Cooked rice has a histological structure that correlates to its eating quality. One of the features of what affects the chain polysaccharide matrix structure of the cell wall. In this study, we clarified the relationships between cooked rice palatability and the decomposition of pectin, hemicellulose and cellulose as cell wall components during cooking.Upon electron microscopy, the degradation of fibrous tissue was confirmed in the pectin fraction, as well as the degradation of the dense disk-shaped structures of the hemicellullse A and B fractions. However, the cellulose structure showed no change under the same conditions. No changes in the cell wall occurred with HgCl2 treatment, which designed to inhibit enzyme activity. The molecular sizes of pectin and hemicellulose A and B decreased owing to the degradation of these components’ during cooking. The galacturonic acid content of the pectin fraction was reduced from 63.7% to 19.7%. In addition, the galactose and glucose contents of the hemicellulose A and B fractions were also reduced. The activities of enzymes for cell wall decomposition (polygalacturonase, β-galactosidase, β-xylanase, β-glucanase and α-mannosidase) were observed in the endosperm of rice. Results of the current study indicate that the chain polysaccharide matrix structure of the rice endosperm may be degraded by the action of endospormous enzymes during rice cooking, thereby influencing cooked rice texture regaredless of rice grain freshness or cultivar.
