Tracing Mechanism And Aqueous Preparation Of Maillard Reaction Intermediates Of Peptides

Maillard reaction intermediates?MRIs?are important flavor precursors.MRIs are stable in physical and chemical properties at room temperature and have no obvious aroma.But they retain high reactivity under heating.MRIs are easy to crack and complete the subsequent Maillard reaction,producing a large number of fresh volatile flavor substances,which can avoid the flavor loss of Maillard reaction products.Meanwhile,MRIs can provide consumers a sense of achievement and pleasure,and have broad development prospects.The aroma of Maillard reaction products prepared by single amino acid is simple,while the mixed peptides can produce rich flavors that cannot be formed by the monomer amino acid.Thus,the mixed peptides have obvious application potential and advantages.In this research,diglycine-arabinose was taken as the research object.A novel tracer,glutathione,was used to inhibit Maillard browning and indicate the formation conditions of intermediates.Then,the soy peptides-arabinose MRIs were prepared with this tracer,and their antioxidant capacity and processing flavor formation ability were also studied.The details are as follows:The soybean peptides were prepared by enzymatic hydrolysis of soybean protein isolate with complex protease?and aminopeptidase.Setting the degree of hydrolysis and the dissolution rate as indexes,experiments were performed to determine the optimal preparation conditions:substrate concentration was 8%,complex protease?addition amount was 2500 U/g,hydrolyzed at 60?for 4 h,and aminopeptidase addition amount was 400 U/g,hydrolyzed at50?for 3 h.Under this condition,64.33%of the enzymatic hydrolysates had molecular weight less than 500,and free amino acids only accounted for 5.18%of total amino acids.This indicates the main component of the enzymatic hydrolysis were small molecular peptides,which can be used as raw material for preparing peptide Maillard reaction intermediates.Compared with the effect of glutathione or cysteine on the color of Maillard reaction products and the curve of A₄₂₀-addition time,it was confirmed that glutathione presents a similar function as cysteine for inhibition of Maillard browning which can indicate the formation conditions of intermediates.The water solubility of glutathione is significantly better than that of cysteine,so glutathione is a suitable novel tracer.Then,the effects of temperature,pH,and substrate concentration on the generation time of intermediates were clarified.Based on the feasibility of industrial production,the optimal preparation conditions of intermediates were determined:the p H was 7.5,the reaction temperature was 80?,and the reaction time was60 min.Diglycine-arabinose was used as a model system to study the mechanism of glutathione inhibiting Maillard browning.The intermediate was prepared by aqueous phase.The molecular weight was determined to be 264 and the molecular formula was C₉H₁₆O₇N₂.Compared the effect of glutathione and oxiglutathione on Maillard browning,it was confirmed that sulfhydryl was the key point to achieve browning inhibition.The effect of glutathione addition on the formation of several characteristic products were studied,which proved that the action time of glutathione was between the ARP and short chain dicarbonyl compounds.Further analysis of the direct reaction products of glutathione and ARP proved that the sulfhydryl could react with deoxypentosone to form an adduct with molecular weight of 440,which could inhibit the formation of subsequent products via the change of Maillard reaction path,and slow the degradation rate of ARP.The effect of adding glutathione at different reaction time was studied.It was found that the formation of the intermediate was the largest at 60 min,and the amount of products were the least and browning was the lightest,which proved that glutathione can indicate the formation conditions of intermediate.By measuring changes of several dicarbonyl compounds with time in the first stage,the mechanism of tracing was revealed:When the intermediate just reached the peak value,the accumulation of deoxypentosone was moderate,and glyoxal and glyoxal were relatively few.At this time,glutathione could most effectively inhibit the degradation of the intermediate and reduce the subsequent reaction.Thus,the lowest browning index indicated the best formation condition of the intermediate.The antioxidant capacity of soybean peptides-arabinose intermediates was studied.It was found that when the concentration was 5 g/L,DPDP free radical scavenging ability of Maillard reaction products reached 87.98%,and that of intermediates was 41.99%,while the peptide-sugar mixtures was only 17.55%.The reducing power showed a similar rule.Besides,intermediate has strong Fe²⁺chelation ability,which is almost the same as the Maillard reaction products,indicating intermediates had good antioxidant capacity.The flavor forming ability of soybean peptides-arabinose intermediates was studied.Under the sameconditions,the content of flavor produced by the intermediates was the highest,which was 1.63 times of peptides-sugar mixtures and 1.81 times of Maillard reaction products.Further study on the application of intermediates in the actual system showed that adding 2%of intermediates to fried cabbages increased the formation of 13 flavor substances,which indicating that intermediates can enrich the flavor profile and enhance aroma characteristics of foods.