Extrusion cooking of rice-groundnut-cowpea mixtures - effects of extruder characteristics on nutritive value and physico-functional properties of extrudates using response surface methodology

Abstract

Response surface methodology was used to study the effect of extruder characteristics on product quality of rice-groundnut-cowpea extrudates using a single-screw extruder. The combined effect of cowpea (0-20%), groundnut (0-10%) and feed moisture (12.02-44.06%) were used to formulate the products. Product moisture, protein, fat, ash, bulk density, expansion ratio, water absorption capacity (WAC) and swelling capacity were determined. Well-expanded rice-legume blend extrudates of less bulk density and lower moisture content were produced at low feed moisture. Addition of legumes resulted in significant increases in protein, fat and ash contents of the rice-legume extrudates while increasing cowpea increased all the physico-functional properties. The models developed gave R 2 values ranging from 64.01% (WAC at 70C) to 86.5% (bulk density) and suggested that the optimal process variables of low feed moisture (10-12%), cowpea level (20%) and groundnut level (10%) would produce ready-to-eat puffed snack with enhanced nutritive value and physico-functional properties from rice-groundnut-cowpea blend extrudates. © 2011 Wiley Periodicals, Inc.