Effects of frying on starch structure and digestibility of glutinous rice cakes

In this study, the starch structure and digestibility of glutinous rice cakes were investigated. The rice cakes were steamed or fried at different temperatures; the fried cakes were then separated into three parts-crust, middle, and core. Scanning electron microscopy and X-ray diffraction indicated that the starch structure in both the steamed and fried cakes was completely gelatinised and destroyed. As determined through differential scanning calorimetry, the starch structure became more seriously altered with increasing frying temperatures, with the crust tending to be more severely altered than the middle and core. The fried cakes contained 67.48%-73.64% of rapidly digestible starch, comparable to that in the steamed cakes, but higher than that in raw glutinous rice. Moreover, the fried cakes contained 19.89%-27.95% of slowly digestible starch, comparable to that in the steamed cakes and raw glutinous rice. However, the fried cakes 4.57%-6.57% of resistant starch-significantly lower than that in the steamed cakes and raw glutinous rice. Frying temperatures did not lead to significant changes among the three starch categories. The in vivo test results showed that steamed and fried glutinous rice cakes were both medium-glycaemic index foods.