Understanding the Influences of Rice Starch Fine Structure and Protein Content on Cooked Rice Texture

Abstract Amylose content, fine structure, and protein content affect the hardness and stickiness of cooked rice. However, the mechanisms of those effects have not been fully understood especially the fine structure of amylose. Here, 22 rice varieties with large ranges of both starch chain‐length distributions and protein content are examined, and the starch structural results are parameterized using biosynthesis‐based models. The ratios of the activities of branching enzyme and starch synthase for amylose showed positive and negative correlations with rice hardness (coefficient 0.556 and 0.838) and stickiness (coefficient −0.498 and −0.639), respectively. Protein content is strongly positively correlated with hardness, with nitrogen application up to the panicle development stage (coefficient 0.640). New findings could be obtained from these correlations, which reveal that in the whole region of amylose, the shorter the amylose is, the harder and less sticky the cooked rice is, which has not been reported previously. In addition, protein is found to influence rice hardness significantly, while rice stickiness is less affected by it. Therefore, a comprehensive mechanism of protein effects on rice texture is proposed. This work provides information for breeders to develop improved rice varieties.