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

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 R2 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. PRACTICAL APPLICATIONS Rice constitutes a primary food for millions of people in sub-Saharan Africa, Asia and Latin America, where it forms a major source of proteins and calories in the diet of large segments of the population. However, its protein is “incomplete” and is deficient in the essential amino acids such as lysine and methionine. Fortification with legumes (groundnut and cowpea) has shown to lead to improvement in the total protein quality and quantity. Extrusion cooking involves a high-temperature short-time process, whereby a single- or mixed-food material is modified through the unique combination of high temperature, pressure and shear forces causing large numbers of complex changes to the food. Extrusion cooking of the rice-groundnut-cowpea blends is expected to produce a convenient puffed snack food, ready-to-eat and breakfast cereal of high nutritional value, comprising of complementary proteins that have increased nutritional value and better product of physical and functional characteristics.