Study on Structures and Physical Properties of Endosperm Starches of Rice and Other Cereals

Abstract

1. Structural and physicochemical characteristics of endosperm starches of rice cultivars bred in Japan. Properties of rice starches were investigated using 4 types of endosperm starches, waxy, low amylose (AM), medium AM and high AM starches of rice cultivars bred in Japan. There was a highly negative relationship between the real AM contents and the peak viscosity measured by 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 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 the 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 rice starches in water at 75°C. 2. Structure and properties of endosperm starches from cultivated rice of Asia and other countries. Starch granules were prepared from mature grains of 75 cultivars of rice originating in Asia and other countries. Non-waxy cultivars of the indica and Chinese indica varieties had higher contents of apparent AM and SLC in AP. HPAEC-PAD of isoamylase-debranched starches showed that the starches of non-waxy cultivars of indica and Chinese indica had decreased amounts of branch chains with DP 6-12 (Fr.A). The Fr.A contents correlated negatively with the peak temperature of gelatinization of the rice starches. There was a high positive relationship between amounts of Waxy (Wx) protein and SLC contents in starch. This appears to show that Wx protein is concerned with synthesis of SLC. We proposed a scheme of the relationship between the SLC and the Fr.A contents of AP as a classification of endosperm starches of rice. 3. Effects of variations in starch synthase on starch properties. We evaluated the effects of functional variation in three starch synthases in rice granule-bound starch synthase I (GBSSI, wx), starch synthase I (SSI, SSI), and starch synthase IIa (SSIIa, alk) between indica cultivar Kasalath and japonica cultivar Nipponbare on starch properties. We used three near-isogenic lines-NIL (Wx^a), NIL (SSI^K), and NIL (Alk)-containing chromosomal segments of Kasalath on a Nipponbare genetic background. The Wx^a allele explained most of the difference in AM content between the two cultivars, and decreased the peak viscosity and breakdown to less than half of those of Nipponbare. NIL (Alk) showed very similar profiles to those of Kasalath in having fewer short chains of DP 6-11 and more mid-length chains of DP 13-23 for the chain length distributions of amylopectins among the lines. Differential scanning calorimetry revealed faster retrogradation of the once-gelatinized starch in NIL (Alk).