Rice Starch Properties and Grain Quality

The effects of various starch complexing : amylose-waxy gene protein complex, mylose-lipid complexes, amylopectin retrogradation and amylose retrogradation (resistant starch) were recently studied in selected rice samples differing in starch properties. Amylose-bound protein (starch synthase) is higher in indica rice than in japonica rice and the specific activity was lower in indica, consistent with their similar amylose contents. Processing temperature determines the type of amylose-lipid complex formed, with complex II formed only above 100°C. Cooked-rice and starch-gel staling that is reversed partially by reheating at 100°C was shown to be due to amylopectin staling by DSC and storage modulus G'-time profiles . They tended to be related to d.p.n of amylopectin among waxy rices. Intermediate-high GT with greater resistance to corrosion of raw granules to HC1 and Chalara paradoxa amylases showed greater amylopectin and amylose staling of cooked rice. Amylose staling was measured by glycemic index and resistant starch. These studies provide evidence on the causes of varietal differences in qualities of rices with similar amylose contents. It is worthwhile to estimate the molecular properties of amylopectin and amylose of these selected rice samples to determine what properties actually affect cooked rice texture.