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

Novel Pink Pigments Produced by Thermal Interaction of Theaflavins, Theanine, and Glucose: Color Formation, Isolation, and Structural Characterization

A color-deepening effect of theaflavins on the theanine-glucose thermal reaction model was revealed. Generated chromogenic intermediates in the initial stage and an accelerated browning rate through the promoted degradation of theanine-glucose Amadori rearrangement product in the intermediate and final stages are responsible for the color-deepening effect. Four pink-to-red theaflavin-theanine intermediates were verified as theaflavinies referencing the nuclear magnetic resonance and liquid chromatography-mass spectrometry information on theaflavins and l-theanine, including one accurately identified as theaflavinie 4. Theaflavinie 4 showed two maximum absorption peaks at 401 and 506 nm with parallel intensities, which resulted in a significant dichromic color change from pale pink to orange and red. Theaflavinies also could undergo further thermal reactions to yield brown polymers under higher temperatures (130 and 140 °C). This research provided new insight into realizing thermally formed polymers during black tea processing, which may be formed by oxidation products and amino acids or proteins through non-enzymatic thermal reactions.

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.

Regulated Formation of Inhibited Color and Enhanced Flavor Derived from Heated 2-Threityl-Thiazolidine-4-Carboxylic Acid with Additional Cysteine Targeting at Different Degradation Stages

This study explored the addition of cysteine (Cys) affecting the color formation of heated 2-threityl-thiazolidine-4-carboxylic acid (TTCA) models under different reaction conditions and pointed out that temperature was considered to be the key parameter influencing the color inhibition behavior of Cys on TTCA reaction models. Results revealed that additional Cys not only controlled the reaction progress and blocked the formation pathway of browning but also changed the formation rate, intensity, and profile of the flavor generated from the TTCA reaction model. Meanwhile, the mechanism of Cys simultaneously regulating the formation of color and flavor was revealed through monitoring of the characteristic downstream products during TTCA degradation and model reaction systems. At the initial stage, the additional Cys acted as a color inhibitor before the deoxyxylosone degradation, preventing the formation of downstream browning precursors. With the continuous depletion of Cys as well as the generation of furans or α-dicarbonyl compounds, Cys became a flavor enhancer to act on the browning precursors and to provide more sulfur/nitrogen elements for the TTCA thermal reaction system. Therefore, Cys had the potential to act as both color inhibitor and flavor fortifier to match with TTCA for the preparation of a light-colored flavoring base with a desired flavor during thermal processing.

Exogenous Threonine-Induced Conversion of Threonine-Xylose Amadori Compound to Heyns Compound for Efficiently Promoting the Formation of Pyrazines

The involvement of exogenous threonine during the degradation of l-threonine-d-xylose Amadori rearrangement product (Thr-ARP) was found to promote the formation of pyrazines. A model including Thr-ARP and ¹⁵N-labeled l-threonine was applied to reveal the role of free threonine in Thr-ARP conversion to pyrazines. Quantitative analyses of pyrazines in the model of Thr-ARP/¹⁵N-labeled threonine showed a precedence of the endogenous threonine (formed by the degradation of Thr-ARP) over the exogenous threonine in pyrazines formation, and the ratio of ¹⁵N to ¹⁴N content in pyrazines increased significantly over time. According to the observed occurrence of the Heyns rearrangement products (HRP) derived from ¹⁵N-threonine, as well as the sharp decrease of ¹⁵N-threonine content and a rapid increase of ¹⁴N endogenous threonine at the initial stage of heat treatment, it was proposed that aldimine condensation between exogenous threonine and Thr-ARP followed by the hydrolysis led to the endogenous threonine and the generation of HRP. Then, the HRP underwent dehydration followed by hydrolysis to form exogenous threonine and deoxyxyosones, and the dehydration and hydrolysis of deoxyxyosones to form organic acids was inhibited, but the retro-aldolization of deoxyxyosones was promoted, facilitating the generation of reactive α-dicarbonyl compounds. In this way, exogenous threonine accelerated the release of endogenous threonine and α-dicarbonyl compounds and the pH decline was slowed down, which was favorable for the formation of pyrazines.

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.

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.

Key Aspects of Amadori Rearrangement Products as Future Food Additives

Flavor is one of the most important factors in attracting consumers and maximizing food quality, and the Maillard reaction (MR) is highly-involved in flavor formation. However, Maillard reaction products have a big drawback in their relatively low stability in thermal treatment and storage. Amadori rearrangement products (ARPs), MR intermediates, can alternatively act as potential flavor additives for their better stability and fresh flavor formation ability. This review aims to elucidate key aspects of ARPs’ future application as flavorings. The development of current analytical technologies enables the precise characterization of ARPs, while advanced preparation methods such as synthesis, separation and drying processes can increase the yield of ARPs to up to 95%. The stability of ARPs is influenced by their chemical nature, pH value, temperature, water activity and food matrix. ARPs are associated with umami and kokumi taste enhancing effects, and the flavor formation is related to amino acids/peptides of the ARPs. Peptide-ARPs can generate peptide-specific flavors, such as: 1,6-dimethy-2(1H)-pyrazinone, 1,5-dimethy-2(1H)-pyrazinone, and 1,5,6-trimethy-2(1H)-pyrazinone. However, further research on systematic stability and toxicology are needed.

Proline-glucose Amadori compounds: Aqueous preparation, characterization and saltiness enhancement

Amadori rearrangement product (ARP) derived from proline and glucose was prepared in aqueous medium, and purified by ion exchange chromatography and identified by mass spectrometry and nuclear magnetic resonance spectrometry. The ARP was confirmed as 1-deoxy-1-L-proline-D-fructose (C₁₁H₁₉O₇N, 277 Da) with four main isomers. A preliminary vacuum dehydration coupled with subsequent spray drying was used to improve the yield of ARP conversion from 3.63% to 69.15%. Furthermore, the taste characteristics of spray dried ARP products were analyzed by electronic tongue and sensory evaluation. The results indicated that when the dosage of ARP products was above 0.4%, a 20% salt reduction could be achieved without reduction in the salty taste as well as having a significant enhancement in the umami attribute. The products at low- and medium- extents of reaction could stimulate more secretion of aldosterone in oral cavity and then improve its sensitivity to the salt, while the product at high- extent of reaction inhibits aldosterone secretion.

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.