Formation of pyrazines in hydroxyacetaldehyde and glycine nonenzymatic browning Maillard reaction: A computational study

By considering the formation of pyrazines (C₄N₂H₆ and C₄N₂H₄) as one of the possible final Maillard flavour compounds, Density Functional Theory computations at the standard state have been performed on the proposed mechanisms of glyoxal and glycine in the advanced stage of hydroxyacetaldehyde and glycine nonenzymatic browning reaction under different pH conditions. The results reveal that the basic condition is the most favourable for the production of pyrazines (Pzs), and the aqueous solution is more favourable than that of the gaseous state. The reactions at the isoelectric point of glycine and under neutral conditions are the second and third most favourable for the production of Pzs, respectively. The reaction under acidic conditions is the least feasible for the production of Pzs. Amino acetaldehyde is the most likely precursor of the pyrazine ring in the reaction. Presence of air or oxygen is necessary for the production of 2,3,5,6-tetrahydropyrazine (C₄N₂H₄) from 3,6-dihydropyrazine (C₄N₂H₆). Water is necessary with glyoxal and glycine species for the formation of Pzs and water is produced as a by-product during the formation of Pzs.     

Formation of methyl glyoxal in dihydroxyacetone and glycine Maillard reaction: A computational study

By considering the formation of methyl glyoxal as one of the possible intermediates, mechanisms for the intermediate stage of the Maillard reaction of dihydroxyacetone and glycine under different pH conditions have been proposed, following the Hodge-scheme. Density functional theory calculations have been performed at the standard state on the proposed mechanisms to calculated the Gibb’s free energy changes for the formation of different compounds in different steps of the reaction. Thus, the possibility for the formation of different compounds in the proposed mechanisms has been evaluated. Electronic energy changes for the formation of different compounds in the proposed mechanisms have been calculated to observe the internal energy changes of the reaction. The total mass balance has been followed during the calculation of electronic and Gibb’s free energies. The result reveals that methyl glyoxal is one of the most likely intermediates in the reaction, and dihydroxyacetone + deprotonated glycine and dihydroxyacetone + unprotonated glycine reactions are assumed favorable for the production of methyl glyoxal. The gaseous phase reaction is supposed to be more feasible than the aqueous phase reaction for the production of methyl glyoxal. Glyceraldehyde + protonated glycine and glyceraldehyde + glycine zwitterion reactions are postulated as less feasible for the formation of methyl glyoxal.     

Formation of pyrazines in dihydroxyacetone and glycine Maillard reaction: A computational study

Based on the electronic and Gibb’s free energy changes, the possibility of the formation of 2,5-dimethyl pyrazine (25Pz) as one of the probable final products in dihydroxyacetone (DHA) and glycine Maillard reaction under different pH conditions is described. Mechanisms for the reaction have been proposed following the Hodge-scheme. Density functional computational calculations at the standard state have been performed on the proposed mechanisms of the reaction. Electronic and Gibb’s free energy changes for the formation of different compounds have been estimated by following the total mass balance for different steps of the reaction. The possible order of feasibility for the production of 25Pz has been found as DHA + deprotonated glycine (DGly) gaseous > DHA + DGly aqueous > DHA + unprotonated glycine (UGly) gaseous > DHA + glycine zwitterion (GlyZ) gaseous > DHA + UGly aqueous > DHA + GlyZ aqueous > DHA + protonated glycine (PGly) aqueous > DHA + PGly gaseous phase reactions. Amino-acetone has been found to be the most likely precursor of the pyrazine ring. Oxidation plays an important role during the production of 25Pz. Water has been found as a by-product during the formation of 25Pz.     

Formation of the Heyns rearrangement products in dihydroxyacetone and glycine Maillard reaction: A computational study

Density functional theory computations at the standard state on the proposed mechanisms of dihydroxyacetone and glycine Maillard reaction under different pH conditions have revealed that dihydroxyacetone + deprotonated glycine and dihydroxyacetone + unprotonated glycine reactions are more favorable than dihydroxyacetone + protonated glycine and dihydroxyacetone + glycine zwitterion reactions for the formation of the Heyns rearrangement products (HRPs). The gaseous phase reaction is assumed more feasible than the aqueous phase reaction for the production of HRPs. Due to the possibility of the production of both of the enol and keto forms of HRPs, the rate of browning in the dihydroxyacetone + deprotonated glycine reaction is assumed higher than that of the others. Dihydroxyacetone + protonated glycine and dihydroxyacetone + glycine zwitterion reactions are not favorable for the formation of HRPs and, therefore, the reaction is assumed hindered under these conditions and the rate of browning is supposed to be lower than that of the others. Possibilities for the conversion of dihydroxyacetone to glyceraldehyde and formation of hydroxyacetaldehyde from dihydroxyacetone as a C2-fragmentation product have also been evaluated.     

Density functional computational studies on the intermediate stage of the ribose and glycine Maillard reaction: Formation of deoxyosones in aqueous solution

Mechanisms in an aqueous solution of the Maillard reaction are proposed under several pH conditions for the interaction of glycine with cyclic ribose (c-Rib) and open-chain ribose (Rib). According to the Gibbs free energy relationships as well as internal energies values derived from our density functional theory calculations, the c-Rib/Rib + DGly (glycine) are the most favourable reaction pathways for the formation of deoxyosones under basic conditions, where Rib is more reactive than c-Rib. The intermediate stage of the Maillard reaction leads to the formation of deoxyosones.     

Coordinate contribution of lipid oxidation and Maillard reaction to the nonenzymatic food browning

Lipid oxidation and the Maillard reaction are probably the two most important reactions in Food Science. Both include a whole network of different reactions in which an extraordinary complex mixture of compounds are obtained in very different amounts and produce important changes in food flavor, color, texture, and nutritional value, with positive and negative consequences. This article analyzes the interactions between both reactions, with special emphasis in nonenzymatic browning development, by discussing the influence of lipid oxidation products in the Maillard pathway and vice versa, as well as the existence of common intermediates and polymerization mechanisms in both reactions. The existing data suggest that both reactions are so interrelated that they should be considered simultaneously to understand the products of the Maillard reaction in the presence of lipids and vice versa, and should be included in one general pathway that can be initiated by both lipids and carbohydrates.     

美拉德反应产物的褐变、荧光吸收及抗氧化性的研究

采用以还原糖-氨基酸(木糖/葡萄糖分别与甘氨酸、赖氨酸、谷氨酰胺、半胱氨酸)模式美拉德反应(Maillard Reaction,MR)制备得到美拉德反应产物(MRPs),研究反应条件对MRPs的褐变程度、荧光吸收强度以及其抗氧化活性的影响,并分析MRPs的光学特征与抗氧化活性之间的联系。结果表明,还原糖和氨基酸的种类对MR的褐变强度有很大影响,其影响程度由强到弱分别为:Xly>Glc,Lys>Gly>Glu>Cys。随着反应时间的延长,各体系MRPs的褐变程度逐渐变强;而荧光吸收强度随着加热时间的延长而增强,然后在出现最大值后趋于平缓或者表现出下降的趋势。MRPs的抗氧化能力也随反应时间的延长而增强,抗氧化活性与褐变强度呈正相关,与荧光吸收特性没有表现出明显的关联。     

Inhibition of enzymatic browning in actual food systems by the Maillard reaction products

BACKGROUND: The Maillard reaction occurring between amino acids and sugars produces neo‐formed compounds having certain levels of antioxidant activity depending on the reaction conditions and the type of reactants. The objective of this study was to investigate enzymatic browning inhibition capacity of Maillard reaction products (MRPs) formed from different amino acids including arginine (Arg), histidine (His), lysine (Lys) and proline (Pro). RESULTS: The inhibitory effects of the MRPs on polyphenol oxidase (PPO) were determined. The total antioxidant capacity (TAC) of MRPs derived from different amino acids were in the order Arg > His > Lys > Pro. The TAC and PPO inhibition of MRPs were evaluated as a function of temperature (80–120 °C), time (1–6 h) and pH (2–12). Arg‐Glc and His‐Glc MRPs exhibited strong TAC and PPO inhibition. Increasing temperature (up to 100 °C) and time also increased TAC and PPO inhibition. Kinetics analysis indicated a mixed type inhibition of PPO by MRPs. CONCLUSION: The results indicate that the MRPs derived from Arg and His under certain reaction conditions significantly prevent enzymatic browning in actual food systems. The intermediate compounds capable of preventing enzymatic browning are reductones and dehydroreductones, as confirmed by liquid chromatographic–mass spectrometric analyses. Copyright © 2010 Society of Chemical Industry     

Phospholipid oxidation and nonenzymatic browning development in phosphatidylethanolamine/ribose/lysine model systems

Fatty acid losses, lipid oxidation, pyrrole formation, and browning and fluorescence development were determined in four mixtures of phosphatidylethanolamine (PE), ribose (RI), and/or lysine (lys) incubated at 37 °C to study the influence of lipid oxidation on the Maillard reaction and vice versa. Under the conditions assayed, the amino group of PE was preferentially damaged compared with the amino group of lys. In addition, oxidized lipid/amino acid reactions produced more pyrrolization, browning and fluorescence than carbohydrate/amino acid reactions, but both oxidized lipid/amino acid and sugar/amino acid reactions were produced in the PE/RI/lys system and both of them were inhibited by the presence of the other. Thus, fewer RI/lys reaction products were produced in the PE/RI/lys system than in an analogous system with no PE added. All these results confirm that there is an interaction between lipid oxidation and the Maillard reaction, and both of them should be considered simultaneously to understand their consequences on foods when lipids, carbohydrates, and amino acids or proteins are present.     

枸杞干制过程中褐变反应研究

从宁夏枸杞干制过程中色泽变化入手,测定与色泽变化相关的主要活性物质的变化,研究枸杞干制中褐变反应,以期为枸杞干制生产中的色泽保护技术提供依据。结果表明:随着干制的进行,多酚氧化酶活性逐渐降低,结合枸杞色差值的变化,确定枸杞热风干制前期有酶促褐变的发生。此外,枸杞热风干制后期,不同温度下还原糖和氨基酸态氮的含量都成下降趋势,枸杞色差值逐渐增大,且增速放缓,5-羟甲基糠醛含量逐渐下降,且温度越高越有利于美拉德反应发生。根据各非酶褐变特点,确定了枸杞热风干制后期有美拉德反应褐变存在。      

A critical evaluation of fluorescence as a potential marker for the Maillard reaction

During storage of foods and biological systems, fluorescent products are developed through the Maillard reaction, along with the brown pigments. Fluorescent products have been proposed as early indicators of this reaction. The aim of present work was to compare the kinetics of fluorescence and pigment development in order to define adequate early markers. Model glucose–aminoacid systems were prepared in several salts and buffers and stored at 55 °C. Pigment and florescence development was evaluated as a function of time. The results showed that, under unfavourable conditions for the reaction (low pH, presence of retardant salts), fluorescence was detected after important colour changes had occurred. However, under favourable conditions for the reaction (neutral pH, accelerating salts) fluorescent products could be considered as adequate markers because they sensitively reflected early steps of the reaction. Compositional factors and/or environmental conditions are the key factors for defining the performance of fluorescence as an adequate early marker.     

葡萄糖-甘氨酸美拉德反应产物对脂肪氧合酶的抑制作用研究

以葡萄糖和甘氨酸为原料制备美拉德反应产物（Glu/Gly-MRPs）,研究其对大豆脂肪氧合酶（LOX）的抑制作用以及机理。结果表明:随着反应中甘氨酸浓度、反应初始pH、反应温度和反应时间的增大,Glu/Gly-MRPs的褐变程度加深,pH下降,对LOX的抑制作用增强;当甘氨酸浓度大于0.6mol/L、反应体系初始pH高于8.0、反应温度高于110℃、反应时间长于3h时,MRPs对LOX的抑制率均趋于稳定值（80%¹00%）。Glu/Gly-MRPs对LOX酶促反应的迟滞时间具有延长作用,通过Lineweaver-Burk双倒数法确定Glu/Gly-MRPs对LOX的抑制类型为混合型抑制。      

木糖与甘氨酸美拉德反应产物抗氧化性能的研究

以木糖和甘氨酸为底物,控制不同的物质的量(木糖与甘氨酸物质的量之比分别为1∶0.1、1∶0.2、1∶0.4)进行美拉德反应,制备了三种不同的美拉德反应产物,并通过还原能力、清除H2O2能力、清除羟基自由基(.OH)、清除超氧阴离子自由基(O2-.)、清除亚硝酸根(NO2-)等体系研究了美拉德反应产物的抗氧化性能。结果表明,三种反应产物均具有较强的抗氧化能力,随着反应产物浓度的增加,抗氧化能力增强;三种产物的还原能力和清除O2-.的能力相当;木糖与甘氨酸物质的量之比为1∶0.2的美拉德反应产物清除H2O2、.OH和NO2-的能力要强于物质的量之比为1∶0.1和1∶0.4的反应产物。     

Effect of reactant concentrations on the Maillard reaction in a fructose–glycine model system and the inhibition of black tiger shrimp polyphenoloxidase

The characteristics and the inhibitory activity towards black tiger shrimp polyphenoloxidase of Maillard reaction products (MRPs), prepared by heating an equimolar mixture of fructose and glycine at various concentrations (0.75–30 mM) at 100 °C for 12 h, were investigated. Increase in the intermediate products was observed with increasing reactant concentration, as evidenced by the increase in A₂₉₄ and fluorescence intensity. Furthermore, development of browning (A₄₂₀) was noticeable when the reactant concentration increased. The inhibitory activity of MRPs towards PPO gradually increased when the concentration of each reactant increased and reached a maximum at 30 mM (80% inhibition). The increase in the inhibitory activity of MRPs was coincidental with the increase in the reducing power, A₂₉₄, fluorescence intensity, as well as browning intensity. Generally, the development of Maillard reaction products was associated with decrease in pH and loss of reducing sugar and free amino groups, with coincidental increase in reducing power and copper-chelating property. MRPs with the reactant concentration of 4.5–30 mM were able to chelate the copper ion. Therefore, the inhibitory activity of MRPs towards browning, induced by PPO, was most likely due to their copper-chelating property as well as reducing power.     

Maillard reaction products as "natural antibrowning" agents in fruit and vegetable technology

The effects of Maillard reaction products (MRPs), synthesized from a sugar (pentose, hexose, or disaccharide) and either a cysteine-related compound, an amino acid, or a sulfur compound, were investigated on polyphenoloxidase (PPO) activity from apple, mushroom, and eggplant. The optimal conditions for the production of inhibitory MRPs were performed using two-factor and five-level central experimental designs. It resulted that thiol-derived MRPs were highly prone to give rise to inhibitory compounds of PPO activity. Technological assays were also performed to test the efficiency of selected MRPs in the prevention of enzymatic browning in raw and minimally processed fruits and vegetables.     

Interaction between Maillard reaction products and lipid oxidation in starch‐based model systems

The effect of Maillard reaction products (MRPs) on the kinetics of lipid oxidation in intermediate‐moisture model systems containing pregelatinised starch, glucose, lysine and soybean oil has been studied. The samples, either containing all components or excluding one or more of them, were heated at 100 °C for different times. Lipid oxidation and browning indices were measured and the results confirmed the ability of MRPs to retard peroxide formation. Under the conditions adopted, the rate of the Maillard reaction was increased by the presence of the oil and its oxidation products. The antioxidant action of MRPs was also evaluated using a peroxide‐scavenging test based on crocin bleaching. The results demonstrated that antioxidant activity developed with increased browning of the samples. © 2000 Society of Chemical Industry     

Impact of the reducing sugars on the relationship between acrylamide and Maillard browning in French fries

The relationship between acrylamide content and Maillard browning in French fries was studied as a function of different glucose/fructose ratios in the raw product using several colour measurement methods. An exponential correlation was found between acrylamide formation and surface colour, as evaluated by the parameters a*, delta E and Agtron. As a consequence, small differences in product colour could result in more pronounced differences in acrylamide contamination. This relationship however appeared to be dependant upon the glucose/fructose ratio of the raw material. An excess of fructose compared to glucose stimulated acrylamide formation to a higher extent than Maillard browning. The opposite effect was established with an excess of glucose. In addition, a linear relationship was found between the absorbance of aqueous French fries extracts and acrylamide content, which moreover appeared to be less affected by the addition of extra reducing sugars prior to frying. To predict acrylamide formation, sugar analysis however remains an important instrument and is complementary to surface colour measurement.     

On the reaction of glyoxal with proteins

 The reaction of arginine and arginine derivatives with glyoxal under mild conditions revealed the formation of a previously unknown amino acid, designated as “Glarg”. ¹H-, ¹⁵N- and ¹³C-NMR analysis of the new compound elucidated its structure to be 1-(4-amino-4-carboxybutyl)-2-imino-5-oxo-imidazolidine. Experiments with solutions containing N ^α -acetylarginine and glyoxal showed that “Glarg” is formed quickly under physiological conditions, but is labile at higher temperatures as well as at low pH values. After incubation of β-casein with glyoxal, the formation of protein-bound “Glarg” in enzymatic hydrolysates via amino acid analysis could be demonstrated. Due to the fast reaction of glyoxal with arginine residues, under physiological conditions, proteins may act as scavengers for glyoxal. Received: 8 November 1996 / Revised version: 10 January 1997