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

Structural and physicochemical properties of rice starches were investigated using four types of endosperm starches (i.e., waxy, low amylose (AM), medium AM, and high AM starches) of rice cultivars recently bred in the agricultural experiment station of the Ministry of Agriculture, Forestry, and Fisheries of Japan and harvested mainly in 1998 and 1999. There was a highly negative relationship between the true AM contents and the peak viscosity measured by a Rapid Visco Analyser (RVA) for non-waxy starches. In the group of high AM starches, there were two types of rice starch samples with similar apparent AM contents (about 30%), different contents of super-long chains (SLC) in amylopectin (AP), and different values in the peak viscosity and setback of starches measured by RVA. Since there was a highly positive relationship between SLC contents and setback, the SLC in AP seems to have a great influence on the setback of starch. Both of side-chain length distribution within the short-chain range of AP and the SLC content of AP greatly influence the gelatinization temperature of rice starches. The SLC in AP contributed to neither swelling nor dissolution of the rice starches in water at 75 degrees C. We proposed a scheme for the relationship between the SLC and Fr.A (DP 6-12) contents of AP 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 into three zones determined by the SLC contents in the scheme.