TEXTURE DETERMINANTS IN COOKED, PARBOILED RICE .1. RICE STARCH AMYLOSE AND THE FINE-STRUCTURE OF AMYLOPECTIN

The constituent starches from eleven cultivars of non-waxy rice with d ifferent degrees of cooking hardness were subjected to detailed analys is. No significant differences were observed in the granule morphology , crystallinity and size distribution of the starch granules that coul d be correlated with the textures of the cooked, parboiled rices. Diff erences in the contents of amylose and the fine structures of amylopec tin were detected, however, which did correlate with texture. It appea red that the texture of the rices was critically controlled by the pro portion of the longest (DP 92-98) and shortest (DP less than or equal to 25) amylopectin chains but not the intermediate (DP 43-68) chains. Hard cooking rice tended to have a higher amylose content (or amylose: amylopectin ratio) and more longer chain amylopectin than soft cooking rice, which feature is thought to encourage more extensive intra and/ or inter molecular interactions with other components in rice grain, s uch as protein, lipid and nonstarch polysaccharides and results in a f irmer texture. The different amylopectin structures may explain why ri ces that possess similar amylose contents can have different textural properties. Such a correlation suggests that the structure of the star ches determined from the SE-HPLC profile of the debranched amylopectin could be useful as a sensitive screening method in the classification of cooked rice texture.