Abstract
The amylose content and the amylopectin unit-chain distribution were determined by gel filtration chromatography (GFC) to obtain the physicochemical properties of low-amylose rice starch. The gelatinization and retrogradation properties of rice starch and flour samples were also determined by a viscosity and gel texture analysis. Four kinds of low-amylose rice and one kind of large-grain rice were tested as samples, while Nipponbare, as a reference, and two kinds of glutinous rice and high-amylose rice, as a comparison, were also examined. The amylose content of the four kinds of low-amylose rice was in the range of 7.2-10.4% by GFC. The amylose content was lowest in Hokuriku 161, being followed by Milky Princess, Asatsuyu, Snow Pearl and Nipponbare with respective contents of 8.1%, 8.9%, 10.4% and 17.1%. The longer chain length fraction of amylopectin, Fr. II, was in the range of 23.0-24.3%, and the shorter chain length fraction, Fr. III, of 66.6-68.5%. The ratio of Fr. III /Fr. II in the low-amylose rice samples was in the range of 2.8-2.9, being lower than that of Nipponbare at 3.0. Breakdown of the low-amylose rice starch and flour samples was large, while the setback was small, these being similar characteristics to those of glutinous rice. The texture of the low-amylose starch and flour pastes was soft when first prepared, and the viscosity characteristics were similar when cooled to 50°C. There was little change in the firmness and adhesiveness of the rice starch and flour gels while storing at 5°C for seven days, these characteristics differing from those of Nipponbare.
