For the purpose of determining physicochemical properties of low-amylose rice starch, amylose content and amylopectin unit-chain distribution were studied by amperometric titration and gel filtration methods. Further, also examined were photopastography, viscosity and gel texture to determine characteristic gelatinization and retrogradation. Four kinds of low-amylose rice, an aromatic rice, a large-grain rice and a high-yield rice were used as the rice samples for comparison with two kinds of high-amylose rice, Hoshiyutaka and Yumetoiro, with Nipponbare as the control. The amylose content of low-amylose rice ranged from 4.3 to 9.6%. Snow pearl was the lowest, Ou 354 at 4.4%, Milky queen at 7.5%, Soft 158 at 9.6%, and Nipponbare at 17.1%. Fr. II, the longer chain length fraction in amylopectin, was noted at 24.0-26.3%, which was large, similar to the 4 kinds of low-amylose rice. Fr. III, the shorter chain length fraction in amylopectin, was noted at 55.8-69.8%. Fr. III/Fr. II was noted at 2.6-2.8, which was smaller, similar to the 4 kinds of low-amyloserice, than Nipponbare by 3.0. With respect to the rice starch, the amylose content showed a negative correlation for both maximum viscosity and breakdown, and there was a positive correlation with the viscosity when cooled at 50°C. The firmness of rice flour paste negatively correlated with the highest viscosity of the rice starch, while the firmness of rice flour paste and starch paste positively correlated with the setback.
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