| Maillard Reaction is a common reaction that is occured during food processing or storage.In the modern food industry,Maillard reaction has been used to produce foods that possess the colour and flavor demanded by the consumer.However,harmful substances to human health,e.g.,imidazoles,acrylamide and 5-hydroxymethylfurfural,are also generated during the Maillard reaction,which aroused public concern about food safety issues.This study systematically reviewed the sources,formation pathways,detection methods and control mechanisms of ?-dicarbonyl compounds and imidazole compounds in Maillard reaction,respectively.Moreover,the formed ?-dicarbonyl compounds in the Maillard reaction of glucose and lysine were isolated and identified,and the effects of reaction conditions on the formation of ?-dicarbonyl compounds and 4-methylimidazole in the reaction system were also studied.Besides,the competitive Maillard reaction mechanism of lysine and ammonium ions was studied.Finally,the main degradation products of glucosamine were isolated and identified,and the mechanism of nonenzymatic browning of glucosamine treated by thermosonication was also investigated.The main results and conclusions are shown as follows:A simple method for simultaneous determination of three ?-dicarbonyl compounds,e.g.,glyoxal(GO),methylglyoxal(MGO)and diacetyl(DA),in food samples was developed basing on solid phase extraction-dispersive liquid-liquid microextraction using high performance liquid chromatography(HPLC-PDA).Solid phase extraction(SPE)was used to removes many interfering substances present in matrix,dispersed liquid-liquid microextraction(DLLME)was employed to enrich the target analytes in trace chloroform,and the target analytes were finally detected by HPLC-PDA.The method has the advantages of good resolution,low solvent consumption and high enrichment factor.The developed showed good linearity in the range of 20-200 ?g/L,with correlation coefficients greater than 0.9975 satisfactory under optimized conditions.The satisfactory recoveries ranging from 91 to 110% was obtained,with acceptable precision(RSD<10%).The method can be applied to the determination of trace ?-dicarbonyl compounds in food matrices.A method for simultaneous determination of 2-methylimidazole,4-methylimidazole and 2-acetyl-4-(1,2,3,4-tetrahydrobutyl)imidazole in foods was developed basing on ion exchange micro-solid phase extraction coupled to high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).The sample purification was employed by micro-solid phase extraction using cationic exchange polymer as the sorbent fixed in self-made equipment.The developed pretreatment method greatly simplifies the extraction and purification process of imidazoles,and has the advantages of low solvent consumption,short sample treatment time and low cost.The linearity,limit of detection,recovery and precision of the method were also evaluated.The results showed that good linearity in the range of 1-200 ?g/L,with correlation coefficients greater than 0.9991.The recoveries of developed method were in the range of 91.5-110.9%,with precision less than 13.1%.Finally,the developed method was applied to the determination of imidazoles in beverages containing caramel colors.The separation and identification of main ?-dicarbonyl compounds formed in Maillard reaction of glucose and lysine was performed using HPLC-MS/MS.Meanwhile,the generation of ?-dicarbonyl compounds and 4-MEI in the model reaction system of glucose and lysine during heat treatment was investigated by HPLC-PDA and HPLC-MS/MS respectively.Moreover,the effects of reaction conditions on the formation of ?-dicarbonyl compounds and 4-MEI in the reaction system were also studied.The results showed that ?-dicarbonyl compounds,formed in the degradation of Amadori rearrangement products,reacts with free ammonium ions that were degraded by Strecker degradation from amino acid to form 4-MEI.Moreover,the formation MGO in the model reaction system of glucose and lysine had a high positive correlation with 4-MEI(correlation coefficient 0.986,P=0.014)at 120 ?.However,there was no positive correlation at 140 ?,which may be related to the degradation of 4-MEI under high temperature conditions.The competitive Maillard reaction mechanism between lysine and ammonium ions was studied.The changes of glucose,ammonium ion and formic acid in the reaction system were detected by high-performance anion-exchange chromatography-pulsed amperometry(HPAEC-PAD),high-performance cation-exchange chromatography-conductivity detection(HPCEC-CD)and high-performance anion-exchange chromatography-conductivity detection(HPAEC-CD),respectively.The results showed that lysine could compete with ammonia to consume glucose in the reaction system,which led to the increase in the formation of MGO and formic acid.Amadori rearrangement products(fructosamine)in Mailalrd reaction of glucose and ammonia were synthesized,identified and used as the reactant to further study the effect of lysine on 4-MEI formation.The results showed that the generation of 4-MEI in both reaction system,i.e.,glucose-ammonia and fructosamine,was inhibited.The possible explanations could be related to the nucleophilic reaction of lysine to 2-aminopropanal or methylamine,which are the precursor of 4-MEI.The effect of thermosonication on nonenzymatic browning of glucosamine was studied,and the ?-dicarbonyl compounds formed in the degreadation of glucosamine was isolated and identified.The results showed that the thermosonic treatment could promote the non-enzymatic browning reaction of glucosamine,the formation of acidic substances and the antioxidant capacity of reaction products.The main degradation products of glucosamine were G and 3-DG under the condition of thermosonic treatment and thermal treatment at 65 oC.In addition,the oxidative degradation of glucosamine to form G was promoted.Besides,no 4-MEI and short-chain ?-dicarbonyl compounds were found in the caramel produced by thermosonication. |
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