Functional and pasting properties of fortified complementary foods formulated from maize (Zea mays) and African yam bean (Sphenostylis stenocarpa) flours

Studies were conducted on the functional, pasting and micronutrient content of complementary weaning foods from maize (Zea mays) and African yam bean (AYB; Sphenostylis stenocarpa). The complementary foods were fortified with cattle bone meal, Brachystegia eurycoma (achi)/potash emulisified with red palm oil and Moringa oleifera, to improve the micronutrient content. Maize and AYB (malted and unmalted) were processed into flours, and the fortificants were subjected to different treatments to ascertain the treatment that has the highest micronutrient contents for use in the formulation of the weaning food. Functional properties (water absorption capacity [WAC], bulk density [BD], wettability [WB]) and dispersability [DISP]), pasting properties and micronutrient contents of the formulated blends were determined using standard methods. Ashed fermented by back‐slopping, dried and milled (AFDm) treatment for cattle bone meal, unfermented B. eurycoma/potash emulsion (PU) and fresh fermented M. oleifera treatment had the highest micronutrient contents. The Vitamin A and zinc contents of the formulated infant food were significantly higher (p ≤ 0.05) than the control (Nutrend, an infant complementary cereal food product made from maize and produced by Nestle Nigeria PLC). The WAC and BD ranged from 155 to 195 g/mL for maize–AYB fermented and enriched with fortificant PU (MAFEP) and maize–AYB fermented enriched with fortificant achi emulsion (MAFEA) and 0.86 to 1.43 g/mL for MAFEA and MAFEP, respectively. The WB values ranged from 16 to 40 s for maize–AYB malt‐fermented (MAMF) and MAFEP. There was no significant difference (p ≥ 0.05) in the dispersability. There were significant differences (p ≤ 0.05) in pasting temperature, set‐back viscosity, final viscosity, peak viscosity and breakdown viscosity except for the peak time. The fortified complementary foods prepared from maize flour and malted AYB significantly improved the functional and pasting properties of the flour blends due to their high micronutrient contents and low BD which can serve as alternative to commercial products.


| INTRODUCTION
Intake of cereal-based food products such as maize (Zea mays), sorghum (Sorghum bicolor) and millet (Pennisetum typhoideum) is common in developing countries. These products are mainly used as staple food (Gernah, Ariahu, & Ingbian, 2011), resulting in high incidence of protein deficiency particularly among children (Agiriga & Iwe, 2009;Oosthuizen, Napier, & Oldewage-Theron, 2006) because cereals are known to be low in protein content. Therefore complementary foods are, important in the life of a child to ensure adequate growth and prevent malnutrition, stunting, anaemia and other infectious diseases common in infancy and early childhood. When breast milk nutrients become inadequate for their growth needs, foods of high biological value must be provided to supplement the breast milk in order to meet demand for various activities of the child. The nutritional qualities of weaning foods in Nigeria, as most developing countries, are often low in protein content and devoid of vital nutrients that are required for normal child growth and development (FAO, 2004).
Complementary feeding is introduced early between the ages of 6 and 24 months of birth. Transitional foods are usually produced from cereals, and thus supplementing cereal with legume like African yam bean (AYB) may likely improve the protein content of the cereallegume-based complementary weaning food. In spite of this and other attempts, problems associated with micronutrient inadequacies still persist and relate to deficiencies in calcium, iron, zinc and Vitamin A. It is important to note that Vitamin A deficiency is reported to be endemic in sub-Saharan African, certainly because its content in complementary foods falls below the Recommended Dietary Allowance (RDA) for infants (World Bank Nigeria, 1996). Food fortification with vitamins and minerals has been used in many countries to solve the problems of micronutrient deficiency (Canibe & Jensen, 2007;Salve, Mehrajfatema, Kadam, & More, 2011). However, the use of vitamin and mineral premix results in expensive products to the middle-and low-income earners. Uvere, Onyekwere, and Ngoddy (2010) reported that micronutrient-dense complementary foods could be produced from maize and Bambara groundnut in the ratio of 70:30 with good physical and functional characteristics and increased calcium, iron, zinc and Vitamin A contents. This was achieved by adding processed cattle bone, Roselle calyces and palm oil before fermentation. Incorporating processed Moringa oleifera leaves, cattle bone meal and red palm oil may likely increase the iron, zinc, calcium and Vitamin A contents of the maize-AYB complementary diet (Uvere et al., 2010). It is against this background the study was designed to produce a micronutrient-rich complementary diet for infants.
Functionality of a food is the property of a food ingredient that has a great impact on its utilization (Mahajan & Dua, 2002). In processing most complementary food, prominence had been given to nutritional quality and quantity while functional properties are given less attention. Functional properties are a function of consistency because consistency of complementary food aids in easy swallowing of the food by an infant. The consistency, energy density (energy per unit volume) of complementary food and regular feeding are factors that determine the extent to which an infant can meet his energy and nutrient requirements. According to WHO (2003), a good complementary diet must have high nutrient density (macroutrients and micronutrients), low bulk density (BD), viscosity, appropriate texture and consistency that allows easy consumption.
In most developing countries, complementary foods for infant are cereal-and starch-based. Cereal and starch provides the main source of energy; however, starch forms gel when heated, forming a thick and bulky diet with low energy density but liquid consistency that makes it easy to consume. The volume needed to meet the infant energy need often exceed the maximum volume the infant can ingest. Owing to the low energy and nutrient density, large volumes are usually given to meet the infant requirement without considering the infant's limited gastric capacity and number of meals offered per day. Therefore, the general acceptability of weaning foods by infants is thus influenced by its functionality such as water absorption capacity, bulk density, wettability, dispersibility and pasting properties (peak viscosity, break down viscosity, set-back viscosity, final viscosity and pasting temperature). These functional properties are very necessary to ensure the appropriateness of the diet to the growing child (Omueti, Otegbayo, Jaiyeola, & Afolabi, 2009). Although, there have been studies on fortification of complementary foods with emphasis on nutritional content (Omueti et al., 2009). This work evaluated the functional and pasting properties of complementary weaning food products formulated from maize and AYB fortified with M. oleifera leaves, cattle bone meal, red palm oil, Brachystegia eurycoma (achi) and potash.

| Preparation of maize flour
Maize flour was prepared according to method of Canibe and Jensen, (2007). Seven hundred grammes (700 g) of maize seeds were cleaned by winnowing and hand sorting to remove dirt and other extraneous materials. The grains were sprinkled with water for 15 s, degermed using a Bentall attrition mill (Model 200 L090,E.H. Bentall and UK) and sun dried at 28 ± 2°C to a moisture content of 10%. The dried maize grains were winnowed and milled into flour (200-μm particle size). The flour was packaged in polyethylene bags and stored in a refrigerator at 4°C prior to use.

| Preparation of AYB flour
Malting and unmalting processes were used for preparation of AYB flour.

| Malting process
The AYB seeds were cleaned by hand sorting to remove dirt, stones and other extraneous materials. Two hundred grammes (200 g) of AYB were weighed into a porous bag (25 cm × 45 cm) and malted at room temperature (28 ± 1°C) using the modified "two-step wet-steep" method as described by Etokakpan and Palmer (1990). The steeping schedule was based on the 16-h procedure for maximum water absorption by the undehulled AYB seeds. The seeds were steeped for 8 h, air rested for 6 h and resteeped in clean water for 8 h. The soaked seeds were then brought out and spread in the malting bags to germinate in a dark room for 72 h during which they were turned once every 24 h. The samples were moistened on alternate days by dipping the malting bags containing the germinating grains in water for 30 s.
After 72 h, the malted grains were dried in an oven (Gallenkamp oven Model IH-150 with chamber dimensions 48 × 37 × 34 cm, England) at 50 ± 1°C for 12 h. The moisture content was reduced from 41% to 7%. The seeds were cleaned of sprouts, and hulls were removed by abrasion between the palms and winnowed. The malts were milled into flour with a particle size of 200 μm using Bentall attrition mill (Model 200 L090) and stored in polyethylene bags at 4°C.

| The preparation of unmalted AYB seeds
AYB seeds were cleaned by hand sorting. Five hundred grammes (500 g) of the AYB grains were steeped in excess water at 28°C ± 1 for 8 h. This was followed by wet dehulling by abrasion between the palms and drying in an oven (Gallenkamp oven Model IH-150, Gallenkamp, England) at 50 ± 2°C to 11% moisture content. The dried grains were milled using a mill (Foss Cyclotec 1093, Sweden), sieved through 200 μm and stored in air-tight polyethene at 4°C. The malted and unmalted AYB flour were mixed manually at 70:20 ratio separately with maize flour to obtain malt-fermented maize-AYB and fermented maize-AYB flour each. Each portion of the same quantity was used in formulation of the fortified complementary food.

| Processing of food materials used as fortificants
The food materials used as fortificants were subjected to different processing treatments in order to determine the best processing methods that would give high values of nutrients.

| Processing of cattle bone meal
The method of Uvere et al. (2010)

| Processing of M. oleifera leaves
The method of Uvere et al. (2010) for processing R. calyces (Hibiscus saddariffa) was adopted. M. oleifera leaves were hand sorted to remove extraneous materials. The leaves were subjected to six different treatments as shown in the Table 1.
Back-slopping method was carried out by using 10% of the pervious fermented slurry as starter culture for the next fermentation as described Nout, Romboutus, and Hautvart (1989).

| Emulsification of red palm oil.
B. eurycoma (achi) seeds and potash were used differently in forming 24-h stable emulsion with red palm oil according to the method of Uvere et al. (2010). The two materials were subjected to the same type of treatment following the assessment and selection of the treatment with higher micronutrient in the two food samples (achi and potash) for use in fortifying the complementary food. B. eurycoma seeds were roasted at 150°C for 30 min, soaked in excess water for 3 h, dehulled by abrasion and milled into powder. The powder was used in the emulsification of red palm oil. The treatments were as follows: 1. A 24-h stable emulsion of red palm oil, water and B. eurycoma (1:1:2 v/v/w) was formed, dried at 50°C and the cake was milled into flour = B. eurycoma unfermented emulsion (BEU).

A 24-h stable emulsion of red palm oil, water and B. eurycoma
(1:1:2 v/v/w) was formed and fermented by back-slopping for 72 h, dried and milled = B. eurycoma fermented emulsion (BEF).
3. Half of the emulsified and fermented emulsion was dried at 50°C, and the cake was milled in a laboratory mortar = mixture of fermented and unfermented B. eurycoma emulsion (BEM).
Ground potash was also used to form emulsion with palm oil under the same treatment as described for B. eurycoma. For potash treatment, the samples were as follows 1. PU = unfermented potash emulsion, 2. PF = fermented potash emulsion, and 3. PM = mixture of fermented and unfermented potash emulsion.

| Determination of micronutrients in the fortificants
The micronutrients (β carotene, iron, zinc and calcium) of the fortificants that were processed using different treatments were determined as follows: β carotene content of the emulsified red oil was determined using the method described by Onwuka (2005). The samples were mixed with 10-ml acetone and a few crystals of anhydrous sodium sulphate were added and the mixture was allowed to settle. This process was repeated twice. The supernatant was decanted into a beaker and transferred to a separator funnel. Petroleum ether (10 ml) was added to the supernatant, mixed thoroughly and allowed to separate into two layers. The lower layer was discarded and the upper layer was collected in a 100 ml volumetric flask, and the volume was made up to a 100-ml volumetric flask with petroleum ether. The optical density (OD) of the solution was determined at 452 nm using petroleum ether as blank. The content was calculated as β carotene = Dñ13:9ñ10,000ñ100 Weight of sampleñ560ñ1,000 , where OD of the solution is at 452 nm.
M. oleifera samples and raw cattle bone were wet acid digested using a nitric acid and per chloric acid mixture (HNO, HCLO, 5:1 w/v).
The total amounts of iron, zinc and calcium in the digested samples of the M. oleifera and cattle bone were determined by atomic absorption spectrophotometry (Thermo Elemental, model 300 VA, UK, 1969).
The treatment that gave highest micronutrient in each fortificant was used in the formulation of the complementary food.

| Formulation of the complementary foods
The quantity of each of the processed food fortificants used was based on the level of the required nutrients as analysed in the processed food fortificant and the proposed RDA for infant's nutrients between 6 to 12 months of age with slight modification (Lutter & Dewey, 2003). The treatment that showed higher micronutrient in the fortificants after each method of processing were mixed in the ratio of 2

| Bulk density
The BD was determined by the method of Mulla, Ahemed, and Al-Sharrah (2018) with slight modification. Each sample (50 g) was filled into graduated a cylinder and their weight was noted. The cylinder was tapped continuously until there was no further change in volume.
The weight and final volume of flour in the cylinder was noted, and the differences in weight and volume were determined. BD was calculated as grammes per millilitre (g/mL) of the sample.

| Water absorption capacity
The water absorption capacity (WAC) was determined by the method of Mulla et al. (2018) with slight modification. One gramme of each sample was weighed into graduated 25-mL conical centrifuge tubes, and 10 mL of distilled water were added. The suspensions were allowed to stand 30 ± 20C for 1 h. The suspensions were centrifuged (Model No. L-708-2, Phillips Drucker, Oregon USA) at 200 rpm for 30 min. The supernatants were was decanted, and then the sample was reweighed.
Change in weight was expressed as gramme per gramme (g/mL).

| Determination of WB and dispersability (DISP)
WB and dispersability were determined by the method of Onwuka (2005). WB measures the time to moisten completely 1 g of the flour after it is suspended in distilled water. Dispersability was determined by dispersing the samples in water, and particle-size distribution was determined using a laser diffraction particle size analyser (CILAS 1064 Compagnie Industrielle Des Lasers, France).

| Determination of pasting properties
Pasting properties were determined using a rapid visco analyser (RVA)

| Determination of micronutrient content of fortified maize-AYB complementary food
The micronutrient contents (β carotene, iron, zinc and calcium) of the all the six different complementary food formulations were determined as described above.

| STATISTICAL ANALYSIS
Each determination of the functional, pasting and micronutrient properties were carried out in triplicates. Mean values and standard deviation were obtained from each triplicate data.
The results were subjected to analysis of variance using SPSS 2007 Version 16 to detect significant differences among sample means. Fisher's least significant difference was used to separate means. Significance difference was accepted at 5% confidence level.

| DISCUSSION
The fortificants were subjected to different processing treatments.
These treatments were carried out in order to determine the best processing methods that showed high values of nutrients. The result showed that emulsification of red palm oil with B. eurycoma or potash followed by drying at 50°C led to reduction in β-carotene content, suggesting that emulsifiers bind β carotene and drying at 50°C resulted in a loss of β carotene. The mechanism of destruction of β carotene has been reported to be through isomerisation (conversion of all trans-β-carotene to stereoisomers having lower pro-Vitamin A activity) during heat treatment (Mahesh & Uday, 2013). Food materials contain many heat-sensitive nutrients.
Cooking conditions and heat treatment caused vitamin loss (Mahesh & Uday, 2013   obtained in this work were higher than the values obtained by Suresh, Samsher, and Durvesh (2015). High WAC of MAFEA may be attributed to increase in amylose leaching, solubility and loss of starch crystalline structure (Suresh et al., 2015). B. eurycoma are high in protein content and proteins are naturally hydrophilic in nature and will absorb and bind more water while low WAC may be due less availability of polar amino acid as reported by Suresh et al. (2015). Low WAC also implies lower water absporption capacity, which is desirable for making thinner gruels with high energy density per unit volume (Omueti et al., 2009). Statistical analysis showed significant difference (p ≤ 0.05) among the samples. The WAC is the ability of a product to associate with water under condition where water is limiting (Omueti et al., 2009). A good WAC may be useful in products where good viscosity is required.

| Functional properties of maize-AYB complementary food
The BD depicts the behaviour of the material in dry mixes and is an important parameter that determines the packaging requirements of products (Mohamed, Zhu, Issoufou, Fatmata, & Zhou, 2009). The BDs of the different formulations (Table 5)  have been reported to be poor in gelation ability (Omueti et al., 2009 its limited gastric capacity, whereas a too thin diet will have a reduced energy nutrient density. The WB values ranged from 16 to 40 s ( Table 5) The dispersability values ranged from 66 to 72 mL (Table 4)

| Pasting properties of maize-AYB complementary food
The results of the pasting properties of maize-AYB complementary diets are presented in (Table 6). Pasting properties are results of combination of processes that follow gelatinization from granule rupture to subsequent polymer alignment due to mechanical shear during the heating and cooling of starches. The PV, which is the ability of starch to swell freely before their physical breakdown, ranged from 45 to 235 RVU. The maize-AYB fermented (MAF) had the highest PV of 235 RVU. The maize-AYB malted, enriched with potash emulsion (MAMEP), had the lowest PV of 45 RVU, whereas the control had a PV of 119 RVU. Low PV implies that the weaning food will form a low viscous paste rather than a thick gel on cooking and cooling. This means that the gruel will be a high caloric density food per unit volume rather than a dietary bulk (Ikujenola & Fashakin, 2005). Statistical analysis showed significant difference (p ≤ 0.05) among the samples.
High PV of MAF is an indication of high starch content and the ratio of amylase and amylopectin and the resistance granules to swelling (Ikegwu et al., 2010), whereas low PV of MAMEP implies that the complementary diets will form a low viscous gel rather than a thick gel on cooking and cooling (Omueti et al., 2009) (Table 6). Ikegwu et al., 2010 reported that the lower the break down viscosity, the higher the ability of the flour to withstand heating and shear stress during processing. High holding strength exhibited by MAF showed that the diet could withstand heating and shear stress during processing without significant change in consistence than the control. The break down viscosity reported in this work is higher than that reported by Okorie, Ikegwu, Nwobasi, Odo, and Egbedike (2016)  has been reported that low set-back value is an indication that the starch has a low tendency to retrograde or undergo syneresis during freezing or thawing (Ikujenola & Fashakin, 2005). This means that MAFEP and the control might be stored at low temperature with low tendency to retrograde. Low SB implies that the complementary diet on cooking will not be a cohesive gruel. This is in agreement with the work on cooking potato paste.
FV ranged from 106 to 249 RVU (  (Ikegwu et al., 2010). Low gelatinization temperature implies shorter cooking time. It has been reported that the PT is related to water-binding capacity (Ikegwu et al., 2010). A higher PT implies higher gelatinization, higher water-binding capacity and lower swelling property of starch due to a high degree of association between starch granules.
Peak times obtained from the formulated diets ranged from 6.09 to 6.35 min (   (Dijkahuizen, 2003). It may also be due to the emulsifiers acting as stabilizers for the retinol formed by delaying or inhibiting oxidation of β carotene (Dijkahuizen, 2003). The β-carotene contents of the maize-AYB blends were higher than the control (Nutrend). This indicate that red palm oil is a good source of pro-Vitamin A for infant formula.

| Micronutrient content of fortified maize-AYB complementary food
The iron content of the maize-AYB complementary food ranged from 0.06 mg/100 g to 1.80 mg/100 g ( Table 7). The maize-AYBmalted, enriched with potash emulsion, had the highest iron content (1.80 mg/100 g), whereas the maize-AYB fermented had the lowest iron content (0.06 mg/100 g). The iron contents of the blends of unmalted AYB and B. eurycoma were significantly lower (p ≥ 0.05) than others and the control. This could be due to the phytic acid present in unmalted legumes which has a strong binding affinity to minerals like iron and copper, as reported by Cheryan and Rackis (1980).
The zinc content ( than the control due to freshness of the leaves and fresh fermented Moringa leaves than dried Moringa leaves. The microorganisms associated with fresh leaves may have been eliminated during drying. High zinc content helps children fight against infections such as diarrhoea (Aggarawal, Szent, & Miller, 2007).
The calcium contents of maize-AYB complementary food ranged from 300.60 mg/100 g in maize-AYB malt-fermented to 360.7 mg/100 g in maize-AYB fermented, enriched with potash emulsion (Table 7). The calcium content of the fortified maize-AYB complementary foods were significantly higher. High calcium content could be made possible for reduction in the risk of osteoporosis and colon cancer (Meinrad, Enkoe, & Heide, 2013).

| CONCLUSION
The hence, the diet will have a low dietary bulk, which is desirable for growing infant. The functional properties of these diets will provide an appropriate complementary diet in terms of texture, dietary bulk and caloric density. There is, therefore, a need to develop and adopt technologies that lower BDs in complementary foods. Again, this study has shown that maize and AYB-malted was the best among samples. The method for the production of these diets is simple, and the ingredients are readily available, cheap and affordable. These products are rich in micronutrient Vitamin A, zinc and calcium and will be valuable for the growing infant who is transiting from breast milk to semisolid food that will help the child fight against disease and hidden hunger. The complementary foods, therefore, could be recommended as an alternative to commercial products which are more expensive and not within the purchasing power of the poor populace.

CONFLICTS OF INTEREST
None declared.