Cooked Rice Grains Research Articles

Effects of Storage Period, Milling Degree of Stored Brown Rice Grains, and Soaking of Milled Rice Grains on the Properties of Cooked Rice Grains

Effects of Storage Period, Milling Degree of Stored Brown Rice Grains, and Soaking of Milled Rice Grains on the Properties of Cooked Rice Grains

Effect of cell wall degrading enzymes on the cooking properties of milled rice and the texture of cooked rice.

Effect of the partial degradation of endosperm cell walls on the cooking properties of rice grains and also on the texture of cooked rice was examined by using two different enzyme preparations, i.e., crude enzyme from Aspergillus japonicus and purified endoxylanase from Streptomyces sp. E-86. Texturometer analysis showed that the partial degradation of the cell walls softened the cooked rice grains and made them more sticky. When the excess water was supplied, cooked rice grains expanded more after the enzyme treatment. Moreover, this treatment affected the amylogram of milled rice flour and lowered its viscosity, especially in the retrogradation process. Purified endoxylanase showed these effect without any other enzyme, suggesting the important role of hemicellulosic polysaccharides for the physical properties of endosperm cell walls.

Luster and Fine Surface Structure of Cooked Rice Grains in Relation to the Eating Quality

Cooked rice grains were fxed with liquid air, then freeze-dried, and their surface and cross-sectional structures were observed by a scanning electron microscope. The surface of the cooked rice grain was consisted of two parts; the smooth areas and the rough areas. The smooth areas were liable to be positioned on the top of a grain and at the conjunction of two grains, and supposed to be evenly coated with some gel substances. Differences were observed among five tested varieties in the ratio of the smooth and rough areas (Fig. 1). Grains from high palatable varieties tended to show a higher ratio of the smooth to rough areas accompanied with a higher luster evaluation (Table 1). The height of the protuberances in the rough part tended to be lower in grains from high palatable varieties (Fig. 2). Besides the ratio of the smooth to rough areas, the height of the protuberances may affect the degree of luster of the grain surface. Varietal differences were also observed in the cross-sectional structures of the cooked grain. Storage cells in the endosperm from high palatable varieties such as Sasanishiki (Fig. 3-1eft) were more completely broken down as compared with those from lower palatable varieties such as Toyonishiki (Fig. 3-right). The degree of breakdown of the endosperm cells seems to have a relation to the degree of evenness of the grain surface.