Initial Maillard Pathways To Form Meat Flavors In "Cysteine-xylose-glycine" Reaction Systems

Maillard reaction is one of the most important ways to form meat flavor compounds,and cysteine plays an irreplaceable role in it.Cysteine reacts with reducing sugars to form volatile compounds with meat flavor.However,in the actual system,in addition to cysteine,other amino acids are also involved in the formation of meat flavor compounds,when the cysteine and other amino acids coexist in the meat flavor system,for the initial Maillard reaction,there are two reaction pathways,One is the formation of thiazolidine,which transforms into cysteine-Amadori,the second is the formation of other amino acids-Amadori,the two routes go through 1,2-enolization or 2,3-enolization and dehydration,deamination and other thermal degradation process to form the degradation products of hydroxymethyl furfural,furfural,dicarbonyl compounds and other degradation products,and these degradation products related to reducing sugars react with hydrogen sulfide produced by degradation of cysteine Strecker to form sulfur compounds.The paper mainly studied the two initial reaction pathways,which approach was more favorable for the formation of meat flavor,no research was reported on this aspect.This paper was divided into two parts to study.Firstly,the fiber coating,extraction temperature and time of solid phase microextraction were optimized;Then,based on the preliminary work,the effect of pH on Maillard reaction was studied,the design of complex Maillard reaction system "cysteine-xylose-glycine" at different initial pH(4.5,5.5,6.5,7.5).The absorbance at the wavelength of 420 nm and p H were measured,and analyzed by solid phase micro extraction-gas chromatography-mass spectrometry(SPME/GC-MS),high performance liquid chromatography(HPLC)and liquid chromatography-mass spectrometry(LC-MS).The results showed that the larger the initial pH value,the greater the degree of browning of the reaction solution and the higher the decrease of the pH value.The flavor substances identified were mainly sulfur-containing compounds,followed by nitrogen-containing heterocyclic compounds,oxygen-containing heterocyclic compounds in each reaction system.The total amount of all the compounds and the total amount of sulfur-containing compounds increased first and then decreased with the increase of pH value,and peaked at pH 5.5.In this part,the effect of pH on volatile compounds was analyzed from view of the initial intermediates.It was found that the formation of flavor substances was carried out by cysteine-Amadori degradation pathway under acidic conditions,degraded by Cysteine-Amadori and reacted Glycine-Amadori with cysteine in two ways under alkaline conditions.Under alkaline conditions,the reaction activity of amine-containing compounds(such as amino acids,ammonia)was high,the reaction rate was fast,the initial content of cysteine-Amadori in the system was high,but it was more to generate the production of melanoids and pyrazines in the middle and late stages;Glycine-Amadori,which appears under alkaline conditions,can form a relatively stable thiazolidine derivative by binding to cysteine and does not promote the formation of sulfur-containing compounds.The second part,it was studied to form sulfur-containing compounds in two ways mainly from the "cysteine-xylose-glycine" system early stage.The initial preparation of the three intermediates was carried out.The purity and structure of the prepared intermediates was determined by high performance liquid chromatography(HPLC),high performance liquid chromatography-mass spectrometry(LC-MS)and nuclear magnetic resonance spectroscopy(NMR).Second,the design of "glycine-Amadori/cysteine","2-xylulosylthiazodine-4-carboxylic acid / glycine" and "cysteine-Amadori/glycine" and at the same time as "glycine-Amadori,2-xylulosylthiazodine-4-carboxylic acid,cysteine-Amadori " blank experiment and " cysteine-xylose-glycine " control experiment.The reaction solution was measured at the absorbance of the wavelength of 294 nm,420 nm and pH value,and the solid phase microextraction-gas chromatography-mass spectrometry(SPME/GC-MS),gas chromatography-sniffing(GC-O),high performance liquid chromatography(HPLC)and high performance liquid chromatography-mass spectrometry(LC-MS).The results showed that although the reaction rate of "glycine-Amadori/cysteine" system is much larger than "2-xylulosylthiazodine-4-carboxylic acid/glycine" system,but the latter system was more conducive to the formation of meat flavor substances,and the former system was less to form meat flavor substances,mainly due to the formation of thiazolidine-4-carboxylic acid by the reaction of glycine-Amadori with cysteine.This compound was detected on high performance liquid chromatography-mass spectrometry(LC-MS).By comparing the three experimental systems and the control system,it was found that when the molar ratio of "cysteine-xylose-glycine" was 1:1:1,the main intermediate formed in the initial stage was 2-xylulosylthiazodine-4-carboxylic acid.