Physicochemical properties, phenolic identification and in vitro digestion profile of Chinese black rice (Oryza sativa L.)

Yangxian black rice, as one of ancient Chinese black rice varieties, is widely planted in Yangxian area of China. This study investigated physicochemical properties, phenolic identification and in vitro digestion profile of Chinese black rice under gradient milling treatment. The chemical composition, color, pasting and thermal properties of black rice with different milling degree were comprehensively compared. In vitro digestion analysis indicated that cooked rice flour had higher rapidly digestible starch (RDS) and lower resistant starch (RS) contents compared with uncooked one. Besides, all cooked black rice samples exhibited high predicted glycemic index (pGI) value and whole black rice showed a lower pGI than refined rice. The microstructure and the abundance of phenolic compounds in the solid matrix during different treatment or digestion stage were observed by CLSM. Furthermore, a total of 102 phenolic constituents were absolute quantified by targeted metabolomics techniques. Methanol extraction and moderate cooking treatment contributed to the release of phenolic compounds from solid matrix of whole black rice. Besides, compared to gastric digestion stage, the transition in the intestinal environment caused a decrease in majority of analyzed polyphenols. Identifying the phenolic constituents was favorable to a better elucidation of the chemical basis of function and nutritional value of Chinese black rice.