Abstract
High temperature effects attributable to climate change can affect rice quality. The chalky area of rice grains is often used to evaluate of rice grain starch quality, but the overall effect of high temperatures on grain chalkiness and overall nutrient quality has not been fully clarified. Thus, in this study, we assessed high temperature effects on grain weight, chalkiness, and nutrient contents. Rice grains were classified into four groups on the basis of the chalky area in scanned grain images: P (0%), S (0–15%), M (15–40%), and L (≥40%). Then, the amylose, protein and mineral nutrient concentrations were assessed in each chalkiness classification. High temperatures during grain filling markedly decreased the grain weight and the amylose content of milled rice but increased the chalky area of the grains as well as protein content and the concentrations of most minerals. There were significant negative correlations between mineral contents and both grain weights and amylose contents of milled rice. These results indicate that increases in grain chalky areas due to high temperatures during grain filling also increase grain mineral contents.
Highlights
Rice is the staple food for more than half the global population, supplying them with important calories and nutrients [1]
We investigated how changes in temperature during the grain filling period of rice affected grain amylose, protein, and mineral concentrations, and how these changes were related to the chalkiness of the harvested grains
There was a close positive relationship between the grain weight of milled rice and amylose content, but a negative one between grain weight of milled rice and protein content (Figure 1). These results suggest that differences in the chalky area of rice, which result from high temperatures during the grain filling stage, occur because of the poor accumulation of starch, decreased grain weight, and increased protein content
Summary
Rice is the staple food for more than half the global population, supplying them with important calories and nutrients [1] It is the most important crop in Asia, where more than 90% of rice is produced, but it is an important food source in Madagascar and West Africa [2,3]. Various studies have reported that high temperatures above 26–27 ◦C during the grain filling stage reduces yield [4,5,6] and quality due to poor accumulation of storage materials such as starch [7]. One study reported that high temperature could reduce the starch content by up to 40% [8]. High temperatures in the period after heading cause the emergence of chalky grains, immature thin grains, and cracked grains, leading to decreased quality of rice in external appearance and taste [7,9,10]
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