Studies on the Texture of Cooked Rice : II. Effects of kernel size, apparent quality of brown rice and degree of kernel maturation

Abstract

Effects of kernel size, apparent quality of brown rice and grain maturity on the texture of cooked rice were investigated using a General Foods Texturometer. The results obtained are summarized as follows: 1. Primary parameters of texture such as hardness, adhesiveness and viscousness which are shown as the strength of force or the amount of work were sharply affected by the size of the test kernel, although the other primary parameters were not affected (Table 1). And it was revealed that the degree of these effects were just proportional to the kernel weight of test rice. Consequently, revising of texture value in consideration of the kernel weight was thought to be necessary for an accurate measurement of rice texture. 2. Rice texture was also affected by apparent quality of brown rice from which the test rice had been made. Cooked rice from white belly kernels and white core kernels showed lower values of stickiness and the textural palatability index (TPI) as compared with normal perfect kernels. Green kernels and rusty kernels were a little low in hardness and chewiness, though they showed rather high values in stickiness. Thus their TPI values were not inferior to the perfect kernels (Table 2). 3. Texture values markedly changed with the progress of maturation (Fig. 1-3). Values of hardness and chewiness were very high at the early stage of ripening, but they were rapidly decreased with maturity. On the other hand, adhesiveness, viscousness and stickiness increased during maturation, and showed their peak values at the right stage of maturity. Overripening seemed to increase the values of hardness and chewiness and decrease those of adhesiveness, viscousness and stickiness. TPI, therefore, were almost the highest at the right time of maturation (Fig. 4). Above results suggest that harvest of rice should be done at the right time of grain maturation to secure the palatability of cooked rice.