Properties of Endosperm Starches and Physical Properties of Cooked Rice from Japanese Upland Rice Cultivars Containing M-type Amylopectin

Abstract

Starch is the major component of rice seeds, and the quality of rice is infl uenced by the properties of endosperm starch.1,2) Starch is composed of amylose and amylopectin. Amylose is a primarily α-1,4-linked linear glucan, and amylopectin is a highly branched polymer, consisting of α-1,4-linked linear glucan branched with α-1,6-linkages.Amylose is synthesized by ADP-glucose pyrophosphorylase (AGPase) and granule-bound starch synthase I, (GBSSI). ADP-glucose pyrophosphorylase catalyzes the reaction of glucose-1-phosphate with ATP to form ADP-glucose. The ADP-glucose then serves as a substrate for GBSSI to produce amylose. GBSSI is encoded by the Wx gene, which was mapped to chromosome 6.3 Villareal et al. 5) reported that amylose content is usually higher in starch of indica rice than in that of japonica rice. On the other hand, amylopectin is synthesized by concerted reactions catalyzed by four classes of enzymes; AGPase, a soluble starch synthase (SS), starch branching enzyme (BE) and starch debranching enzyme (DBE). Each class has multiple isozymes, some of which form subunits.6 8) The mechanism of the synthesis of the cluster structure of amylopectin is not yet fully understood, although several models have been proposed. 8 11) All of these models show that the ratio of SS and BE activities is important to make up the normal tandem cluster of amylopectin. 12)Many factors infl uence the eating quality of rice, but physicochemical properties such as the hardness and stickiness of cooked rice, and the gelatinization temperature of rice starch, determine about 70% of the total evaluation of the eating quality of cooked rice.13) Japanese people usually eat japonica rice, which is softer and stickier than indica rice. The amylose content of the starch in rice endosperm is

Characterization of the New Amylopectin Long-chain Rice Cultivar Chou 2418 and Its Boiled Rice Grains

“…However, the setback value calculated from viscosity under the same gelatinization condition, which reduced the influence of gelatinization on viscosity, may reflect the original properties of the starch granules. Nakaura et al (2012) demonstrated a positive correlation between the pasting temperature and AAC in non-glutinous rice cultivars. In this study, significant correlation was not observed between these two parameters (r = 0.76; p > 0.05); instead, the pasting temperature of Koshinomenjiman was very low despite the high AAC.…”