Effect of freezing and thawing on the properties of glutinous rice starch

The properties of samples of moisturised glutinous rice starch (30% and 40% w∶w±, respectively) and glutinous starch-water suspension (1∶1.5 w∶v) were evaluated, followed by repeatedly freezing and thawing. The study included particle morphology, crystal properties, gelatinization properties and damaged starch. It was found that after treating, the edges of the starch granules were injured and with the increasing of freezing-thawing cycles, the particle surface appeared more pit. Though the rice starch crystal type did not changed, staying as A-type, the relative degree of crystallinity reduced from 25.19% to 21.34% (starch∶water 1∶1.5 w∶v) , but the relative degree of crystallinity increased from 25.19% to 32.47% and 31.65% (30% and 40% w ∶w ± , respectively) . Also between freezing-thawing cycle, there was a downward trend of the relative degree of crystallinity.The initial gelatinization temperature decreased by 0.3～0.67℃, the paste viscosity (hot paste viscosity, keeping paste viscosity, cold paste viscosity) reduced by 30～60BU (starch∶water 1∶1.5 w∶v) , and the paste viscosity reduced by 150～300cp (30% and 40% w∶w±) . However, between freezing-thawing cycle, there was no significant difference. Moreover, after treating, the damaged starch content decreased.