Chemical Behavior Of The Non-enzymatic Browning Reaction In L-ascorbic Acid/Amino Acid Systems

Non-enzymatic browning(NEB)reaction is a browning reaction without enzyme catalysis,which is very critical in food processing and storage.Non-enzymatic browning(NEB)reaction includes Maillard reaction,ascorbic acid browning and caramelization reaction,among which Maillard reaction is the most common reaction.It refers to the complicated reaction that reacts between amino groups and carbonyl groups,resulting in brown materials,such as melanoidin.The reaction process is complex and the products are various,therefore,the study on it is significantly difficult.L-ascorbic acid(ASA)is a Maillard reaction system in the traditional food industry.It is a new substance after reducing sugar with potential carbonyl groups and can react with amino acids.If the chemical behavior of non-enzymatic Browning reaction based on l-ascorbic acid can be studied and discussed from the perspective of chemistry,and the mechanical characteristics of Browning change and the mechanism of volatile substance generation in the reaction process can be analyzed and discussed from the perspective of dynamics,the study on non-enzymatic Browning reaction in food industry will be further improved.This study will provide theoretical basis and basic data for us to discuss the non-enzymatic Browning reaction based on l-ascorbic acid in the food industry.In this thesis,the kinetic behavior of chemistry and mechanism formation of VPs of self-degradation of ASA,Maillard reaction of L-ascorbic acid/glycine and Maillard reaction of L-ascorbic acid/glycine/cysteine were studied.1.The NEB reaction of self-degradation reaction of ASA.The effects of reaction parameters,including temperature,time,surrounding of pH the solution on the self-degradation of ASA,the formation of uncolored-intermediate-products(UIPs)and BPs were discussed.The kinetic formation characteristics of BPs were also discussed.The results showed that the higher temperature,the longer time andstronger alkaline of the solution would be more favorable for the self-degradation of ASA and the formation of UIPs and BPs.The kinetics studies had shown that the formation of BPs was only related the self-degradation of ASA.The formation kinetics model of BPs was established,which showed that the formation of BPs was consistent with pseud-zero-order kinetics.Surrounding in the different pH conditions,the activation energy(Ea)of BPs was different.When the pH value was of 9.5,the Ea for formation of BPs was 27.62 kJ/mol,which was much less than those other pH solution.2.The ASA/glycine system was studied.The non-enzymatic browning behavior and kinetics of ASA/glycine in different pH environments were investigated by the excess concentration method.By adjusting the concentration ratio of ASA to glycine,the effects of ASA and Gly on self-consumption,formation characteristics of UIPs and BPs were analyzed.The formation kinetic characteristics of BPs during the reaction were studied.The results showed that formation rate of BPs were derived from the self-degradation of ASA,Maillard reaction of ASA and glycine.When the concentration ratio of ASA was slightly larger,it was more conducive to the formation of BPs.When the pH was 4.5 and the ASA/Gly concentration ratio was 4:1,the Ea for formation of BPs was 17.57±4.50 kJ/mol.3.The response surface methodology was used to optimize the L-ascorbic acid self-degradation process conditions.According to the central combination Box-Benhnken experimental design,the 4-factor level analysis method was used to analyze and optimize the conditions process of self-degradation ASA.Based on the consumption rate of ASA,the mathematical model was established,and the linear regression equation was fitted.The best theoretical prediction of ASA was obtained by response surface analysis.The optimal degradation conditions were: 146 min;temperature was 149℃;pH was 4.52;molar ratio was 1:2,the degradation rate was88.69%.4.The behavior of reaction system of L-ascorbic acid/glycine/cysteine was analyzed.The formation of VPs was investigated in different pH(pH 4.5,5.8,7.0,8.0,9.5)solutions in each system,which include the self-degradation of ASA,cysteine,Maillard reaction of L-ascorbic acid/glycine,Maillard reaction of L-ascorbic acid/cysteine,Maillard reaction of glycine/cysteine and Maillard reaction of L-ascorbic acid/glycine/cysteine.The results showed that pH has a great influence on the formation of VPs and the kinds of VPs.Under acidic conditions,furfural and derivatives of furan were generated in the system of L-ascorbic acid/glycine;while in alkaline solution,pyrazines and thiophenes was the major products in the Maillard of L-ascorbic acid/glycine and L-ascorbic acid/cysteine.In acidic surrounding,thiophene was the main products for the system of L-ascorbic acid/glycine/cysteine;while the thiophene,thiazole and little amount of a pyrazine were the VPs in alkaline surrounding.It was a compete reaction for formation of VPs,which generated from the reaction of glycine or cysteine reacted with ASA,respectively.The results showed that the formation of VPs mainly came from the reaction of ASA and cysteine.