Interactions between leached amylose and protein affect the stickiness of cooked white rice

Stickiness is a major factor determining the eating quality of cooked rice, but the molecular mechanisms governing this property are not fully understood. In the present study, two different starch structures were examined: that in the uncooked grain, and that of starch leached out of the grain during cooking, and these results were parameterized by fitting to biosynthesis-based models. Protein content and stickiness were measured using a Kjeldahl apparatus and texture analyzer, respectively. In addition to protein content, the spatial distribution of the protein in the grain was obtained by microscopy after fluorescence labelling. Results showed that the extra-long amylose (ELA) chains were largely leached out during cooking. The amount of leached ELA chains was positively correlated with the amylose content in rice grain and negatively correlated with the stickiness of cooked rice, respectively. The difference in average chain length of ELA between parent and leached starch was negatively correlated with protein content. This implied that the protein network was wholly or partially entangled with ELA chains, which could retard ELA-chain leaching and consequently influence the stickiness of cooked rice. This suggests that stickiness, a quality important to consumers, could be managed by rice breeders through manipulating genes controlling the chain-length distribution.