Digestibility and structural changes of waxy rice starch during the fermentation process for waxy rice vinasse

Abstract

During the fermentation process of waxy rice vinasse, the waxy rice starch granules were collected and their digestibility and structural changes were investigated, and the fermentation time–starch structure–starch digestibility relationships were revealed. It was found that the waxy rice starch digestibility from the fermented waxy rice was changed significantly during the fermentation. The fermentation reduced rapidly digestible starch (RDS) and resistant starch (RS) content but increased the slowly digestible starch (SDS) content in the cooked waxy rice starch. The SDS obtained from the fermentation process ranged between 24.53 and 43.85%, which is about 3.6–6.4 times over that of the cooked waxy rice starch. After fermentation, the Mw of waxy rice starch decreased. The A type crystallinity and molecular helices were increased during the early stage of the fermentation and then decreased as the fermentation time increased, compared with that of the cooked waxy rice starch, suggesting that the higher A type crystallinity and more molecular helices induced slow digestion of the fermented waxy rice starch. But when the fermentation time increased further, the slightly thicker semi-crystalline repeat structure, a thicker crystalline lamellar structure and the higher starch molecular aggregation orders contributed to the higher SDS contents in the fermented waxy rice starches. By controlling the extent of waxy rice fermentation, the waxy rice starch digestibility could be reduced which is benefited for improving the nutrition of the waxy rice vinasse with low glycemic response.