Treatments and uses of Moringa oleifera seeds in human nutrition: A review

Abstract This work reviews treatments and uses of Moringa oleifera seeds in human nutrition. Moringa oleifera seeds are considerable sources of proteins (mean 19%) and lipids (mean 31%). Previous reports presented the nutritional properties of the seeds and oil. Moringa seeds are sources of lipids, and their removal leads to Moringa seed flour with a high protein content which might play a role in food technology and human nutrition. Moringa oil has been tested in frying and was found to be more stable than groundnut oil; its incorporation in groundnut at level lower than 10% improved on the acceptability of chips. Several treatments like roasting, germination, and boiling have been applied to Moringa seeds to produce flour with improved nutritional properties. In particular, defatted Moringa flour has been applied in different formulations including cakes, cookies, burgers, infant porridges. Generally, the products deriving from the flour were more stable in conservation and well accepted for low substitution while high substitution increased the bitterness. Notwithstanding their high content in protein and oil, defatted M. oleifera seed flour and oil are still fairly investigated in order to envisage their integration in the food habits of people. The present wrote up reviews the treatments applied on M. oleifera seeds and applications of the defatted M. oleifera flour and oil in food systems for human nutrition.

properties, recognized by popular use and corroborated by the scientific community.
This article reviews the treatment and application of M. oleifera seeds in human nutrition. The originality of this review compared to previous review is the emphasis on the food application of the defatted Moringa flour and oil. For our point of view, this is the first review on the application of defatted Moringa flour and oil in food systems. A recent review by Leone et al. (2016) reports the characteristics and uses of M. oleifera seeds and oil for human health, while previous review discussed the properties of the seeds without a link to seed treatment.

| N UTRITI ONAL P OTENTIAL OF MORINGA S EEDS
Beyond the interesting presence of proteins, lipids, and carbohydrates, M. oleifera seeds (Table 1) contain vitamins A and B1 (Mbah, Eme, & Ogbusu, 2012). They are also sources of minerals, micronutrients, and bioactive compounds such as flavonoids, saponins, sterols, phytates, and trypsin inhibitors. The seed could be considered as oilseeds from its lipid content varying from 13% to 46%. This presents M. oleifera seeds not only as a protein source but also as a source of lipids and fibers  Compaoré, Nikièma, Bassolé, Savadogo, Mouecoucou, et al., 2011).

| Proteins
Proteins are the main source of nitrogen for human nutrition by bringing the essential amino acids for construction and renewal of body tissue (Biesalski & Grimm, 2010). Moringa oleifera seeds are a protein source, and they represent the second major component of these seeds after lipids. Recent studies reported protein content varying between 18.6% (Kawo et al., 2009) and 37.2% (Bridgemohan, Bridgemohan, & Mohamed, 2014). However, the analysis of defatted M. oleifera seed showed a protein content varying from 32% to 62.8% (Anwar & Rashid, 2007;Govardhan Singh et al., 2011). However, the protein composition of the seeds can cover only the requirements in some essential and semiessential amino acids for humans (histidine, threonine, tyrosine, leucine, isoleucine, phenylalanine) except methionine, lysine, valine, and tryptophan, considered as limiting amino acids (Table 2).
Treatments such as fermentation and germination increased all the amino acids ( Table 2). The nutritional property of Moringa seeds can be improved through complementation with other foods rich in sulfur amino acids or lysine. In this respect, M. oleifera seed can be combined with cereals (rice, corn, sorghum, millet) to produce complementary foods with balanced proteins.

| Vitamins and minerals
Studies by Mbah et al. (2012) showed that M. oleifera seeds contain provitamin A (2.04%) and vitamin B group, in particular B1 or thiamin (0.94%). Vitamin A plays a key role in vision and possesses antioxidant properties in the form of β-carotene by limiting oxidation of molecules such as vitamin E. Vitamin E has been reported in M. oleifera seed oil in the forms of alpha-tocopherol, gamma-tocopherol, and delta-tocopherol.
Moringa oleifera seeds are rich in minerals (Table 3) of which potassium, phosphorus, sodium, zinc, magnesium, and calcium are the principal minerals. Ijarotimi et al. (2013) revealed that M. oleifera seeds exhibited a Ca/P ratio higher than 1, while the Na/K ratio is higher than the recommended value (0.60) (Nieman, Butterworth, & Nieman, 1992). However, the mineral composition of M. oleifera seeds differs significantly (Table 3) from one region of the world to another.

| Biological activity of Moringa oleifera seed
Very few studies are reported on M. oleifera seed as proteins sources. Oliveira, Silveira, Vasconcelos, Cavada, and Moreira (1999) reported that consumption of crude seeds of M. oleifera induced deleterious effects in Wistar rats. They associated the toxicity of the seeds to lectin (hemagglutinin) previously reported in M. oleifera seeds (Santos, Argolo, Coelho, & Paiva, 2005). Ben Salem and Makkar (2009) Igwilo et al. (2013) showed that 30 min soaked M. oleifera seeds did not support growth, and induced threat for the liver of Wistar albinos rats fed for 21 days. No study reported the utilization of Moringa seeds. Ijarotimi et al. (2013) evaluated the effect of germination and fermentation on the functional properties of M. oleifera flour. The apparent mass density 0.45 g/ml (measured without packing) and the true mass density of M. oleifera seeds (0.63 g/ml) did not vary significantly with seed fermentation and germination (Ijarotimi et al., 2013). As some leguminous seeds (bambara groundnut: 0.60-0.75 g/ml), the flour of M. oleifera seeds has a low mass density (Onimawo & Egbekun, 1998). Globally, studies on the functional properties revealed that defatted Moringa flour exhibited higher foaming capacity and stability, higher emulsifying capacity, and lower WAC and viscosity. In addition, the fat absorption capacity was significantly higher than the WAC, making Moringa flour a potential stabilizer for food emulsion and foaming systems.

| COMPREHENSIVE FOOD SCIENCE TRE ATMENTS AND CHEMIC AL COMPOSITION OF MORINGA OLEIFER A SEED
The M. oleifera seeds have a bitter taste and contain antinutritional factors which reduce digestibility making raw M. oleifera seeds/flour unsuitable for consumption. Some treatments were reported on Moringa seeds to reduce their antinutriments and bitterness which can make them easy to use as food or food ingredients (Ijarotimi et al., 2013), the goal that we want to achieve with the improvement of the nutritional quality of the seeds and oil. Mbah et al. (2012) Mbah et al. (2012)  This also affected some mineral ratios such as sodium/potassium ratio (5.65 to 6.42) and calcium/phosphorus (1.24-1.33) which are indicators of body balance and bone formations (Nieman et al., 1992). Irrespective of the treatment, the Na/K ratios were higher than 1, suggesting M. oleifera seeds should be prohibited in people with risk of hypertension (Ijarotimi et al., 2013). The Ca/P ratio higher than 1, along with the contents in Ca and P (Ijarotimi et al., 2013), gives M. oleifera seeds advantage to support growth of children (Nieman et al., 1992).

| Roasting
The protein content in M. oleifera seeds increased during fermentation, but the amino acids lysine and methionine were in all cases the limiting amino acids (Table 2). In addition, the fatty acid profile of M. oleifera seeds significantly varied with fermentation, the polyunsaturated fatty acid increasing from 58.8% to 62.1%, the saturated from 26.8% to 28.7%, and the monounsaturated from 13.54% to 8.54% (Ijarotimi et al., 2013).
Comparatively, alkaloid content of M. oleifera seeds was lower compared to recommended level of 60 mg/100 g for healthy food (McDonald, Edwards, Greenhalgh, & Morgan, 1995).

| Germination
Germination is a normal biological process of plants by which the seeds leave the latency stage (Sangronis & Machado, 2007). During germination, some changes occur in terms of quantity and type of nutrients in seed. These changes could be due to the type and variety of seed and germination conditions (Dhaliwal & Aggarwal, 1999).
An increase of minerals, increase of protein bioavailability, and a reduction of secondary metabolites of foodstuffs are observed during germination (Hassan, Babiker, & Tinay, 2007;Kouakou, Alexis, Adjehi, Marcelin, & Dago, 2008). Several studies reported the effect of germination on the nutritional properties of M. oleifera seeds.
According to Chinma, Gbadamosi, Ogunsina, Oloyede, and Salami, (2014), germination of 12h with changing of water all the 2 hr in order to avoid any spontaneous fermentation reduced the bitterness and astringency caused by antinutrients.

| Oil
Moringa seed oil gathered good thermal, oxidative, and frying stabilities. Ogunsina et al. (2014)  ing. They observed that the free fatty acids increased for 28.6% in Moringa oil and 48.6% in groundnut oil. The increase in free fatty acid during frying is a normal reaction which starts with water liberation from the product being fried followed by thermal hydrolysis of the acylglyceride into fatty acid and glyceride.
The mechanism involves nucleophilic attack of the ester bond of acylglycerol by water (Choe & Min, 2007). Whatever the case, Moringa oil is less likely to hydrolysis than groundnut oil. In this respect, cold-pressed oils from M. oleifera seeds are better than the raw commercial oils and refined groundnut oils. In the same vein, Khattab and Shakak (2012) showed that during frying of potato chips, M. oleifera oil was more stable to oxidation (based on peroxide, free fatty acid, density, viscosity, and refraction index) compared to groundnut oil and the mixture (1/1 ratio) of both. In addition, the acceptability (taste, color, odor, texture, and general acceptability) of potato chips analyzed by a panel of seventeen students was higher as compared to those made from groundnut oil, but lower than that obtained from the mixture of Moringa and groundnut oils (Khattab and Shakak, (2012). Based on the current results, M. oleifera seed oil showed enough promises to be regarded as a more stable and healthy oil in cooking and frying. Chinma et al. (2014) studied the addition of germinated M. oleifera seed flour to wheat flour for cake production. Increase in Moringa level up to 40% increased the protein content from 13.14% to 23.10%.

| Flour
In addition, the fiber, iron, zinc, calcium, lipid, and ash contents also increased significantly with increase in Moringa level in the blend. In contrast, the increase in the level of M. oleifera reduced gradually the pasting properties in general, and particularly peak, final, and breakdown viscosities. The cake made from the blend showed significant decrease in acceptability. The bitter and astringent tastes were more pronounced on 40% substitution, while up to 30% substitution, the cake were rated favorably (Chinma et al., 2014).
Ogunsina, Radha, and Indrani (2011)  Al-Juhaimi, Ghafoor, Hawashin, Alsawmahi, and Babiker (2015) studied the addition of M. oleifera seed flour (2%, 4%, and 6%) in beef burger preparation and found no significant change on the sensory attributes (appearance, juiciness, flavor, taste, tenderness, and overall acceptability  with immunomodulatory and anti-inflammatory actions, may also offer good perspectives to the seeds. Investigations of the effect of consumption of Moringa seeds and products enriched with Moringa seeds on some markers of toxicity in humans are also envisaged.

ACK N OWLED G EM ENTS
The authors thank the members of the doctoral program Food Sciences and Nutrition of the National School of Agro-Industrial Sciences (ENSAI) for their contribution to this review.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.

AUTH O R CO NTR I B UTI O N
NYN, EBN, and RWS have made substantial contributions to conception and design, while RWS and ENF contributed to drafting the manuscript. All the authors critically revised and approved the final submitted version of the manuscript. Prior to submitting the article, all authors agreed on the order in which their names are listed in the manuscript.

E TH I C A L S TATEM ENT
This study does not involve any human nor animal testing.