Carbonyl-amine Reaction Research Articles

Mechanism of Pyrazine Formation Intervened by Oxidized Methionines during Thermal Degradation of the Methionine-Glucose Amadori Compound.

Methionine (Met) oxidation was observed during thermal degradation of methionine/glucose-derived Amadori rearrangement product (MG-ARP). The effects of oxidized methionine products, methionine sulfoxide (MetSO) and methionine sulfone (MetSO2), on pyrazine yields of the MG-ARP model were investigated. The pyrazine contents in the MG-ARP/Met and MG-ARP/MetSO models were found lower compared to those in the MG-ARP/MetSO2 model, and the inefficiency of pyrazine formation in the MG-ARP/Met model was proposed due to the fact that Met oxidation competitively inhibited the oxidation of dihydropyrazines for pyrazine formation in spite of relatively high methylglyoxal (MGO) content. The models of MGO mixed with Met, MetSO, or MetSO2 were established for further investigation of the mechanism for the involvement of Met oxidation in pyrazine formation. It was observed that the aldolization or carbonyl-amine reaction of MetSO with MGO was another important reason for the inhibition of pyrazine formation, except for the competitive inhibition of oxidative formation of MetSO on dihydropyrazine oxidation, and the adduct of MGO-MetSO was identified by MS/MS. These results also accounted for the phenomenon of low pyrazine yields but high yields of long-chain substituted pyrazines, which were converted from dihydropyrazines with the aldehyde involvement.

The simultaneous inhibition of histidine on 5-hydroxymethylfurfural and acrylamide in model systems and cookies

5-Hydroxymethylfurfural (HMF) and acrylamide (AA) are neoformed food contaminants. In this study, the simultaneous inhibition of HMF and AA by histidine (His) were investigated. In the asparagine (Asn)/glucose (Glc) model system, the inhibition ratios of HMF and AA were in the range of 28–58% and 0–71% when 20 mmol/L His was added. In cookies, His also exhibited excellent inhibition effects on both HMF and AA. At the His concentration of 2% (w/w), the inhibition ratios of HMF and AA reached 90% and 65%. Additionally, the sensory quality of cookies was not affected significantly. Qualitative results suggested that His inhibited the formation of AA by the competitive reaction between His and Asn for Glc, as well as directly eliminated the formed HMF and AA via the carbonyl–amine reaction and the Michael addition, respectively. This study revealed that His could be applied for the inhibition of HMF and AA in heated food.

Free Radical Scavenging Activity of Carbonyl-Amine Adducts Formed in Soybean Oil Fortified with Phosphatidylethanolamine.

Non-enzymatic browning reactions between lipid aldehydes and aminophospholipids might play an important role in the oxidative stability of cold-pressed vegetable oils. We, therefore, aimed to study the Maillard-type reaction between hexanal, a lipid oxidation product of linoleic acid, and phosphatidylethanolamine (PE (16:0/18:1)) at a ratio of 2:1 at conditions representative of the extraction of cold-pressed soybean oils (CPSBO) and determine the radical scavenging activity of the carbonyl-amine adducts with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The reaction product, 2-pentyl-3,5-dibutyl-dihydropyridine, could be identified by means of LC-ESI-QTOF-MS/MS. The formation of this nitrogen-containing heterocycle significantly increased with time and temperature (p < 0.05). The products formed during the carbonyl-amine reaction between PE (16:0/18:1) and hexanal at 60 °C showed a radical scavenging activity of approximately 20% (p < 0.05). The fraction, containing 2-pentyl-3,5-dibutyl-dihydropyridine, contributed to, but was not solely responsible for, the radical scavenging activity (p < 0.05). Incubation of CPSBO fortified with PE (16:0/18:1) at 60 °C for 60 min had the strongest radical scavenging activity of 85.1 ± 0.62%. Besides 2-pentyl-3,5-dibutyl-dihydropyridine, other carbonyl-amine adducts might impact the radical scavenging activity of CPSBO as well. The oxidative stability of CPSBO might be increased by promoting the formation of carbonyl-amine reaction products, such as 2-pentyl-3,5-dibutyl-dihydropyridine.

Effect of β-sitosterol in the antioxidative activity of oxidized lipid–amine reaction products

Abstract Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for activity in a polar compound-stripped olive oil (SOO) and in the same oil after addition of 1500 ppm of β-sitosterol (phytosterol-added olive oil, PAO) to evaluate the role of phytosterols in the antioxidant activity of oxidized lipid–amine products. None of the added compounds protected either SOO or PAO, when tested alone at 0–400 ppm. However, mixtures of PE/Lys and PC/Lys (100/300, 200/200, and 300/100 ppm) significantly increased the induction periods of both oils. Furthermore, there was a synergism between the phospholipids and Lys, which was a consequence of the reaction between the carbonyl compounds produced in the oxidation of the phospholipid fatty acid chains and the amino group of Lys. Some of these carbonyl–amine reaction products were determined by gas chromatography–mass spectrometry after converting them into volatile derivatives. In addition, stepwise multiple regression analysis demonstrated the relationship between the induction periods and the formed products. However, the contribution of carbonyl–amine reaction products to oil stability also depended on the type of oil, therefore suggesting a role of β-sitosterol in the antioxidative activity of the compounds produced by carbonyl–amine reactions. This contribution was also confirmed by the higher synergism observed for PE/Lys and PC/Lys mixtures in PAO than in SOO.

The role of amino phospholipids in the removal of the cito- and geno-toxic aldehydes produced during lipid oxidation

The role of amino phospholipids in the removal of 4-hydroxy-2-alkenals and 4,5-epoxy-2-alkenals was studied to determine the fate of highly toxic oxygenated aldehydes produced in foods as a consequence of lipid oxidation. The results obtained showed that phosphatidylethanolamine rapidly removed both exogenously added aldehydes as well as the endogenously produced aldehydes when its fatty acid chains were oxidized in the presence of an oxidative stress inducer. This removal, which was always produced in the range of pH (6–9) and temperature (25–60 °C) studied, produced the corresponding carbonyl–amine reaction products between the aldehydes and the amino group of the amino phospholipid. These results suggest that, in the presence of amino phospholipids, the oxidation of polyunsaturated fatty acid chains is not likely to produce free oxygenated aldehydes in enough concentration to pose a significant risk for human health. On the other hand, these compounds contributed to the formation of specific carbonyl–amine reaction products whose toxicity is mostly unknown at present.

당-Lysine 모델 수용액을 이용한 감마선 조사에 의한 비효소적 갈변반응 연구

당 및 lysine 혹은 당-lysine 혼합모델 수용액에서 감마선 조사에 의한 갈변도 변화 및 화학적 특성을 연구한 결과 감마선 조사에 의한 비효소적 갈변반응은 당 및 아미노산 단독 환경에서는 일어나지 않았으며, 당-아민 환경에서 진행되는 것으로 나타났다. 당-lysine 혼합용액의 감마선 조사에 의한 갈변 반응성은 당의 종류에 따라 다르게 나타났으나, 당의 감소와 갈변도 사이의 상관관계는 없었다. 비환원당인 sucrose는 감마선 조사에 의해 환원력이 생성되었으며, 다른 당에 비해 높은 갈변 반응성을 나타냈다.

Monitoring carbonyl-amine reaction between pyruvic acid and alpha-amino alcohols by FTIR spectroscopy--a possible route to Amadori products.

The carbonyl-amine reaction between pyruvic acid and alpha-amino alcohols was monitored by Fourier transform infrared spectroscopy at a temperature range between 20 and 100 degrees C and under acidic and basic conditions. To avoid interference, the reactions were conducted in the absence of solvent using liquid reactants such as methyl pyruvate, pyruvic acid, ethanolamine, and 1-amino-2,3-propanediol. Analysis of the time- and temperature-dependent spectra indicated that under basic conditions and at room temperature, the initial imine formation and its subsequent isomerization through a 1,3-prototropic shift occur very rapidly and the reaction goes to completion within 12 min. Interestingly, the isomerization product of the initial imine is the so-called Schiff base intermediate formed when the corresponding amino acid and the reducing sugar react during a typical Maillard reaction. Furthermore, the detailed studies also indicated that during the first 30 s, the rate of formation of the initial imine was faster than the rate of its isomerization; however, after 60 s, its rate of isomerization becomes faster than the rate of its formation. The data also indicated that under acidic conditions, this isomerization was prevented from occurring and the reaction was terminated at the initial imine formation stage. In addition, temperature-dependent spectra indicated that the isomerization of the Schiff's base into eneaminol can be achieved at or above 60 degrees C and its subsequent rearrangement into Amadori product can be attained at temperatures above 80 degrees C even under basic conditions, thus providing a novel route to Maillard reaction products starting from a keto acid and an amino alcohol. This observation was also confirmed through identification of the common Amadori product in both keto acid/amino alcohol and sugar/amino acid mixtures, by the application of tandem mass spectrometry and chemical ionization techniques.

Monitoring Carbonyl−Amine Reaction and Enolization of 1-Hydroxy-2-propanone (Acetol) by FTIR Spectroscopy

Infrared absorption bands characteristic of the aldehydo, keto, and enediol forms of 1-hydroxy-2-propanone (acetol) were identified and used to study the effect of solvent on the absorption frequencies and the effect of temperature and acid/base catalysis on the enolization reactions. The data indicated that, in addition to water, acids and bases can catalyze the enolization of 1-hydroxy-2-propanone and that the temperature inversely effects the rate of enolization under basic conditions. However, under acidic conditions, increasing the temperature favors the enolization process. In addition, the reaction of 1-hydroxy-2-propanone with a primary and a secondary amine was also monitored by Fourier transform infrared spectroscopy. The data indicated that at room temperature the rate of amine reaction was faster than the rate of its catalysis of enolization; however, below room temperature, the rate of base-catalyzed enolization became comparable with the rate of carbonyl-amine reaction forming both Heyns and Amadori adducts.

Carbonyl compounds cross-link cellular proteins and activate protein-tyrosine kinase p60c-Src.

Glyoxal, a dicarbonyl compound, is produced under oxidative stress by the autoxidation of glucose and reacts with the protein amino group to form Schiff base. In vitro treatment of murine thymocytes and fibroblasts with glyoxal induced extensive tyrosine phosphorylation of multiple proteins, which was drastically inhibited by the addition of OPB-9195, an inhibitor of the carbonyl reaction with proteins. Glyoxal induced cross-linking of a number of cellular proteins, including glycosylphosphatidylinositol (GPI)-anchored cell surface Thy-1. We then demonstrated that treatment of cells with glyoxal promptly induced activation of non-receptor protein-tyrosine kinase c-Src, which was partially inhibited by OPB-9195. It is suggested from these results that carbonyl amine reaction quickly activates c-Src, possibly through cross-linkage of GPI-anchored proteins or putative specific receptors.

New biomarkers of Maillard reaction damage to proteins.

The amount of advanced glycation end-products (AGE) in tissue proteins increases in diabetes mellitus, and the concentration of a subclass of AGEs, known as glycoxidation products, also increases with chronological age in proteins. The rate of accumulation of glycoxidation products is accelerated in diabetes and age-adjusted concentrations of two glycoxidation products, N epsilon-(carboxymethyl)lysine (CML) and pentosidine, correlate with the severity of complication in diabetic patients. Although AGEs and glycoxidation products are implicated in the development of diabetic complications, these compounds are present at only trace concentrations in tissue proteins and account for only a fraction of the chemical modifications in AGE proteins prepared in vitro. The future of the AGE hypothesis depends on the chemical characterization of a significant fraction of the total AGEs in tissue proteins, a quantitative assessment of their effects on protein structure and function, and an assessment of their role as mediators of biological responses. In this manuscript we describe recent work leading to characterization of new AGEs and glycoxidation products. These compounds include: (1) the imidazolone adduct formed by reaction of 3-deoxyglucosone with arginine residues in protein; (2) N epsilon-(carboxyethyl)lysine, an analogue of CML formed on reaction of methylglyoxal with lysine; (3) glyoxal-lysine dimer; and (4) methyl-glyoxal-lysine dimer, which are imidazolium crosslinks formed by reaction of glyoxal or methylglyoxal with lysine residues in protein. The presence of 3-deoxyglucosone, methylglyoxal and glyoxal in vivo and the formation of the above AGEs in model carbonyl-amine reaction systems suggests that these AGEs are also formed in vivo and contribute to tissue damage resulting from the Maillard reaction.

The Reaction of Amines with Carbonyls: Its Significance in the Nonenzymatic Metabolism of Xenobiotics

The studies cited above indicated that many carbonyl amine reactions can alter both in vitro and in vivo rates of xenobiotic metabolism. The carbonyl amine reaction may be enzymatic or nonenzymatic and in most instances is readily reversible with few examples of the isolation and identification of the Schiff bases (azomethine). Endogenous primary amine and amines generated by metabolic N-dealkylation can react with biogenic ketones and aldehydes and under selected physiological conditions give further condensation products. The new products in most instances alter the biological activity and/or toxicity. It is apparent that these findings can be extended to carbonyl hydrazine reactions. The rates of reaction for simple alkyl and aryl hydrazine are more rapid and the products of these reactions and more stable, with the condensation products of alpha-keto acids being isolated and characterized the most frequently. The further reaction of hydrazones to yield condensation products is also observed with selected hydrazines such as hydralazine. It is now clear that the inherent toxicity of many exogenous ketones and aldehydes exists. Many of these toxicities are due to the reactions which occur with the amino groups of amino acids and proteins. The condensation reactions in most instances are readily reversed and are only dependent on the physiological concentration of aldehydes of ketones. However, there are a number of ketones and aldehydes, some of which are metabolically produced that are capable of forming azomethine intermediates which are not readily reversed under physiological conditions. There are an increasing number of examples of further nonenzymatic condensations which result in stable products which can alter xenobiotic metabolism.

Carbonyl-amine reaction products as a possible source of nitrosatable nitrogen.

Carbonyl-amine reaction products as a possible source of nitrosatable nitrogen.