Functional Properties of Extrudates Prepared with Blends of Wheat Flour/Pinto Bean Meal with Added Wheat Bran

Abstract

Blends made of wheat flour and bean meal at various levels of moisture and bran content, were subjected to extrusion cooking by varying temperature and screw speed. Extrudates were analysed for expansion index, bulk density, apparent viscosity, water absorption index and water solubility index using a second-order rotatable central composite design. Excepting water absorption index, functional properties were significantly affected ( p<0.05) by levels of moisture, bran or extrusion conditions. Expansion index decreased with increasing levels of moisture in the blends; for bran the effect was the inverse. Response surface solution for apparent viscosity was maximum at 24% levels of moisture, 209r.p.m., 180°C and 10% bran. For water absorption index the response surface solution was a saddle point, with a minimum at 29% levels of moisture, 232r.p.m., 177°C and 25% bran. The higher apparent viscosity and lower absorption index reflected minor damage to starch and proteins, which was attributed to a protective role of the added fibre.