Analysis of phenolic compounds and antioxidant activity with H4IIE cells of three different rice grain varieties

The phenolic content and the antioxidant capacity of ethanolic extract of rice grains were examined using three different rice (Oryza sativa L. var. japonica) varieties, Jakwangchalbyeo (red pericarp glutinous rice), Hwasunchalbyeo (white pericarp glutinous rice), and Ilpumbyeo (white pericarp non-glutinous rice). Quantitative high performance liquid chromatography (HPLC) analyses showed that Jakwangchalbyeo contains the highest amount of total phenolic substances. Radical scavenging activities measured by the 1,1-diphenyl-2-picryl hydrazyl (DPPH) assay were 87.5% (Jakwangchalbyeo), 45.0% (Hwasunchalbyeo), and 50.0% (Ilpumbyeo). The results suggest a positive correlation between the phenolic content and the antioxidation capacity. Antioxidant activity in the ethanolic extract of rice grain was further assessed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay and fluorescence-activated cell sorting (FACS) analysis of H4IIE cells treated with hydrogen peroxide (H₂O₂). Hwasunchalbyeo and Ilpumbyeo extracts showed no significant effects on H₂O₂-induced oxidative stress. Jakwangchalbyeo extract increased cell viability by up to 82% and 74% after 5- and 24-h treatments at 100 μg/mL, respectively. Consistent with the results of DPPH and MTT assays, dichlorofluorescein (DCF) fluorescence was further reduced when H₂O₂ was applied with Jakwangchalbyeo extract. In conclusion, red pericarp Jakwangchalbyeo grain extracts exerted significantly higher inhibitory effects on H₂O₂-induced oxidative stress in H4IIE cells than did other white pericarp rice grain extracts.