Sensory and nutritional quality of an extruded sorghum and cowpea blend as a complementary food for school age children

Abstract

Protein-energy malnutrition (PEM) is a major problem in sub–Saharan Africa, which is predominant in children and women. Poverty is the underlying cause. Children rely on cereal staples like sorghum for nutrient supply. However, sorghum is limiting on indispensable amino acid lysine and has poor protein digestibility, compromising its protein quality. Cowpeas are major subsistence crops in sub-Saharan Africa due to their tolerance to harsh climatic conditions and notable protein quality. Snacks are widely consumed by school-going children during break lunches and convenient, palatable, ready-to-eat and have long-shelf life. Therefore sorghum-cowpea snack blends have potential to address PEM. Hence, objectives of the study were to develop and evaluate the effects of compositing sorghum with cowpea on nutrient quality and sensory properties of snack blends. Ready-to-eat sorghum-cowpea expanded snacks were produced using a twin screw extruder. Snacks were made from 0, 25 and 50% ratios of wholegrain cowpea flour (Glenda variety) to commercial decorticated red non-tannin sorghum flour and 1% salt. The nutritional and sensory characteristics of snacks were investigated in terms of proximate and nutrient composition, protein digestibility, lysine content, mineral content and bioaccessibility and descriptive sensory analysis coupled with instrumental texture (breaking force) and colour analyses. Inclusion of cowpea significantly improved nutrient composition of the snacks. A 30 g packet of composite snacks would provide 4-5 g protein which is 15-31% of the protein daily requirement for school-age children. Cowpea inclusion significantly increased lysine by 97% of daily requirement for school-age children. The sorghum-cowpea blend snacks had some 16% improved in-vitro protein digestibility. Hence, the calculated Protein Digestibility Corrected Amino Acid Scores of the blend snacks was more than double that of the sorghum only snacks. Mineral contents of snacks were improved on cowpea inclusion. However, phytate content increased also, decreasing the bioaccessibility of the minerals. Conversely, inclusion of cowpea flour darkened the colour and increased dark specks in the snacks. Snack hardness was similarly rated by panellists and the instrumental texture analysis. Beany, cocoa, burnt, boiled and roasted nut flavours with metallic aftertaste were highly perceived in the 50:50 blend. Salt addition affected salty flavour only. Inclusion of cowpeas in extruded cereal snack formulations has the potential to address PEM in school-going children in sub-Saharan Africa because it substantially improves the protein content and quality of the snacks. Although inclusion of 50% cowpea gave the highest nutritional quality, it resulted in a beany flavour and metallic aftertaste. These may require masking through commercial flavouring for consumer acceptability.