6 ± 9.4/14.0 ± 2.1 μmol/100 g dw11
A. seeds: 18 different genotypesup to 17.2 μg/g*8
p-Hydroxybenzoic acid  
A. paniculatus/A. caudatus seeds15.62 ± 1.3/20.89 ± 0.8 μg/g5
A. cruentus seeds: var. Aztec/Rawa8.5/20.7 mg/kg dw3
A. hypochondriacus seed flour: var. Tulyehualco/DGETA/Gabriela/Nutrisol1.7/2.0/2.2/1.9 μg/g flour6
A. seeds: 18 different genotypesup to 8.8 μg/g*8
A. cruentus seeds: 7 accessions88.68 to 141.92 mg/kg7
Caffeic acid  
A. paniculatus/A. caudatus seeds51.67 ± 0.45/55.79 ± 0.96 μg/g5
A. hybridus/A. hypondriacus/A. cruentus seeds: methanol extract6.41 ± 0.8/6.49 ± 0.9/6.61 ± 0.7 μg/g dw9
A. cruentus seeds: 7 accessions3.08 to 5.51 mg/kg7
Sinapic acid: A. paniculatus seeds0.48 ± 0.1 μg/g5
Salicylic acid: A. paniculatus/A. caudatus seeds2.65 ± 0.2/1.92 ± 0.2 μg/g5
Caffeoylquinic acids: A. spinosus stems109.2 ± 15.6/5.5 ± 0.5 mg/100g12
Cumaroylquinic acids: A. spinosus stems54.6 ± 6.0/17.5 ± 2.0 mg/100g12
Feruoylquinic acids: A. spinosus stems57.4 ± 5.5/6.5 ± 0.2 mg/100g12
A. hybridus raw/cooked16.9 ± 0.8/21.1 ± 0.7 mg QE/100g13
A. cruentus: treated vegetables18.6 to 49.4 CE/100 g fw2
Amaranthus flour65 ± 8 μg CE/g dw14
Ethanol extract of hydrolised defatted flour37.43 ± 2.10 mg RE/100 g dw4
A. seeds (PI 604671 cultivar)37.43 ± 0.210 mg RE/100 g dw15
A. cruentus: dried leaves water extract275 ± 2.8 10−2 g/kg dw16
A. hypochondriacus seeds 1.2 M/L HCl in 50% methanol:water18.66 ± 2.10 mg CE/100 g dw17
A. cruentus v. Aztec sprouts light/darkness690/300 mg/kg dw3
A. cruentus v. Rawa sprouts light/darkness620/460mg/kg dw3
A. hypochondriacus seed flour: Gabriela/Nutrisol/Tulyehualco/DGETA var.4.0/4.7/10.1/5.8 μg/g flour6
A. hypochondriacus leaves/stems/flowers/seeds (full flowering)13950 ± 566/4543 ± 67/11925 ± 180/70 ± 7 mg/kg dw18
A. caudatus leaves/stems/flowers/seeds (full flowering)12010 ± 658/3505 ± 149/6130 ± 226/55 ± 3 mg/kg dw18
A. hybrid leaves/stems/flowers/seeds (full flowering)27500 ± 1626/3723 ± 124/15426 ± 532/99 ± 4 mg/kg dw18
A. retroflexus leaves/stems/flowers/seeds (full flowering)13050 ± 636/3360 ± 99/8725 ± 50/11 ± 1 mg/kg dw18
A. tricolor leaves/stems/flowers/seeds (full flowering)2385 ± 203/932 ± 54/459 ± 30/7 ± 1 mg/kg dw18
A. seeds: 18 different genotypesup to 68 μg/g8
A. spinosus whole plant powder0.15%19
A. spinosus stems36.4 ± 9.8 mg/100g12
Isoquercetin: A. hypochondriacus seed flour freeze dried methanol:water extract (70:30): var. Tulyehualco/Nutrisol/DGETA/Gabriela0.5/0.5/0.3 μg/g flour6
Quercetin: total:released from rutin: A. hypochondriacus seeds/flowers/stems/leaves (beginning of growth/harvest time/full flowering)68 ± 3:65 ± 5.77/5155 ± 205:5765 ± 70/3083±152:3411 ± 76/(6765 ± 191:6531 ± 433/8750±566:7322 ± 541/7375 ± 262:7704 ± 289) mg/kg dw18
Quercetin: total:released from rutin: A. hybrid/A. caudatus/A.tricolor leaves (full flowering)15600 ± 424:16913 ± 505/6695 ± 219:7755 ± 685/1395 ± 78:1217 ± 105 mg/kg dw18
Quercetin diglycoside: A. spinosus stems1.9 ± 0.3 mg/100g12
Quercetin-3-O-glucoside: A. spinosus stems9.0 ± 1.9 mg/100g12
Nicotiflorin: A. hypochondriacus seed flour: var. Tulyehualco/DGETA/Gabriela/Nutrisol5.5/5.6/7.2/4.8 μg/g flour6
Nicotiflorin: A. seeds: 18 different genotypesup to 6.1 μg/g*8
Vitexin: A. cruentus v. Rawa seeds410 mg/kg dw3
Isovitexin: A. cruentus v. Rawa seeds266 mg/kg dw3
Kaempferol diglycoside: A. spinosus stems7.0 ± 1.8 mg/100g12
A. hypochondriacus/A. cruentus seeds0.060 ± 0.11/0.12 ± 0.04% dw9
A. caudatus seeds raw/extruded1305 ± 0.23/1284 ± 0.52 mg CE/100g20
A. cruentus: treated vegetables5.4 to 20.4 mg/100 g2
Amaranthus 8 varieties0.043 to 0.116% CE21
Amaranth seeds: dark/light1.04 to 1.16/0.8 to 1.2 mg/g22
Amaranthus 10 samples0.8 to 4.2 mg/g23
Amaranthus samples0.4 to 1.2 mg/g24
Polyphenolics: A. cruentus (4genotypes)/A. hybridus (1)4.5 to 5.2/4.1 mg tannic acid/g25
Total anthocyanins: A. cruentus var. Aztec/Rawa seeds103.6 ± 10.4/90.83 to 9.2 mg CGE/100 g dw26
Anthocyanins: A. hypochondriacus seeds 1.2 M/L HCl in 50% MeOH:W35.33 ± 1.70 mg/100 g dw17
Table 5. Vitamins and other microconstituents in various Amaranthus spp
Constituent, Amaranthus materialContentRef
  1. dw, dry weight; fw, fresh weight; *measured from the bars in the article figures.

  2. 1 Veeru and others (2009); 2 Jagannath and others (2012); 3 Ozsoy and others (2009); 4 Adefegha and Oboh (2011); 5 Oboh and others (2008); 6 Gamel and others (2006a); 7 Schoenlechner and others (2010b); 8 Adebooye and others (2008); 9 Khandaker and others (2010); 10 Ali and others (2009); 11 Stintzing and others (2004); 12 Repo-Carrasco-Valencia and others (2009); 13 Ferreira and Arêas (2010); 14 Teutonico and Knorr (1985); 15 Gamel and others (2006b); 16 Lorenz and Wright (1984); 17 Sanz-Penella and others (2012); 18 Smeds and others (2007a); 19 Pedersen and others (2010); 20 Smeds and others (2007b); 21 Musa and others (2011).

Ascorbic acid  
A. caudatus leaf methanol extract3.86 ± 0.20 mg/100 g1
A. hybridus paste from leaves28 ± 1 mg/100 g2
A. lividus stems/leaves/flowers: water/methanol/ethyl acetate extracts0.191 ± 0.007/0.196 ± 0.014/nd mg/g dw3
A. hybridus raw/cooked321.4 ± 1.0/227.7 ± 0.7 mg/100g4
A. cruentus dried leaves: water extract445 ± 0.21 mg/kg dw5
A. caudatus seeds: raw/cooked/popped/germinated and dried 30 °C/60 °C/90 °C29.8/2.3/18.3/13.7/11.4/nd mg/kg6
A. cruentus seeds: raw/cooked/popped/germinated and dried 30 °C/60 °C/90 °C23.0/nd/16.1/14.3/10.7/nd mg/kg6
A. cruentus vegetables: market maturity/heading (β-carotene, depending on N fertilizer)94.60 ± 5.60 to 78.90 ± 4.50/160.50 ± 7.10 to 149.90 ± 8.20 mg/100 g fw21
A. caudatus seeds: raw/high protein flour/cooked/poped/germinated and dried 30 °C/60 °C/90 °C12.5/23.6/1.0/0.7/13.1/9.3/9.1 mg/kg6
A. cruentus seeds: raw/high protein flour/cooked/poped/germinated and dried 30 °C/60 °C/90 °C21.3/44.9/1.2/0.7/22.9/20.2/17.9 mg/kg6
A. caudatus seeds: raw/high protein flour/cooked/popped/germinated and dried 30 °C/60 °C/90 °C28.0/66.5/2.4/nd/30.0/23.7/23.8 mg/kg6
A. cruentus seeds: raw/high protein flour/cooked/poped/germinated and dried 30 °C/60 °C/90 °C15.9/32.2/0.8/nd/17.1/15.5/15.2 mg/kg6
A. caudatus seeds: raw/high protein flour/cooked/popped/germinated and dried 30 °C/60 °C/90 °C4.5/7.6/2.2/0.5/4.3/4.4/2.5 mg/kg6
A. cruentus seeds: raw/high protein flour/cooked/popped/germinated and dried 30 °C/60 °C/90 °C6.1/8.5/3.1/0.6/5.5/4.5/1.9 mg/kg6
A. caudatus seeds: raw/high protein flour/cooked/popped/germinated and dried 30 °C/60 °C/90 °C2.4/4.9/1.0/1.7/5.3/4.6/1.6 mg/kg6
A. cruentus seeds: raw/high protein flour/cooked/popped/germinated and dried 30 °C/60 °C/90 °C4.1/6.5/1.6/2.0/8.3/6.5/2.1 mg/kg6
Total folate  
4 varieties: seeds52.8 to 73.0 μg g/100 g dw7
4 samples: wholemeal flour unstored/stored 3 mo59.9 to 70.6/43.7 to 61.2 μg/100 g dw7
4 samples: flour fraction/bran fraction unstored45.5 to 53.6/60.5 to 81.6 μg/100 g dw7
4 samples: noodles/cookies/bread (60% wheat 40% a.)38.9/36.3/35.5 μg/100 g dw7
A. cruentus: treated vegetables (total)11.3 to 24.2 mg/100 g8
A. caudatus leaf methanol extract (total)15.33 mg/100g1
A. cruentus: dried leaves water extract (total)132 ± 8 mg/kg dw5
A. lividus: stems/leaves/flowers: methanol/ethyl acetate extracts (β-carotene)1.24 ± 0.020/0.37 ± 0.013 mg/g dw3
A. gangeticus leaves: fresh/pressure cooked 10 min/boiled in water 10 min (β-carotene)7.36/5.391/2.4 mg/100g fw8
A. cruentus vegetables: market maturity/heading (β-carotene, depending on N fertilizer)7.45 ± 0.47 to 8.04 ± 0.87/2.48 ± 0.33-4.86 ± 0.57 mg/100 g fw21
A. cruentus: treated vegetables (chlorophyll a)53 to 132 mg/100 g fw8
A. cruentus: treated vegetables (chlorophyll b)18.0 to 43.7 mg/100 g fw8
A. tricolor, cv “Rocto alta” leaves (total)∼6.9 to 8.6* mg/L9
A. tricolor (red) leaves photoperiodic levels from 6 to 24 h (0.13 g in 20 mL 96% ethanol)∼5.1 to 11.9* mg/L10
A. tricolor (green) leaves photoperiodic levels from 6 to 24 h∼1.7 to 5* mg/L10
A. spinosus stems: amaranthine/isoamaranthine/betanin/isobetanin15.3/5.87/1.77/0.50 mg/100 g11
A. tricolor, cv “Rocto alta” leaves (betacyanin)∼316 to 450 μg/g fw9
A. tricolor (red) leaves photoperiodic levels 6 to 24 h (betacyanin)∼204 to 400 μg betanin equiv/g fw*10
A. tricolor (green) leaves photoperiodic levels 6 to 24 h (betacyanin)∼22 to 31μg betanin equiv/g fw*10
A. tricolor (red) veins photoperiodic levels 6 to 24 h (betacyanin)∼148 to 295 μg betanin equiv/g fw*10
A. tricolor (green) veins photoperiodic levels 6 to 24 h (betacyanin)∼17 to 27 μg betanin equiv/g fw*10
A. caudatus (Centenario and Oscar Blanco) raw grain (phytic acid)0.3%12
A. caudatus seeds raw/extruded82.0 ± 0.10/82.0 ± 0.13 mg 100 g13
A. cruentus seeds5.0 to 5.8 g/kg14
A. hypochondriacus seeds5.4 to 6.2 g/kg14
A. cruentus seed: raw flours/high-protein flour fraction/cooked/popped/germinated (dried at 30, 60, and 90 °C)4.0/4.4/3.3/3.4/3.1 to 3.2 g/kg15
A. caudatus seed: raw flours/high-protein flour fraction/cooked/popped/germinated (dried at 30, 60, and 90 °C)4.1/4.4/3.3/3.5/3.2 to 3.3 g/kg15
Amaranthus 8 varieties0.52% to 0.61%16
A. cruentus raw seed flours21.1 μmol/g17
Resinols in Amaranthus seed bran  
(+)-Pinoresinol53 μg/100 g18
(−)-Secoisolariciresinol98 μg/100 g18
(+)-Lariciresinol45 μg/100 g18
(−)-7-Hydroxymatairesinol519 μg/100 g18
Syringaresinol47 μg/100 g18
Secoisolariciresinol-sesdquilignan3.7 μg/100 g18
Cyclolariciresinol8.4 μg/100 g18
(+)-Medioresinol114 μg/100 g18
7-Oxomatairesinol207 μg/100 g18
(−)-Matairesinol33 μg/100 g18
Todolactol19 μg/100 g18
Isohydroxymatairesinol20 μg/100 g18
α-Conidendrin5.9 μg/100 g18
Nortracheloghenin15 μg/100 g18
Lariciresinol-sesquilignan21 μg/100 g18
(−)-Arctigenin8.2 μg/100 g18
Amines in A. hypochondriacus (Nutrisol) leaves, 2 samples  
Cinnamoylphenethylamine0.48; 0.71 μg/g19
Caffeoyltyramine0.16; 0.72 μg/g19
p-Coumaroyltyramine5.26; 5.26 μg/g19
Feruoyl-4-O-methyldopamine10.87; 7.38 μg/g19
Amines in A. mantegazzianus (Don Juan) leaves 2 samples  
Cinnamoylphenethylamine4.47; 22.31 μg/g19
Caffeoyltyramine0.53; 10.27 μg/g19
Feruoyldopamine0.60; 5.67 μg/g19
Sinapoyltyramine0.65; 0.35 μg/g19
p-Coumaroyltyramine114.31; 113.99 μg/g19
Feruoyl-4-O-methyldopamine9.49; 31.64 μg/g19
Enterolactone: Amaranthus extracts0.52 μg/100 g20

Among the green leafy vegetables, Amaranthus species are a rich store house of vitamins, including carotene, vitamin B6, vitamin C, riboflavin, folate, as well as essential amino acids and dietary minerals like Ca, P, Fe, Mg, K, Cu, Zn, and Mn (Musa and others 2011 and references herein). Processing of amaranth vegetables may influence the contents of microconstituents: for instance, steam cooking of A. hybridus resulted in 29.2% vitamin loss; however, the content of flavonoids increased by 25%, probably due to the release of some flavonoids during cooking (Adefegha and Oboh 2011). Green leafy vegetables are also prone to vitamin losses during preprocessing handling conditions, exposure to light, refrigerated storage, and other factors (Faboya 1990).

Different plant constituents may be isolated from the matrix by using various solvents. The yields of the extracts from the leaves of A. tricolor isolated successively with petroleum ether, benzene, acetone, chloroform, ethanol, and water were 11.26%, 3.3%, 1.33%, 2.4%, 8.66%, and 9.8%, respectively (Rao and others 2010). Preliminary assessment of the extracts by TLC indicated that carbohydrates were present in water and ethanol extracts; glycosides, phenolic compounds, flavonoids, and saponins in chloroform, ethanol and water extracts; and steroids in petroleum ether, benzene, acetone, and chloroform extracts (Rao and others 2010).

Phenolic acids, flavonoids, and other polyphenolics

Several studies were focused on polyphenols in various Amaranthus species, which resulted in the identification of several phenolic acids, flavonoids, and their glycosides (Table 4, Figure 1). The total amount of phenolic acids in A. caudatus grains was 16.8 to 59.7 mg/100 g, whereas the proportion of soluble phenolic acids was 7% to 61%; however, it did not contain quantifiable amounts of flavonoids and only 1 variety contained low amounts of betalains (Repo-Carrasco-Valencia and others 2010). Free phenolic acids were isolated from A. caudatus and A. paniculatus with ethanol and purified; significant differences in their profiles of both species were observed (Klimczak and others 2002). The rutin content in 5 amaranth species ranged from 0.08 (seeds) to 24.5 g/kg dw (leaves), A. hybrid and A. cruentus being the best sources of rutin. Quercetin, or other quercetin derivatives than rutin, was not quantitatively important constituent: only mature amaranth leaves probably contained quercetin or its derivatives (Kalinova and Dadakova 2009).

Figure 1.

Amarantholidosides from A. retroflexus (Fiorentino and others 2006) and cinnamoylphenethylamines (R = H, OH, OMe) from A. hypochondriacus and A. mantegazzianus (Pedersen and others 2010).

Seven phenolic acids were quantified in expanded seeds and flakes of 7 A. cruentus accessions from Poland; their total amounts were 327.93 ± 18.87 and 398.36 ± 22.63 mg/kg, respectively. Vanillic, p-hydroxybenzoic, and ferulic acids were the major ones (>80 mg/kg each), while caffeic acid constituted less than 5 mg/kg; sinapic and cinnamic acids were found in traces (Ogrodowska and others 2012). The ripe seeds of 18 Amaranthus genotypes, including A. cruentus, A. hybridus, A. hypochondriacus, and A. mantegazzianus cultivated in Argentina, Mexico, Spain, and 2 different locations in the Czech Republic were studied for their contents of flavonoids, rutin, isoquercitrin, and nicotiflorin, and also the phenolic acids, namely, protocatechuic, vanillic, 4-hydroxybenzoic, p-coumaric, syringic, caffeic, ferulic, and salicylic, and the variations among genotype, species, and location (Steffensen and others 2011). Among flavonoids, rutin exhibited large variations (<1 to 68 μg/g) with varying environmental conditions; for some genotypes, it also varied greatly between the different seasons and experimental sites, whereas nicotiflorin exhibited variations mainly between species and genotypes. Among the species, environmental factors had lesser effect for A. hypochondriacus displaying the most stable amount of polyphenols with a high end content of flavonoids. The variations in the contents of p-coumaric and protocatechuic acids were more dependent on the variations between environmental conditions and location. The authors concluded that the effects of environmental factors on the content of phenolics in amaranth seeds may be clearly observed; however, the trials did not reveal any consistent differences between the species or genotype (Steffensen and others 2011). Most likely, more comprehensive cultivation trials would be needed to evaluate possible effects of plant genotype on the accumulation of polyphenolics in amaranth.

Gallic acid was the main phenolic acid found in the seeds and sprouts of A. cruentus var. “Rawa” and var. “Aztek”: p-hydroxybenzoic, p-coumaric, vanillic, caffeic, and cinnamic acids were found in the seeds, whereas p-coumaric, ferulic, and syringic acids were present in the sprouts. The sprouts contained rutin as the main flavonoid and smaller amounts of isovitexin, vitexin, and morin, whereas orientin, morin, vitexin, isovitexin, and traces of neohesperidin and hesperidin were detected in the seeds. The light during sprouting had no effect on gallic acid content but increased the amount of rutin, whereas at darkness, conditions caused an increase in amounts of vitexin and isovitexin (Paśko and others 2008).

The extract of spiny amaranth (A. spinosus), a wild-growing weed plant used in traditional African medicine, contained 305 mg/100 g of quercetin, hydroxycinnamates, and kaempferol glycosides (Stintzing and others 2004). Caffeic, ferulic, sinapic (traces), p-coumaric, cinnamic (traces), p-hydroxybenzoic, and vanilic acids were quantified in 7 varieties of A. cruentus from Poland (Table 4); their total content was in the range of 287 to 385 mg/kg and the values were significantly different for almost all tested accessions (Ogrodowska and others 2012). Three complex compounds were identified in the enzymatically hydrolyzed IDF of A. caudatus; O-(6-O-trans-feruloyl-β-D-galactopyranosyl)-(1→4)-D-galactopyranose, O-(2-O-trans-feruloyl-α-L-arabinofurano-syl)-(1→5)-L-arabinofuranose, and O-α-L-arabinofuranosyl-(1→3)-O-(2-O-trans-feruloyl-α-L-arabinofuranosyl)-(1→5)-L-arabinofuranose, showing that ferulic acid in amaranth IDF is predominantly bound to pectic arabinans and galactans (Bunzel and others 2005).

Detailed studies of the content of quercetin and rutin in different amaranth anatomical parts (leaves, stems, flowers, and seeds) of 12 plant accessions belonging to 5 Amaranthus species, and their variations during plant vegetation, demonstrated that leafy parts of the plants contained many times higher amounts of flavonoids than the seeds. There were also remarkable variations between the species and even between the varieties belonging to the same species: for instance, the content of rutin was as high as 30.65 g/kg dw in A. retroflexus leaves before harvest, whereas A. tricolor contained remarkably a lower amount of rutin, from 0.459 (flowers) to 2.62 g/kg (leaves before harvest) (Kalinova and Dadakova 2009). Polyphenols, rutin (4.0 to 10.2 μg/g flour), and nicotiflorin (7.2 to 4.8 μg/g flour) were determined in 2 commercial (“Tulyehualco” and “Nutrisol”) and 2 new (DGETA and Gabriela) varieties of A. hypochondriacus from the Mexican Highlands (Barba de la Rosa and others 2009).  The presence of flavonoids and phenolics in A. spinosus was suggested to be responsible for hepatoprotective activity, which was evaluated against CCl4-induced hepatic damage in rats (Zeashan and others 2008).

The content of tannins reported in various Amaranthus cultivars was in a very wide range, from 0.4 to 5.2 mg/g (Table 4); however, these fluctuations might be due to the differences between plant species and cultivars and due to the differences in measurement method. The condensed tannin extracts of raw, cooked, and roasted grains, as well as raw, cooked, and blanched vegetables, showed antidiabetic effects by inhibiting α-amylase and α-glucosidase activity up to 50% and 78%, respectively. Roasting of grains and cooking of vegetables better preserved the tannins and their functional properties than soaking + cooking and blanching (Kunyanga and others 2011).

Phytates and enzyme inhibitors

Whole grains of amaranth contain comparatively high concentrations of phytic acid, an inhibitor of intestinal absorption of Fe and other minerals; therefore, it was measured in several studies, mainly in association with the Fe uptake studies when amaranth is used in food formulations. In earlier studies, the presence of phytates in amaranth grain was reported as between 4.8 and 34.0 μmol/g, while recently the measured amount of phytates in the amaranth seed was 21.1 μmol/g (Sanz-Penella and others 2012 and references herein). The content of phytates may be reduced by germination of the seeds (Gamel and others 2006b).

Several groups have studied antinutritional factors of amaranth seeds. The phytic acid and phenol contents in A. cruentus, A. hybridus, and A. hypochondriacus ranged from 5.2 to 6.1 g/kg, and as phytate is present throughout, kernels dehulling did not reduce its content, whereas the tannin content in dehulled seeds decreased by 80% (Lorenz and Wright 1984). The content of phytate in A. cruentus and A. hypochondriacus seeds was reported as 5.0 to 5.8 and 5.4 to 6.2 g/kg, respectively (Teutonico and Knorr 1985), while in the other study, the levels of phytic acid in A. caudatus and A. cruentus seeds were 4.4 and 3.2 g/kg, respectively, which decreased on germination (Colmenares de Ruiz and Bressani 1990).

Different trypsin inhibitor levels have been reported for amaranth seeds: for instance, in light-colored seed species, it was 3.07 to 5.46 TIU/mg protein (Bressani 1994), while in other study, it was estimated as 0.94 TIU/mg protein (Williams and Brenner 1995); for comparison, this value for wheat was 0.54 TIU/mg protein. Later, it was shown that trypsin inhibitory activity of A. hybridus was remarkably lower (0.26 and 1.3 TIU/mg, respectively, for whole meal and protein concentrate), than that of 4 A.cruentus genotypes (1.49 to 1.98 and 1.76 to 5.45 TIU/mg, respectively) (Bejosano and Corke 1998a). The contents of trypsin, chymotrypsin, and amylase inhibitors in raw A. caudatus were estimated to be 4.34, 0.21, and 0.23 AIU/mg, respectively, while in raw A. cruentus, these values were 3.05, 0.26, and 0.27 AIU/mg, respectively (Gamel and others 2006b). The content of inhibitors remarkably decreased and in some cases was not  detectable after cooking, popping, or during germination.

Other microconstituents

Raw amaranth seeds are almost flavorless. The main volatile compounds of raw seeds isolated with a dynamic headspace procedure were 2,4-dimethyl-1-heptene, 4-methylheptane, branched C11H24 alkane, and dodecene C12H24 isomer (about 70% of the total volatile constituents). Volatiles identified in popped seeds and not present in the raw material were the Strecker degradation aldehydes 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, and phenylacetaldehyde and alkylpyrazines such as vinylpyrazine, methylpyrazine, 2,5-dimethylptrazine, and 3-ethyl-2,5-dimethylpyrazine, possessing cornlike, hazelnutty, nutty, and having roasty odors (Gamel and Linssen 2008). More than 100 volatile compounds emitted from several cultivars of crude and heat-treated A. cruentus and A. hypochondriacus were collected by solid-phase microextraction and identified by GC/MS (Ciganek and others 2007). Total concentrations of quantified volatile constituents were between 2.2 and 68.9 μg/g of dried sample, hexanal being the most abundant compound constituting from 0.46 to 2.5 μg/g in crude grain amaranth to 8.6 to 23.4 μg/g in heat-treated and dried biomass. The content of 2,5-dimethylpyrazine also increased many times during thermal treatments indicating that intensive Maillard reactions proceed at elevated temperatures.

Several new polyhydroxylated terpenes with a nerolidol skeleton were isolated and characterized in the methanolic extract of redroot pigweed (A. retroflexus) leaves, possessing strong dose-response antioxidant capacity, while antioxidant power of pure nerolidol derivatives was comparable to α-tocopherol (Pacifico and others 2008). An N-acetyl-α-D-galactosamine-specific lectin, which agglutinated normal and papain-treated rabbit and human A, B, and O erythrocytes, was purified from the seeds of A. paniculatus and a homo dimer and a glycoprotein (10.5% carbohydrate w/w) with molecular weight of the subunit being 27000 ± 1410. It contained high amounts of Val, Leu, Met, Trp, Lys, and acidic amino acid residues (Sawhney and Bhide 1992).

The contents of total folate in amaranth ranged from 52.8 to 73.0 μg/100 g dw (Table 5); its content in the bran fractions was more than 2 times higher than in the flour fractions (124% compared with 57%). The content of total folate in flour after 3 mo storage reduced to 34% (Schoenlechner and others 2010b).

Lignans are widely distributed in edible plants as natural defense substances; most of them are metabolized by the gut microflora to phytoestrogens enterolactone and enterodiol (Sok and others 2009).  The contents of individual compounds, among 16 determined lignans in amaranth seed bran (Table 5), depending on the extraction method were from 3.7 (secoisolariciresinol-sesquilignan) to 519 μg/100 g [(-)-7-hydroxymatairesinol] (Smeds and others 2007a). Such activities as antioxidant, antiviral, antitumor, antibacterial, fungistatic, insecticidal, estrogenic, and antiestrogenic, as well as protective effects against coronary heart disease have been assigned to lignans (Smeds and others 2007b and references therein).

An extract of the wild-growing weed plant A. spinosus was characterized with respect to its betalains and it was determined that the total amount was 24 mg betacyanins in 100 g of the ground plant material, the main betalains being amaranthine and isoamaranthine (Stintzing and others 2004).  Amaranthin-type betacyanins were also identified later in the fresh crude extract samples of A. tricolor seedlings by direct analysis with MALDI-QIT-TOF/MS, and with 2,5-dihydroxybenzoic acid as the matrix (Cai and others 2006).

Carotenoid in the foliage of 61 accessions of the grain and vegetable types of Amaranthus (10 species in total) varied from 90 to 200 mg/kg in vegetable types and from 60 to 200 mg/kg in the leaves of grain types. Variation for nitrate was 1.8 to 8.8, 4.1 to 9.2 g/kg; oxalate 5.1 to 19.2 and 3 to 16.5 g/kg in vegetable and grain types, respectively. Such factors as the leaf position in vegetable types and age in grain types were also studied (Prakash and Pal 1991). Toxic substances cyanide (223 to 435 mg/kg dw) and nitrate (7.62 to 23.41 g/kg dw) as well as antinutrients oxalates (soluble 2.37 to 3.86 and total 4.40 to 5.27 g/100 g dw) were reported in A. cruentus vegetables and it was shown that the concentrations of cyanide and total oxalates increased during plant heading, whereas the amount of nitrates decreased (Musa and others 2011).

Seven structures of unusual sesquiterpene glucosides amarantholidosides (Figure 2) from A. retroflexus were identified and their phytotoxicity shown in tests with Taraxacum officinale (Fiorentino and others 2006). 2,3-Dihydroxypropyl ester of hexadecanoic acid, 6 9,12-octadecadien-1-ol, (3β,5α)-ergost-7-en-3β-ol, (3β,5α)-stigmasta-7,16-dien-3β-ol, and (3β,5α,24S)-stigmasta-7-en-3β-ol were detected by GC/MS in the unsaponifiable fraction of hexane extract that was obtained by partitioning crude methanolic extract of A. caudatus seeds (Conforti and others 2005).

Figure 2.

Phenolic compounds identified in Amaranthus.

The contents of P, Na, K, Mg, Ca, Cu, Fe, Mn, and Zn were similar among 14 selections of A. caudatus, A. hybridus, A. cruentus, and A. hypochondriacus (Bressani and others 1987b). Later, it was reported that the concentrations of minerals in seeds of 8 groups of A. cruentus and A. hypochondriacus grain samples grown in Hungary and Austria varied through a relatively wide range; the microcomponents, like Fe, Zn, and Cu, were present in higher concentrations in amaranth seeds compared to the average values determined in wheat (Tömösközi and others 2009). The contents of some minerals (Fe, Cu, and Na) in A. cruentus were affected by plant heading, while the concentrations of others (Mg, Zn, Ca, and K) did not change significantly (Musa and others 2011). Presowing electromagnetic stimulation of amaranth seeds with laser light or/and magnetic field significantly decreased the levels of K, Ca, Mg, Na, Cu, and Mn, while stimulation with both electromagnetic methods significantly increased the level of Zn and Fe (Sujak and Dziwulska-Hunek 2010). Air classification increased the content of minerals by more than 35%; thermal treatments did not have effect, whereas germination increased the contents of Ca and Zn in A. caudatus and A. cruentus seeds (Gamel and others 2006a). NPK fertilization was shown to affect the contents of Cu, Zn, and Fe levels in A. cruentus leaves, and Cu and Mn in seeds (Skwaryło-Bednarz and others 2011).

Saponins were not detected in the Peruvian ecotype of A. caudatus by fast atom bombardment-MS of the saponin extracts and GC analysis of the sapogenols after acid hydrolysis of the extract (Cuadrado and others 1995). However, later, 4 saponins, 3-β-O-[α-L-rhamnopyranosyl(1→3)-β-glucurono-pyranosyl]-2 β,3 β-dihydroxyolean-12-en-28-oic acid 28-O-[β-D-glucopyranosyl] ester, 3-β-O-[α-L-rhamnopyranosyl(1→3)-β-glucuronopyranosyl]-2 β,3 β,23-trihydroxyolean-12-en-28-oic acid 28-O-[β-D-glucopyranosyl] ester, 3-β-O-[α-rhamnopyranosyl(1→3)-β-glucuronopyranosyl]-2 β,3 β-dihydroxy-23-oxoolean-12-en-28-oic acid 28-O-[β-D-glucopyranosyl] ester, and 3-β-O-[β-glucuronopyranosyl]-2 β,3 β-dihydroxy-30-norolean-12,20(29)-diene-23,28-dioic acid 28-O-[β-D-glucopyranosyl] ester were identified in A. cruentus (Junkuszew and others 1998); their total concentration was 0.09% to 0.1% dw, which increased during 4 d of germination to 0.18%, remained stable for 3 d, and afterward dropped to 0.09% (Oleszek and others 1999). It was concluded that amaranth saponins due to their low content and relatively low toxicity do not create a significant hazard for the consumer. Saponins, phytic acid, and trypsin inhibitors were present in the A. cruentus concentrate obtained by extraction at pH 11 and precipitation at pH 4.5; it was suggested that consumption of the APC might reduce the risk of heart disease by favoring lipid metabolism (Escudero and others 2004).

Caffeoyltyramine, feruloyldopamine, sinapoyltyramine, and p-coumaroyltyramine were identified in Amaranthaceae by LC-MS/MS for the first time in 2010, while one rare compound, feruloyl-4-O-methyldopamine, appeared to be quite common in the genus Amaranthus (Pedersen and others 2010). Feruloyldopamine showed moderate antifungal activity toward an isolate of Fusarium culmorum, while cinnamoylphenethylamines have been associated with various biological activities, such as the potentiation of antibiotics, inhibition of prostaglandin biosynthesis, and antioxidant effects.

AsIII and AsV were found in the amaranth shoots, the content of AsIII being higher. Arsenic concentration in spinach of amaranth shoot after acid digestion was 5.6 ± 0.39 μg As/g; inorganic As, especially AsIII, a more toxic and bioavailable form than organic and methylated species, was prevailing in the edible part (>90%) (Rahman and others 2009).

Effects of growing conditions and treatments on the content of microconstituents

Growing experiments with red amaranth (A. tricolor) in the spring season under 5 different shades made of polyethylene, and a nonshaded frame, showed that the highest temperature was obtained under the blue polyethylene shade compared to white, green, yellow, and black, and the plants achieved highest plant height, stem length, and leaf number, fresh and dry matter biomass, betacyanins, total polyphenol, and antioxidant activity; however, the plants grown under green polyethylene shade accumulated the most chlorophyll (Khandaker and others 2010). The yield of biomass and the contents of bioactive constituents were almost similar to field-grown red amaranth in the summer season; the same characteristics were lower in the nonshaded plants, which received the highest sunlight intensity, than in the plants grown under the blue polyethylene shade, most likely due to low air temperature.

The highest contents of betacyanin and chlorophyll were determined in red-fleshed leaf cultivars (A. tricolor L. subsp. mangostanus L. Allen) grown in full sunlight (open shade) comparing to 4 selected shading regimes covered by 1 layer of white, 1 layer of black, 2 layers of black, and 4 layers of black-neutral density synthetic shading clothes, respectively. These cultivars were also found to contain more pigments than green-fleshed cultivars in case of exposing to different levels of shade (Ali and others 2010). In another study, the effects of photoperiod (6 to 24 h) were evaluated: the highest and the lowest contents of betacyanin and chlorophyll in the leaves were under a 12- and a 24-h photoperiod, respectively (Ali and others 2009). The content of vitamin C was remarkably lower in A. cruentus vegetables at market maturity stage than at heading stage, whereas the concentration of β-carotene, on the contrary, was approximately 2 to 3 times higher at heading stage (Musa and others 2011).

The 6 pretreatment methods were evaluated for processing A. cruentus: chopping (raw sample) (M1); chopping and drying at 50 °C for 5 h (M2); chopping and squeezing in water (at room temperature) (M3); chopping and soaking in water (60 °C), then cooling and squeezing (M4); chopping and soaking in salt-treated water (20 g NaCl/L) for 15 min, then squeezing (M5) and chopping and soaking in boiling water (100 °C), then cooling and squeezing (M6) (Adebooye and others 2008). Chlorophyll a and b occurred in a ratio of 3 : 1, irrespective of the pretreatment imposed, none of the samples possessed peroxidase activity. In the case of M6, the losses in total carotenoids, phenolics, flavonoids, and total tannins compared with M1 were in the range of 53.3% to 73.5%. There was a sharp drop in the contents of carotenoids, phenolics, flavonoids, and tannins of the 2 vegetables at M4 and M6, with both treatments having closely similar values for each parameter.

The retention of β-carotene after pressure-cooking and open-pan-boiling for 10 min in A. gangeticus leaves was 73% and 32.5%, respectively (Table 5), however, using citric acid and spice tamarind and onion, alone or in combination, enabled to increase the retention of β-carotene after boiling from 48 (tamarind) to 80.5% (citric acid + onion) (Gayathri and others 2004). The content of ascorbic acid in A. caudatus and A. cruentus decreased after heat treatments, germination, and air classification, whereas the levels of niacin, pyridoxine, niacinamide, and riboflavin increased in the high-protein fractions of A. caudatus (263.9 g/kg of proteins) and A. cruentus (246.6 g/kg of proteins) and decreased in the heat-treated flours (Table 5). Germination in most cases had positive effect on the amounts of vitamins, while drying had negative effect (Gamel and others 2006a).

Antioxidant Potential of Amaranth

All plant species elaborated their own antioxidant defense mechanisms, which are based mainly on the chemical properties of various secondary metabolites, particularly polyphenolic compounds. Amaranth seeds could be a source of antioxidatively valuable phenolic compounds, particularly in those arid zones where commercial crops cannot be grown (Barba de la Rosa and others 2009). Antioxidant potential of amaranth seeds and leafy parts was studied using various well-known in vitro methods and new assays (Jung and others 2006). The results of these studies are summarized in Table 6.  It may be observed that in many cases, the results on amaranth antioxidant properties obtained in different studies are difficult to compare due to different extraction, sample preparation, and antioxidant activity evaluation procedures as well as the expression of their results. When radical-scavenging capacity is expressed in the percentage of the inhibition of a free radical used in the assay, the value depends on the concentration of plant preparation and radical itself. Therefore, the results expressed in the concentration equivalent to some reference antioxidant, or at least as the amount of extracts required to scavenge 50% of radicals present in the reaction media, are more informative for comparison reasons.

Table 6. Antioxidant and radical scavenging properties of Amaranthus
Analyzed materials, methodsValuesRef
  1. TE, Trolox equivalents; GAE, gallic acid equivalents; CAE, caffeic acid equivalents; TAE, tannic acid equivalents; AAE, ascorbic acid equivalents; TP, total phenols; TAC, total antioxidant capacity, β-C-LA = β-Carotene-linoleic acid; LPI , Lipid peroxidation inhibition; ds , dry sample; dwb , dry weight basis; IPLO , Inhibition of the FeCl3/ascorbic acid induced phosphatidylcholine liposome oxidation EC50; RP EC50, Fe3+/ferricianyde complex reducing power EC50; Fe (II) EC50, Iron chelation (II) activity EC50; Fe3+ RP, Fe3+ reducing potential; RC = reducing capacity.

  2. 1 Veeru and others (2009); 2 Repo-Carrasco-Valencia (2009); 3 Klimczak and others (2002); 4 Morrison and Twumasi (2010); 5 Queiroz and others (2009); 6 Kunyanga and others (2011); 7 Kunyanga and others (2012a); 8 Skwaryło-Bednarz and Krzepiłko (2009); 9 Amin and others (2006); 10 Zeashan and others (2009); 11 Mošovska and others (2010); 12 Odukoya and others (2007); 13 Paśko and others (2008); 14 Paśko and others (2009); 15 López and others (2011); 16 Oboh and others (2008); 17 Khandaker and others (2010); 18 Ali and others (2009); 19 Gorinstein and others (2008); 20 Asao and Watanabe (2010; 21 Ogrodowska and others (2012); 22 Gamel and others (2006b); 23 Alvarez-Jubete and others (2010c); 24 Tikekar and others (2008); 25 Ozsoy and others (2009); 26 Adebooye and others (2008; 27 Conforti and others (2012); 28 Conforti and others (2005); 29 Pacifico and others (2008); 30 Cai and others (2003); 31 Jung and others (2006); 32 Chlopicka and others (2012); 33 Rao and others (2010); 34 Adefegha and Oboh (2011); 35 – Kraujalis and Venskutonis (2013b); 36 Milán-Carrillo and others (2012).

A. caudatus leaves: MeOH-E: TP; DPPH3.43 mgGAE/g ; IC50 = 0.14 mg/L1
A. caudatus Centenario raw grain: TP; DPPH/ABTS+•98.7 mg GAE/100 g; 410/827.6 μmol TE/g2
A. caudatus Oscar Blanco raw grain: TP; DPPH/ABTS+•112.9 mg GAE/100 g; 398.1/670.1 μmol TE/g2
A. caudatus/A. paniculatus seeds: TP; β-C-LA39.17/56.22 CAEmg/100 g; 0.05, 0.1% ≈ 0.02% BHA3
A. cruentus leaves: MeOH-E: TP; TAC; DPPH0.238 ± 0.053 mg TAE/mL; 0.228 ± 0.053 AAE mg/mL; EC50 = 0.1364 mg/mL4
A. cruentus leaves: W-EtOH-E: TP; TAC; DPPH0.339 ± 0.076 mg TAE/mL; 0.312 ± 0.069 AAE mg/mL; EC50 = 0.1378 mg/mL4
A. cruentus leaves: MeOH/W-EtOH-E: Fe3+RPEC50 = 0.1378 mg/mL4
Non processed/processed grain: TP31.7/22.0 mg GAE/g dry residue5
Raw/cooked/roasted seeds (Ac-E 0.1 mL): DPPH89.67 ± 0.33/87.00 ± 0.01/89.33 ± 0.33%6
Raw/cooked/roasted seeds (30 μL sample): FRAP31.01 ± 3.91/97.22 ± 15.50/26.59 ± 1.35 mmol Fe2+/g6
Raw/cooked/roasted vegetables (Ac-E 0.1 mL): DPPH88.33 ± 0.67/87.33 ± 0.88/78.33 ± 1.20%6
Raw/cooked/roasted vegetables (30 μL sample): FRAP573.5 ± 22.6/366.9 ± 18.1/147.1 ± 5.9 mmol Fe2+/g6
A. cruentus: raw/soaked-cooked/roasted grains (MeOH-E, 0.025 g/L): DPPH84.67 ± 1.18/87.33 ± 1.77/81.00 ± 1.77%7
A. cruentus: raw/soaked-cooked/roasted grains (MeOH-E): FRAP44.94 ± 2.95/233.78 ± 70.32/417.56 ± 27.77 mmol-1 Fe2+/g extract dw7
A. hybridus: raw/soaked-cooked/roasted vegetables (MeOH-E, 0.025 g/L): DPPH85.33 ± 1.18/80.33 ± 1.18/81.67 ± 1.18%7
A. hybridus: raw/soaked-cooked/roasted vegetables (MeOH-E): FRAP475.25 ± 88.65/239.05 ± 53.19/343.41 ± 33.04 m/mol Fe2+/g extract dw7
A. cruentus: raw/soaked-cooked/roasted grains (MeOH-E): TP*1.08/0.24/0.34 CEg/100 g extract7
A. hybridus: raw/soaked-cooked/roasted vegetables (MeOH-E): TP*2.45/1.35/0.63 CEg/100 g extr7
A. cruentus Aztek/Rawa leaves, depending on NPK fertilization: TAC (ABTS+•)8.23-12.50/7.35-14.55 TE/cm3/g leaf extract8
A. paniculatus/A. gangeticus/A. blitum/A .viridis spinach: TP101 ± 0.36/107 ± 1.08/69.4 ± 2.17/85.6 ± 4.71 GAEg/kg9
A. spinosus whole plant 50% EtOH-E: TP/RC/DPPH•/O2/H2O2/OH/NO336 ± 14.3 mg GAE/g/2.26 times of BHA/IC50 = 29/66 to 70/120 to 125/140 to 145/135 to 140 μg/mL10
EtOH-E of hydrolised defatted flour: TP104.08 ± 2.297 mg GAE/100 g dw11
A. paniculatus/A. caudatus seed EtOH-E: β-C-LA0.05∼0.1%∼0.9≈ 0.02%BHT/0.1%≈0.02%BHT3
A. hybridus/A. caudatus leaves W-E: TP406.33 ± 0.17/312.18 ± 5.19 mg TAE/100 g12
A. hybridus/A. caudatus leaves W-E 200 mg/L: LPI3.67 ± 0.11/17.89 ± 0.004%12
A. cruentus var. Aztec seeds/sprouts light/sprouts darkness: FRAP3.37 ± 0.40/248.1 to 148.0 to 163.2/127.4 to 80.6 to 91.3 mmol Fe2+/kg13
A. cruentus var. Rawa seeds/sprouts light/sprouts darkness: FRAP3.73 ± 0.20/149.4 to 111.9 to 103.8/126.2 to 85.4 to 61.1 mmol Fe2+/kg13
A. cruentus var. Aztec seeds: TP/DPPH/ABTS+•2.95 ± 0.07 mg GAE/kg dw/4.42 ± 0.5/12.1 ± 1.1 mmol trolox/kg dw14
A. cruentus var. Rawa seeds: TP/DPPH/ABTS+•3.0-0.42 mg GAE/kg dw/3.15 to 0.3/11.42 to 1.2 mmol trolox/kg dw14
A. hypochondriacus seeds 1.2 M/L HCl in 50% MeOH:W: TP/NO/DPPH•/β-C-LA57.07 ± 1.70 mg GAE/100 g dw/35.20 ± 1.60%/86.93 ± 1.40%/69.51 ± 1.50% RSA 5 mg extract/mL15
A. cruentus dried leaves W-E: TP/DPPH•*/ABTS+•*/FRAP*/FE2+ chelating*884.5 ± 2.2 10−2 g/kg dw/21%/2.0 mmol TEAC/g/0.3 mmol ascorbic acid/g/64%16
A. cruentus dried leaves hexane extract: TP/DPPH•*/ABTS+•*/FRAP*/FE2+ chelating*72.0 ± 4.2 10−2 g/kg dw/12%/0.36 mmol TEAC/g/0.17 mmol ascorbic/g/54%16
A. tricolor cv “Rocto alta” leaves: TP*/AA*1.48 to 2.22 mg GAE/100 g dw/5.5 to 12.8%17
A. tricolor leaves and veins photoperiodic levels 6-24 h: green TP/A. tricolor, red/green AA*1.29 to 2.7 mg GAE/100g/6.3 to 14%/4.2 to7.4%18
A. hybridus/A. hypondriacus/A. cruentus seeds: TP (AE:WE)(0.03/0.017% dw)/(0.027/0.011% dw)/(0.034/0.018% dw)19
A. hybridus/A. hypondriacus/A. cruentus seeds:  
(AE-TRAPAC:WE-TRAPW)(309 ± 21.7/388 ± 23.1 nm/mL)/(288 ± 17.1/373 ± 23.1 nm/mL)/(345 ± 22.9/384 ± 23.5 nm/mL)19
A. hybridus/A. hypondriacus/A. cruentus seeds extracted with 40% methanol water 0.2 M HCl: NO23.0 ± 1.9/23.0 ± 1.9/25.0 ± 1.9%19
A. hybridus/A. hypondriacus/A. cruentus seeds extracted with 40% methanol water 0.2 M HCl: FRAP1.96 ± 0.3/1.96 ± 0.3/1.99 ± 0.3 μmol TE/g19
A. hybridus/A. hypondriacus/A. cruentus seeds extracted with 40% MeOH:W 0.2 M HCl: CUPRAC3.11 ± 0.7/3.25 ± 0.8/3.94 ± 0.8 μmol TE/g19
Amaranth W-EtOH-E 5 mg/mL: DPPH/ferric thiocyanate method/TP22.6 mg GAE/g/1.4 mg BHA equivalent/g/0.51 mg GAE/g20
Seeds, variety PI 604671: TP104.08 ± 2.297 mg GAE/100 g dw11
A. cruentus seeds of 7 accessions: TP/DPPH272.6 to 615.3 mg/kg CE/11064 to 15327 μmol DPPH/kg21
A. cruentus raw seed flours/high-protein flour fraction/cooked/popped/germinated: TP5.16/5.89/3.53/4.46/3.04 to 3.68 g/kg22
A. caudatus raw seed flours/high-protein flour fraction/cooked/popped/germinated: TP5.24/6.86/3.96/4.28/3.41 to 4.20 g/kg22
A. caudatus seeds/sprouts/bread: TP21.2 ± 2.3/82.2 ± 4.6/13.8 ± 0.0 mgGAE/100 g dw23
A. caudatus (seeds)/(sprouts)/bread DPPH[16.2 ± 0.4 TEAC (IC50trolox/IC50) × 105 ; 28.4 ± 1.3 mgTE/100 g dw]/] 22.4 ± 1.2 TEAC (IC50trolox/IC50) × 105; 27.1 ± 2.7 mgTE/100 g dwb]/10.3 ± 0.2 mgTE/100 g dw23
A. caudatus seeds/sprouts/bread: FRAP55.3 ± 1.6/122 ± 11.1/0.6 ± 6.2 mgTE/100 g dw23
Blend of Amaranthus seed flour/puffed (250 °C, 75 rpm)/(270 °C, 100 rpm)/(290 °C, 125 rpm) roasted (150 °C, 20 min): ORAC0.14 ± 0.03/0.71 ± 0.65/0.62 ± 0.30/0.29 ± 0.41/0.39 ± 0.55 μmol TE/g24
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E: TP1.55 ± 0.098/1.51 ± 0.130/0.46 ± 0.039 mg/g dw25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E/gallic acid/BHA: IPLOEC50 = 33.3 ± 0.98/17.5 ± 0.51/7.33 ± 0.53/1.7 ± 0.043/11.6 ± 0.26 mg/mL25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E/gallic acid/BHA: ABTS+•84.6 ± 1.16/81.9 ± 2.51/95.5 ± 1.06% (60 mg/mL)/99.2 ± 0.15% (0.31 mg/mL)/98.4 ± 0.77% 0.625 mg/mL25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E: ABTS+•1.98 ± 0.01% mM TEAC (60 mg/mL) (4.28 mM/g dw)/1.92 ± 0.056% mM TEAC (40 mg/mL) (5.62 mM/g dw); 2.25 ± 0.026 mM TEAC (20 mg/mL) (2.30 mM/g dw)25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E: DPPHEC50 = 42.3 ± 0.86/24.8 ± 0.36 = 6.75 ± 0.083 mg/mL25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E/BHA/gllic acig: HOEC50 = 37.4 ± 0.43/9.53 ± 0.27/3.58 ± 0.13/0.195 ± 0.019/13.28 ± 0.11 mg/mL25
A. lividus stems/leaves/flowers MeOH-E/EtAc-E/BHA/gallic acid: RPEC50 = 22.79 ± 0.03 mg/mL; EC50 = 28.19 ± 0.28/0.053 ± 0.0066/0.09 ± 0.002 mg/mL25
A. lividus stems/leaves/flowers H2O-E/MeOH-E/EtAc-E/EDTA: Fe2+EC50 = 27.8 ± 0.057; EC50 = 2.35 ± 0.09 mg/mL; EC50 =15.6 ± 0.25 mg/mL; EC50 = 0.160 ± 0.003 mg/mL25
A. cruentus treated vegetables: TP27.4 to 61.8 GAE/100 g FW26
A. retroflexus leaves: TP/DPPH/NO59.0 ± 0.9 mg chlorogenic AE/g/IC50 = 510 ± 3.2/56 ± 0.9 μg/mL27
A. caudatus seeds var. Oscar blanco/Victor red EtAc-E: LPIIC50 = 0.50/0.620 mg/mL28
A. retroflexus leaves: DPPHIC50 = 92.7 μg/mL29
Amaranthine isolated from A. tricolor: DPPHEC50 = 8.37 μM30
A. caudatus seeds/sprouts: antioxidant power27 AU (AP of 1 ppm vit C) 409 ± 203 AU31
Amaranth seed/flour: TP/FRAP/DPPH2.71 ± 0.1 mg GAE/g dw/38.0 ± 1.2 mg TE/100 g dw/3.60 ± 0.34 mmol TE/kg dw32
A. tricolor leaves W-E, 0.1 mg/mL: DPPH62.96% scavenging33
A. hybridus leaves raw: TP/ABTS+•*/DPPH*/Fe2+* FRAP*198.1 ± 1.1 mgGAE/100g/17 mmol TEAC/100 g/21% scavenging/59% chelating/34 AAE/100 g34
A. hybridus leaves cooked: TP/ABTS+•*/DPPH*/Fe2+*/FRAP*300 ± 1.6 mgGAE/100g/59 mmol TEAC/100g/53% scavenging/64% chelating/44 mg AAE/100 g34
SC-CO2 extracts of amaranth grain (ORAC): grain/oil2.38 to 9.96/64.08 to 257.6 μmol TE/g35
A. hypondriacus grain: raw/extruded flour (ORAC)3475/3903 μmol TE/100 g dw36

The vitamins present in Amaranthus along with carotenoids, flavonoids, and phenolic acids contribute to their high antioxidant activity, whereas squalene and tocols are important lipophilic antioxidants present mainly in amaranth grain. The antioxidant activity of “Oscar blanco” and “Victor red” varieties of A. caudatus did not differ significantly from each other; IC50 values of ethyl acetate extracts were 0.50 and 0.62 mg/mL, respectively (Conforti and others 2005). The methanolic crude extracts of A. caudatus were screened for DPPH° scavenging, using ascorbic acid as a standard antioxidant for comparison. The IC50 value of the methanolic extract was 0.14 mg/L; it contained 3.86 ± 0.20 mg ascorbic acid, 15.33 mg carotenoids, and 343 mg total phenols in 100 g (Veeru and others 2009). The total antioxidant capacity (TAC) and TPC in the methanol extracts (6.3% yield) of 8 edible leafy vegetables from Ghana, including A. cruentus, was lower than in hydro-ethanol extracts (9.4% yield) (Morrison and Twumasi 2010). The TPC ranged from 39.17 mg/100 g of A. caudatus to 56.22 mg/100 g of A. paniculatus seeds, and the extracts inhibited degradation of β-carotene in a model emulsion; the addition of 0.05% of extract was proposed as practically applicable (Klimczak and others 2002). Water, methanol, and ethyl acetate extracts from overground parts of A. lividus were shown to inhibit peroxidation of phosphatidylcholine liposomes, induced with Fe3+/ascorbate, to scavenge ABTS°+, DPPH°, and hydroxyl radicals, to chelate Fe2+ ions, and to reduce Fe3+ to Fe2+(Ozsoy and others 2009). The TPC in “Centenario” and “Oscar Blanco” varieties of A. caudatus was 98.7 and 112.9 mg GAE/100 g, respectively. Antioxidant activity in a DPPH° assay for the raw seeds was 410.0 μmol TE/g for “Centenario” and 398.1 μmol TE/g for “Oscar Blanco,” whereas in the ABTS°+ assay, those values were 827.6 and 670.1 μmol TE/g, respectively; the TPC and the antioxidant activity decreased during extrusion (Repo-Carrasco-Valencia and others 2009). The polar fraction of A. cruentus isolated with water contained a remarkably higher content of phenolics and flavonoids and possessed higher antioxidant activity than the nonpolar fraction isolated with hexane (Oboh and others 2008). The L-ORAC values of the SC-CO2 extracts of amaranth seeds were in the range of 64 to 258 μmol TE/g oil, and it was shown that antioxidatively active compounds were extracted more efficiently by adding of a polar cosolvent ethanol (Kraujalis and Venskutonis 2013b). Antioxidant activity of hot water extracts of A. hybridus and A. caudatus leaves was evaluated by the DPPH° assay and in a linoleic acid model system, while TPC and ascorbic acid were evaluated spectrophotometrically; antioxidant activity of A. hybridus determined in this was very low (3.67%) in the applied assays (Odukoya and others 2007).

All the applied methods showed that pseudocereals, including 3 amaranth cultivars, had higher antioxidant activity than some cereals (rice and buckwheat), whereas the TPC well-correlated with antioxidative indicators (Gorinstein and others 2008). Polyphenol extracts of amaranth seeds isolated with acidified methanol/water exhibited higher inhibition of lipid peroxidation than the ones extracted without adding HCl; their antioxidant activity was comparable to that of butylated hydroxyanisole at a concentration of 0.2 mg/mL. The antioxidant activities in ABTS°+, β-carotene bleaching, and DPPH°-scavenging assays showed high-correlation coefficients with the presence of TPC, while proteins possessed only minimal values of bioactivity (Gorinstein and others 2007).

Amaranth proteins, their fractions, as well as hydrolyzed products were also shown to possess antioxidant activity. For instance, the IC50 values in ABTS°+ assay of peptides, present in the phosphate buffer-soluble fraction of A. mantegazzianus protein isolate, albumin, globulin, and glutelin fractions, were 92.4, 423.1, 127.1, and 25.1 mg protein, respectively. The radical-scavenging capacity of alcalase hydrolysates of isolates and protein fractions was even higher (Tironi and Añón 2010). It is interesting to note that globulin P fraction, which did not possess any activity at the dose of 114 μg, was the strongest antioxidant after hydrolysis, with an IC50 value of 16.5 μg. Linoleic acid oxidation was also inhibited by the naturally occurring peptides and polypeptides; however, after hydrolysis, it was partially lost. Several antioxidatively active peptides and polypeptides were present in the isolate and its hydrolysates: the IC50 values of FPLC fractions were 15.3 to 46.4 μg protein, while linoleic acid oxidation inhibition was 0.08% to 13.4% inhib/μg protein (Tironi and Añón 2010). In another study, a simulated gastrointestinal digestion was applied to A. mantegazzianus proteins by hydrolyzing a protein isolate (I) first with pepsin (pH 2, 37 °C) and then with pancreatin (pH 6, 37 °C); the soluble fractions scavenged free radicals after gastrointestinal digestion in the ORAC and ABTS°+-scavenging assays and were suggested as promising functional food ingredients (Delgado and others 2011). IC50ABTS and ORAC values of amaranth protein digests were in the ranges of 1.16 ± 0.09 to 1.71 ± 0.45 mg prot/mL (trolox = 0.28 ± 0.04) and 0.199 ± 0.003 to 0.308 ± 0.007 μg trolox/μg prot. The antioxidant activity of the protein isolate was remarkably lower, with IC50ABTS and ORAC values of 10.2 ± 0.8 mg prot/mL and 0.112 ± 0.018 μg trolox/μg prot, respectively (Delgado and others 2011).

Addition of amaranth at a 30% dose increased the content of total phenolics, flavonoids, and antioxidant power in FRAP and DPPH° assay systems of bread by 54%, 72%, 79%, and 71%, respectively; however, sensory quality of the product with amaranth was inferior as compared with whole wheat flour bread (Chlopicka and others 2012).

Effects of environmental factors and fertilization on antioxidant properties

It is well known that environmental factors may affect the phytochemical composition of plants, and consequently, their antioxidant properties. For instance, the highest TPC and AA values were determined for red-fleshed-leaf cultivars (A. tricolor L. subsp. mangostanus L. Allen) grown in full sunlight (open shade) compared to 4 selected shading regimes; strong positive correlations were found among betacyanin, chlorophyll, TPC, and antioxidant activity in red-fleshed-leaf cultivars compared to green-fleshed-leaf cultivars under different shading conditions (Ali and others 2010). In the other study, the effect of 6 to 24 h length photoperiods was evaluated; the highest antioxidant activity and TPC values in the leaves were under a 12 h and the lowest under a 24 h photoperiod. All measured characteristics were higher for red amaranth than for green amaranth (Ali and others 2009). The TPC and antioxidant activity differed among the leaves of 7 red amaranth (A. tricolor) cultivars grown under full sunlight and shaded conditions: the leaves of “Rocto Joba” and “Rocto Lal” had the highest TPC and antioxidant activity, respectively (Khandaker and others 2008). Comparatively, the leaves from plants grown under full sunlight without shading and red-fleshed cultivars had higher TPC and antioxidant activity values than green-fleshed cultivars. The positive correlation between antioxidant activity and TPC suggests that phenolic compounds are the major antioxidant components in red amaranth.

The physiological activities were affected by different light quality treatments during amaranth germination. The TPCs were extremely increased in amaranth sprouts grown under the blue color light and the mixed light of blue and red color. The total flavonoid content increased under the red + blue light by 21.2 mg/L and was 2 times higher than the control. DPPH°-scavenging activity at a concentration of 2 g/L was increased over 34% in the samples, which were sprouted and grown under the blue or mixed light of red and blue color compared with the control. Nitrite radical-scavenging activities of sprouts were most decreased compared with the control when grown under all lights except yellow light. Mushroom tyrosinase inhibition activity of amaranth sprouts was much lower than the control under the blue and mixed light of blue and red color (Cho and others 2008). The effects of sprouting on TAC, TPC, and anthocyanin contents in A. cruentus seeds were also studied and amaranth seeds and sprouts were suggested as a good source of anthocyanins and TPC, with high antioxidant activity (Paśko and others 2009).

The TAC of amaranth depended on the plant variety (“Rawa” and “Aztek”) and on the doses of the NPK fertilizer; dependencies between TAC of the soils and leaves and the levels of NPK, as well as between the TAC of the soil and of amaranth leaves were shown by the statistical data analysis (Skwaryło-Bednarz and Krzepiłko 2009).

Effects of processing on antioxidant properties

Green leafy vegetables are seldom consumed raw and often some amount of processing is inevitable to increase their palatability; however, processing conditions may lead to significant losses in nutritive properties. Processing conditions like blanching are known to reduce 50% to 70% ascorbic acid content, which is a strong antioxidant, and 10% to 45% losses in free radical scavenging ability (Oboh 2005). Green leafy vegetables are also prone to vitamin and antioxidant power losses during preprocessing handling, conditions like exposure to light, refrigerated storage, and so on (Faboya 1990). The effects of processing on antioxidant properties were also studied. Antioxidant activity increased during puffing at 250 °C/75 rpm and roasting at 150 °C/20 min from 0.14 to 0.71 and 0.39 μmol TE/g flour, most likely due to the formation of Maillard reaction antioxidants (Tikekar and others 2008). However, it should be noted that antioxidant activity of grain determined in this study was extremely low. The TPC in amaranth grain reduced during processing by 30%; however, only ethanol extract from toasted grain possessed a lower antioxidant capacity index compared with the raw grain, 1.3 compared with 1.7 (Queiroz and others 2009). The capacity to inhibit amaranth lipid oxidation was not affected by extrusion, popping, and toasting, whereas cooking that continues longer time at high temperatures (100 °C/10 min) increased the inhibition of lipid oxidation (79%). The TPC of amaranth grain was reduced by the most common processing methods, whereas the antioxidant power of extruded and popped grain, evaluated in β-carotene/linoleic acid system and the Rancimat method, was similar to that of the raw grain (Queiroz and others 2009). Later, Milán-Carrillo and others (2012) reported that ORAC value of bound phytochemicals present in A. hypochondriacus flour increased after extrusion, whereas antioxidant capacity of free phytochemicals decreased; however, the TAC of extruded flour was higher by 11%.

Antioxidant potential of 4 types of amaranth, namely, A. paniculatus, A. gangeticus, A. blitum, and A. viridis species, locally known as spinach, assessed in β-carotene–linoleate, DPPH°-scavenging model systems, and with Folin-Ciocalteu reagent was different and it decreased during blanching. For instance, TPC decrease during blanching (15 min) depending on the species was in the range of 9% to 71% (Amin and others 2006). A significant reduction was found in TPC and antioxidant activity in β-carotene and linoleic acid emulsion after shallow frying of amaranth (Gitanjali and others 2004).

Amaranth in the Production of Cereal-Based Products and Other Applications

Amaranth seeds can be cooked, roasted, popped, flaked, or extruded for human consumption, whereas overground parts are used as green leafy vegetables consumed fresh or processed. Processing may influence starch and protein properties, fatty acid composition, microconstituents, antioxidant properties, and other characteristics. For instance, differences in chemical composition of A. caudatus seeds due to popping (175 and 195 °C for 15 to 25 s), flaking (adjusting moisture content to 26% and using heated 200 °C rotating drums for a contact time of 1 to 3 s), and roasting (heating at 150 °C for 60 to 90 s) were small and insignificant, except for lower available Lys values, and insoluble fiber with higher values in the roasted sample than in the flaked and popped samples (Bressani and others 1987c). The changes of amaranth constituents during processing were discussed in previous sections; therefore, this section will focus on the use of amaranth as a substitute for cereals in the production of bread and other cereal-based foods.

The main purpose of amaranth application in cereal products is to obtain gluten-reduced and gluten-free products, while enrichment of such products with valuable nutrients is another important task. From this point of view, it is important that amaranth can be grown in many drought-prone semitropical countries for producing high-protein flour that is a nutritional complement to wheat flour (Samiyi and Ashraf 2007). However, many parameters of processing and quality characteristics of final products should be considered in order to develop cereal-based foods with amaranth flour because the production of high-quality bread from gluten-free flour, due a very low gas binding and crumb structure forming capacity in gluten-free batters, is a complicated task.

Partial replacement of cereals by amaranth flour and its fractions

The levels of added amaranth flour to bakery products depend on many factors, primarily the type of the product, its production technology, and others. The effects of substitution of wheat, rye, and other cereals by amaranth on dough properties, final product quality, sensory characteristics, consumer preference, and nutritive value were reported in many articles, which in most cases emphasized the need for an improvement in the quality of cereal-based gluten-free products. Therefore, the research focusing on the use of pseudocereals as amaranth, quinoa, and buckwheat in the development of high-quality bread, pasta, and other “healthy” products has been increasing in order to ensure an adequate intake of nutrients in humans with celiac disease (Alvarez-Jubete and others 2010a). However, commercialization of palatable pseudocereal-containing gluten-free products is limited, because such foodstuffs remain a challenge due to poor functional and nutritional properties of alternative ingredients (Calderón de la Barca and others 2010). Bread making includes many methods of dough preparation; therefore, replacement of wheat or rye flour by amaranth flour was studied taking into account the effects of such replacement on dough and bread quality characteristics, as well as fermentation processes.

The properties of the main amaranth and wheat components, proteins and polysaccharides, are different and therefore admixture of amaranth flour into wheat-based recipes affects various technological parameters of dough and quality characteristics of the final products. These effects depend on many factors, primarily on the replacement ratio and production technology. Sometimes, literature data provide rather controversial results on this matter. Many studies have been trying to determine an optimal amount of amaranth, which could be used for substitution of wheat; however, it is not an easy task because of the complicated bread making processes and numerous quality characteristics that are important for the dough and for the final product. It was shown that pure wheat flour developed significantly higher pasting viscosity than pure amaranth flour and this was attributed mainly to the higher swelling power of wheat starch and to the coarser particle size distribution in the amaranth flour; however, the amaranth flour absorbed more water than the wheat flour during dough making and this was explained by the presence of larger amounts of crude fiber in the amaranth flour, which tended to imbibe and retain more water in the dough (Keya and others 1999). It was concluded that amaranth flour could be used in making high dry matter content gruels at desired viscosity; the composite flours compared to wheat flour produced dough with weaker viscoelastic properties and the composite bread had smaller, darker-colored and denser-textured slices than the pure wheat bread (Keya and others 1999). In addition, a slightly bitter after-taste sensation was recognizable in the composite bread and it was concluded that amaranth has high potential as a low-level partial substitute for wheat in order to increase the nutritional value of bread and to spread out the utilization of limited available wheat. Another study showed that the increase of amaranth flour substitution for wheat flour increased water absorption, arrival time, weakness, and modulus of elasticity and viscosity coefficients of dough, while pasting properties of starch prepared from 10% amaranth flour-substituted wheat dough with the addition of hemicellulose, lipase, or both decreased peak viscosity and setback (Park and Morita 2004). By increasing the wholegrain amaranth replacement ratio from 10% to 30% in cereal flours, the water absorption, gelatinization temperature, development time, and stability increased. The amaranth addition also strengthened the dough, mainly by decreasing its extensibility and, in spelt-containing composite flours, also by increasing the resistance to extension; it was concluded that 10% to 20% of amaranth strengthens the dough and improves some rheological properties (Mlakar and others 2009). The frequency-dependent elastic G’ and viscous G’’ moduli calculated by dynamic tests revealed that, in general, the amaranth added to the recipe increases both of them. It was also suggested that amaranth has a double effect in dough, as causing large discontinuity in the matrix (due to the presence of high amounts of teguments), and acting as a filler of the dough matrix (due to a very small starch granules and high protein content) (Mariotti and others 2009).

Substitution of 10% and 15% (w/w) wheat flour by amaranth flour improved dough processing (increased binding of flour, production of CO2), porosity of bread-inside (more regular with softer pores), and increased nutritive value of products; however, 20% substitution resulted in a considerable decreased content of gluten and a negative effect on the quality of dough (adhesiveness) and bread (very low specific volume, amaranth flavor) (Burisová and others 2001a). However, in the case of 3 Iranian breads, the replacement of up to 30% of wheat by amaranth had little adverse effect on sensory characteristics but improved calculated nutrient composition (Samiyi and Ashraf 2007). When the concentration of whole amaranth flour was raised up to 40% crumb hardness and elasticity increased, and color values were significantly affected; therefore, it was concluded that 10% to 20% of amaranth flour could be used for increasing nutritional value with a slight depreciation in bread quality (Sanz-Penella and others 2013).

Popped A. cruentus (10% to 20%) increased protein, crude fiber, and ash content and improved crust color and flavor; however, popped grain reduced crumb elasticity and loaf volume (from 3.54 to 2.36 mL/g), increased crumb hardness, contributed to denser crumb structure, and more uniform porosity. It was concluded that sensorially acceptable supplementation levels were up to 15% (Bodroža-Solarov and others 2008). Incorporation of up to 30% (w/w) of amaranth in the dough improved the score of loaf color, 10% of substitution had positive effect on specific volume, whereas taste, aroma, texture, and overall acceptability of bread were not influenced (Mlakar and others 2008). In another study, the addition of 10% amaranth flour and protein isolate prepared from amaranth seeds did not cause significant changes of rheological properties in wheat flour dough and bread; however, higher additions (20 and 30%) changed the stability, the degree of elasticity, and softening. Substitution of wheat flour by amaranth flour increased water absorption capacity, resistance to deformation (firmness) of the crumb, but reduced specific volume. The main rheological parameters of dough and bread crumb were not significantly affected by the addition of protein isolates (Tömösközi and others 2011).

The negative effect of amaranth addition may be compensated by the use of additives. For instance, 5% to 20% of amaranth flour substitution reduced the loaf volumes of bread to 94% to 83% of the control; however, lipase (2250 units/kg flour) and hemicellulase (1 × 104 units/kg flour) added to the 10% amaranth flour-substituted wheat flour increased the loaf volumes by about 18% and 23%, respectively (Park and Morita 2004). In addition, the firmness of bread-crumbs in case of using enzymes became significantly softer than that of the control bread after 3 d storage, and the bread with 10% amaranth flour and lipase obtained higher sensorial scores than the control, except for its color. Bread with amaranth scored significantly higher than did bread without amaranth for earthy aroma, earthy flavor, and astringent taste, while the scores for intensity of color, cereal aroma, and cereal taste were significantly lower (Kihlberg and others 2005). The flour obtained by total grinding of the grain contains more minerals; however, this process also leads to the presence of higher concentrations of phytates acting as antinutritional components: it was shown that citric acid and phytase added in fermented baked products with whole amaranth flour enabled to obtain nutritional advantages (Dyner and others 2007). Addition of amaranth at a 30% dose increased the content of total phenolics, flavonoids, and antioxidant power of bread; however, sensory quality of the product with amaranth was inferior as compared to whole wheat flour bread (Chlopicka and others 2012). Addition of 20% and 40% of whole amaranth flour increased the mineral content in bread; for instance, the content of Fe increased up to 1.6 (29.94 μg/g) and 2.3 times (43.88 μg/g), respectively.

Amaranth was also used in sourdough bread making processes and it was reported that it had no effect on the product volume and moisture; however, baking loss was lower, while the porosity was higher in the case of sourdoughs with amaranth as compared with other gluten-free flours such as buckwheat, millet, and rice (Wolska and others 2010). It was shown that acidification in A. hypochondriacus dough preparation (the use of lactic acid or fermentation with lactic acid bacteria) may positively change the rheological behavior of amaranth. However, addition of lactic acid up to 20 mL/kg flour had a significant positive effect only at the higher stress level, while sourdough fermentation by Lb. plantarum produced doughs with elasticity and viscosity similar to that of pure wheat flours (Houben and others 2010). Lb. plantarum and Lb. paralimentarius showed small variations in fermentation pH, TTA, and lactic acid concentration in amaranth-based sourdoughs, while Lb. helveticus reached the most intensive acidification after initial adaptation to the substrate. In this case, lactic acid metabolism did not influence acetic acid production, while the lactic/acetic acid ratio exceeded recommendation by 10 to 35 times; sensory properties of bread were dependent on the microorganisms but not significantly different at the 2 tested fermentation temperatures (Jekle and others 2010). Sourdough fermentation of cereal, pseudocereal, and leguminous flours with Lb. plantarum C48 and Lactococcus lactis subsp. lactis PU1 were tested and it was found that amaranth, chickpea, quinoa, and buckwheat were the most suitable for enriching with γ-aminobutyric acid (Coda and others 2010). A sourdough bread produced with a blend of amaranth, buckwheat, chickpea, and quinoa flours (ratio 1 : 1 : 5.3 : 1) and fermented with Lb. plantarum C48 had the highest concentration of free amino acids and γ-aminobutyric acid (4467 and 504 mg/kg, respectively), phenolic compounds, and antioxidant activity, whereas the rate of in vitro starch hydrolysis was the lowest. Sourdough fermentation enhanced several characteristics of such bread with good palatability and overall taste appreciation, thus approaching the features of wheat flour bread (Coda and others 2010).

Whole amaranth flour was tested in conventional and reduced-fat pound cakes for replacement of wheat flour and corn starch by 10% to 30%. The replacement resulted in lower color acceptability due to darker crust and crumb; however, texture characteristics of fresh amaranth-containing cakes were similar to the controls (Capriles and others 2008a). It is interesting to note that the highest replacement dose of 30% decreased overall acceptability scores of conventional cakes (lower specific volume and darker color); however, had no significant effect on overall acceptability of reduced-fat cakes. Moisture losses were approximately to 1% per day for all cakes; however, conventional and reduced-fat cakes with amaranth had higher chewiness and hardness values than the control cakes after 6 d of storage (Capriles and others 2008a).

Replacement ratios of 0.04, 0.08, and 0.12 with hyperproteic A. cruentus flours containing 0.41 and 0.51 of proteins (N × 6.25 dry basis) increased the protein content by 9% to 38% compared to purely wheat flour bread and at low replacement ratios did not cause remarkable changes in bread quality for the whole flour, while in case of defatted flour, only a 0.04 replacement was acceptable (Tosi and others 2002). Increasing the level of amaranth flour from 0% to 50% (w/w) increased the water absorption of dough, decreased loaf volume index from 3.29 to 1.9, increased moisture content from 22% to 42%, and decreased mean scores of the odor, taste, color, and texture from 6.9 to 4.0, 7.1 to 4.8, 7.1 to 6.8, and 6.9 to 4.7, respectively; it was concluded that above 15%, the product becomes unacceptable (Ayo 2001). The rheological test based on alveograms and farinograms showed that wheat flour supplemented with 1% amaranth albumins extracted from 2 new Mexican amaranth varieties increased mixing stability of dough and improved bread crumb characteristics (Silva-Sánchez and others 2004). Amaranth albumin proteins (1%, 3%, and 5%) increased proportionally the mixing time requirements, dough strength, and stability of the reconstructed dough; it was shown that amaranth albumins are capable of interacting with gluten proteins through disulfide bonds (Oszvald and others 2009).

Starch from A. paniculatus was used in a blend with soy flour to produce fried noodle-like products; it was reported that the oil content in fried products decreased with increased starch content and was also dependant to the amylose content (Ahamed and others 1997). A composite flour consisting of 25% A. paniculatus flour and 75% wheat flour slightly increased the percentage in protein, fat, and dietary fiber contents of the blend; popped amaranth and its products such as porridge, chikki laddoo, and snack mixture had excellent taste and were well accepted; composite flour was also preferable for chapatti and poori compared to pulka (Sarojini and others 1996). The addition of 2% to 4% of isoelectric protein concentrates isolated from 5 Amaranthus genotypes to wheat noodle dough significantly increased its strength, which correlated to the water-insoluble fraction level of the concentrate. Various quality characteristics of the noodles were also affected by the concentrate at different levels (Bejosano and Corke 1998b).

Wheat flour-based formula was supplemented with inulin in combination with amaranth for developing improved biscuits. Although the biscuits with amaranth had a slightly lower amount of total proteins than the reference produced from wheat, the amount of available proteins and their digestibility was higher by 22% (Vitali and others 2009). In addition, the content of insoluble and soluble fiber also increased by 30.9% and the contents of Ca, Mg, Fe, Mn, and Cu were higher in the product with amaranth by 44%, 49%, 67%, 19%, and 43%, respectively. The content of total phenols increased by 28%, while bioaccesible phenols increased by 65%. ABTS°+-scavenging measured in TEAC of chemical extract (MeOH:H2O:HCl) was almost similar for the reference and amaranth biscuits, while the activity of physiological extract of biscuits with amaranth was higher by 44%. The biscuits enriched with carob, amaranth, soy flour, and crude apple fibers possessed better antioxidant properties due to significantly higher amounts of extractable phenolic components and probably also due to the formation of Maillard reaction compounds that have also been referred to as compounds possessing antioxidant capacity (Vitali and others 2008). Amaranth flour was substituted for extra fancy and fancy durum wheat flours at 5% to 30% levels to produce multigrain pastas with higher contents of Lys, acceptable cooking quality, and sensory characteristics; the changes in texture and flavor were detected at 25% amaranth (Rayas-Duarte and others 1996). Amaranth seed flour (5% to 10%) was used for enhancing the fiber and protein contents in the pasta produced from Indian Triticum aestivum with dehydrated green pea flour and additives (Sudha and Leelavathi 2012).

The effects of substitution of wheat by amaranth in the proportion of 1 :  3 (w/w) on the formation of acrylamide was tested for shortcrust cookies baked at 180 °C for 10 min. The concentration of acrylamide precursors, aspartic acid + asparagine, and reducing sugars in the mixture was 381 and 10.87 mg/g solid substance (s.s.), respectively, while in pure wheat, it was 245 and 12.04 mg/g s.s. Acrylamide content in pure wheat flour cookies was 41.9, while in the mixture 36.7 mg/kg, thus indicating that substitution of wheat by amaranth had only a slight effect on the content of acrylamide (Miśkiewicz and others 2012).

Amaranth contains a remarkably higher content of total folate (52.8 to 73.0 μg/100 g dw) than wheat (13.5 μg/100 g dw) and therefore was used to enrich such staple foods as bread, noodles, and cookies with this important vitamin by replacing 40% of wheat by amaranth. And even the total folate in bread, noodles, and cookies during thermal processing decreased by 48.2%, 36.3%, and 16.4%, respectively; its content in the final products was as high as 35.6 to 38.9 μg/100 g dw (Schoenlechner and others 2010b). Average loss of total folate in bread, noodles, and cookies after storage was 51%, 24%, and 16%, respectively; despite these losses, total folate content was 17 to 98 μg/100 g dw in noodles, 18 to 62 μg/100 g dw in cookies, and 26 to 41 μg/100 g dw in breads.

The replacement of wheat flour by A. cruentus flour (up to 40 g/100 g) significantly increased lipid, protein, dietary fiber, ash, and mineral contents in bread; however, the content of phytates was also significantly higher, while the amount of myo-inositol phosphates was lower, which could cause low mineral bioavailability at high levels of substitution (Sanz-Penella and others 2013). The levels of soluble phytates in the breads with amaranth increased up to 1.20 μmol/g dw for the 40% of substitution causing negative effects on Fe availability (Sanz-Penella and others 2012).

Extruded breakfast cereal products produced from amaranth, buckwheat, and millet flours as a replacement for wheat and maize flour, exhibited increased product and bulk density; however, expansion ratio was not significantly different (except for 65% of amaranth) compared to the control sample. In addition, predictive in vitro glycemic profiling showed that readily digestible carbohydrates and slowly digestible carbohydrates were reduced in all of the extruded products with pseudocereals compared to the controls (Brennan and others 2012).

An interesting study was performed in order to evaluate consumer attitude toward the use of amaranth in bread. Although the loaf volume of bread baked with organic winter wheat and 25% A. cruentus grain decreased by 9%, the information concerning added amaranth (neophobic factor) did not result in significant differences in liking bread among 480 consumers (Kihlberg and others 2005). The effects of wheat substitution by amaranth flour on dough and bread characteristics are summarized in Table 7. Negative amaranth effect on loaf volume reported by the majority of studies, most likely is one of the main factors limiting the level of such substitution. Generally, 10% to 15% amaranth flour was reported as the optimal substitution rate; however, in some cases, admixture of up to 20% amaranth flour was also acceptable in terms of bread quality.

Table 7. Effects of amaranth addition to wheat dough and bread
Dough characteristicEffectsBread characteristicEffects
Production of CO2Loaf volume↓↓↓
Water absorption↑↑↑Moisture
Modulus of elasticityPorosity
Modulus of viscosityCrumb elasticity↑↓
Gelatinization temperatureCrumb hardness
Development timeCrumb firmness
StabilityColor↓, no
ExtensibilityOdor↓, no
Resistance to extensionTaste↓, no
StrengthCrust color
  Crust flavor

Use of amaranth in the production of gluten-free products

Partial replacement of wheat or rye by amaranth does not eliminate the gluten problem; therefore, there were attempts to produce bread and other foods using only gluten-free materials and amaranth was one of the main ingredients in such tests. The impact of various factors on the structural, textural, and sensory characteristics of gluten-free bread containing amaranth flour was evaluated using 23-factorial screening experimental design; the amount of water had the greatest influence, the variations in fat amount did not have any significant influence, whereas the combined addition of fat and albumen resulted in the best rankings in overall sensory acceptance (Schoenlechner and others 2010a). Amaranth flour increased resistance to freezing of gluten-free dough, but decreased its resistance to storage conditions: rheological properties of dough were more altered at the temperature of −30 °C than at −18 °C (Leray and others 2010). In another study, the best formulation for gluten-free bread containing around 12 ppm gluten included 60% to 70% popped and 30% to 40% raw amaranth flours, which gave loaves with homogeneous crumb and higher specific volume compared to other gluten-free breads. The best cookie recipe had 20% of popped amaranth flour and 13% of whole-grain popped amaranth (Calderón de la Barca and others 2010).

Bread produced from 50% A. caudatus grain and 50% rice flour contained 3.4 times higher content of fat, 28% higher dietary fiber, and 2 times higher content of Mg as compared with the wheat control, while the differences in protein, total starch, Ca, and Zn were less remarkable (Alvarez-Jubete and others 2009). Although significant differences were observed in the scanning electron micrographs of the pseudocereal flours, rice flour, wheat flour, and potato starch, as well as color characteristics of bread crumb (L*/b*), crumb hardiness, cohesiveness, and springiness, there were no significant differences in the loaf volume and only slightly lower acceptability of the amaranth/rice-containing gluten-free breads in comparison with the gluten-free control bread (Alvarez-Jubete and others 2010b). Significantly softer crumb texture of pseudocereal-containing breads was characterized by an effect that was attributed to the presence of natural emulsifiers in the pseudocereal flours. Recently, it was shown that one of the most abundant and important storage proteins of the amaranth grain, 11S globulin, possesses good emulsifying property (Tandang-Silvas and others 2012), which might have a positive effect on dough formation.

The substitution of 40% A. hypochondriacus flour for 40% corn starch decreased the amount of water necessary to yield good dough consistency (especially when no thickening agent and fiber source Psyllium fiber was present in the mixture), possibly be due to the larger amaranth flour particle size than corn starch. Many wide plates of teguments (width: even P600 μm) together with specific small starch granules (diameter: 0.5 to 2 μm) or their agglomerates (width: 80 μm) were present in amaranth flour. Rheological, ultrastructural, and nutritional properties of the experimental gluten-free doughs were improved by such protein and fiber sources as pea isolate and amaranth (Mariotti and others 2009). A softer crumb texture effect of the pseudocereal-containing breads (buckwheat, quinoa, and amaranth) was confirmed by the confocal images and attributed to the natural emulsifiers that are present in the pseudocereal flours; however, there were no significant differences between the acceptability of the pseudocereal-containing gluten-free and control breads (Alvarez-Jubete and others 2010b).

The properties of amaranth seed meals depend on the presence of salts and the level of pH. For instance, it was shown that NaCl and NaHCO3 improved the water absorption capacity and protein solubility of A. tricolor seed meal; however, the salts had adverse effects on foaming capacity and foam stability, which was better at lower concentrations of NaCl (0.2 to 0.6 M). Salts did not change the emulsification properties, while relative viscosity of amaranth meal, which was highest at pH 10 and lowest at pH 4, significantly increased at higher concentrations of NaCl and NaHCO3 (0.6 to 1.0 M) (Mahajan and Dua 2002).

Amaranth was used in pasta products and it was shown that without emulsifier, the production of amaranth-containing pasta products with good cooking and sensory properties were not possible: the best pasta was produced from A. cruentus with 1.2% of diacetyl-tartaric ester of monoglyceride (Kovács and others 2001, 2002). In the case of some emulsifiers, the authors detected a protein-emulsifier and emulsifier-carbohydrate interaction with 50% to 90% complexing rate. In the other study, the effects of sodium carboxymethyl cellulose, whey protein, casein isolate, chitosan, and pregelatinized starch on the amaranth dough rheological properties and the extruded tagliatelle dough mechanical characteristics were evaluated and it was shown that the additive caused a rise in tenacity of the amaranth tagliatelle (Chillo and others 2009).

Enrichment with amaranth improved mineral and fiber contents, and protein digestibility of rice-based pasta, while a novel extrusion-cooking process was applied prior to pasta-making for improving the textural characteristics (Cabrera-Chávez and others 2012). The novel process also decreased protein solubility and the content in accessible thiols in the amaranth-enriched pasta, indicating that amaranth proteins may be involved in forming disulfide bonds. The results also suggested that rice flour starch interacts best with amaranth proteins when starch gelatinization and protein denaturation occur simultaneously during the extrusion-cooking (Cabrera-Chávez and others 2012).

Four novel antifungal peptides, encrypted in amaranth agglutinin sequences, were identified in the water-soluble extract of amaranth seeds inhibiting a large number of fungal species isolated from bakeries, which was applied for extending the shelf-life of gluten-free and wheat flour breads: the inhibitory activity was demonstrated during long-term storage studies (Rizzello and others 2009).

Other Applications

Although cereal-based baked products are the main area of amaranth applications, amaranth flour and its constituents were tested for other uses as well. For instance, “high-nutritional-value product” with amaranth grain, sweet potato, pigeon pea, groundnuts, and brown sugar was the most acceptable supplement among 4 developed food supplements in Kenya; it contains 453.2 kcal energy, 12.7 g crude protein (21% total essential amino acid), 54.3 g soluble carbohydrates, 20.8 g crude fat, 10.1 g crude fiber, 93.0 mg Ca, 172.4 mg Mg, 2.7 mg Zn, 5.7 mg Fe, 0.8 mg vitamin B1, 0.2 mg vitamin B2, 7.9 mg niacin, 100 μg folic acid, and 140 μg retinol per 110 g (Kunyanga and others 2012b). This study demonstrated that acceptable, nutritious, low-cost, and shelf-stable supplementary foods may be produced for vulnerable groups from the locally available indigenous foods. A. tricolor leaves have been used in the recipes of various traditional products in India and it was shown that the leaves themselves and their products are good sources of protein, Ca, Fe, and β-carotene (Punia and others 2004).

Replacement of 15% beef protein in an emulsion-type meat product by Amaranthus protein concentrates isolated from 5 plant genotypes considerably affected both the emulsion and the cooked meat gel properties; however, some positive effects were obtained only in the case of genotype K112 (Bejosano and Corke 1998c). The addition of red Amaranthus pigments in the manufacture of pork sausage at 0.1% to 0.3% concentrations for substituting nitrates resulted in a significant increase of a*-values, sensory color, flavor, and overall acceptance scores, but also in the significant reduction of b*-values, thiobarbituric acid (TBA) values, and volatile basic nitrogen (VBN) values. Based mainly on the results of overall acceptance during 29 d of storage, it was concluded that Amaranthus pigments might be a potential nitrite alternative (Zhou and others 2012).

Protein- and starch-rich A. cruentus seed fractions obtained by the air classification were used in infant formulas matching a previously developed soy-oats formula; in proximate chemical composition and calorie distribution patterns, amaranth formulas satisfied all requirements; however, both were inferior to the soy-oats formula in essential amino acid profile. It was concluded that a formula produced with an amaranth-protein-rich fraction would be an effective lower cost alternative to the soy-oats formula (Del Valle and others 1993).

Small-sized starch granules, isolated from A. paniculatus and polysaccharide bonding agents, were used for entrapment of a model flavoring compound, vanillin, and it was shown that gum Arabic at 1.0% with amaranth starch gave better encapsulation of vanillin than carboxymethyl cellulose and carrageenan. Amaranth was better encapsulating material than colocasia, chenopodium, and rice starches, which was explained by the amount of amylose in the starches (Tari and others 2003).

Hydroperoxide lyase naturally originating from A. tricolor was used to catalyze the reaction to generate (2E)-hexenal from 13-hydroperoxy-9Z,11E,15-Z-octadecatrienoic acids for providing a green method for the large-scale production of this aroma compound: a maximum yield of (2E)-hexenal was 1156.4 mg/L (Xiong and others 2012).

Edible films

The amaranth flour was tested as a raw material for the production of edible films and coatings (Tapia-Blácido and others 2013 and references herein). Statistical analysis results showed that the optimized conditions for producing amaranth-based films were 10 g stearic acid, 26 g glycerol/100 g flour, and a stirring speed of 12000 rpm. The films produced under these conditions demonstrated better mechanical properties when comparing to those of other protein and polysaccharide composite films, low solubility (15.2%), and optimal barrier properties (Colla and others 2006).

The films of amaranth flour were obtained in a casting process using glycerol as plasticizer (Tapia-Blácido and others 2007) and it was determined that glycerol content, pH, and process temperature were significant factors affecting mechanical and barrier properties. The biofilms were characterized by a yellowish color, moderate opacity, high flexibility, and low tensile strength; however, they had less oxygen and water permeability than other polysaccharide and protein films (Tapia-Blácido and others 2005a). Drying curves revealed that a long period with a constant drying rate is predominant in all the studied conditions. This trend was also observed in other studies using A. caudatus flour, chitosan, soy protein, and alginate films (Tapia-Blácido and others 2005b, Tapia-Blácido and others 2013 and references herein). Glycerol and sorbitol act as a water-holding agent and plasticizer, respectively; the optimal formulation as a function of their concentration and heating temperature (Tapia-Blácido and others 2011), as well as the influence of drying temperature and relative humidity on the mechanical properties, solubility, drying time, and water vapor permeability of amaranth flour films were reported (Tapia-Blácido and others 2013).

Amaranth edible films were also produced with antimicrobial essential oils of Mexican oregano, cinnamon, or lemongrass and antifungal activity was evaluated against Aspergillus niger and Penicillium digitatum after exposure to vapors arising from added essential oils. Amaranth films possessed antifungal activity; however, it was weaker than chitosan films (Avila-Sosa and others 2012).

Conclusive Remarks

The review is summarizing the numerous data on different compositional aspects of grain and vegetable amaranths, as well as their uses, technological, antioxidant, and other properties, which have been presented in 242 literature sources. The review covers the period of research and development up to 2013. Although the intensive studies of amaranth grain composition were begun in 1970s and their results were reviewed in several articles, a comprehensive review on Amaranthus providing more exhaustive data was not available until now, particularly regarding plant antioxidant potential, the contents of various microconstituents, the application of novel processing techniques, such as supercritical fluid extraction and fractionation, extrusion, high pressure, as well as the prospects of wider uses of plant grains and fractionated components. The analysis of the research performed during last 2 decades reveal such tendencies as increasing studies of fractionation of amaranth components and their applications in the production of high-quality baked goods, edible films, functional ingredients, and other products. Also, increasing number of studies on determining the effects of the traditional agrotechnological practices and novel treatments on amaranth compositional characteristics may be observed. It may be concluded that the expanding research of Amaranthus during last 2 decades may have an important impact on further commercialization of a wider cultivation and more extensive uses of raw materials obtained from valuable Amaranthus plant species in human nutrition and other applications.


This work was funded by Research Council of Lithuania, grant nr MIP064/2011.


2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation


Amaranth protein concentrate


Docosahexaenoic acid


2,2-diphenyl-1-picrylhydrazyl radical


Dry weight


Equivalent carbon number


Ferric reducing antioxidant power


Gas chromatography


Liquid chromatography


High pressure


High-performance liquid chromatography


Inhibitory concentration


Insoluble dietary fiber


Lipophilic oxygen radical absorbance capacity


Matrix-assisted laser desorption/ionization, quadruple ion trap, time of flight, mass spectrometry




Net protein ratio


Polyacrylamide gel electrophoresis


Protein efficiency ratios


Rapidly digestible starch


Response surface methodology


Supercritical carbon dioxide


Supercritical fluid extraction with carbon dioxide


Soluble dietary fiber


Sodium dodecyl sulfate-polyacrylamide gel electrophoresis




Thiobarbituric acid


Total dietary fiber


Trolox equivalent


Trolox equivalent antioxidant capacity


Trypsin inhibitor activity


Total phenol content


Volatile basic nitrogen


Water vapor permeability