| The main focus of this article is to investigate the role of chicken peptide in the Maillard reaction. The flavor character of the Maillard reaction products was also measured.Firstly, the enzymatic hydrolysis of chicken by papain PSM 500, Protamex,Flavorzyme and Alcalase were optimized by monitoring the hydrolysis degree and peptide distribution as indicators. The optimal enzymatic hydrolysis was found by simultaneously hydrolysising with Protamex and Flavorzyme for 4h. At this condition, a well flavor enzymatic hydrolysate was obtained with the maximum 200-5000 Da peptide distribution.The moderate DH obtained under this condition was 12.8%.After removing fat followed by ultrafiltration with a 5000 Da membrane, chicken peptide was prepared. On the basis of chicken peptide, several model reaction systems were established to investigate the contribution of chicken peptide on the generation of aroma-active compounds. It was found that the chicken peptide mainly contribute roast/nutty and sweet aroma elicit by pyrazines such as 2,5-dimethylpyrazine,2,3-dimethylpyrazine, trimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine, which was described as the “basic meat flavor” or “enhanced meaty flavor” to the products. Studies on the Maillard reaction systems with the addition of Cys showed that the chicken peptide could significantly promote the generation of sulfur-containing aroma-active compounds,while the generation of pyrazines was inhibited. The addition of Cys could enhance the meat flavor while induce the roast/burnt aroma. By comparison, the effect of chicken peptide in the Cys-xylose system was complex. The addition of chicken peptide to the reaction mixtures caused a reduction in contents of some important meaty flavor compounds such as 2-methyl-3-furanthiol and its dimers, 2-methyl-3-(methylthio)furan.On the other hand, it facilitated the generation of thiophenes, pyrazines and thazoles. The content of 2-furfurylthiol with a harsh roast coffee smell was also decreased, which led to an enjoyable meaty flavor of the reaction products.The flavor characters, volatiles, non-volatiles of the MRPs prepared with different heating treatment were tested. The result showed that high temperature(110-120℃) could remarkably increase the formation of meaty aroma, while lower temperature(80-110℃)tended to generate a broth-like taste(i.e., umami and kokumi). When the heating temperature was risen above 120oC, these flavors were obviously decreased and were replaced by the burnt and bitter taste with the increase of heating time. The analysis of theamino acid in the MRPs showed that the chicken peptide could release large amount of umami amino acids with the heating process, which could cause the enhancement of the umami taste. However, the concentrations of Cys in all the reaction products were very low and result to the low content of the sulfur-containing volatiles. Analysis of the distribution of peptide in the MRPs showed that the 1000-3000 Da and 200-500 Da chicken peptides could degrade to 500-1000 Da and <200Da respectively in the initial reaction stage. And,this result indicated that the <500Da peptides could be the ultimate reactant in the Maillard reaction. Particularly, result obtained in this study also demonstrated that the cross-linking reaction could be involved in the Maillard reaction with the peptides.Application of ultrafiltration, liquid chromatography, the peptide with the most activity in the Maillard reaction was purified. The lowest activity was obtained for the >5000Da peptide, while the <1000Da fraction was exhibited the most reaction activity.The identification of peptides was performed by the Q-TOF-MS/MS technologies and 42 peptides were found in the fractions. It was showed that there are many peptides with the structures of Leu(Ile)-X-, Ala-X- and pGlu-X- in the enzymatically hydrolyzed of chicken meat. Among them, peptide with a Leu in the N-terminal exhibited the higher reaction activity. And, the pGlu-X peptides were the important compounds for the umami taste of the MRPs. Moreover, it seems that the structure of the N-terminal amino acid is determinative for the property of peptide.The model Maillard reaction system was estimated based on the pure peptides. Then,GC-MS, LC-MS and isotope labeling technology of Xyl and 13C5-Xyl(1:1) were used to investigate the path of peptide participate in the Maillard reaction. The result showed that the carbon skeletons of pyrazines generated in the system were all from xylose. The condensation of α-aminoketones was the main pathway. The sulfur-containing volatiles involved C5 carbon skeletons were formed by three pathways: furfural pathway, the major products were 2-furfurylthiol; 2-methyl-furfuryl pathway, the main products were2-methyl-3-furanthiol and its dimers; 2-methylfuran pathway, the major products were2-methylthiophene and 2-methyl-5-methylthiothiophene. The carbon atoms of thiophene mercaptans came partly from xylose and partly from cysteine. The distribution of the isotope ratio indicated that the condensation of mercaptoacetaldehyde was the main pathway of this compound. Moreover, thiophene and 3-methylthiothiophene were partly generated based on the thiophene mercaptans. For 3-thiophene-carbaldehyde,5-methyl-2-thiophenealdehyde and 3-methyl-2-thiophenecarboxaldehyde, the same isotope distribution of [M + 3] and [M + 5] or [M +2] and [M + 4], other isotope peaks were notdetected, which could infer these substances were generated from the bind from mercaptoacetaldehyde and the C3 or C4 fragment of xylose.For the non-volatile products, the peptide could cleavage and cyclize by the thermal degradation, which were seemed as the common phenomenon in the peptide Maillard reaction. Amadori product was generated from the peptide and xylose, and then, two reaction pathways were occurred. The Amadori product could degrade to a series of peptide-C2/C3/C4 Schiff bases. On the other hand, the peptide could bond with furfural, this products could enhance the generation of sulfur-containing compounds based on the furfural. |
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