Effects of Frozen Storage and Thawing Conditions on Physical Properties of Glutinous Rice: (Part 1) Ice Crystal and Color Measurement

抄録

The effect of the freezing process and frozen storage periods on the microstructure of cooked glutinous rice has been investigated. Cooked glutinous rice (cv. Koganemochi) was frozen and stored in a household freezer (about -22 °C) during 1, 5, 10, 30 and 60-day storage periods. Its microstructure was observed by using fluorescence staining method and the morphology of ice crystals including equivalent diameter and number was analyzed. Colorimetric measurements were conducted after natural and steaming thawing on samples of each storage period. It was found that average equivalent diameter and number of ice crystals increased with storage period from 5 days, and recrystallization occurred in temperature fluctuation during freezing process and storage affected microstructure of glutinous rice. Moreover, by analyzing the distribution of ice crystals, it was found that most of them are under 10µm in each storage period. Frozen stored glutinous rice after 60 days showed darker and more unpleasant color than freshly cooked one by both thawing methods. Since the tendency of color change during the whole frozen storage was unstable, it could be assumed that the control of thawing process should not be neglected.