Relationship between Physical Properties and Amylopectin Structure of Waxy Rice Starch

Abstract

Starches from three waxy rice cultivars (Hakuchoumochi, Hiyokumochi and Koganemochi) showing different physical properties were studied in order to identify the relationship between physical properties and their amylopectin structures. Pastes of Hakuchoumochi, Hiyokumochi and Koganemochi are known as soft, intermediate and hard, respectively. Pasting properties of the soft type starch showed the lowest setback (SB) and the highest breakdown (BD) among the three. The hard type showed the reverse relationship and the middle type showed an intermediate property. To follow these physical properties, partial hydrolysates of starches with debranching enzymes were prepared and the distributions of debranched short side-chains in amylopectin existing mainly in the outer layer of the amylopectin were analyzed by HPAEC-PAD. Hakuchou mochi was composed of plentiful shortish chains and scarce longish chains and suggested to be resistant toretrogradation. Koganemochi had the reverse properties and was suggested to be sensitive to retrogradation. Hiyokumochi was intermediate. From these results, it could be presumed that a feature of chain-length distribution on the outer layer of the amylopectin molecule influenced the physical properties relating to retrogra dation.