Development of cowpea-based (Vigna unguiculata) extruded snacks with improved in vitro protein digestibility

Cowpea contains an extensive amount of protein, carbohydrate, fibre and other nutrients but their bioavailability and utilization by humans relatively low and less explored due to the presence of antinutritional factors. The present study aimed to evaluate the physicochemical and sensory properties of extruded product by using response surface methodology, the influence of different moisture content in raw material and the temperature of extrusion processing on properties of extruded product prepared using cowpea. The study also focused on the assessment in vitro protein digestibility. The die temperature varied from 160-180°C with screw speed of 160-200 rpm at constant feed rate 16 rpm (70 g/ min) and the feed moisture of the raw material was in the range of 16-24%. From the result it was observed that increase in feed moisture content and decrease in die temperature significantly increases the density and hardness of extrudates and decreases the expansion, water absorption index, water soluble index and organoleptic scores. Furthermore, it was also found that the associated thermal treatment was the most effective in improving protein digestibility (up to 89%). The overall best quality product was obtained when using cowpea flour with 16% moisture content, under 180°C die temperature and 200 rpm screw speed.