Rice Starch Structure and Physicochemical Properties of Good Taste japonica Rice Varieties and Their Regulations by Nitrogen
[Objective]Starch is the main component of rice grain,and its composition and physicochemical properties play a fundamental role in shaping the taste characteristics of rice.Investigating the starch composition characteristics of good taste rice varieties and analyzing the effect of nitrogen levels at grain filling stage are of great significance for the optimization and cultivation of good taste rice varieties.[Method]Taking rice varieties Jinxiangyu 1,Wuyujing 3,Wumijing and Huaidao 5,which have significant differences in taste,as experimental materials,the relationship between the physicochemical properties of rice starch and taste quality and its response to varing nitrogen levels at the grain filling stage were explored.[Result]The taste value ranking was as follows:Jinxiangyu 1＞Wuyujing 3＞Wumijing＞Huaidao 5,which was consistent across different nitrogen levels.For good taste rice varieties,they exhibited low amylose and protein contents,high breakdown and low setback in the RVA spectrum,easy gelatinization,better solubility,swelling power and starch granule morphology,along with higher relative crystallinity of starch.Furthermore,they displayed a higher proportion of short branches in the distribution of amylopectin chain length.With the increase of nitrogen level at the filling stage,the taste value of rice decreased significantly,combined with decreased amylose content,increased protein content,shortened gel consistency,decreased peak viscosity and breakdown in RVA spectrum,and increased setback;The starch granule morphology of starch became worse;The gelatinization enthalpy,relative crystallinity of starch and the chain B2 and chain B3 contents in the branching of amylopectin increased,while the solubility,swelling power,chain A and chain B1 contents decreased.Varieties responded variously to nitrogen in terms of their physicochemical properties and taste value to nitrogen.Good taste rice varieties displayed relatively stable taste,being less sensitive to nitrogen.[Conclusion]The results showed that good taste rice varieties had low amylose and protein contents,better cooking properties and starch granule morphology,better starch crystallization features and a well-balanced amylopectin structure with higher short amylopectin content.Elevated nitrogen level at the grain filling stage increased the proportion of long branched amylopectin,and the energy required for starch gelatinization,reduced starch solubility and swelling power,and significantly degraded the cooking and eating quality.
riceeating qualitystarch structurephysicochemical properties of starchchain length distributionnitrogen
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