Antioxidant activities and antiproliferative activity of Thai purple rice cooked by various methods on human colon cancer cells.

The changes in anthocyanins, phenolic compounds, and antioxidant activities of Thai purple rice cooked by various cooking devices, including an electric rice cooker, an autoclave and a microwave oven, were investigated. In raw rice, cyanidin-3-glucoside (cy-3-glu) and peonidin-3-glucoside (pn-3-glu) are predominant anthocyanins, whereas protocatechuic acid (PCA) and vanillic acid (VA) are major free phenolic acids, and ferulic acid (FA) and VA are major bound phenolic acids. The microwave cooking method resulted in a marked loss of phenolics, anthocyanins and antioxidant activities (p<0.05). A decrease of cy-3-glu occurred concomitantly with an increase of PCA upon any cooking methods applied. A methanolic extract of rice cooked under sterilization exhibited the highest content of PCA and the highest inhibition of Caco-2 cell proliferation with an IC50 (16.11 μg/mL) comparable to that of raw rice. Thai purple rice cooked under sterilization could be a potential source of PCA exerting high antiproliferative activity.