Relationships between transparency, amylose content, starch cavity, and moisture of brown rice kernels

Rice with low amylose content (AC) is popular due to the unique eating and cooking quality, but its transparency is poor. It is unclear why low AC rice has poor transparency until now. In this study, the transparency and microstructure of brown rice kernels were investigated in rices with different ACs. Chalkiness of endosperm resulted from the loosely packed starch granules, and existed in rice kernels with low and high moisture. However, dry kernels with low AC were opaque or dull due to the cavities in the center of starch granules, and could become transparent gradually with the increase of moisture. For rices with the same genetic background but different ACs, the cavity size was negatively correlated with AC, and the transparency of dry kernels was significantly correlated positively with AC and negatively with cavity size. The transparency of kernels was positively correlated with moisture of kernel, and the effect of moisture on transparency was significantly correlated positively with starch cavity size and negatively with kernel AC. The above results showed that the transparency of low AC rice was remarkably influenced by cavity size and AC of starch, and could be regulated through controlling the moisture of kernel.