Investigation on molecular and morphology changes of protein and starch in rice kernel during cooking.

The composition and structure of starch are important indicators to evaluate the quality of rice, but the effect of protein on structural properties of rice has always been controversial. In the present study, the rheological properties and thermal properties were combined to investigate the effects of protein on mechanical and inner structure changes of rice kernel during cooking. The morphologic changes in overall form and inner structure of the kernel showed the limited and uneven gelatinization of starch, and reflected the good heating stability of protein. The comparison of molecular mobility in H2O/D2O reflected the special gelatinization behavior of starch and the hydrophobicity of protein during cooking. The similar proton distributions between starch, starch-protein mixture and rice flour indicated the weak interactions between starch and protein. The results of Fourier transform infrared spectra, thermogravimetric analysis and transmission electron microscope confirmed the wrapping effect of starch and surface interactions with protein.