Abstract
Changes in the quality of nonwaxy and waxy rice during grain development were investigated, laying emphases on the texture of cooked rice and protein, amylose and fat-by-hydrolysis contents. In terms of textural features, chewiness value decreased with maturity, but stickiness and the textural palatability index values increased. The trends of decrease or increase became constant after 30-40 days after heading. There were no clear differences in the formation mechanism of texture during maturation between nonwaxy and waxy rice. Changes in the contents of protein, amylose and fat-by-hydrolysis with maturity were similar to those in chewiness. At the early maturing stage, the protein content of the rice kernels was very high. Protein seemed to restrict starch swelling, so that cooked rice from immature kernels were thought to be harder and less sticky. Amylose was considered to be a dominant factor in determining texture during ripening. The texture of waxy rice also changed although amylose was not detected throughout the ripening period. Hence, amylose could not be the only factor that might control textural changes. Since fat-by-hydrolysis was relatively abundant at the early stage of ripening, it was thought to make cooked rice harder and less sticky by limiting starch swelling. For the reasons mentioned above, protein, especially water-insoluble protein, amylose and fat-by-hydrolysis were found to play an important role in restricting the expansion of starch.
