Protein-energy malnutrition (PEM) among children remains a huge burden in Africa. Due to poverty, such children rely on the same starchy staples, such as sorghum, consumed in the household, as both their source of energy and protein. However, sorghum has a low protein quality, particularly with respect to the indispensable amino acid lysine and also protein digestibility. Local pulses such as cowpea are important vehicles to address PEM. Biscuits are favoured as means of fortification because they are palatable, nutrient-dense, in ready-to-eat form and have a long shelf-life. Therefore, the objectives of this study were to develop and evaluate the effect of fortifying whole grain sorghum with whole grain cowpea on the nutritional quality, instrumental, sensory characteristics and consumer evaluation of the biscuits.
Composite biscuits were produced from two types of whole grain sorghums, white tan-plant, non-tannin (WTP) and red non-tannin (RNT) composited with whole grain cowpea at 60:40 ratio. These were compared with commercial economic wheat biscuits.
Sorghum-cowpea biscuits had 50-60% higher protein content than 100% sorghum biscuits but were the same as that of wheat biscuits. The mineral content of sorghum-cowpea biscuits was 27-29% and 37% higher than that of 100% sorghum and wheat biscuits, respectively. The pepsin in-vitro protein digestibility (IVPD) of the sorghum-cowpea biscuits was 71-81% higher than that of 100% biscuits due to inclusion of the more digestible cowpea globulin proteins. However, the average pepsin IVPD of the sorghum and sorghum-cowpea biscuits was 211% and 76% lower than that of wheat biscuits, respectively. There was no trypsin inhibitor activity in the sorghum-cowpea biscuits due to the dilution of the trypsin inhibitors in cowpea. The total phenolic content of the sorghum-cowpea biscuits was 30-45% and 70% higher than that of 100% sorghum and wheat biscuits, respectively.
Sorghum-cowpea biscuits were stronger than 100% sorghum biscuits due to water soluble-globulin proteins from cowpea. Correspondence analysis (CA) revealed that 64% of the variation in terms of texture and flavour of the biscuits was due to type of cereal (sorghum or wheat) and 23% was due to the presence of cowpea in biscuits, respectively. Standard wheat biscuits were the most liked. However, using cluster analysis, individual overall liking of consumers varied and four different clusters of consumers with similar liking of the biscuits were identified. Two clusters with substantial percentage of consumers (41%) liked the sorghum-cowpea biscuits. These findings suggest that sorghum-cowpea composite biscuits could well serve as an acceptable high quality protein-rich complementary food to alleviate PEM, and generate income for smallholder farmers in rural areas of Africa where sorghum and cowpea are produced and consumed as staples.