Abstract: The microstructure of raw rice and cooked rice from japonica rice cultivars with similar amylose contents and significantly different protein contents (12.32%, 8.42% and 5.72%, respectively), m 119,  m 90 and Koshihikari, was observed under a scanning electron microscope (SEM) and a confocal laser scanning microscope (CLSM) to explore the relationship between protein content and cooking and eating quality. Koshihikari had the best eating quality followed by m90 and m119 as demonstrated by sensory evaluation and rapid viscosity analysis (RVA). Cross-sectional observations of brown rice under SEM and CLSM showed that compound starch granules in m 119 were surrounded by large amounts of spherical protein bodies in honeycomb-like patterns. The roughness of fracture surfaces of water-soaked brown rice grains increased, and consequently water absorption declined with increasing protein content as observed under CLSM, suggesting that protein content can affect water absorption in rice. The microstructure of cooked rice as observed under SEM and CLSM displayed that water absorption and gelatinization of starch granules were limited because compound starch granules in m 119 were surrounded by large amounts of spherical protein bodies, resulting in deterioration of cooking and eating quality.

Key words: rice, cooking and eating quality, protein, microstructure, confocal laser scanning microscope (CLSM)