NUTRITIONAL AND PHYSICO-CHEMICAL EVALUATION OF MALTED AND UNMALTED MAIZE FORTIFIED WITH COWPEA OR SOYBEAN USING EXTRUSION COOKING

Abstract

Supplementary foods were prepared with malted or unmalted maize. The malted maize was fortified with cowpea (MC) and soybean (MS) at a ratio of 45.35% and 55.25% respectively. The unmalted maize was also fortified at the same ratio with cowpea (UMC) and soybean (MS). The grains were dehulled and ground into a gritty form before extrusion.The proximate analysis and anti-nutritional factors in the blends were evaluated before and after extrusion. The blends were then compared with two different popular weaning formulas in the Nigerian market. The protein quality evaluation was done using weaning albino rats and amino acid assay. Biochemical assay was done on blood plasma of the rats. Histological evaluation was done on the organs of the rats. The blends were subjected to sensory evaluation with nutrend and cerelac as controls. The functional properties of the blends determined were viscosity measurement, nitrogen solubility index (NSI), water absorption capacity (WAC ), emulsification capacity (EC) gelation properties and protein fractions of the blends. The protein content was highest in soybean based blends with 18.19% for UMS and 16.75% for MS after extrusion. Corresponding values for UMC and MC were 16.74% and 16.25% respectively. Protein contents of all blends except UMS were similar, Protein (16.33%) in nutrend was similar to that of MS, MC, and UMC, but significantly lower and higher than UMS and cerelac respectively. Fat content of 6.47, 6.40, 6.34, and 6.34 observed for MS, UMS. MC, and UMC respectively were significantly higher (P<0.05) than that obtained for cerelac (4.90) and nutrend (3.80). Gross energy values for MS, MC. UMC and UMS were 4.67, 4.87 4.36, and 4 26 Kcal/gm while that of cerelac and nutrend were 4.15 and 4.20 respectively. Extrusion cooking significantly (P<0.05) increased the protein content of all formulated blends while malting significantly reduced the protein value. Soybean bean blends had a significant (P<0.05) higher level of trypsin inhibitor (6.1mg/g for MS and 6.8mg/g for UMS) and phytic acid (1.20%) MS and 1.50% for UMS) before extrusion. These reduced to a non-significant level after extrusion. The tannin concentration in soybean based blends were slightly higher than that of cowpea based blends. Extrusion cooking and malting had a significant reducing effect on the anti-nutritional factors of the blends. All the formulated blends were good sources of phosphorus, calcium, copper and iron and fair sources of magnesium, manganese and potassium. The values obtained for phosphorus, iron and zinc were significantly (P<0.05) higher than the commercial weaning blends. These higher values obtained for the mineral might be due to the mineral fortification of formulated blends. The amino acid pattern of soybean based blends compared well with suggested patterns of amino acid requirement for infants while that of cowpea based blends were within acceptable range. The amino acid scores for MS, UMS, MC, and UMC were 78, 67, 68. and 62 respectively. The biological evaluation of protein quality observations revealed a protein efficiency ratio (PER) value above 2.1 for all the blends. The soybean based blends had a significant higher net protein ratio (NPR) than the cowpea based blends. The rat pellet (RP) and casein blends gave a significantly higher (P<0.05) true digestibility value than the formulated blends while malting significantly increased the true digestibility of the blends. The values obtained for all the blends were however above the minimum recommended value. All the blends had net protein utilisation (NPU) higher than 60% recommended by Senti (1969) and PAG (1971) for weaning foods. There was no significant difference (P<0.05) in the liver and kidney weights for rats on all diets. The values observed in different blood parameters in rat fed formulated blends compares favorably with rats fed with casein and RP. The days of feeding were also found to have an effect on the level of some blood parameters. Histological studies revealed no toxicological effect on the internal organ of the blends. The blends had good functional characteristics with a particularly low viscosity. The inclusion of malted maize to cowpea reduced the viscosity value and gelation property. Malting was found to have an effect on the functional properties of the blends. The scores obtained from the sensory evaluation test showed that all the blends were accepted by the consumers. Malting improved the flavour of the blends and consumer acceptability of malted based blends compares well with the two controls. It was concluded that soybean and cowpea should be used as raw materials in the preparation of supplementary commercial baby food to reduce cost. Malting is also recommended in order to reduce viscosity; thus increasing total nutrient intake.