THE STRUCTURE AND GELATINIZATION PROPERTIES OF RICE STARCH PREPARED FROM DIFFERENT VARIETIES - (STUDIES ON PHYSICAL AND CHEMICAL-PROPERTIES AND TASTE CHARACTERISTICS OF RICE .2.)

In this study, a distribution of chain-length of amylopectin and gelatinization properties of rice starch prepared from six varieties, namely Koshihikari, Sasanishiki, Akitakomachi, Varieties A (high amylose rice), Varieties B (high protein rice) and Nipponbare, were investigated. The following results were obtained. The distribution of chain-length of amylopectin, expressed as a value of Fr. III/ Fr. II, were 3.52 for Koshihikari, 3.78 for Sasanishiki, 3.72 for Akitakomachi, 4.98 for high-amylose rice, 4.13 for high-protein rice and 3.38 for Nipponbare. The long-chain content of Koshihikari was especially high as 12.5 mol% whose average chain-length was 50 to 60 compared with five other varieties. Although a chain length of 10 to 20 was dominant in the short-chain of other varieties, 37.5 mol% of that of Koshihikari was less than 10. The average chain-length of the sum of Fr. II and Fr. M was 21 to 23, and no difference was observed between varieties. However, the average chain length of Fr. III was 10.6 in high-amylose rice, showing a tendency of being shorter than those of the other five varieties. The proportions of B3 chain, B2 chain, and A + B1 chain of amylopectin were 4.2 to 12.5, 12.5 to 20.8, and 68 to 79.2 mol% in nonglutinous rice starch, so nonglutinous rice starch had a larger mol% for the long-chain fraction of amylopectin and a small mol% for the short-chain fraction of amylopectin compared with 1.1, 8.0 and 90.0 mol % of the corresponding fractions in glutinous rice starch. The complex elastic modulus (G*) of the dynamic viscoelasticity of rice starch suspensions at 95-degrees-C showed the following order, from the higher to the lower, Koshihikari, Nipponbare, Akitakomachi, Sasanishiki, High protein, High amylose rice. The negative correlation of r=-0.871 was observed between the Fr. III/Fr. II value and the complex elastic modulus (G*) of the dynamic viscoelasticity. In addition, a negative correlation of r=-0.963 was observed with respect to the transition calory of DSC.