Study On The Regularity Of Aqueous Preparation Of Maillard Reaction Intermediates And Its Formation Of Processing Flavors

Maillard reactions are important for the preparation of thermal processed flavorings.Usually the flavor of the Maillard reaction products?MRPs?is desirably rich,however,the main aroma components show physicochemical instability.Aroma loss,flavor profile distortion and lowered flavor stability have become noticeable problems limiting the application of MRPs,especially during processing at high temperatures such as in cooking and baking.Nowadays,the high pace of modern life has led consumers to pursue a sense of pleasure and achievement through an independent cooking.Thus,a higher quality of Maillard reaction flavors has been in demand.Some stable flavor precursors which complete their Maillard reaction in the subsequent thermal processing,can be used as the primary flavor enhancers to derive controlled fresh flavor.Since Amadori compounds possess stable physicochemical properties,but tend to degrade into flavor compounds at high temperatures,they were selected to create a technology of processing flavor formation.The existing method for the preparation of Amadori compounds in organic medium can result in serious pollution and high technology costs,which can only be applicable to theoretical research but cannot be applied for modern industrial production.According to the principle that browning can be inhibited through the interaction between cysteine and Amadori compounds,the Maillard reaction performed under stepwise increase of temperature with cysteine as an indicator was proposed for the aqueous preparation of Amadori compounds.The critical formation conditions of the Amadori compound derived from xylose-phenylalanine?Xyl-Phe?in aqueous medium were determined as follows:the carbonyl-amino molar ratio was 2:1,the reactant concentration was 0.06 g/L,the initial pH was 7.4,the reaction temperature was 80°C and the reaction time was 70 min.The Maillard reaction was conducted under these conditions,and the reaction solution was purified.Then the solid product with a purity of 98.26%was obtained.The structure of the product was characterized and confirmed by mass spectrometry?MS?and nuclear magnetic resonance?NMR?.Five isomers of the product were found in aqueous medium and a dynamic transformation among the isomers was also confirmed.The Amadori compound formed during the Maillard reaction was quantitatively analyzed by high performance liquid chromatography?HPLC?.The methodology accuracy of the Maillard reaction performed under a stepwise increase of temperature was verified.The formation conditions of Amadori compounds derived from both alanine and aspartic acid were determined through the Maillard reaction performed under stepwise increase of temperature.Then,the Amadori compounds were prepared,purified and characterized to verify the universal applicability of the Maillard reaction performed under a stepwise increase of temperature.Since the yield of the Amadori compound in aqueous medium was low,further research was focused on the mechanism of transformation between N-substituted D-xylosamine and Amadori compounds.The effect of moisture on the yield of the Amadori compound was investigated.The results showed that N-substituted D-xylosamine decreased to zero during the synergistic treatment of thermal reaction and vacuum dehydration;while the Amadori compound and the deoxyosone increased.However,the increment of the deoxyosone concentration was considerably lower than that of the Amadori compound.Thus,the synergistic effect between thermal reaction and vacuum dehydration was proposed to be an important factor to the directional formation of the Amadori compound.It was confirmed that the synergistic effect had improved the formation and accumulation of the Amadori compound through a gradual and dynamic process.Key parameters of the technology were optimized to increase the yield of the Amadori compound in aqueous medium from 13.62%to 47.23%.Furthermore,the facilitation mechanism of the added sodium sulfite for directional formation of the Amadori compounds was analyzed.The important role of the pH buffering effect of sodium sulfite was observed in Maillard reaction.The effect of sodium sulfite dosage and pH on the directional efficient conversion of Xyl-Phe to the Amadori compound was clarified.The addition of sodium sulfite at the optimal pH 7.4 maintained the pH at the optimal level,consequently improved the yield of the Amadori compound from 47.23%to 74.86%.The optimal preparation conditions of the Amadori compound derived from Xyl-Phe were determined as follows:the dosage of sodium sulfite was 4.00%,initial pH was 7.4,the reaction under normal pressure was at 90°C for 60 min,the dehydration reaction under vacuum was at90°C for 20 min.The Amadori compound derived from Xyl-Phe was prepared in aqueous medium through the synergistic effect between thermal reaction and vacuum dehydration.After the product was purified,it was stored under different conditions for 60 d.The Amadori compound showed a favorable stability during its storage at 4°C,15°C and 25°C.While the stability of Amadori compound slightly decreased when stored at 37°C or coexisted with free amino acids in the solution.Under neutral or acidic pH conditions,the stability of Amadori compound was better than that under basic conditions.On the other hand,the sample of MRPs was not stable during its storage at 25°C for 60 d.The flavor profile of the solution changed greatly,and the particle size increased significantly.The changes in both the Amadori compound and MRPs during the heat treatment were researched.The total concentration of volatile compounds was found to have decreased during the heat treatment at 100°C.Flavor profile of the solution altered,and the particle size also significantly increased.Under the same conditions of heat treatment,the Amadori compound degraded rapidly,and generated volatile compounds and melanoidins.The kinetic characteristics of thermal degradation of the Amadori compound derived from Xyl-Phe were further researched.The thermal degradation of the Amadori compound in aqueous medium was determined as a second-order reaction,with an activation energy?E_a?of 80.10 kJ/mol.The formation of browning products from the Amadori compound was a zero-order reaction,and its E_a was 28.57 kJ/mol.During the heat treatment at 100°C,the total concentration of volatile compounds formed from the Amadori compound increased and then decreased.The flavor compounds were optimally formed at 80^th min as 9.44 times and 8.77 times as that of MRPs and Xyl-Phe mixture,respectively.Thus,the Amadori compound showed an obvious advantage in controlled formation of processing flavors.The in vitro antioxidant activity of the Amadori compound was further studied and compared with MRPs and Xyl-Phe.Fe²⁺chelating ability,reducing ability and free radical scavenging ability of the Amadori compound derived from Xyl-Phe was observed at the concentration range of 0.2¹.2 mg/mL.Free radical electrons can reach the carbonyl group on xylose fragment of the Amadori compound or reach the hydroxyl carbon adjacent to the carbonyl group to form an intramolecular hydrogen bond.Thermodynamically stable free radical intermediates were consequently generated.Thus,free radical chain reaction was inhibited during the oxidation reaction.A stronger antioxidant activity of MRPs was confirmed than that of the Amadori compound.In order to improve the quality and stability of cooked food or semi-processed food,the Amadori compounds were proposed to be applied as an antioxidant with combination of MRPs.The Amadori compound derived from Xyl-Phe was applied to crisp cakes.Sensory characteristics of the crisp cakes were evaluated.The crisp cakes with the Amadori compound addition showed a significant roasting aroma before eating compared with the control.The aroma of the crisp cakes with Amadori compound addition was even stronger.Particularly,its flowery and fruity aroma was improved,and ideal compatibility of different aroma was shown.Maillard reaction of the Amadori compound occurred during the baking process of crisp cakes,and more volatile compounds were formed.Some gaseous components were retained inside of the crisp cakes,which developed a porous structure.Thus,the crispy taste of crisp cakes was improved.The remained aroma components inside the crisp cakes were released during chewing,which increased the aroma continuity of crisp cakes and improved its sensory quality.The solid Amadori compound showed a controlled formation of processing flavor during the increase of temperature,which indicated its great potential application in cigarettes.The Amadori compound derived from Xyl-Phe was prepared and added in cigarettes.A significant improvement of both quantity and quality of the aroma was observed.With the addition of Amadori compounds,the content of free radicals in mainstream cigarette smoke was reduced by 28.15%.Accordingly,a desirable effect of the Amadori compound on both aroma enhancement and tobacco harm reduction was confirmed.