Studies Of Maillard Reaction Of Oligopeptides Obtained From Sea Cucumber(Stichopus Japonicus)Gut

The protein content of sea cucumber gut was 61.13±0.89%.So,it was a good source of marine protein and could be used for higher value applications.Firstly,the radical scavenging activities of four kinds of oligopeptides obtained by hydrolyzing sea cucumber gut was studied by using neutrase（Hn）,papain（Hp）,alcalase（Ha）and flavourzyme（Hf）.The molecular weight distribution and amino acids composition of oligopeptides were analyzed by size exclusion chromatography（SEC）and HPLC respectively,and the scavenging activities of oligopeptides on hydroxyl（·OH）radical and 1,1-diphenyl-2-picrylhydrazyl（DPPH）radical were determined by an ESR spectrometer.The results showed that all the four oligopeptides were mainly composed of components below 10 KDa,and the contents of components below 3KDa were higher than 78%.All the four oligopeptides were rich in amino acids with antioxidant activities,and the total contents of Arg,Ala,Val,Leu and Lys approximately reached to 35%.At the concentration of 6-20 mg/m L,all the four oligopeptides showed obviously scavenging abilities on ·OH and DPPH radical.According to the values of IC₅₀,the scavenging abilities of oligopeptides were in the order of Hp≈Ha≈Hf>Hn,Hn>Ha>Hp>Hf.But the scavenging abilities of oligopeptides were significantly less than GSH.These results suggest that oligopeptides from sea cucumber gut have potentially valuable in antioxidant activities.But the activities should be further increased.Secondly,the antioxidant activities of these oligopeptides were increased mostly by Maillard reaction in this paper.The oligopeptide which obtained by hydrolyzing for 3h with neutrase（Hn）was the best fit for Maillard reaction.Because of the antioxidant activity of this MRP was higher than others.The mixture（pH 7.0,8.0）which obtained by mixing oligopeptides of sea cucumber gut hydrolysis（10mg/m L）with ribose（20 mg/m L）was incubated at 75、85、95℃ for 1-12 h to get MRPs.The decrease in free amino group,composition of middle products(OD₂₉₄),fluorescence intensity and browning development(OD₄₂₀)were measured.And these variables were regarded as reaction factors of the kinetic studies.The DPPH radical scavenging ability was also measured.By means of the kinetics analysis,the decrease in free amino group followed the first-order kinetics;the composition of middle products,fluorescence intensity,and browning development in the Maillard reaction process followed zero-ordered kinetics.The higher reaction temperature and pH value were good to promote reaction.The activation energy was increased along with the process,but the higher pH value was good to decrease the activation energy.When the pH value in the reaction system was 8.0,the activation energies of all the reaction factors mentioned above were 11.5,62.5,66.2 and 90.1 respectively.The DPPH radical scavenging abilities have increased by increasing pH value,temperature and reaction time.Except decrease in available amino group,all the factors were extremely positive related with DPPH radical scavenging abilities especially fluorescence intensity.The factors had radical scavenging abilities.These results suggest that MRPs as base stock obtained from oligopeptides of sea cucumber gut had strong antioxidant activity.Thirdly,the application value of MRPs had been studied in this paper.The strong linoleic acid peroxidation inhibiting ability had been found in MRPs.And the ability was increased along with reaction time increased.Finally,the relationship between volatile substances of MRPs and antioxidant activities was studied in this paper.It had been found that,5 types of antioxidative compounds（aldehydes,alcohol,ketone,furan,acids）were in the volatile substances of MRPs.And aldehydes influenced antioxidant activities most.