Study On The Changes Of Rice Dreg By Double Step Enzymatic Hydrolysis And Antioxidant Stability Of Rice Dreg Peptide

In this paper,rice dreg protein was used as raw material to prepare rice dreg peptide by bio-enzymatic hydrolysis and spray drying.Analysis of the surface hydrophobicity,sulfhydryl content,intrinsic fluorescence,particle size,degree of hydrolysis,secondary structure,amino acid composition and molecular weight distribution of the peptides during enzymatic hydrolysis,and explore the influence of process changes and its regularity.The effects of various factors on the stability of rice dreg polypeptide during processing and storage,especially its antioxidant stability,and its mechanism were studied.Two peptides RDPH-1 and RDPH-2 were prepared by trypsin + flavourzyme,neutral protease +flavourzyme.During preparation of peptides,samples were taken at regular intervals to determine the hydrolysis degree,sulfhydryl content,intrinsic fluorescence and particle size,and to study the dynamic changes of rice dreg enzymatic.The degree of hydrolysis of RDPH-1 was 13.62% higher than that of RDPH-2 at 4 h,indicating that the hydrolysis efficiency of trypsin and flavourzyme was higher.The surface hydrophobicity of RDPH-1 and RDPH-2 decreased first and then increased,and the surface hydrophobicity of RDPH-1 was more than 10 times larger than the RDPH-2.The intrinsic fluorescence has red shifted with the maximum absorption wavelength of enzymatic hydrolysis,and the peak intensity has also changed.The secondary structure of RDPH-1 and RDPH-2 increased the ?-turn angle compared with the rice dreg protein(RDP).It indicated that the protein conformation has changed significantly during the hydrolysis process.RDPH-1 and RDPH-2contain essential amino acids other than tryptophan,which are 25.58% and 23.86%,respectively.The amino acid composition basically meets the nutritional needs of the human body.In the process of preparing rice dreg peptide by two type enzymes,enzymatic hydrolysis is a dynamic process,in which the enzymatic hydrolysis process of trypsin and flavourzyme is more regular.This provide guiding significance for the preparation of peptide efficiently.The effect of external environment on the solubility,emulsifying and antioxidant stability of RDPH-1 and RDPH-2 was investigated.The results showed that the solubility of the two rice dreg polypeptides was excellent(> 80%),the solubility was better than the acidic and alkaline conditions in neutral conditions,and the emulsifying activity increased with the p H.The effects of metal ion concentration,temperature,light and p H on the DPPH and ABTS free radical scavenging ability of RDPH-1 and RDPH-2 were studied to determine the antioxidant stability of the peptide.As the metal ion concentration increased,the effect on the antioxidant activity of the rice dreg polypeptide was not significant.Under different light conditions and dark storage conditions,the ability of rice dreg polypeptide to scavenge DPPH and ABTS free radicals decreased with the illumination time.Rice dreg polypeptide had antioxidant stability at 25-100 °C.During range of the p H 4-8,the little loss of antioxidant activity of the peptide was found.Therefore,RDPH-1 and RDPH-2 have the ability to resist the change of the external environment.The effects of four methods,including fast low temperature(-18 °C),4 °C,boiling water bath and untreated,on the structure and function of the peptide were investigated.The results showed that there was no significant difference in the degree of hydrolysis between the fast low temperature(-18 ° C)and 4 °C and boiling water treatment peptides(P>0.05).The solubility was excellent,both were higher than 85%.There was no significant difference in emulsifying properties(P>0.05).The peptides treated by fast low temperature(-18°C)to inactive enzyme had the best emulsion stability,followed by the untreated and the 4°C,and the boiling water bath was the worst.Four different enzyme-inhibiting methods have little effect on the ability of peptides to scavenge DPPH free radicals and ABTS free radicals,but boiling water treatment reduced hydroxyl radical scavenging ability and reducing power,causing loss of peptide activity.The reason for this result may be that thermal action altered the structure and composition or was related to the antioxidant mechanism of the peptide.