Identification Of Maillard Reactive Peptides In Beef And Deducing The Mechanism Of Its Flavor Products Formation

In this paper,the enzymic beef hydrolysate-Cys-xylose Maillard reaction model system with odor,taste and taste enhancement was constructed.At the same time,the influence of factors on the flavor characteristics of Maillard reaction products was analyzed,and the relationship between flavor substances and sensory was studied.Based on this,the Maillard reactive flavor precursor peptides in enzymic beef hydrolyzate were isolated and identified.The isotope labeling method was used to study the mechanism of beef pure peptides in the formation of flavor compounds via Maillard Reaction.The hydrolysis of the beef protein was carried out by enzymatic hydrolysis of the endoprotease Protamex with an enzyme content of 1000 U/g and the exoprotease Flavourzyme with an enzyme content of 800 U/g,when the degree of hydrolysis is about 15%,the Maillard reaction products are full of meat aroma,umami&kokumi taste and to be a taste enhancer in the blank chicken soup solution.The flavor profile of the Maillard reaction system is affected by the type of endoprotease,and the softness of its flavor is affected by the degree of hydrolysis.Under different enzymatic conditions,the flavor substances did not change regularly.With the increase of pH value and temperature,the sensory characteristics of Maillard reaction system mainly from meat,umami to roast,bitter flavor,the umami taste intensity of white chicken soup was enhanced from significant to weak but the kokumi taste intensity was improved more and more stronger.When the reaction conditions were 125?and pH5.5,the comprehensive flavor of the products were the best.Roast intensity too strong not only could cover the meaty,but also means the formation of bitter substances,and it would suppress the umami&kokumi taste intensity.The reaction temperature mainly affects the rate of Maillard reaction.As the temperature increased,the content of aroma substances and the content of free amino acids were increased,and the distribution of peptide molecules is shifted to small peptides.pH value mainly affects the path of Maillard reaction,and the change of flavor compounds is not obvious.There was a significant positive correlation between the total content of pyrazine&thiazole and the roast intensity under different reaction conditions.The peptide fraction with different Maillard reaction flavors was isolated and purified form the enzymic beef hydrolysate by ultrafiltration,gel filtration and reverse phase chromatography combined with the flavor dilution analysis on the Maillard reaction products of the beef hydrolysis fraction.A total of 20 Maillard reactive flavor precursor peptides were detected by ESI-Q-TOF MS/MS.Including Leu?Ile?-X,Val-X,Phe-X.Some representative peptides were selected to synthesis by liquid phase.The pure peptides were verified that all peptide molecules were Maillard reactive flavor precursor peptides.?Glu-Cys-Gly,Leu-Cys,Val-Met and Cys-Gly-Val?were used to construct the Maillard reaction system with xylose or ¹³C₅ xylose.GC-MS&LC-MS was used to determine the volatile&nonvolatile products in the Maillard reaction,and to track the isotopic distribution of the products,for deducing the mechanism of beef pure peptide in the formation of flavor compounds via Maillard reaction.The meat aroma substances such as 2-methyl-3-furanthiol and its dimer were identified in the peptide system containing Cys,and the Met-containing peptide was unable to contribute to the sulfur-containing heterocyclic compounds.The carbon skeleton of these substances is mainly derived from the C₅ units of xylose,the degradation products of xylose with thiol-acetaldehyde and H₂S from Cys Strecker degradation reacted to generate.The specific 2-isobutylpyrazine was formed in the Leu-Cys system,and it was deduced based on the isotopic distribution that two aminoketone condensation to generated which one from Leu-self-degraded and another from Leu-Cys Strecker degradation.Cyclic peptide with xylose cross-linked products were founded for the first time in non-volatile products,and it may be a way for the whole peptide molecule to participate in the Maillard reaction.