Impact of cowpea addition on the Protein Digestibility Corrected Amino Acid Score and other protein quality parameters of traditional African foods made from non-tannin and tannin sorghum

Protein malnutrition is a problem in Africa where sorghum is a staple foodstuff. Improvement in the protein quality of traditional African sorghum (Sorghum bicolor L. Moench) foods through the addition of cowpea (Vigna unguiculata L. Walp), an indigenous African legume, was investigated. Two sorghum cultivars, a red, tannin-type (NS 5511) and a white tan-plant, non-tannin type (Orbit) were complemented with cowpea (70:30 ratio). Ugali (thick porridge), uji (fermented thin porridge) and injera (fermented flatbread) were prepared. The protein lysine scores of cowpea-complemented foods were about double the levels of sorghum-only foods. The in vitro protein digestibility of the foods increased by 13–62%. The increase in lysine and protein digestibility improvement resulted in three- and two-fold improvement in the Protein Digestibility Corrected Amino Acid Score (PDCAAS) of NS 5511, and Orbit foods, respectively. Addition of cowpea to tannin, as well as non-tannin sorghum is a viable option for improving the protein quality of a wide range of traditional African foods.