Abstract
Global warming has caused devastating damage to starch biosynthesis, which has led to the increase in chalky grains of rice. This study was conducted to characterize the qualities of chalky rice grains and to develop the estimation formulae for their quality damage degree. We evaluated the chalkiness of 40 Japonica rice samples harvested in 2019, in Japan. Seven samples with a high ratio of chalky rice grains were selected and divided into two groups (whole grain and chalky grain). As a results of the various physicochemical measurements, it was shown that the surface layer hardness (H1) of cooked rice grains from chalky grains was significantly lower, and their overall hardness was significantly lower than those from the whole grains. In addition, α- and β-amylase activities, and sugar contents of the chalky rice grains were significantly higher than those of the whole rice grains. The developed estimation formula for the degree of retrogradation of H1 based on the α-amylase activities and pasting properties, showed correlation coefficients of 0.84 and 0.81 in the calibration and validation tests, respectively. This result presents the formula that could be used to estimate and to characterize the cooking properties of the rice samples ripened under high temperature.
Highlights
Rice (Oryza sativa L.) is one of the main food crops throughout the world and the staple food for about half of the global population [1]
We previously found that the iodine absorption curve of rice starch differed among the various sample rice cultivars and we developed the estimation formulae for apparent amylose content (AAC), resistant starch (RS) content, and amylopectin chain length distribution [4,5]
We developed novel estimation formulae for oleic and linoleic acid contents based on the pasting properties of brown rice flours measured by an Rapid Visco Analyzer (RVA) [8]
Summary
Rice (Oryza sativa L.) is one of the main food crops throughout the world and the staple food for about half of the global population [1]. As starch is the main component of rice grains, its characteristics, such as apparent amylose content (AAC), amylopectin chain length distribution, and resistant starch, affects rice quality markedly. Rice quality consists of apparent quality and internal quality The former quality is evaluated through a human test by trained inspectors and graded based upon the ratio of whole grains, damaged grains including chalky grains, foreign grains and foreign matters, and grain characteristics. Analysis of the pasting properties of rice starch by a Rapid Visco Analyzer (RVA) and the texture of the cooked rice grains are very important. We tried to develop an estimation formulae for the degree of quality damage of chalky rice grains ripened under high temperatures in 2019
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