Formation Mechanism And Selective Preparation Of Amadori Compounds Of Diglycine-xylose And Their Secondary Products

The Maillard reaction intermediate Amadori rearrangement product（ARP）has stable physical and chemical properties at room temperature,while retaining strong reactivity,and has the characteristics of controlled formation of flavor and color during thermal processing.It is expected to be developed as a new food flavor raw material.ARP is used for food flavor enhancement.The method for industrialized preparation of ARP is immature at present,and the industrialization of ARP is limited,and the limited research on the flavor formation characteristics of ARP for thermal processing hinders its practical application.Aiming at these problem,this research chose the diglycine-xylose system as the model experiment object,and studied the method of preparing ARP with the new tracer propyl gallate in aqueous phase.The study found that a secondary product coexisting with the ARP during the preparation process was the diglycine-xylose cross-linking product.By studying the law and mechanism of the interconversion between diglycine-xylose cross-linking product and ARP,a selective preparation method of ARP and diglycine-xylose cross-linking product was proposed.The effect of exogenous diglycine addition on the flavor formation of ARP thermal processing was clarified.This study is helpful to deepen people’s understanding of Maillard reaction in food and promote the industrial application of ARP.The specific research contents are as follows:A Maillard reaction of stepwise increase of temperature was used to screen propyl gallate as an effective tracer for ARP of diglycine-xylose system.Under the tracer effect of propyl gallate,the critical conditions for the formation of the aqueous phase of the diglycine-xylose ARP were determined as 80 min at the reaction temperature of 80°C,the initial p H 7.5 and the ratio of xylose to diglycine was 2:1.The formation and accumulation of the intermediates accelerated as p H or reaction temperature increased.The concentration changes of the main intermediates during the low-temperature Maillard reaction were further analyzed,and compared with the browning curve of the Maillard reaction products performed under stepwise increase of temperature,it was determined that the target intermediate traced by propyl gallate was ARP.According to the ARP formation conditions determined by the propyl gallate tracking method,the aqueous Maillard reaction was carried out for the preperation of ARP,and the ARP in the reaction product was separated and purified to obtain ARP with a purity of 97.37%.The structure of ARP was analyzed by Fourier transform infrared spectroscopy,liquid chromatography-mass spectrometry and nuclear magnetic resonance technology,and its relative molecular mass was determined to be 264,its molecular formula was C₉H₁₆N₂O₇,and it had three interconverted isomer forms in water.A model system of propyl gallate-ARP was established to study the mechanism by which propyl gallate inhibits Maillard browning and traces the formation of ARP.The thermal reaction product of propyl gallate and ARP was identified by UPLC-MS analysis,and it was found that propyl gallate and ARP underwent nucleophilic addition reaction to form a adduct with a relative molecular mass of 476.It was clear that propyl gallate captured ARP to generate adducts during the Maillard reaction,thereby inhibiting the degradation of ARP to form browning precursors,inhibiting the formation of color,and achieving the purpose of ARP preparation by tracer.In the process of preparing diglycine-xylose ARP,there was always an interconversion between the diglycine-xylose cross-linking product and ARP.The diglycine-xylose cross-linking product was purified by HPLC,and the structure of diglycine-xylose cross-linking product was analyzed and characterized by Fourier transform infrared spectroscopy,liquid chromatography-mass spectrometry,nuclear magnetic resonance.It was clear that the relative molecular mass of diglycine-xylose cross-linking product was 378,its molecular formula is C₁₃H₂₂N₄O₉,and it was composed of one molecule of xylose and two molecules of diglycine.By analyzing the correlation between the concentration of ARP and diglycine-xylose cross-linking product during the Maillard reaction,combined with the molecular structure characteristics of the two substances,it was elucidated that the reaction process of ARP forming diglycine-xylose cross-linking product through the carbonylation reaction and molecular rearrangement with diglycine again.The molecular mechanism that the diglycine-xylose cross-linking product can improve the dynamic stability by forming a p-π-p conjugated structure was revealed.By investigating the variation law of the concentration of ARP and diglycine-xylose cross-linking product in the system under different reaction conditions,the dependence of the yields of the two compounds on the reaction process parameters was clarified,and the key parameters for the selective preparation of ARP and diglycine-xylose cross-linking product were clarified.It was found that low temperature,high p H,and low ratio of xylose to diglycine can promote the directional formation of ARP.Under the reaction conditions of70°C,p H 8.0,and the ratio of xylose to diglycine was 1:1 for 10 min,the highest yield of ARP reached 73.80μmol/m L,while the concentration of diglycine-xylose cross-linking product was only 4.67μmol/m L,which effectively realized the directional preparation of ARP.And high temperature,low p H and high ratio of xylose to diglycine can promote the formation of diglycine-xylose cross-linking product.The reaction was carried out at a reaction temperature of 80°C,p H 7.5,and the ratio of xylose to diglycine was 3:1,then combined with the high temperature reaction at 120°C for 60 min,the ARP yield was 3.60μmol/m L,and the concentration of the diglycine-xylose cross-linking product reached the maximum value of 43.54μmol/m L at 60 min,and the selective preparation of diglycine-xylose cross-linking product was achieved.The formation law of ARP heat-processed flavor was studied,and the type and concentration changes of heat-processed volatile flavor compounds under the condition of compounding ARP and exogenous diglycine in different ratios was investigated,the intervention effect of exogenous peptide addition on the formation of ARP heat-processed flavor was clarified.It was found that the characteristic flavor compounds of ARP in the diglycine-xylose system were furans and a few pyrazines.The addition of exogenous diglycine can effectively increase the production of furfural,and can also promote the production of furan compounds,but does not promote the formation of pyrazine compounds,which was more significant at elevated temperatures.The addition of exogenous diglycine can effectively promote the formation of ARP thermal processing flavor in the diglycine-xylose system,enrich the types of flavor compounds,increase the content of flavor compounds,and enhance the processing adaptability of ARP.