Study of the migration and molecular structure of starch and protein in rice kernel during heating.

ABSTRACT

Leaching and re-absorption of leached solids and changes in kernel structure are of prime importance for the quality of cooked rice. This paper describes the contents and structural changes of both starch and protein in leached solids and rice kernels. Under actual cooking conditions, the leached solids increased with heating temperature and then decreased at specific temperatures relating gelatinization. Starch content of leached solids increased with the heating temperature, especially after gelatinization. As proteins are mainly distributed on the surface of the kernel, their release increased between 30 and 50 °C but then decreased with increasing leaching of starch at high temperatures. The molecular weight distribution of leached solids at different temperatures is significantly different, while it is similar in rice kernels. At 30-50 °C, the amylose contents in the leached solids were slightly higher than those in rice kernel, while the contents were similar at high temperatures. The transformation of the kernel structure during heating confirmed that the kernel surface and the formed cracks are the main path for leaching; the rearranged structures of the surface and cracks influence the final texture of cooked rice.