Structural and physicochemical characteristics of endosperm starches of rice cultivars recently bred in Japan

Abstract

Structural and physicochemical properties of rice starches were investigated using fourtypes of endosperm starches (i.e., waxy, low amylose (AM), medium AM, and high AMstarches) of rice cultivars recently bred in the agricultural experiment station of theMinistry of Agriculture, Forestry, and Fisheries of Japan and harvested mainly in 1998and 1999. There was a highly negative relationship between the true AM contents and thepeak viscosity measured by a Rapid Visco Analyser (RVA) for non-waxy starches. In thegroup of high AM starches, there were two types of rice starch samples with similarapparent AM contents (about 30%), different contents of super-long chains (SLC) inamylopectin (AP), and different values in the peak viscosity and setback of starchesmeasured by RVA. Since there was a highly positive relationship between SLC contentsand setback, the SLC in AP seems to have a great influence on the setback of starch. Bothof side-chain length distribution within the short-chain range of AP and the SLC contentof AP greatly influence the gelatinization temperature of rice starches. The SLC in APcontributed to neither swelling nor dissolution of the rice starches in water at 75°C. Weproposed a scheme for the relationship between the SLC and Fr.A (DP 6-12) contents ofAP as a classification of endosperm starches of rice cultivars recently bred in Japan.There were significant differences among the setback values of the starches plotted intothree zones determined by the SLC contents in the scheme. © 2006 Nova Science Publishers, Inc. All rights reserved.