| Similar to cysteine,glutathione is also an important precursor compound for the formation of meat flavors.Therefore,based on the “glutathione+glucose” Maillard reaction,chicken fat,oxidized chicken fat,or fat oxidation degradation products was added to the system.The thesis mainly studied the effect of fat oxidation degradation on the "glutathione-Maillard reaction" and discussed the mechanism of the reaction.The results of the study are of great significance for further understanding of the formation mechanism of meat flavors,and for improving the process of “fat-controlled oxidation-thermal reaction” in meat flavors.(1)Using chicken fat or oxidized chicken fat as a representative of fat,“glutathione + glucose + chicken fat or oxidized chicken fat” reaction systems were designed to study the effect of fat oxidation on the “glutathione + glucose” reaction system.The reaction solutions were measured for pH,absorbance at 294 nm and 420 nm.The volatile flavor substances were extracted by solid-phase microextraction and analyzed by gas chromatography-mass spectrometry and gas chromatography-olfactometry.The results showed that the addition of chicken fat or oxidized chicken fat had little effect on pH and absorbance at 294 nm,but the browning degree of the reaction solution decreased.After adding chicken fat or oxidized chicken fat,the contents and FD values of the sulfur-containing meaty flavor compounds formed from the reaction of glutathione and glucose decreased such as thieno[3,2-b]thiophene,2-methylthiophene[3,2-b]thiophene,etc..And 10 alkyl chain thiophene or pyridine compounds like 2-pentylthiophene,2-hexylthiphene,2-pentylpyridine,etc.,were generated,and these newly alkyl chain compounds also had certain odor activity.Compared with the oxidation degradation of chicken fat or oxidized chicken fat,aldehydes,especially unsaturated aldehydes,were notably decreased in the presence of glutathione and glucose,while alcohols and furans were increased.By the method of isotope labeling,it was found that chicken fat or oxidized chicken fat had almost no influence on the formation pathways of 38 compounds generated from the original glutathione and glucose such as 2-methylthiophene,2,5-dimethylthiophene,5-methyl-2-furancarbaldehyde,etc..Based on the results of isotope labeling,formation pathways of the 50 flavor compounds were performed,especially the 20 compounds not currently reported including: 3 1-(2-thienyl)-1-alkylketone,5 compounds with a single thiophene ring,8 compounds with two thiophene rings,2 benzene compounds and 2 thiazoles.(2)Using hexanal,(E)-2-heptenal and(E,E)-2,4-decadienal as the representative products of the fat oxidation degradation,“glutathione + glucose + aliphatic aldehydes” reaction systems were designed to study the mechanism of “glutathione + glucose” reaction under the influence of fat oxidation.In the “glutathione + glucose” system,4 intermediates formed from the glutathione and glucose were identified by isotope labeling methods and mass spectrometry,including 3 kinds of thiazolidines and a glutathione-Amadori compound respectively.Among them,the m/z 251 and 281 intermediates were identified for the first time.After addition of fatty aldehydes,one intermediate formed between glutathione and hexanal,three intermediates formed between glutathione and(E)-2-heptenal and six intermediates formed between glutathione and(E,E)-2,4-decadienal were detected by liquid chromatography-mass spectrometry.And the structure of these intermediates have not been reported.The main intermediates were prepared,and the structures of these intermediates were identified by mass spectrometry and nuclear magnetic resonance spectroscopy.The intermediates includes the structure of semi acetal formed from glutathione and fatty aldehyde,thiazolidine formed from aliphatic aldehyde and cysteine-glycine peptide etc.The prepared intermediates were used as materials for thermal reaction,and the volatile flavor compounds extracted by solid-phase microextraction and analyzed by gas chromatography-mass spectrometry.According to the structure of intermediates,the formation pathway of main compounds such as 1-hexanethiol,2-propylthiophene and 2-hexylthiophene were performed furtherly.Under the heating conditions,these intermediates could react directly with hydrogen sulfide and lose the peptide chain,then release the volatile compounds. |
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