Dynamic changes in the free and bound phenolic compounds and antioxidant activity of brown rice at different germination stages.

Germinated brown rice is a good source of the phenolics associated with antioxidant effects. Germination significantly increased by 63.2% and 23.6% the total phenolic and flavonoid contents, respectively. The percentage contribution of bound phenolics to total was 42.3% before and decreased slightly to 37.6% after germination. The percentage contribution of bound flavonoids to total, 51.1%, was the same before and after germination. The change in the amounts of free and bound forms indicated that transformations could occur during the germination process. Six individual phenolics were detected by HPLC. The levels of ferulic, coumaric, syringic, and caffeic acid significantly increased. The ratio of bound ferric reducing antioxidant power to total was basically constant, while germination increased the ratio of bound oxygen radical absorbance capacity to total. This indicated that the increase of bound phenolics exerts beneficial health effects throughout the digestive tract after absorption and may reduce mutations.