Changes in histological tissue structure and textural characteristics of rice grain during cooking process

Textural-related property including histological tissue structure changes in rice grain (Oryza sativa L.) during cooking process was investigated in this study. Forty grams of polished grain were added to 60 ml of water, and cooked using the Japanese style cooking method. Rice grains were removed at 30, 50, 70, 85, and 100 °C during cooking, and moisture content, overall firmness, surface firmness, and histological tissue structures were examined. The leached material amount in cooking water at each temperature was also measured. Results showed moisture content in rice grains linearly increased from 70 °C to 100 °C, while moisture remained almost constant at from 30 °C to 50 °C. The overall firmness almost linearly decreased from 30 °C to 85 °C and decreased from 85 °C to 100 °C significantly, though no significant difference in surface firmness change between 70 °C and 85 °C was found. The leached material amount increased approximately 1.5 times between 50 °C and 70 °C. Voids in the cooked grains were generated between 85 °C and 100 °C, where gelatinization and morphological changes in grain shape, with histological cell wall disruptions occurred. The results shown in this study indicate that structural tissue properties, i.e. cell wall properties, are one of the important factors responsible for the textural-related properties of cooked rice grains.

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