Main starch molecular structures controlling the textural attributes of cooked instant rice

Instant rice is increasingly popular around the world due to its convenience, while the molecular mechanism how its texture is determined remains unclear. This study aimed to investigate features of starch molecular structures i.e. chain-length distributions (CLDs), which could contribute and reflect the textural attributes of instantly cooked rice. CLDs from 15 different rice varieties with a wide range of amylose content (AC) were characterized by fluorophore-assisted capillary electrophoresis and size-exclusion chromatography, which were then correlated with the hardness and stickiness of both regularly and instantly cooked rice from these 15 rice varieties. Results showed that a significant variance of textural attributes existed among different cooked rice samples. Typically, instantly cooked rice had a lower stickiness compared to regularly cooked rice, while the difference of hardness between them was not consistent. Correlation analysis showed that regularly cooked rice with a higher AC, higher amount of amylopectin long chains, and longer amylopectin intermediate to long chains had a harder and less sticky texture. Whereas, instantly cooked rice with a higher AC, higher amount of amylopectin long chains, relatively longer amylopectin A chains, shorter amylopectin B1 and B2 chains, as well as longer amylopectin intermediate to long chains had a harder and less sticky texture. These results could potentially help rice manufacturer develop new generation of instant rice products with desirable textures.