The Research On Enzymatic Preparation And Properties Of Antioxidant Peptide From Rice Bran Protein

China has plenty resource of rice bran which contain lipid, protein, and other nutrients. Rice bran protein is a high quality plant protein which with high nutritional value. Low solubility limits the application of rice bran protein in the food industry. Defatted rice bran was used as raw material to prepare rice bran antioxidant peptide by enzymatic hydrolysis in the present study, the parameter of enzymatic hydrolysis was optimized by valuation of antioxidant activity in vitro, the relationship between structure and antioxidant activity was primary characterized; finally, application of rice bran antioxidant peptide in the preservation of chilled pork was studied.Degree of hydrolysis and hydroxyl radical scavenging activity were used to value the antioxidant activity of hydrolysates which prepared by enzymatic hydrolysis of defatted rice bran protein by alcalase, neutrase, and acidic protease. The results indicated that rice bran protein hydrolysates which prepared by acidic protease exhibited much better degree of hydrolysis and antioxidant activity. Degree of hydrolysis of rice bran protein hydrolysates which catalyzed by acidic protease reached14.52%as pH of enzymatic hydrolysis solution was4, temperature was45℃, concentration of substrates was0.5%, ratio of enzyme to substrate was0.5%, and time of enzymatic hydrolysis was2h. The hydroxyl radical scavenging activity of the corresponded rice bran protein hydrolysates reached74.9%which was higher than rice bran protein hydrolysates prepared by catalyzed by alcalase and neutrase.Acidic protease was selected as hydrolyzed enzyme, single factor experiments were firstly employed to optimize concentration of substrate, pH value, temperature, and ratio of enzyme to substrate. Then, the orthogonal experiment was used to further optimize the parameter of enzymatic hydrolysis. The optimal parameter of enzymatic hydrolysis were: pH4, temperature45℃, ratio of enzyme to substrate0.5%, concentration of substrate5%, time of enzymatic hydrolysis3h. In addition, the results implied that the relationship between antioxidant activity of hydrolysates and degree of hydrolysis was not a positive correlation.To characterize antioxident activities of rice bran protein hydrolysates by using alcalase, neutrase,and acidic protease,its scavenging activity towards superoxide radical,hydroxyl free radical,hydrogen peroxide,and reducing ability were compared by using ascorbic acid as control.The results indicated that all rice bran protein hydrolysates showed strong antioxidative activities in vitro,which was far weak than ascorbic acid.However,their ability of scavenging superoxide radical by alcalase protease ranked the highest,which was almost98.41%(t=1h,IC50=1.08mg/mL).The ability of scavenging superoxide radical of rice bran protein hydrolysates by acidic protease showed the highest,which was up to77.08%.Intrinsic fluoresence spectra,surface hydro phobicity,total sulphydryl content,SDS-PAGE and Sephadex G-25were applied to characterized the structure-activity relationship of rice bran protein hydrolysates.The results indicated that the rice bran protein hydrolysates molecular structures unfolded during the process,for the maximum emission peaked higher in intrinsic fluorescence experiments as the enzymatic treating time got longer and DH become stronger. Surface hydrophobicity of rice bran protein hydrolysates decreased in the beginning but then followed by increased.The hydrophobic groups in the hydrolysates may affect these antioxidative activities.Total sulphydryl content remained low during the hydrolyzation because of the thiol oxidation.The molecular weight of hydrolysates of rice bran protein were under lOkDa by using SDS-PAGE.The highest antioxidant component was isolated in the Sephadex G-25chromatography profile.In the final stage of the study,the rice bran protein hydrolysates which showed relative high antioxidant activities were applied in chilled pork preservation,and the effects of which was evaluated by sensory,physico-chemical and microbiological indicators.The results indicated that rice bran protein hydrolysates showed positive effects on prohibiting the oxidation by lipid,maintaining acid value at low level and retarding the increase of pH during the storage period.However,no obvious effect of its antimicrobial properties of hydrolysates was observed,and the preservation effects of component by Sephadex G-25showed the best among all the tested hydrolysates..