Study On The Formation Pathway And Regulation Mechanism Of Main Bitter Compounds In Maillard Reaction

Maillard Reaction?MR?is a brown reaction that is widely found in food heat processing and its storage.The reaction involves a reversible or irreversible chemical recombination reaction such as oxidation,cyclization and polymerization between the hemiacetal group of the reducing sugar and the protein,peptides,amino acid or free ammonium?ammonia?.MR can provide the food a pleasant color and flavor and produce some compounds that have a negative impact on food due to the complex reaction mechanism and the wide variety of products.For example,some Maillard reaction products?MRPs?such as acrylamide?AM?,heterocyclic amines?HAAs?,4-methylimidazole?4-MI?and furan are classified as possible or suspected carcinogens by the World Health Organization International Cancer Research Institute.At the same time,some MRPs with bitter taste,such as 5-hydroxymethylfurfural?HMF?,2,3-dihydro-3,5-dihydroxy-6-methyl-4?H?-pyran-4-one?DDMP?,5-methylfurfural?MF?also seriously affect the acceptability of related foods.This paper systematically reviewed the advances of the sources,formation pathways,detection and regulation methods of bitter substances in MR and related foods;isolated and identified the main bitter compounds in MR and caramel color;established the analytical method for determination of main bitter compounds in caramel colors;researched the formation route of bitter taste enolization products;the effect of microwave heating on bitterness and aroma compounds in MR;the regulation of bitterness in Maillard reaction by phenolic acid;The formation of bitterness,aroma and harmful compounds from MR in stewed pork balls with brown sauce?SPB-BS?.The main results and conclusions are as follows:Bitterness in caramel colors can negatively influence product acceptability.Application of sequential solvent extraction,followed by semi-preparative liquid chromatography?SP-LC?combined with the taste dilution analysis,identified of the most intense bitter-tasting compounds in caramel colors.The compounds with the highest bitterness intensities were selected and structurally elucidated based on HR-ESI-MS,NMR spectroscopy and GC-MS.Four bitter compounds were isolated and identified:DDMP,HMF,furfural and MF.Two volatile bitter compounds were identified:[5-?di-methoxymethyl?furan-2-yl]methanol?DMFM?and 2,3,4,4-tetramethyl-pentane-1,3-diol?TMP?.Based on the composition of the caramel colors and the structures of these compounds,Maillard reaction was supported to generate these bitter compounds.A practical and simple method for the simultaneous analysis of the DDMP,HMF,furfural and MF in caramel colors and beverages was proposed using high performance liquid chromatography-diode array detector-atmospheric pressure chemical ionization-mass spectrometry?HPLC-DAD-APCI-MS?.For the sample preparation,the extract solvents and QuEChERS salt pockets were optimized.The correlation coefficients?R²?of all analytical curves were?0.9914.The satisfactory recoveries ranged between 77.9%and 107.3%,with RSDs ranged from 2.5%to 9.6%.The matrix effect was evaluated,and most of the compounds showed signal enrichment.This method was successfully applied to the analysis of bitter compounds content in several caramel colors,beverages and MR.DDMP and HMF are the Mallard reaction products with intense bitter.Insight into their formation pathways is important to manage Maillard reaction products quality.In this work,wet-and dry-heating glucose-amino acid model reactions were investigated to understand their formation pathways.Lysine and proline facilitated the HMF generation in wet-heating system,while proline facilitated the DDMP foemation in dry-heating system,suggesting the reaction intensity and amino acid properties are primary factors mediating their generation.Fundamental mechanism on their formation or inhibition was evaluated via quantitatively monitoring 1-or3-deoxyglucosone?1-or 3-DG?,which suggested that the formation of DDMP was facilitated at lower moisture content condition caused by more 1-DG generation via 2,3-enolization.However,increasing moisture content resulted in the decay of DDMP because of the transformation of 2,3-enolization to 1,2-enolization,which inhibited DDMP generation but transformed to form HMF.The effect of microwave and oil bath heating on the evolution of heating glucose-ammonium system including pH,color and degree of glycation,and flavor compounds was investigated.Results indicated that microwave heating was more effective than traditional oil bath heating in Maillard reaction.The more decrease of pH values,higher A₄₂₀,lower whiteness and chroma,and stronger glycation were recorded in the model system heated by microwave.Moreover,microwave heating did not affect the contents of pyrazines extracted by dichloromethane but affect the formation of D-limonene extracted by ethyl acetate from model system.In addition,3-methyl-2-pyrazinyl-methanol and 6-methyl-2-pyrazinyl-methanol were firstly reported as flavor compounds in the glucose-ammonium system.DDMP is one of the Mallard reaction products with intense bitter.Insight into the regulation effects on DDMP formation is important to manage Maillard reaction products quality.In this work,gallic,protocatechuic,caffeic and ferulic acids were employed to regulate DDMP formation in micro-aqueous glucose-proline model.Low concentrations of gallic,protocatechuic and caffeic acid inhibited,while 10.0mM of them facilitated DDMP generation,suggesting the antioxidant and releasing of hydrogen peroxide worked competitively to affect the DDMP formation.5.0mM of them provided the best inhibitory effects on the DDMP formation.Ferulic acid always inhibited the DDMP formation due to the absence of catechol groups on its benzene ring.Regulation mechanism on DDMP was evaluated via quantitatively monitoring glucose,proline,1-DG and phenolic acids,which suggested that the formation of DDMP was regulated by antioxidant or peroxide on three sites:degradation of glucose itself,or ammonia-induced,ARP oxidative and 1-DG.Content of harmful compounds from MR such as AM,4-MI,furan and HAAs was analyzed and 57 volatiles were identified in SPB-BS.The amounts of these compounds were in the range of 0.05-0.50 mg kg^-1 in test sample.The main bitter compounds were HMF and amino acids.GC-MS results indicated that alcohols,aldehydes,acids and esters could contribute to the most of aroma in SPB-BS.Lipid oxidation and MR are the main sources to form these harmful compounds and volatiles on the strength of the structures of these compounds and the composition of the food system.