The role of bioconversion processes to enhance bioaccessibility of polyphenols in rice

Polyphenols are a group of natural antioxidants with various beneficial effects. They are natural antioxidants due to the presence of hydroxyl groups in their structure. Rice is an important part of the human diet, including as a source of polyphenols. The majority of polyphenols in rice, are found in the bound form esterified with cell wall components. The bound form of polyphenols cannot be extracted using conventional extraction methods. The conversion of bound polyphenols to free ones can occur using bioconversion methods including solid state fermentation, enzymatic extraction, and germination. In all of these processes, the activation of hydrolyzing enzymes leads to the cleavage of the linkages between the cell wall components and bound polyphenols. Polyphenols have various biological and therapeutic effects due to their antioxidant activity. Several studies have reported that the health effects of rice polyphenolic extracts increased after these bioconversion processes. This review provides an overview of various factors that affect the efficiency of different bioconversion methods on the enhancement of free polyphenols in rice and also their biological and therapeutic effects on human health.