Evaluation of Chemical, Functional and Sensory Properties of Flour Blends from Sorghum, African Yam Bean and Soybean for Use as Complementary Feeding

The use of sorghum, African yam bean and soybean flour blends in the formulation of low cost, nutritive complementary diet was studied. The blends of sorghum, African yam bean and soybean flour considered were coded as SASA, SASB, SASC and SASD for 90:5:5, 80:10:10, 70:15:15, 60:20:20, respectively. The blends were compared with a commercial weaning diet (cerelac) coded as CTR and 100% sorghum flour (SG). The formulated diets were analysed for their proximate, mineral, anti-nutritional, functional and sensory properties using standard methods. The results showed that there were increases in the proximate and mineral compositions, with a decrease in anti-nutrient content as the substitution level increased. Sensory evaluation of the sample showed that the SASA after reconstitution with hot water was well accepted by the panelists, though the panelists preferred SG and CTR, this could be explained that the panelists are more familiar with them compared to the new formulations. As indicated by the results, food-to-food supplementation would be a suitable form of home fortification for regions where protein energy malnutrition is prevalent.


Introduction
Complementary feeding is necessary for both nutritional and developmental reasons, and is an important stage in the transition from milk feeding to family foods. It is defined as the process starting when breast milk alone is no longer sufficient to meet the nutritional requirement of infants so that other foods and liquids are needed, along with breast milk. In developing countries like Nigeria complementary foods are mainly based on starch tubers like cocoyam, sweet potatoes or on cereals like sorghum, maize or millet. Children are normally given these staples in the form of porridge [1]. There is a prevailing problem of protein-energy malnutrition in infants during the period of complementary feeding which can be attributed to the consumption of much cereal based pap and porridges, thus the need for incorporation of legumes in increasing the protein content of cereal based foods. The development of nutritious complementary foods from local and readily available raw materials has received considerable attention in many developing countries [2].
Sorghum (Sorghum bicolor [L] Moench) is one of the most underutilized crops in the semi-arid tropics of Asia and Africa. It is the principal source of energy, protein, vitamins and minerals for millions of the poorest in these regions. Sorghum products are deficient in essential amino acids such as lysine, methionine, tryptophan and the presence of antinutritional factors such as tannin and phytate which limit their nutritional value [3]. As cereals are generally low in protein, supplementation of sorghum with locally available legume that is high in protein increases protein content of cereal-legume blends [4]. African yam bean (Sphenostylis stenocarpa) is one of the lesser known edible grain legumes that is predominantly cultivated and utilized in Africa [5], and its protein is made up of over 32% of essential amino acids with lysine and leucine being predominant [6]. It ranks well among neglected crops and can contribute to food security if its genetic resources are saved for utilization in breeding and improvement [7]. Soybean (Glycine max) is a legume species native to East Asia, widely grown for its edible bean which has numerous uses. Soybeans are included in the category of oilseed, which is a generic reference to crops with seeds that can produce edible and/or non-edible oil in economic quantities. It has a protein content of approximately 43% [8] and about 3% lecithin which are helpful for the brain development especially of infants. Soybean has essential minerals such as calcium, phosphorous and vitamins A, B, C and D and other health promoting compounds [1]. Therefore, the objective of the study was to determine the nutritional, anti-nutritional and functional properties of sorghum-based complementary flour supplemented with African yam bean and soybean flour blends as well as sensory properties of the formulated diets.

Material Procurement
Sorghum, African yam bean and soybean seeds were procured from Itam market in Uyo Local Government and Siangaran market in Ini Local Government Area.

Processing of Fermented Sorghum Flour
Fermented sorghum flour was produced using the method of [9]. The grains were cleaned and steeped in water (1:3) to encourage fermentation which was for 72h. The fermented sorghum was then washed and dried in a hot air oven (Model PP 22 US, Genlab, England) at 70°C for 24h. It was dry milled (Model Corona) and sieved (500µm mesh of pore size) to obtain fine sorghum flour, packaged in an airtight container.

Processing of Sprouted African Yam Bean Flour
The cleaned African yam bean was steeped in water (1:3) at room temperature for a period of 24h to achieve easy germination. The beans were spread on a jute bag for germination at room temperature for 72h after which the beans was dehulled manually. Thereafter the dehulled beans were washed with tab water to remove the outer coat. The beans were oven dried (Model PP 22 US, Genlab, England) at 70°C for 24h, after which it was dry milled (Model Corona) into flour. It was sieved (500µm mesh of pore size) and packaged in an airtight container according to the method described [10].

Processing of Soybean Flour
One (1) kg of soybean was sorted, washed and blanched at 85°C using a water bath (Model Griffin and George BJL-400-110F). It was then soaked in 3L of water for 24h with a change of water after every 6h to prevent fermentation after which it was dehulled, washed and oven dried (Model PP 22 US, Genlab, England) at 50°C for 48h. It was dry milled (Model Corona), sieved (500µm mesh of pore size) into fine flour and packaged in an airtight container as described [11].

Formulation of Sorghum, African Yam Bean and Soybean Flour Blends
The blending of the flour was done using a mechanical blender (Model Philips HR 7762-90, China) to obtain uniform blends. The flour blends were in the proportion 100:0:0, 90:5:5, 80:10:10, 70:15:15 and 60:20:20 designated as SG, SASA, SASB, SASC and SASD, respectively, as shown in Table 1. These samples were packaged in airtight container at room temperature while the commercial formula (cerelac) was used as control.

Proximate Analysis of Complementary Flour Blends and Commercial Formula
Moisture, ash, crude protein, crude fat and crude fibre contents of the complementary flour blends were carried out. Total carbohydrate was determined by difference method and was quantified based on the percentage difference of the other proximate indexes as follows: %carbohydrate = 100 -(%moisture + %ash + %crude protein + %crude fat + %crude fibre). The total energy was calculated using Atwater factor using the formula: energy value = (%crude protein×4) + (%crude fat×9) + (%carbohydrate×4) according to the method described [12].

Determination of Mineral Content of Complementary Flour Blends and Commercial Formula
Dry digestion method was used. The sample was air dried for 1h and oven dried at 105°C for 1h. Five (5) g of sample was weighed into a crucible and digested with 0.3ml of HNO 3 , made up to 100ml with water in a volumetric flask and heated up to 100°C till a white fume was liberated. It was cooled, filtered and the solution was made up to 100ml and used for further determination of mineral. Filtrate from each sample was analyzed for zinc, iron, calcium and magnesium contents using an atomic absorption spectrophotometer (Thermoelemental UNICAM 969 model) with standard wavelengths. Sodium was analysed using atomic emission spectrophotometer. The real values were extrapolated from the respective standard curves as described [12].

Determination of Anti-nutritional Factors of Complementary Flour Blends and Commercial Formula
Determination of total oxalate, phytate, hydrogen cyanide using alkaline filtration and tannin were determined using the method [12][13][14][15].

Determination of Functional Properties of Complementary Flour Blends and Commercial Formula
Bulk density, water absorption capacity, oil absorption capacity, gelatinization temperature and swelling index were determined following the method described [13,16].

Sensory Evaluation of the Gruel
The complementary flour blends were prepared into gruel by reconstituting different proportions of sorghum-African yam bean-soybean flour blends with boiling water. During preparation, 60g of each sample was suspended with 100ml of potable water in a small plastic bowl. After that, 60ml of boiling water was added to each of the suspended sample to produce hot gruel. Sensory characteristics of the coded gruel were evaluated for different sensory attributes by twenty (20) semi-trained panelists drawn from the Department of Food Science and Technology, University of Uyo of whom five (5) were nursing mothers. All the panelists were briefed before the commencement of the evaluation process. Sensory attributes evaluated were appearance, taste, flavour, mouth feel, consistency and general acceptability. The rating was on a nine-point hedonic scale ranging from 1 (dislike extremely) to 9 (like extremely). All panelists were regular consumers of sorghum gruel, water at room temperature was provided to rinse the mouth between evaluations as described [17].

Statistical Analysis
All the data were subjected to statistical analysis using Analysis of Variance (ANOVA). The means were then separated with the use of Duncan's new multiple range test using the Statistical Package for the Social Sciences (SPSS) 21 software.

Proximate Composition and Energy Value of Complementary Flour Blends and Commercial Formula
The results of proximate composition and energy value of sorghum, African yam bean and soybean complementary flour blends and the commercial formula (cerelac) were presented in Table 2. The moisture content of all the samples was not significantly (p>0.05) different from CTR (commercial formula), it ranged from 3.93-5.03%. Ash content was significantly (p<0.05) different from CTR, it ranged from 2.65% (SG) to 3.35% (SASB) while the CTR was 2.03%. The formulated samples had ash content higher than the CTR.

Anti-nutrient Content of Complementary Flour Blends and Commercial Formula
The result of anti-nutrient content of sorghum, African yam bean and soybean complementary flour blends and the commercial formula (cerelac) are presented in Table 4. Significant (p<0.05) reduction of oxalate, HCN and tannin contents were found in the blends as the substitution level increase. Oxalate was the highest mineral found in all the samples. It ranged from 87.79mg/100g (SASD) to 130.56mg/100g (SG), while CTR had the value of 145.42mg/100g. HCN content ranged from 1.26mg/100g for SASC to 2.27mg/100g for SASA, SASD had the lowest value and all blended samples were lower than CTR (3.18mg/100g). Tannin content ranged from 2.31mg/100g (SASD) to 3.29mg/100g (SASA). Phytate content was significantly (p<0.05) increased as the level of substitution increased. It ranged from 14.39mg/100g (SASA) to 23.61mg/100g (SASD), sample SASA had the lowest value and it was lower than the CTR having 19.64mg/100g.

Functional Properties of Complementary Flour Blends and Commercial Formula
The result of functional properties of sorghum, African yam bean and soybean complementary flour blends and the commercial formula (cerelac) is presented in Table 5. The bulk density of the formulated samples was not significantly (p<0.05) different but higher than CTR. It ranged from 0.62g/ml for SASD to 0.70g/ml for SASA. Significant (p<0.05) differences existed among the formulated samples for water absorption and swelling capacities but lower than CTR. It ranged from 1.30-2.40g/g for SG and SASD, respectively, while the control had the highest value (4.00g/g). The oil absorption capacity of all samples showed no significant (p<0.05) difference, it ranged from 1.60-1.90g/g with SASA having the highest value while CTR had 1.80g/g. The gelatinization temperature of the formulated samples was significantly (p<0.05) different from CTR, it ranged from 75.50°C (SASA) to 81.00°C (SASD) and CTR had 75.00°C.

Sensory Evaluation of Complementary Flour Blends and Commercial Formula
Appearance, taste, flavour, mouth feel and general acceptability level of the formulated samples and CTR showed significant (p<0.05) difference ( Table 6). The appearance and taste ranged from 6.80-6.95 and 6.05-7.20, respectively, with CTR having the highest score of 7.50 for appearance and 7.35 for taste. The flavour ranged from 5.95 (SASD) to 7.20 (SG) with the CTR and SG having the highest score of 7.20. The mouth feel ranged from 6.05-7.25, CTR had the highest score of 7.30. The consistency levels of SG and CTR were not differed significantly (p>0.05), it ranged from 4.80-7.00 for sample SG with CTR and SG having the highest score (7.00). CTR was generally accepted with highest score of 8.05 while the formulated samples ranged from 6.70 for sample SASC to 7.20 for sample SG.

Proximate Composition and Energy Value Complementary Flour Blends and Commercial Formula
Moisture content of the samples was within the acceptable limit for long term storage of flour. Studies have shown that low moisture content in food products will prevent the growth of mould and reduce moisture dependent biochemical reactions [18] and therefore enhance the storage stability of the flour. Ash values obtained was within range compared with 2.08-4.13% as reported [19] but higher than the ash content (0.56-2.00%) of complementary food formulated from fermented maize, soybean and carrot flours reported [11]. The ash content of a food material could be used as an index of mineral constituents of the food [20]. The result of crude protein is within the range (9-22%) of complementary foods from rice, unsprouted/sprouted green gram and apple pulp flour blends reported [21]. Values obtained were lower than the values reported [22] for fermented and roasted sorghum and soybean flour blends. Crude fat content of the formulated samples were higher than 7.00-16.35% as reported [23] for soy-sorghum-roselle complementary food. Fat is important in the diets of infants and young children as it provides high energy density and facilitates the absorption of fat soluble vitamins. It also provides essential fatty acids such as omega-3 and omega-6 polyunsaturated fatty acids (PUFA) needed for proper neural development in infants and young children [1]. Low fat is beneficial as it ensures long product shelf life by reducing susceptibility to oxidative rancidity. Crude fibre is one of the non-energy yielding nutrients; it helps to increase the nitrogen utilization and absorption of some micronutrients [24]. The crude fibre was within the range similar to 0.20-4.40% as reported [25] using malted pre-gelatinized maize, soybean and carrot flour. The high carbohydrate contents observed in this study are nutritionally desirable as children require energy to carry out their rigorous physical and physiological activities as growth continues [26]. Carbohydrate content decreased as amount of supplementation increased, this is in agreement with the work [27]. Energy values obtained are within the range 363.86-442.46kcal reported by [28] using sprouted paddy rice, sprouted African yam bean and pawpaw.

Mineral Content of Complementary Flour Blends and Commercial Formula
Zinc value increased with increasing soybean and African yam bean supplementation. Samples had values higher than values reported [29,30]. Iron values were higher than 2.98-4.38mg/100g as reported [31] using sorghum and African yam bean. This is in line with the report that African yam bean has high iron content [28]. Iron is essential for the formation of blood cells and prevention of anaemia in infants and children. Calcium level was higher than the value (10.52-39.16mg/100g) reported [32] using African yam bean-carrot flours. It was also higher than 15.01-25.10mg/100g as reported [33] using malted millet, plantain and soybean. Sodium level is higher than 6.95-8.57mg/100g as reported [10] using maize, African yam bean and pigeon pea. It is essential in the regulation of water content and in the maintenance of osmotic pressure of the body fluid. It also aids in the transport of CO 2 in the blood. Magnesium level was higher than 2.08-4.88mg/100g as reported [31]. Its level increased with increasing level of soybean and African yam bean supplementation which is in line with [34] who reported that African yam bean is a rich source of magnesium. It helps in the relaxation of nerves and muscle essential for the formation of bone and clotting of the blood.

Anti-nutrient Content of Complementary Flour Blends and Commercial Formula
Oxalate binds with calcium and iron and causes these minerals to crystalize and thus the body cannot properly utilize the calcium and iron. High level of phytate limits the bioavailability and hence utilization of minerals, specifically calcium, magnesium, iron and manganese by forming insoluble compounds that are indigestible. Similar result (1.84-2.67mg/100g) was reported by [35] in evaluating complementary food formulated from local staples using sorghum, soybean and plantain flour. Tannins are known to bind protein including digestive enzymes leading to poor protein digestibility. The tannin level for this study was within the range of 2.55-2.85mg/100g as recorded by [35] for complementary foods based produce from soybean, sorghum and sweet potatoes flour blends.

Functional Properties of Complementary Flour Blends and Commercial Formula
The bulk density of the formulated complementary flour blends was low. Sprouting of African yam bean must have contributed to low bulk density. Similar finding was reported by [37] of 0.60-0.67g/ml for pearl millet and germinated pigeon pea flour blends, as germination has been reported to be useful in preparation of low bulk foods for infants [38]. Low bulk density values of the complementary food samples imply that more of the samples could be prepared using a small amount of water yet give the desired energy nutrient density. The low water absorption capacity (WAC) of formulated samples may have resulted from the inclusion of sprouted grains/seed flours owing to the fact that starch degradation during germination affects starch granules which affect the level of water the available starch is able to hold. Such low WAC values are desirable for making thinner gruels [28]. It also results in increasing the energy and nutrient-density of the infant foods, a very important aspect in complementary feeding. Oil absorption capacity is an important functional property as the ability of flours to absorb and retain oil may enhance flavour retention and improve mouth feel [39]. Complementary foods do not require high swelling capacity as the food would absorb more water and have less solid resulting in low nutrient density for infants [40]. High temperature presented in this study could have been due to a reduced starch content of the flours which may have occurred during sprouting. The same trend was observed by [41] who had increase temperature with increased level of substitution.

Sensory Evaluation of Complementary Flour Blends and Commercial Formula
Appearance is very important as a sensory property which contributes to acceptability and choice of food [28]. Appearance of complementary food formulations in addition to a sufficient energy density correspond to food preferences for infants and young children and are of prime importance. Taste is a parameter for accessing sensory attributes in food; it is a very important property. In this case it would stimulate the child's likeness and acceptance for the food. Indeed, even if a product is appealing and meets nutrient requirements without good taste, the product would likely not be acceptable. The mouth feel is very important in a complementary food as it will determine the amount of food an infant would consume since they can only swallow a smooth gruel not a coarse one. The panels' range of likeness for all the attributes were within 'dislike slightly' to 'neither like nor dislike', this could be attributed to the beany flavour of African yam bean and soybean. SG (Sorghum flour) was generally accepted more than other formulated samples; the difference could be attributed to the unique quality of sorghum flour in preparation of complementary food [42].

Conclusion
Sorghum, African yam bean and soybean are locally available and affordable raw materials that can be used by mothers as home-based complementary foods. There was increase in the nutrient content of the formulated blends that can meet recommended level of protein, energy and other nutrients. SASD with the highest African yam bean and soybean substitution had the highest crude protein, crude fat and energy level contents with highest mineral contents and lowest antinutrient contents. The complementary flour blends had also shown desirable level of functionality with respect to bulk density, water absorption, swelling and gelling temperature.