Studies On Chemical Constituents And Their Biological Activities Of Rice Bran

Rice bran,which constitutes about 10%of the total weight,is a main byproduct produced in the milling process of rice.Rice bran contains abundant phytochemicals,such as phenolic compounds,phytosterols,and phytic acid.These compounds exhibit various bioactivities,such as antioxidant,anti-inflammatory,and anti-cancer properties,and play an important role in the prevention of certain chronic diseases,such as cardiovascular disease,chronic inflammation,diabetes,and cancer.In this study,free and bound compounds in rice bran were isolated and identified by modern separation techniques and spectroscopic methods.The biological activities of these compounds were evaluated preliminarily.Response surface method(RSM)was introduced to optimize the conditions of alkaline hydrolysis for bound compounds in rice bran with the total phenolics content as response value.The optimum parameters were:digestion time of 2 h,alkaline concentration of 2 mol/L,solvent-solid ratio of 8.3 mL/g,and digestion temperature of 25 ?.Under these conditions,the content of bound phenolics was 42.2730 ±0.132?M GAE/g.Rice bran was extracted by organic solvent and concentrated to give the crude extract 1 which was predominately made up of free compounds.The remaining residue was digested under the optimum conditions,and the degradation solution was extracted by organic solvent and concentrated to give the crude extract 2 which was rich in bound compounds.The crude extracts 1 and 2 were separated by various column chromatographic methods to obtain 17 compounds.These compounds' structures were identified by modern spectroscopic techniques and chemical methods.Seven free compounds in crude extract 1 were identified to be oryzalactam(1),oryzasaccharide A(2),oryzasaccharide B(3),momilactone A(4),butyl ?-D-xylopyranose(5),ethyl ?-D-xylopyranose(6),and methyl?-D-xylopyranose(7).Ten bound compounds in crude extract 2 were identified to be cycloeucalenol cis-ferulate(1),cycloeucalenol trans-ferulate(2),trans-ferulic acid(3),trans-ferulic acid methyl ester(4),cis-fe-rulic acid(5),cis-ferulic acid methyl ester(6),methyl caffeate(7),para-hydroxy methyl benzoate glucoside(8),vanillic aldehyde(9)and para-hydroxy benzaldehyde(10).DPPH and ABTS radical scavenging methods were used to evaluate the antioxidant activities of free and bound compounds.Results of free compounds showed that,compound 1 possessed the strongest DPPH and ABTS radical scavenging activities,which were close to that of positive control Vc.Compounds 2-7 exhibited weak antioxidant activities.Results of bound compounds exhibited that,Compounds 3,5 and 7 showed the highest antioxidant activities followed by compounds 4 and 6,and the radical scavenging activities of compounds 3-7 were higher than that of VE.The left bound compounds showed weak antioxidant activities.Eight indicator bacteria were used to evaluate the antimicrobial activities of free and bound compounds.The assay revealed that free compound 4 showed inhibitory activity toward Escherichia coli with a minimal inhibitory concentration value of 5 ?M.