Studies On The Physicochemical Characterization And Antioxidant Activity Of Silver Carp(Hypophthalmichthys Molitrix) Peptide Modified By Maillard Reaction

Due to the weak activity of the antioxidative peptide by enzymatic hydrolysis, thestudy focuses on the antioxidant activity of silver carp（Hypophthalmichthys molitrix）peptide modified by Maillard Reaction, and provides a basis for the production of ahigh level of antioxidant activity of antioxidants.This thesis includes four parts as follows:1. The kinetics of silver carp peptide-glucose Maillard reaction（MR） system werestudied at different temperatures （60-90℃）, pH8.0for up to12h. The results indicatedthat the reactive temperature played a crucial role on the Maillard reaction. When thereaction temperature was low, the extent of MR was really slow, and the content offree amino groups decreased slowly, browning intensity, the UV absorption of theintermediate products and the fluorescence intensity values increased slightly. But therate of Maillard reaction accelerated rapidly with reaction temperature increasing. Bymeans of the analysis of kinetics, the loss of free amino groups followed first-orderedkinetics; browning intensity, the UV absorption of the intermediate products andfluorescence intensity changes in the Maillard reaction process followed thezero-order kinetics. The activation energy of free amino group, browning intensity,UV absorption of the intermediate products and fluorescence intensity changes was89.13kJ/mol,148.7kJ/mol,136.1kJ/mol and138.5kJ/mol, respectively. Thecondensation between carbonyl and amino group took place easily in the initial stageof Maillard reaction and the activation energy required was low; but the formation ofbrown substance was in the final stage of Maillard reaction, so the activation energywas higher.2. When the silver carp peptide-glucose system was heated at90°C and pH8.0, thecontents of furosine and5-hydroxymethylfurfural （HMF） with the reaction time were investigated, and the antioxidant activity of Maillard reaction products（MRPs）werealso determined. The effects of characteristic intermediate products of MR on theantioxidant activities were analyzed preliminarily.The content of furosine increased first and then decreased, and it reached themaximum at8h. The content of HMF increased with reaction time, and there was asignificant time-dependent manner. The level of caramelization was low （about20%）,so it was supposed that HMF was producted from the Maillard reaction in this study.The ferric reducing/antioxidant power of MRPs increased with the reaction time.MRPs prepared at different reaction time inhibited autoxidation of linoleic acid, andthe products after8h showed stronger activity. And there were no significant changesin DPPH radical scavenging activity of MRPs heated more than8h.Furthermore, there was no significant correlation between furosine and HMFgenerated in the process of MR, however the content of HMF and FRAP displayedthe significant correlation （r＝0.9495）. Glucose played a catalytic role on thedegradation and cross-linking of silver carp peptide in Maillard reaction. With theprolonged of reaction time，the degradation of the peptides between1000⁵000Daand below1000Da increased，while the content of the peptides above5000Daincreased showing the obvious effect of cross-linking of glycopeptides.3. MRPs are prepared by heating silver carp peptide-glucose for8h at90°C andpH8.0. After ultrafiltration and ethanol fractionation, the antioxidant activity ofwater-soluble and alcohol-soluble components was studied，respectively. The DPPHradical scavenging activity, metal ions chelating activity and total antioxidant capacitywere analyzed, the chemical properties including browning intensity and fluorescenceintensity and instructual characteristics consisted of FT-IR and FMAAs weredetermined.（1） The DPPH radical scavenging activity, the metal ion chelating activity andFRAP value of water-soluble components MRPs Ⅲ （>5kDa） in sliver carppeptide-glucose MRPs were highest.（2） The browning intensity of MRPsⅢ andMRPsⅡ（1kDa⁵kDa） were strongest and the fluorescence intensity of MRPsⅢ was highest.（3） In the IR spectrums, MRPs had a strong absorption peak at860.66cm^-1,and MRPsⅡand MRPsⅢ had sharp absorption peaks at860.01cm^-1and948.61cm^-1,respectively, which illustrated that the reducing sugar may connect to the skeleton ofpeptide and lead to some changes of structure. It was showed that glucose and aminogroups from Lys、Leu、Ile and Ser in peptide chain were combined and the changes ofstructure and characteristic of MRPs were brought about by HPLC-MS.Therefore, it can be drawn that the water-soluble substances play a majorantioxidant role in the MRPs, the colored water-soluble products of which withrelatively higher molecular weight show stronger antioxidant activity.4. The MRPsⅡ was applied in the catfish to study its inhibitory effect on lipidperoxidation. The POV and TBARS values are determined to explore the impacts ofdifferent treatment on the indicators.There was no significant difference betweenPOV values of catfish added MRPsⅡand that of catfish added PG, that is, in theinitial stage of inhibition of lipid oxidantion the activity of MRPsⅡ was equivalent tothat of PG. The inhibitory effects on secondary oxidation products of catfish （TBARS）of MRPsⅡ was only inferior to PG. The results showed that MRPsⅡ had asignificant role to inhibit the lipid oxidation of the refrigerated catfis, and it makes theeffect mianly through inhibiting the generation of primary and secondary oxidationproducts in the process of lipid oxidation.