Effects Of Protein Oxidation Induced By Rice Bran Rancidity On In Vitro Digestibility Of Rice Bran Protein

Rice bran is a by-product of rice processing,its annual output reached 14 million tons.Rice bran is rich in rice bran nutritive value,including 12?18%protein,which is regarded as a protein resource possessing high potential in food industry.Rice bran contains lipid and strong activity lipase and lipoxygenase.Between polishing brown rice and rice bran stabilization,lipid is hydrolyzed by lipase to free fatty acids(FFAs)rapidly,FFAs can be further oxidized by endogenous rice bran lipoxygenase leading to rice bran oxidative rancidity.Rice bran oxidative rancidity products have strong biological activity,which induced rice bran protein oxidation and changed structure,function and digestion of rice bran protein properties.Effect of protein oxidation induced by rice bran rancidity on in vitro digestibility of rice bran protein were studied in this paper.Fresh rice bran stored in a certain condition for different period,which was made into rice bran with different degree of rancidity after stabilizing and defatting,rice bran protein with different degree of oxidation was prepared.In vitro pepsin digestibility of rice bran protein was compared with raw rice bran protein suspension and heat-treated rice bran protein suspension at 95?,The results showed that as degree of rice bran rancidity increased,in vitro pepsin digestibility,initial digestion rate and antioxidant activity of raw rice bran protein and heat-treated rice bran protein firstly increased,and then decreased.Compared with raw rice bran protein,·OH scavenging ability of in vitro pepsin digests,metal chelating ability and reducing power of heat-treated rice bran protein obviously unchanged,in vitro pepsin digestibility,initial digestion rate and rest antioxidant activity of heat-treated rice bran protein were increased remarkably during storage,in vitro pepsin digestibility of rice rice bran was increased from 28.45?39.79%to 37.79?47.15%,and in vitro pepsin digestibility of fresh rice bran was increased by 50%.With increasing of in vitro pepsin digestion time,surface hydrophobicity of rice bran protein prepared with different rancidity degree increased firstly and then decreased,maximum emission wavelength of intrinsic fluorescence spectra suffered a red shift,average particle size firstly increased and then decreased,peak area percentage of low molecular weight protein gradually decreased,rice bran albumin subunits,glutelin acidic subunits,and globulin subunits could be completely digested and degraded by pepsin,while the rice bran glutelin base subunits and prolamin subunits were more difficult to be digested by pepsin.Compared with raw rice bran protein,the red shift extent of maximum emission wavelength of intrinsic fluorescence spectra of heat-treated rice bran protein increased,average particle size decreased,and the complete pepsin digestion time of three easy digestible subunits advanced,indicated that structure change of rice bran protein after heat treatment was beneficial to in vitro pepsin digestion.As degree of rice bran rancidity increased,the red shift extent of the maximum emission wavelength of intrinsic fluorescence spectra of rice bran protein firstly increased,and then decreased,during in vitro pepsin digestion process,surface hydrophobicity gradually decreased,average particle size increased,the complete pepsin digestion time of three easy digestible subunits firstly advanced,and then delayed.The result showed that rice bran rancidity induced rice bran protein oxidation had important effects on the covalent cross-linking state,aggregation behavior and surface hydrophobicity of rice bran protein during in vitro pepsin digestion process,therefore in vitro pepsin digestion properties of rice bran protein were affected.Rice bran protein suspensions digested by pepsin were digested by trypsin in vitro.It was found that as degree of rice bran rancidity increased,in vitro total digestibility,in vitro trypsin digestibility and initial digestion rate of raw rice bran protein and antioxidant activity of raw and heat-treated rice bran protein were firstly increased and then decreased;as storage time increased,in vitro total digestibility,in vitro trypsin digestibility,and initial digestion rate of heat-treated rice bran protein were obviously inhibited.Compared with raw rice bran protein,metal chelating ability and reducing power of in vitro pepsin digests of heat-treated rice bran protein obviously unchanged,in vitro total digestibility,in vitro trypsin digestibility,initial digestion rate and rest antioxidant activity of heat-treated rice bran protein were huge increased during storage,in vitro total digestibility of rice rice bran was increased from 54.14?75.34%to 69.53?89.07%.After in vitro trypsin,structure changes of rice bran protein digestion were similar to pepsin,and rice bran protein was gradually polarized during in vitro trypsin digestion.