Effective Mechanism of (-)-Epigallocatechin Gallate Indicating the Critical Formation Conditions of Amadori Compound during an Aqueous Maillard Reaction

Effect of the ripening stage on the pulsed vacuum drying behavior of goji berry (Lycium barbarum L.): Ultrastructure, drying characteristics, and browning mechanism

In current work, the effect of ripening stages (I, II, and III) on pulsed vacuum drying (PVD) behavior of goji berry was explored. The shortest drying time of goji berry was observed at stage I (6.99 h) which was 13.95 %, and 28.85 % shorter than those at stages II, and III, respectively. This phenomenon was closely associated with the ripening stage, as contributed by the initial physiochemical differences, ultrastructure alterations, and moisture distribution. In addition, lower maturity suffered more severe browning, primarily due to the enzymatic and non-enzymatic reactions of phenolics, followed by pigment degradation and the Maillard reaction. Additionally, the PVD process promoted the rupture and transformation of the pectin fractions, also causing browning either directly or indirectly through participation in other chemical reactions. These findings suggest that the appropriate ripening stage of goji berry should be considered as having a significant impact on drying behaviors and quality attributes.

Mechanism of Dihydromyricetin-Induced Reduction of Furfural Derived from the Amadori Compound: Formation of Adducts between Dihydromyricetin and Furfural or Its Precursors

Dihydromyricetin (DMY) was employed to reduce the yield of furfural derived from the Amadori rearrangement product of l-threonine and d-xylose (Thr-ARP) by trapping Thr-ARP, 3-deoxyxyosone (3-DX), and furfural to form adducts. The effect of different concentrations of DMY at different pH values and temperatures on the reduction of furfural production was studied, and the results showed that DMY could significantly reduce furfural production at higher pH (pH 5-7) and lower temperature (110 °C). Through the surface electrostatic potential analysis by Gaussian, a significant enhancement of the C6 nucleophilic ability at higher pH (pH ≥ 5) was observed on DMY with hydrogen-dissociated phenol hydroxyl. The nucleophilic ability of DMY led to its trapping of Thr-ARP, 3-DX, and furfural with the generation of the adducts DMY-Thr-ARP, DMY-3-DX, and DMY-furfural. The formation of the DMY-Thr-ARP adduct slowed the degradation of Thr-ARP, caused the decrease of the 3-DX yield, and thereby inhibited the conversion of 3-DX to furfural. Therefore, DMY-Thr-ARP was purified, and the structure was identified by nuclear magnetic resonance (NMR). The results confirmed that C6 or C8 of DMY and carbonyl carbon in Thr-ARP underwent a nucleophilic addition reaction to form the DMY-Thr-ARP adduct. In combination with the analysis results of Gaussian, most of the DMY-Thr-ARP adducts were calculated to be C6-DMY-Thr-ARP. Furthermore, the formation of DMY-furfural caused furfural consumption. The formation of the adducts also shunted the pathway of both Thr-ARP and 3-DX conversion to furfural, resulting in a decrease in the level of furfural production.

Reactive Carbonyl Species Scavenger: Epigallocatechin-3-Gallate

Epigallocatechin-3-gallate (EGCG), a prominent polyphenol found abundantly in tea, has garnered significant attention for its potential in preventing and ameliorating a wide range of diseases. Its remarkable antioxidant properties and ability to capture reactive carbonyl species make it a key player among tea's polyphenolic components. This paper delves into the synthesis and origins of both EGCG and reactive carbonyl species (RCS), emphasizing the toxicity of RCS in various food sources and their formation during food processing. Understanding EGCG's capability to capture and metabolize RCS is crucial for harnessing its health benefits. Thus, this paper explores the underlying mechanisms of EGCG for RCS inhibition and its role in capturing these compounds to generate EGCG-RCS adducts. And the absorption and metabolism of EGCG-RCS adducts is also discussed.

Efficient Formation of N-(1-Deoxy-d-ribulos-1-yl)-Glutathione via Limited Oxidation and Degradation of Glutathione during the Atmospheric-Vacuum Thermal Reaction

The efficient preparation of the ribose-glutathione (Rib-GSH) Amadori rearrangement product (RG-ARP) as a potent precursor of meaty flavor was studied through the atmospheric-vacuum thermal reaction. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed that the oxidation and degradation of GSH occurred during the preparation of RG-ARP via the atmospheric thermal reaction, especially at a low molar ratio of Rib to GSH and high reaction temperature. The RG-ARP and the ARPs derived from the products of GSH oxidation and degradation with the participation of Rib were identified by MS/MS as N-(1-deoxy-d-ribulos-1-yl)-glutathione, N-(1-deoxy-d-ribulos-1-yl)-cysteinylglycine, and N-(1-deoxy-d-ribulos-1-yl)-glutathione disulfide. The selective formation of RG-ARP was disrupted due to the multiple consumption pathways of GSH and Rib. The removal of water and the reduction of oxygen content during vacuum dehydration exhibited an obvious inhibitory effect on the oxidation of cysteinyl and the cleavage of glutamyl, limiting the oxidation and degradation of GSH. Meanwhile, the rapid evaporation of water promoted the molecular collision between the reactants, which allowed the glycation reaction of GSH to be advanced and fragmentation of RG-ARP to be inhibited at a mild dehydration temperature. Accordingly, the atmospheric-vacuum thermal reaction was proposed to limit the generation of secondary byproducts and enhance the yield of RG-ARP, enabling the RG-ARP yield to reach 49.23% at 80 °C and a molar ratio of 2:1 (Rib/GSH) for 20 min.

Effect of cereal bran phenolic profile on Maillard reaction products formation during hydrothermal treatment

Maillard reaction products (MRP) contribute to sensory quality of various foods. Whole grains (WG) are rich in phenols which may influence Maillard reaction pathways during thermal processing and impact WG product sensory attributes. This study investigated how WG phenolic profile affects MRP formation. Amylase-hydrolyzed wheat (white and red) and sorghum (white, red, tannin) brans were hydrothermally processed at 150 °C/6 min, and characterized for MRP using colorimetry, fluorescence spectroscopy, HPLC-MS/MS, and HS-SPME/GC-MS. Bran phenolic structure, and to a lesser extent content, had larger influence on MRP formation than protein/amino acid profile. Polymeric tannins (both in situ and when added to wheat brans) strongly inhibited volatile and non-volatile MRP intermediates and melanoidin formation, likely via their carbocation depolymerization intermediates trapping furans. Principle component analysis demonstrated clear segregation of volatiles formation based on bran phenolic profile. Phenolic composition should be considered in WG product formulation and processing to achieve desired MRP formation.

Formation Mechanism of Di-N-ethyl-2-pyrrolidinone-Substituted Epigallocatechin Gallate during High-Temperature Roasting of Tea

Four di-N-ethyl-2-pyrrolidinone-substituted epigallocatechin gallate (EGCG) and two di-N-ethyl-2-pyrrolidinone-substituted gallocatechin gallate (GCG) flavan-3-ols (di-EPSFs) were prepared by the thermal simulation reaction. The effects of reaction temperature and time, initial reactant ratios, and pH values on the content of di-EPSFs were studied. The formation of six di-EPSFs was most favored when the initial reactant ratio of EGCG and theanine was 1:2 and heated under 130 °C at pH 10 for 120 min. The contents of di-EPSF1, di-EPSF2, and di-EPSF5 in large-leaf yellow tea (LYT) increased with the increase of roasting degree. Through quantitative analysis, it was found that EGCG would interact with the Strecker degradation products of theanine to form EPSFs, which further combined with the Strecker degradation products of theanine to form di-EPSFs. This study further improved the understanding of the transformation pathways of EGCG and theanine during tea processing and contributed to exploring the flavor characteristics and health benefits of di-EPSFs.

Competitive Formation of 2,3-Butanedione and Pyrazines through Intervention of Added Cysteine during Thermal Processing of Alanine-Xylose Amadori Compounds

The intervention of cysteine (Cys) on the formation of 2,3-butanedione and pyrazines was evaluated during the thermal processing of the alanine-xylose Amadori compound (AX-ARP). With the involvement of Cys, the competitive formation of 2,3-butanedione and pyrazines was induced. The formation of 2,3-butanedione in the AX-ARP/Cys model was suppressed due to the inhibitory effect of the precursors of 2,3-butanedione like deoxypentosones, while the added Cys in the AX-ARP/Cys model competed with the recovered alanine (Ala) to capture glyoxal and methylglyoxal to make up for the absence of pyrazines in the AX-ARP model at an initial pH value of 7. The content of pyrazines increased from 0 up to 16.48 μg/L (120 °C, 120 min). Exogenous Cys itself showed lower reactivity with 2,3-butanedione through the Strecker degradation reaction; while the pH was increased to 8, the degradative products of Cys were facilitated to consume the residual 2,3-butanedione giving rise to the formation of 2,4,5-trimethylthiazole at 120 °C. It was the degradative products of Cys that accelerated the reaction for consumption of 2,3-butanedione rather than Cys itself. Additionally, the inhibitory effect of Cys on 2,3-butanedione formation was weakened under a basic condition, while the promotional effect on the formation of pyrazines was further boosted. With more Cys participating in the process of AX-ARP thermal degradation, the formation of 2,3-butanedione was further inhibited, while the yields of pyrazines were increased.

Food polyphenols and Maillard reaction: regulation effect and chemical mechanism

Maillard reaction is a non-enzymatic thermal reaction during food processing and storage. It massively contributes to the flavor, color, health benefits and safety of foods and could be briefly segmented into initial, intermediate and final stages with the development of a cascade of chemical reactions. During thermal reaction of food ingredients, sugar, protein and amino acids are usually the main substrates, and polyphenols co-existed in food could also participate in the Maillard reaction as a modulator. Polyphenols including flavan-3-ols, hydroxycinnamic acids, flavonoids, and tannins have shown various effects throughout the process of Maillard reaction, including conjugating amino acids/sugars, trapping α-dicarbonyls, capturing Amadori rearrangement products (ARPs), as well as decreasing acrylamide and 5-hydroxymethylfurfural (5-HMF) levels. These effects significantly influenced the flavor, taste and color of processed foods, and also decreased the hazard products' level. The chemical mechanism of polyphenols-Maillard products involved the scavenging of radicals, as well as nucleophilic addition and substitution reactions. In the present review, we concluded and discussed the interaction of polyphenols and Maillard reaction, and proposed some perspectives for future studies.

Glycine-Xylose Amadori Compound Formation Tracing through Maillard Browning Inhibition by 2-Threityl-thiazolidine-4-carboxylic Acid Formation from Deoxyosone and Exogenous Cysteine

The browning inhibition of cysteine on the Maillard reaction of glycine-xylose performed under stepwise increased temperature was investigated. The browning degrees of the final products prepared with cysteine addition at different time points were found dissimilar, and the addition time point of cysteine yielding the lightest browning products was consistent with the time when the glycine-xylose Amadori rearrangement product (GX-ARP) reached its maximum yield. To clarify the reason for browning inhibition caused by cysteine, the evolution of key browning precursors formed in the GX-ARP model with cysteine involved was investigated by HPLC with a diode array detector. The results on the browning degree of the thermal reaction products of GX-ARP with cysteine addition showed great inhibition of α-dicarbonyl generation, which resulted in a significant increase in the activation energy of GX-ARP conversion to browning formation during heat treatment. Strong evidence suggested that the additional cysteine got involved in GX-ARP degradation and reacted with the deoxyosones derived from GX-ARP to yield cyclic 2-threityl-thiazolidine-4-carboxylic acid (TTCA). TTCA formation shunted the degradation of deoxyosones into short-chain α-dicarbonyls, which were important browning precursors, and consequently inhibited the Maillard browning.

Promoted Formation of Pyrazines and Sulfur-Containing Volatile Compounds through Interaction of Extra-Added Glutathione or Its Constituent Amino Acids and Secondary Products of Thermally Degraded N-(1-Deoxy-d-ribulos-1-yl)-Glutathione

An Amadori rearrangement product (ARP) derived from ribose (Rib) and glutathione (GSH) was prepared and identified as N-(1-deoxy-d-ribulos-1-yl)-glutathione by ultraperformance liquid chromatography-tandem mass spectrometry and NMR. Thermal treatment of the ARP aqueous solution was conducted, and a relatively high temperature was found to accelerate the degradation of the ARP. The concentration of furans formed at 120 °C was more than 6.39 times that at 100 °C, and especially, the high temperature favored the formation of furfural and 4-hydroxy-5-methyl-3(2H)-furanone through deoxyosone dehydration. The promoting role of extra-added GSH or its constituent amino acids was investigated in the volatile formation during thermal processing of the ARP. Both, the added GSH and its constituent amino acids, could timely capture glyoxal (GO) and methylglyoxal (MGO) to facilitate Strecker degradation, which improved pyrazine formation. Compared with glycine and glutamic acid, cysteine was the most effective extra-added amino acid to react with GO and MGO to produce pyrazine and methylpyrazine. More importantly, the cysteine degraded from extra-added GSH effectively accelerated the generation of sulfur-containing volatile compounds through the reaction of cysteine degradation products with furans and shorter-chain α-dicarbonyl compounds.

Temperature-Dependent Catalysis of Glycylglycine on Its Amadori Compound Degradation to Deoxyosone

The Amadori rearrangement product derived from xylose-glycylglycine (XGG-ARP) is reactive to be attacked by another glycylglycine to generate a xylose-glycylglycine cross-linking product (XGG-CP) as a secondary product of the ARP. In this research, the role of additional glycylglycine in the XGG-ARP degradation was studied, and the dependence of glycylglycine on temperature was further clarified. The yields of XGG-CP and its degradation products were significantly affected by the molar ratio of glycylglycine to XGG-ARP. At the similar total concentration of reactant XGG-ARP and glycylglycine, the yields of XGG-CP, 3-deoxyxylosone, and furfural were dramatically decreased as the molar ratio of glycylglycine to XGG-ARP was increased. However, when the reaction temperature was increased to 120 °C, the increased additional glycylglycine percentage showed an obvious catalytic effect on the XGG-ARP degradation to deoxyosone and thus improved the furfural yield as well. The results revealed that an increased glycylglycine dosage level enhanced both the conversion of XGG-ARP to XGG-CP and the conversion of XGG-CP to 3-deoxyosone. The high-temperature-induced unequal acceleration for XGG-CP formation and degradation at a high glycylglycine dosage further led to a catalytic effect on the ARP degradation to deoxyosone. The concentration of 3-deoxyosone was increased by 37.5% when the molar ratio of glycylglycine to XGG-ARP increased from 1:2 to 2:1 at a temperature of 120 °C.

Structural diversity and concentration dependence of pyrazine formation: Exogenous amino substrates and reaction parameters during thermal processing of l-alanyl-l-glutamine Amadori compound

The Amadori compound of glucose and l-alanyl-l-glutamine (Ala-Gln-ARP) was prepared and characterized by UPLC-MS/MS and NMR. There were no pyrazines produced by heated Ala-Gln-ARP alone due to the asynchronicity of regenerated l-alanyl-l-glutamine and α-dicarbonyl compounds. High temperature (130 °C) and long reaction time could facilitate the 2,5-dimethylpyrazine formation at a small concentration (33.4 ± 3.47 μg/L). The exogenous amino substrates would lower the formation temperature of pyrazines and make it to be generated effectively. Extra supplied l-alanyl-l-glutamine could generate 2,5-dimethylpyrazine at 110 °C, while higher temperature of 140 °C could strengthen the formation of 2,5-dimethylpyrazine (793 ± 119 μg/L) and stimulate the generation of other pyrazines, including methylpyrazine and 2,6-dimethylpyrazine. The exogenous alanine, glutamic acid, and glutamine was also beneficial to enhance the pyrazines formation, especially the glutamic acid. Furthermore, alkaline pH of thermal reaction made pyrazines increase significantly than in neutral medium and further enriched their species such as unsubstituted pyrazine and trimethylpyrazine.

Study on In Vitro Preparation and Taste Properties of N-Ethyl-2-Pyrrolidinone-Substituted Flavan-3-Ols

N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) were prepared by an in vitro model reaction, and the taste thresholds of EPSFs and their dose-over-threshold factors in large-leaf yellow tea (LYT) were investigated. The effects of initial reactant ratios, reaction temperatures and time, pH values, and water addition on the yield of EPSFs were explored. The contents of EPSFs during roasting were determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). When the initial ratio of (-)-epigallocatechin gallate (EGCG) to theanine was 1:2 and roasted under 120 °C for 120 min, the contents of EPSFs were the highest. The bitterness and astringency thresholds of four EPSF isomers were measured by the half-tongue method, of which EPSF2 and EPSF3 had higher thresholds than EGCG. In LYT, four EPSFs had lower bitterness and astringency dose-over-threshold factors than EGCG. This study suggested that the reduction of bitterness and astringency of tea after roasting may be mainly due to the formation of EPSFs.

Effect of the C-Ring Structure of Flavonoids on the Yield of Adducts Formed by the Linkage of the Active Site at the A-Ring and Amadori Rearrangement Products during the Maillard Intermediate Preparation

Flavonoids (dihydromyricetin, dihydroquercetin, epicatechin, and epigallocatechin) were applied to indicate the critical formation condition of the Amadori rearrangement product (ARP) in Maillard reaction performed under a two-step temperature rising process in the threonine-xylose model system. Threonine-ARP (Thr-ARP) was mixed with dihydromyricetin (DM), dihydroquercetin (DQ), epicatechin (EC), and epigallocatechin (EGC) before the heat treatment; then, the mixture was tested by liquid chromatography-mass spectrometry (LC-MS). The results showed that these flavonoids trapped the ARP and generated adducts. The A-ring of flavonoids (the meta-polyhydroxylated benzene ring) was the functional group to capture the Thr-ARP. The relative contents of the adducts of DM-Thr-ARP, DQ-Thr-ARP, EC-Thr-ARP, and EGC-Thr-ARP were compared with each other, and it was found that the structure of the C-ring of the flavonoids (the carbonyl group on C-4) significantly impeded the formation of adducts with Thr-ARP, while the number of hydroxyl groups on the B-ring had little influence. The formation of adducts delayed the degradation of Thr-ARP, decreased the production of α-dicarbonyl compounds, and suppressed Maillard browning. In this way, the flavonoids might trace the critical formation conditions of ARP during the two-step temperature rising process.

Controlled Formation of Pyrazines: Inhibition by Ellagic Acid Interaction with N-(1-Deoxy-d-xylulos-1-yl)-glycine and Promotion through Ellagic Acid Oxidation

The effect of ellagic acid on the formation of pyrazine, methylpyrazine, 2,3-methylpyrazine, 2,6-methylpyrazine, 2,5-methylpyrazine, and trimethylpyrazine in the xylose-glycine Maillard reaction model was researched. Ellagic acid could either inhibit or promote pyrazine formation, depending on its addition time point and the pH of the system. The addition of ellagic acid during the accumulation period of an Amadori compound inhibited pyrazine formation by capturing the Amadori compound in the xylose-glycine Maillard system and decreasing the pyrazine precursors. The inhibitory effect of ellagic acid on pyrazine formation got more obvious with an increase in the pH of the system. However, when ellagic acid was added at the beginning of the xylose and glycine Maillard system and when the oxidizing substances such as glyoxal and methylglyoxal were significantly formed in the Maillard system, its oxidation could promote the formation of pyrazines.

Model Studies on the Reaction Products Formed at Roasting Temperatures from either Catechin or Tea Powder in the Presence of Glucose

During tea processing, roasting significantly affects the transformation pathway of catechins. When (-)-epigallocatechin gallate (EGCG) and glucose were roasted at different pH values, the degree of degradation and isomerization of EGCG was the lowest at pH 7 and the highest at pH 8. Thirty-five products were found in the model reaction of EGCG and glucose under high temperatures, of which four EGCG-glucose adducts were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR). In addition, catechins, gallic acid, and theanine in tea with added glucose were significantly reduced during roasting. The contents of four EGCG-glucose adducts were increased significantly at 150 °C after 30 min and dropped gradually after 60 min. Therefore, based on the present study, EGCG could form crosslinks with glucose under high temperatures in a short time, which provides insight for tea processing and synthesis of catechin-sugar adducts.

Maillard Browning Inhibition by Ellagic Acid via Its Adduct Formation with the Amadori Rearrangement Product

The Maillard reaction performed under a stepwise increase of temperature was applied for researching the inhibition of Maillard browning caused by ellagic acid. Ellagic acid was found effective for the inhibition of melanoidin formation in the xylose-glycine Maillard reaction but depended on its dosage and the point of time it was added in the reaction system. The lightest color of the Maillard reaction products was observed when ellagic acid was added at the 90th min, which was the point of time when the Amadori rearrangement product (ARP) developed the most. LC-ESI-MS/MS analysis results showed a significant tendency of the ellagic acid hydrolysis product to react with the predominant intermediate ARP to yield an adduct. The adduct stabilized the ARP and delayed its decomposition and inhibited the downstream reactions toward browning. After the ARP was depleted, ellagic acid also showed an effect on scavenging some short-chain dicarbonyls which contributed to the inhibition of Maillard browning.

Reduction of 3-Deoxyglucosone by Epigallocatechin Gallate Results Partially from an Addition Reaction: The Possible Mechanism of Decreased 5-Hydroxymethylfurfural in Epigallocatechin Gallate-Treated Black Garlic

5-Hydroxymethylfurfural (5-HMF) is a harmful substance generated during the processing of black garlic. Our previous research demonstrated that impregnation of black garlic with epigallocatechin gallate (EGCG) could reduce the formation of 5-HMF. However, there is still a lack of relevant research on the mechanism and structural identification of EGCG inhibiting the production of 5-HMF. In this study, an intermediate product of 5-HMF, 3-deoxyglucosone (3-DG), was found to be decreased in black garlic during the aging process, and impregnation with EGCG for 24 h further reduced the formation of 3-DG by approximately 60% in black garlic compared with that in the untreated control. The aging-mimicking reaction system of 3-DG + EGCG was employed to determine whether the reduction of 3-DG was the underlying mechanism of decreased 5-HMF formation in EGCG-treated black garlic. The results showed that EGCG accelerated the decrease of 3-DG and further attenuated 5-HMF formation, which may be caused by an additional reaction with 3-DG, as evidenced by LC-MS/MS analysis. In conclusion, this study provides new insights regarding the role of EGCG in blocking 5-HMF formation.

Effect of Methionine on the Thermal Degradation of N-(1-Deoxy-d-fructos-1-yl)-methionine Affecting Browning Formation

The effect of additional dl-methionine (Met) on the thermal degradation of a methionine-glucose-derived Amadori rearrangement product (MG-ARP) was investigated under different reaction conditions. The resulting color formation and changes in the concentrations of MG-ARP, Met, and α-dicarbonyl compounds were investigated. Additional Met did not affect the degradation rate of MG-ARP but got involved in subsequent reactions and resulted in a decrease in the contents of C₆-α-dicarbonyl compounds. During MG-ARP degradation, the formation of glyoxal (GO) and methylglyoxal (MGO) was facilitated by additional Met, through retro-aldolization reaction of C₆-α-dicarbonyl compounds. This effect of Met addition was dependent on the reaction temperature, and the consistent conclusion could be made in a buffer system. The improvement of GO and MGO formation as color precursors caused by the additional Met contributed to the acceleration of browning formation.

Application of a novel microwave energy treatment on brewers' spent grain (BSG): Effect on its functionality and chemical characteristics

The effect of a new microwave energy treatment on brewers' spent grain (BSG) functionality and its application in a bakery product was evaluated. The physicochemical modifications of BSG were studied with special emphasis on the analysis of non-enzymatic browning reactions. Microwave treatment induced the formation of Maillard reaction products with a high antioxidant activity. The structure of these compounds was fully analyzed and it was concluded that melanoidins were formed by polymerization of furanose rings. Results indicated that chlorogenic acids were also reactants involved in the development of this reaction, leading to the formation of new bioaccesible compounds with important antioxidant activity. Although the addition of BSG in cookie formulations negatively affect their texture, this effect was successfully reduced when the microwave treatment was applied on BSG. This was associated to the disrupting effect that the microwaves had on BSG fiber, which significantly reduced its water absorption index (p ≤ 0.05).

Adducts Derived from (-)-Epigallocatechin Gallate-Amadori Rearrangement Products in Aqueous Reaction Systems: Characterization, Formation, and Thermolysis

The interaction mechanism of (-)-epigallocatechin gallate (EGCG) with Amadori compound (Amadori rearrangement product, ARP) in xylose-alanine model reaction systems was investigated. The adducts between ARP and EGCG were identified as two ARP-EGCG isomers, two ARP-EGCG-H₂O isomers, and multiple ARP-deoxypentosone (DP)-EGCG isomers. The structure of an isolated and purified ARP-EGCG adduct was analyzed by means of Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, liquid chromatography-time-of-flight (TOF)-mass spectrometry (LC-TOF-MS), and nuclear magnetic resonance (NMR). Using the two-dimensional NMR analyses, the structure of ARP-EGCG adducts was clarified to consist of a covalent linkage between the C₁₂ position of the ARP and the C₈ position of the A-ring of EGCG, presumably generated by the nucleophilic nature of the EGCG or aromatic substitution reactions. The results showed that slightly alkaline pH and higher temperature could facilitate this reaction. Additionally, the thermal stability of ARP-EGCG and its degradation products revealed that the decomposition pathways of this adduct altered the classic decomposition pathway of ARP, resulting in a lower browning rate and blocking the subsequent Maillard reaction.

Maillard Mimetic Food-Grade Synthesis of N-(β-d-Deoxyfructos-1-yl)-l-glutamic Acid and N-(β-d-Deoxyfructos-1-yl)-β-alanyl-l-histidine by a Combination of Lyophilization and Thermal Treatment

A typical glycoconjugate of glutamic acid, namely, N-(β-d-deoxyfructos-1-yl)-l-glutamic acid, was successfully synthesized as the primary isomer in a yield of 96.08% using a food-grade preparation method, and its chemical structure was clearly demonstrated by mass spectrometry and 1D/2D NMR. The reaction kinetics of glucose and glutamic acid were systematically studied to investigate the effect of lyophilization and thermal treatment on the conversion of reactants to their corresponding Amadori rearrangement product (ARP). Interestingly, besides the initial pH value, temperature, and heating time, the initial concentration of glutamic acid also influenced the final yield because intramolecular dehydration occurred at the same time, competing with the Maillard reaction and degrading reaction. Moreover, a similar Amadori compound of carnosine was also prepared in a yield of about 66.38% and the yield could be further improved to 95% after condition optimization. One major isomer of the corresponding ARP of the peptide was confirmed to be N-(β-d-deoxyfructos-1-yl)-β-alanyl-l-histidine by structure characterization, indicating that this is a good method to prepare the N-(β-d-deoxyfructos-1-yl)-amino acid/peptide.

Interaction of (-)-Epigallocatechin Gallate and Deoxyosones Blocking the Subsequent Maillard Reaction and Improving the Yield of N-(1-Deoxy-d-xylulos-1-yl)alanine

(-)-Epigallocatechin gallate (EGCG) had a significant effect on Maillard reaction intermediate formation in the xylose/alanine model system. A trapping effect of EGCG on the reactive deoxyosones was observed to change the reaction pathways. The rate constant of Amadori rearrangement product (ARP) conversion to deoxyosones was decreased with EGCG addition, indicating an inhibition of ARP degradation. Dehydration improved the ARP formation during the thermal reaction and synergistically improved the yield of ARP with the EGCG trapping effect on the deoxyosones. Additionally, EGCG decreased the activation energy for the conversion of xylose/alanine to ARP (from 77.8 to 62.8 kJ/mol) and in turn accelerated the ARP formation. The effect of EGCG was further facilitated at the optimal conditions of 90 °C, at pH 7.5, and a molar ratio of xylose to alanine of 2:1, which improved the yield of ARP (N-(1-deoxy-d-xylulos-1-yl)alanine) from 2 to 95%.

Aqueous Preparation of Maillard Reaction Intermediate from Glutathione and Xylose and its Volatile Formation During Thermal Treatment

Maillard reaction intermediate (MGX) generated from glutathione and xylose in aqueous medium was prepared via the Maillard reaction performed under a two-stage temperature increase process. The purified MGX was identified by Fourier-transform infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance as N-(1-deoxy-d-xylulos-1-yl)-glutathione (Amadori compound, C₁₅ H₂₅ O₁₀ N₃ S) with five main isomers. The method of Maillard reaction performed under a two-stage temperature increase process was further verified by high-performance liquid chromatography. The optimal reaction time and temperature for the preparation of MGX was determined as 60 min at 90 °C. The yield of MGX was increased from 8.60% to 55.52% through thermal reaction coupled with vacuum dehydration. In addition, rapid and more Maillard-type volatile compounds were formed in MGX during thermal treatment than that in Maillard reaction products or glutathione-xylose mixture. Beside, MGX possessed more pleasing meat-like volatile profile compared with the Amadori compound of glutamic acid-xylose (AAX), cysteine-xylose (ACX), and glycine-xylose (AGX). Therefore, it suggested that the MGX had the potential to achieve a better flavor formation during thermal treatment. PRACTICAL APPLICATION: Maillard reaction intermediates, such as Amadori or Heyns rearrangement products (ARP or HRP), are important flavor precursors, which possess stable physicochemical properties, but tend to degrade into flavor compounds at high temperatures. Maillard reaction intermediate from glutathione and xylose acts as primary flavor enhancers to complete Maillard reaction to produce flavors in the subsequent thermal processing, which can significantly improve and stabilize the flavor quality of the meaty food, and deserves a very broad application prospects. The new developed method will be a significant theoretical basis on research preparation and properties of Maillard reaction intermediates in complex food systems.

N-(1-Deoxy-d-xylulos-1-yl)-glutathione: A Maillard Reaction Intermediate Predominating in Aqueous Glutathione-Xylose Systems by Simultaneous Dehydration-Reaction

The effect of simultaneous dehydration-reaction (SDR) on Amadori rearrangement product (ARP) N-(1-deoxy-d-xylulos-1-yl)-glutathione and its key degradation products, 3-deoxyxylosone (3-DX) and 1-deoxyxylosone (1-DX), were investigated in an aqueous glutathione-xylose (GSH-Xyl) system. The yield of ARP was increased to 67.98% by SDR compared with 8.44% by atmospheric thermal reaction at 80 °C. Reaction kinetics was applied to analyze the mechanism and characteristics of ARP formation and degradation under SDR. ARP formation and degradation rate was highly dependent on temperature, and the latter was more sensitive to temperature. By regulating the reaction conditions of temperature and pH, the ratio of ARP formation rate constant to its degradation rate constant could be controlled to achieve an efficient preparation of ARP from GSH-Xyl Maillard reaction through SDR.

Lipids Promote Glycated Phospholipid Formation by Inducing Hydroxyl Radicals in a Maillard Reaction Model System

Food-derived glycated phospholipids is potentially hazardous to human health. However, there are few studies on the effects of lipids on the formation of glycated phospholipids. In this work, two model systems were established: (1) a model system including 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (PE), glucose, and Fenton reagent and (2) a model system including PE, glucose, and five kind of vegetable oils. The contents of carboxymethyl-PE, carboxyethyl-PE, Amadori-PE, hydroxyl radical (OH•), glyoxal, and methylglyoxal were determined with high-performance liquid chromatography mass spectrometry. The results of the first model system showed that OH• oxidized glucose to produce glyoxal and methylglyoxal, which then reacted with PE to form carboxymethyl-PE and carboxyethyl-PE. OH• also oxidized Amadori-PE to form carboxymethyl-PE. The results of the second model system showed that vegetable oils with higher number of moles of carbon-carbon unsaturated double bond in vegetable oil per kilogram could produce more OH•, which promote the formation of carboxymethyl-PE and carboxyethyl-PE by oxidizing glucose and oil. We elucidated the effects of oils on the formation of glycated phospholipids in terms of OH• and intermediates. This work will contribute to better understanding the formation mechanism of glycated phospholipids with oil.