Hydrothermal stability of phenolic extracts of brown rice

The phenolics were extracted and purified from brown rice and twenty-seven compounds were identified, including six phenolic acids, four phenolic acid glycosides, and eight flavonoid glycosides. Afterwards, the hydrothermal stability of phenolic extracts of brown rice was investigated after treatment at 60, 80, or 100 °C for 120 min. After hydrothermal treatment, ferulic acid, p-coumaric acid and free glucose were increased, while the phenolic glycosides were decreased. In addition, the total phenolic and total flavonoid content were decreased by 5.7%-9.2% and 3.5%-5.8% after initial 30 min, and then they were slightly recovered after treatment for 120 min. Consequently, there was a slight reduction (<10%) in the total antioxidant activity of the phenolic extracts after hydrothermal treatment. These results suggest that hydrothermal treatment of phenolic extracts of brown rice made some phenolic glycosides deglycosylated, but does not lead to a large reduction in their overall antioxidant activity.