Molecular Degradation of Starch During Extrusion Cooking of Rice

Effect of barrel temperature (80°–100°C) and amylose content (28.6 gkg−1, 22.3 gkg−1 and 5.0 gkg−1) of rice upon extrusion cooking on macromolecular profile of starch was studied by gel permeation chromatography (GPC) of the rice flour on Sepharose CL-2B. Starch in all rice samples was separated into two main fractions, viz. Fraction-I, a high molecular weight, was excluded by gel, amylopectin, and Fraction-II, a low molecular weight, that entered the gel, amylose. Extrusion cooking of rice led to the degradation of high molecular weight fraction of the starch, the extent of degradation increasing with increasing severity of extrusion conditions. The absorption maxima (λ max) of iodine complex of the fraction-I showed an increase after extrusion cooking and this increase was more in the non-waxy variety of rice than in waxy.