Difference of Amylopectin Structure Among Rice Varieties Differing in Grain Quality and Its Correlations with Starch Physicochemical Properties

Abstract

To explain the forming mechanism of taste quality in rice ( Oryza sativa L.), the amylopectin structures of 50 rice varieties were characterized using improved fluorophore-assisted carbohydrate electrophoresis method that was based on DNA sequencer. The correlations between amylopectin structure and rice starch physicochemical properties were analyzed on the basis of eliminating the influence of amylose content (AC). The amylopectin structures in the 50 varieties were classified into type-I and type-II according to the chain ratio of ΣDP ≤ 11/ΣDP ≤ 24. The chain ratio of type-I amylopectin was smaller than 0.22, whereas the chains ratio of type-II amylopectin was greater than 0.26. Amylopectins of all the 15 japonica varieties belong to type-II, and those of indica varieties belong to type-I (15 varieties) and type-II (20 varieties). The ΣDP 6–11 and chain ratio of ΣDP ≤ 11/ΣDP ≤ 24 were negatively correlated ( P < 0.01) with pasting temperature (PT) and relative crystallinity (RC). The ΣDP 28–34 had a negative correlation ( P<0.01) with PT, but had no significant correlation with RC. The ΣDP 13–24 and ΣDP 39–49 were correlated with PT ( P<0.01) and RC ( P<0.05). The glutinous, low AC, and high AC varieties showed consistency to the total varieties in the correlations of ΣDP 6–11, ΣDP 28–34, and chain ratio of ΣDP ≤ 11/ΣDP ≤ 24 with PT and RC. Besides, the glutinous varieties were in agreement with the total varieties in the correlation between ΣDP 39–49 and PT; the low AC varieties in agreement with the total varieties in the correlation between ΣDP 28–34 and PT; and the high AC varieties had similar correlations between ΣDP 39–49 and PT and between ΣDP 39–49 and RC to the total varieties. The proportion of amylopectin chain was not correlated with gel consistency and Rapid Visco Analyser (RVA) profile properties despite of different amylopectin branch chain-length. Therefore, the amylopectin structure is mainly related to starch PT and RC in rice rather than GC and RVA profile properties. The short (DP 6–11), intermediate (DP 13–24), moderately long (DP 28–34), and long amylopectin chains (DP 39–49) might have functions on decreasing PT and RC, increasing PT and RC, decreasing PT, and increasing PT and RC of starch in rice grains, respectively.