Effect of high-temperature, short-time cooking conditions on in vitro protein digestibility, enzyme inhibitor activity and amino acid profile of selected legume grains

African yam beans (Sphenostylis stenocarpa), Bambara groundnut (Vigna subterranean) and Pigeon pea (Cajanus cajan) flours were extruded in a single screw extruder at two extrusion temperatures; 100 °C and 140 °C, and the effect of extrusion cooking temperature on the chemical composition; crude protein, crude fibre, ether extract and nitrogen-free extracts, protein digestibility, enzyme inhibitor activity and amino acid profiles was investigated. The crude protein, amino acid profile and ether extract of the grain legumes were negatively affected (p < 0.05) by the extrusion cooking process, with a significant increase in nitrogen-free extracts for all grain legumes, and increased crude fibre of Bambara groundnut and Pigeon pea extrudates. Extrusion cooking of African yam beans and Pigeon pea produced extrudates with significantly lower trypsin, chymotrypsin and amylase inhibitor activity as well as improved protein digestibility. However, extrusion cooking did not modify the chymotrypsin and amylase inhibitor activity of Bambara groundnut extrudates. Extrusion cooking at 140 °C compared to 100 °C significantly reduced the protein quality of extrudates resulting in 22.94–51.27%, 5.11–25.18%, and 7.78–38.42% reduction in amino acid concentration of African yam beans, Bambara groundnut and Pigeon pea, respectively.