Change in Fatty Acid Composition in High-Temperature-Damaged Rice Grains and Its Effects on the Appearance and Physical Qualities of the Cooked Rice

Global warming has caused rice grains to ripen at high temperatures and become increasingly chalky, which also leads to a deterioration in the physicochemical and cooking properties of rice grains. In the present work, we first want to propose how to evaluate the palatability of rice from the high-temperature year 2022. We evaluated the qualities of 32 Japonica rice grains harvested in 2022. These showed no significant correlation with either amylose content or protein content, while the Mido score (=flavor score) showed a positive correlation with palmitic acid (r = 0.66, <i>p</i> < 0.01) and linoleic acid (r = 0.51, <i>p</i> < 0.01), in contrast to a negative correlation with oleic acid (r = -0.57, <i>p</i> < 0.01) and phosphorus content (r = -0.48, <i>p</i> < 0.01). And pasting temperatures (Pts) of polished rice flour showed significant positive correlation with the surface hardness of cooked rice grains (r = 0.53, <i>p</i> < 0.01) and significant negative correlation with their overall stickiness (r = -0.57, <i>p</i> < 0.01). In addition, Pts showed significant positive correlations with oleic acid and negative correlations with linoleic acid. Therefore, fatty acid composition could become one of the new indicators for evaluating the palatability of rice. Our second aim of this study was to determine the effects of high temperature on rice quality. It was found that oleic acid increased significantly and linoleic acid and palmitic acid decreased in 21 rice samples of the same varieties and growing regions in 2023, an abnormally hot year, compared to 2022, a normal hot year. In summary, both oleic acid content and pasting temperatures may lead to lower quality rice grains in 2023.