Protective role of rice polyphenols in oxidative stress.

The oxidative breakdown of membrane polyunsaturated fatty acids is known to be accompanied by the formation of a complex mixture of lipid hydroperoxides and secondary products. These compounds are highly reactive and are capable of rapid reaction with cellular nucleophiles such as phospholipids and proteins; we found that these reaction products are candidates as important biomarkers to evaluate the antioxidative activity of dietary antioxidants. We have been involved in developing immuno-chemical detection methods for oxidative stress by the application of polyclonal and monoclonal antibodies. From our hypothesis that endogenous antioxidants in plants must play an important role in antioxidative defense systems against oxidative stress, an intensive search for novel natural antioxidants has been carried out on numerous plant materials, including those used as foods, and we have isolated and identified a number of lipid-soluble and water-soluble dietary antioxidants from crop seeds, sesame seeds and some spices. In this paper, we review the recent progress of research on functions of rice polyphenols.