Abstract: In this paper, content changes of the major chemical components in Yinmi powder (prepared by fermentation, steaming, drying and grinding using glutinous rice as raw material) and fermentation supernatant during 15-day natural fermentation of rice were investigated, and the effect of traditional natural fermentation on characteristics of Yinmi starch granules, digestibility and intrinsic viscosity was explored. The results showed that during the natural fermentation period, the contents of crude fat and crude protein declined with the maximum amplitude of 22.95% and 63.10%, respectively with increasing fermentation time; similarly, the content of total free amino acids in Yinmi powders with different fermentation times was decreased to different extents compared to unfermented rice, and 5-day fermentation resulted in the highest decrease amplitude of 54.31%. During the early part of the fermentation period, the pH of fermentation supernatant was decreased from 6.44 on the first day to 4.44 on the fourth day as the fermentation time was prolonged, and then tended to stable after reaching 3.90 or so on the fifth day. Throughout the fermentation period, titratable acidity and total free amino acids in fermentation supernatant were increased while the content of soluble sugar was decreased. Yinmi powder contained more digestive starch than raw rice, and their solubility and swelling power had similar temperature dependent changes and ascended with increasing temperature. Under the observation of scanning electronic microscope (SEM), Yinmi starch granules revealed an adhesive form. Compared with original rice, the crystallinity and intrinsic viscosity of Yinmi starch declined.

Key words: Yinmi, natural fermentation, chemical components, granule characteristics, digestibility, intrinsic viscosity