Gelling properties of extruded yam (Dioscorea alata) starch

Yam (Dioscorea alata) starch was pregelatinized in a single screw extruder. Response Surface Methodology was used to study the effect of extrusion var iables: feed moisture (18, 21, 24%), extruder temperature (120, 150, 180 de grees C) and die diameter (3, 4, 5 mm) on cold viscosity, gel-forming capac ity and retrogradation of extruded starches. Cold viscosity was higher from starch samples processed at higher moisture and die diameter, at lower tem peratures. Slurries of the extruded starch (8%, w/v, d.b.) formed opaque an d firm gels. Higher values for gel strength were found in samples extruded at highest and lowest moistures at intermediate temperature and increasing die diameter. Gels of extruded starch had lower retrogradation values than non-extruded gelatinized starch after one and two weeks storage at refriger ation temperature. Prediction equations for the studied functional properti es can be used in selecting processing conditions for specific food applica tions. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.