Comparison between microwave-cooking and steam-cooking on starch properties and in vitro starch digestibility of cooked pigmented rice

The influence of two types of cooking method, that is, steam-cooking and microwave-cooking, on the morphological structure, starch fractions, and starch digestibility of cooked Thai pigmented rice (three cultivars) was examined. The relationship between starch hydrolysis and change in X-ray diffraction (XRD) pattern, including the change of crystallinity degree during in vitro digestion, was also investigated. The results indicated that the cooked rice morphological structure and starch hydrolysis rate during in vitro digestion was varied by the cooking method. All non-waxy rice cultivars exhibited V-h-type crystallinity, whereas, no crystalline peak was detected in the waxy rice cultivar. However, the XRD pattern and crystallinity degree of steam-cooked rice were dramatically changed after simulated small intestinal digestion for 360 and 480 min when compared with microwave-cooked rice. Moreover, steam-cooked rice showed a significantly lower percentage of equilibrium starch hydrolysis than that of the microwave-cooked rice. Practical applications Rice attributes and change of crystallinity in XRD pattern during in vitro digestion have found to correlate with rice starch digestibility, which varied depending on rice cooking methods. Steam-cooking could enhance the degree of crystallinity during in vitro digestion, which would affect to retard rice starch digestion. This finding is interesting for the consumer on the selection of the optimized cooking process that promotes a healthier effect.