Difference of Amylopectin Structure among Various Rice Genotypes Differing in Grain Qualities and Its Relation to Starch Physicochemical Properties

Abstract

As the main constituent of rice starch, amylopectin and its structure is one of the major determinants for the development of starch granule structures and starch physicochemical properties. Understanding amylopectin chain length distribution properties in different rice varieties, and clarifying the correlations between the amylopectin structure and rice starch physicochemical properties, may provide theoretical basis for revealing the mechanism of rice quality development and guide rice quality improvement. In this study, the amylopectin structure of some rice varieties in China and some introduced rice varieties with different qualities were characterized by improved fluorophore-assisted carbohydrate electrophoresis (FACE) method based on DNA sequencer. On the basis of eliminating the impact of amylose content (AC), the correlations between amylopectin structure and rice starch physical chemistry properties were analyzed. The results indicated that amylopectin structure in 50 rice varieties could be classified into I-type and II-type, according to the chain ratio of ∑DP≤11/∑DP≤24. The chain ratio of the I-type amylopectin is less than 0.22, whereas the II-type is higher than 0.26. Amylopectin of all the 15 japonica varieties belonged to II-type. Among the 35 indica varieties, for amylopectin structure, 15 belonged to I-type and 20 belonged to II-type. The ΣDP6-11 and chain ratio had very significantly negative correlations (P0.01) with pasting temperature (PT) and relative crystallinity (RC). The ∑DP28-34 had very significantly negative correlation with PT, but did not have significantly correlation with RC. The ∑DP13-24 and ∑DP39-49 had very significantly positive correlations with PT and significantly positive correlations (P0.05) with RC. In glutinous rice, low AC and high AC varieties, the correlations of ΣDP6-11, ∑DP28-34, the chain ratio of ∑DP≤11/∑DP≤24 with PT and RC were essentially consistent with those in all varieties. The correlations between ∑DP28-34 and PT in low AC, between ∑DP39-49 and PT in glutinous rice and high AC varieties, between ∑DP39-49 and RC in high AC varieties were also consistent with those in all varieties. The proportion of chain amounts in amylopectin with different chain length ranges was not significantly correlated with GC and RVA profile properties. Therefore, the proportion of chain amounts in amylopectin with different chain length ranges has relation to rice starch PT and RC, but not close relation to GC and RVA profile characteristics in most cases. The short chain amounts of DP6-11 have a function of decreasing rice starch PT and RC, the intermediate chain amounts of DP13-24 have a function of increasing rice starch PT and RC, the longer chain amounts of DP 28-34 have a function of decreasing rice starch PT and the long chain amounts of DP 39-49 have a function of increasing rice starch PT and RC.