Isolation, identification and antioxidant activity of bound phenolic compounds present in rice bran

The bound phenolic compounds in rice bran were released and extracted with ethyl acetate based on alkaline digestion. An investigation of the chemical constituents of EtOAc extract has led to the isolation of a new compound, para-hydroxy methyl benzoate glucoside (8), together with nine known compounds, cycloeucalenol cis-ferulate (1), cycloeucalenol trans-ferulate (2), trans-ferulic acid (3), trans-ferulic acid methyl ester (4), cis-ferulic acid (5), cis-ferulic acid methyl ester (6), methyl caffeate (7), vanillic aldehyde (9) and para-hydroxy benzaldehyde (10). The structures of these compounds were determined using a combination of spectroscopic methods and chemical analysis. Among the compounds isolated, compound 3, 5 and 7 exhibited strong DPPH and ABTS+ radical scavenging activities, followed by compounds 4 and 6. Compound 1 and 2 showed potent DPPH and ABTS+ radical scavenging activities, compound 8 displayed moderate antioxidant activity against ABTS+ radical, whereas compound 9 and 10 showed weak antioxidant activity.