Search

Response surface methodology (with central composite rotatable design for k = 3) was used to investigate the product properties of extruded rice--cowpea groundnut blends in a single screw extruder. The combined effect of cowpea (0-20%), groundnut (0-10%), and feed moisture (14-48%) levels were used for formulation of the products. The product moisture, expansion ratio, bulk density and total colour change were studied using standard analytical methods. Well-expanded rice legume blend extrudates of less bulk density and lower moisture content were produced at low feed moisture. Increasing legume addition affected the various shades of colour in the product. Models developed for the indices gave [R.sup.2] values ranging from 52.8% (for the b-value) to 86.5% (for bulk density). The models developed suggested that the optimal process variables for the production of a puffed snack with an enhanced nutrition and spongy structure from a rice--cowpea--groundnut blend are low feed moisture of 14-20% and maximum additions of 20% cowpea and 10% groundnut. A lack-of-fit test showed no significance, indicating that the models adequately fitted the data.

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. [ABSTRACT FROM AUTHOR]