Molecular degradation of rice starch during processing to flakes

Roasting of the soaked paddy (roasting-parboiling) appeared to cause an inc rease in the proportion of the high-molecular-weight component of starch, s eparated in Fraction-I, probably due to retrogradation. The solubility of s tarch also decreased. Flaking of roasted-parboiled paddy in the traditional edge-runner flaker did not cause any further appreciable change in the pro portion of Fraction-I and Fraction-II. Flaking in the roller-flaker unit, o n the other hand, caused a decrease in the proportion of Fraction-I, indica ting molecular breakdown of starch. The total starch solubility increased m arginally in edge-runner flakes but substantially in roller-flaker flakes. Fractionation of starch that was soluble in hot water showed that the major amount of amylose equivalent resided in this portion; as revealed by a hig her proportion of Fraction-II and a high lambda(max) of the peak of this fr action. When retrogradation was induced in the flakes under appropriate con ditions of moisture and temperature, the content of the high-molecular-weig ht Fraction-I of total starch increased slightly in edge-runner flakes but markedly in roller-flaker flakes, indicating an aggregation or reassociatio n of starch molecules or its fractions. (C) 1999 Society of Chemical Indust ry.