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1.
The reaction of methyl 9,10-epoxy-13-oxo-11(E)-octadecenoate, methyl 12,13-epoxy-9-oxo-11(E)-octadecenoate, 4,5(E)-epoxy-2(E)-heptenal, and 4,5(E)-epoxy-2(E)-decenal with phenylalanine in acetonitrile-water (2:1, 1:1, and 1:2) at 80 degrees C and at different pHs and carbonyl compound/amino acid ratios was investigated both to determine if epoxyoxoene fatty esters were able to produce the Strecker-type degradation of the amino acid and to study the relative ability of oxidized long-chain fatty esters and short chain aldehydes with identical functional systems to degrade amino acids. The studied epoxyoxoene fatty esters degraded phenylalanine to phenylacetaldehyde. The mechanism of the reaction was analogous to that described for epoxyalkenals and is suggested to be produced through the corresponding imine, which is then decarboxylated and hydrolyzed. This reaction also produced a conjugated hydroxylamine, which was the origin of the long-chain pyridine-containing fatty ester isolated in the reaction and characterized as methyl 8-(6-pentylpyridin-2-yl)octanoate. Epoxyoxoene fatty esters and epoxyalkenals exhibited a similar reactivity for producing phenylacetaldehyde, therefore suggesting that nonvolatile lipid oxidation products, which are produced to a greater extent than volatile products, should be considered for determining the overall contribution of lipids to Strecker degradation of amino acids produced during nonenzymatic browning. In addition, the obtained data confirm that, analogously to carbohydrates, lipid oxidation products are also able to produce the Strecker degradation of amino acids.  相似文献   

2.
Strecker degradation is one of the most important reactions leading to final aroma compounds in the Maillard reaction. In an attempt to clarify whether lipid oxidation products may be contributing to the Strecker degradation of amino acids, this study analyzes the reaction of 4,5-epoxy-2-alkenals with phenylalanine. In addition to N-substituted 2-(1-hydroxyalkyl)pyrroles and N-substituted pyrroles, which are major products of the reaction, the formation of both the Strecker aldehyde phenylacetaldehyde and 2-alkylpyridines was also observed. The aldehyde, which was produced at 37 degrees C-as could be determined by forming its corresponding thiazolidine with cysteamine-and pH 6-7, was not produced when the amino acid was esterified. This aldehyde is suggested to be produced through imine formation, which is then decarboxylated and hydrolyzed. This reaction also produces a hydroxyl amino derivative, which is the origin of the 2-alkylpyridines identified. All these data indicate that Strecker-type degradation of amino acids is produced at 37 degrees C by some lipid oxidation products. This is a new proof of the interrelations between lipid oxidation and Maillard reaction, which are able to produce common products by analogue mechanisms.  相似文献   

3.
The reaction of 4-hydroxy-2-nonenal, an oxidative stress product, with phenylalanine in acetonitrile-water (2:1, 1:1, and 1:2) at 37, 60, and 80 degrees C was investigated to determine whether 4-hydroxy-2-alkenals degrade amino acids, analogously to 4,5-epoxy-2-alkenals, and to compare the reactivities of both hydroxyalkenals and epoxyalkenals for production of Strecker aldehydes. In addition to the formation of N-substituted 2-pentylpyrrole and 2-pentylfuran, the studied hydroxyalkenal also degraded phenylalanine to phenylacetaldehyde with a reaction yield of 17%. The reaction mechanism is suggested to be produced through the corresponding imine, which is then decarboxylated and hydrolyzed. This reaction also produced a conjugated amine, which both may be one of the origins of the produced 2-pentyl-1H-pyrrole and may contribute to the development of browning in these reactions. 4-Hydroxy-2-nonenal and 4,5-epoxy-2-decenal degraded phenylalanine in an analogous extent, which is likely a consequence of the similarity of the degradation mechanisms involved. These results suggest that different lipid oxidation products are able to degrade amino acids; therefore, the Strecker type degradation of amino acids produced by oxidized lipids may be quantitatively significant in foods.  相似文献   

4.
The reaction of 2,4-decadienal and methyl 13-oxooctadeca-9,11-dienoate with phenylalanine was studied to determine if alkadienals and ketodienes are able to produce the Strecker-type degradation of amino acids to the corresponding Strecker aldehydes. When reactions were carried out at 180 degrees C, both carbonyl compounds degraded phenylalanine to phenylacetaldehyde, among other compounds. The yield of the phenylacetaldehyde produced depended on the reaction pH and increased linearly with both the amount of the lipid and the reaction time. The yield of this conversion was approximately 8% when starting from decadienal and approximately 6% when starting from methyl 13-oxooctadeca-9,11-dienoate, and the reaction rate was lower for the ketone than for the aldehyde. Simultaneous to these reactions, the lipid was converted into pyrrole, pyridine, or aldehyde derivatives as a result of several competitive reactions. In particular, 9-14% of the decadienal was converted into hexanal under the assayed conditions. All these reactions are suggested to be produced as a consequence of the oxidation of the alkadienal or the ketodiene to the corresponding epoxyalkenal or unsaturated epoxyketone, which were identified in the reaction mixtures by GC-MS. All these results suggest that alkadienals and ketodienes, which are quantitatively important secondary lipid oxidation products, can degrade amino acids to their corresponding Strecker aldehydes. Therefore, under appropriate conditions, these products are not final products of the lipid oxidation and can participate in carbonyl-amine reactions analogously to other lipid oxidation products with two oxygenated functions.  相似文献   

5.
2,4-Decadienal was heated under an inert atmosphere and in the presence of phenylalanine to investigate whether this secondary lipid oxidation product is a final product of lipid oxidation or it reacts with the amino acid. The results obtained showed that, in the presence of the alkadienal, the amino acid was degraded to styrene. This reaction was favored in dry systems at pH approximately 6 and in the absence of oxygen. If oxygen was present, the alkadienal was oxidized and the Strecker degradation of the amino acid was produced. The activation energy for the formation of styrene from phenylalanine was 150.4 kJ/mol. The reaction mechanism is suggested to be produced either by an electronic rearrangement of the imine produced between the aldehyde and the amino acid with the formation of styrene, 2-pentylpyridine, carbon dioxide, and hydrogen, or by Michael addition of the amino compound to the alkadienal followed by beta-elimination to produce the same compounds. Both reaction schemes were supported on the results obtained by studying both the degradation of phenylethylamine and phenylalanine methyl ester produced by 2,4-decadienal, and the formation of ethylbenzene in decadienal/phenylalanine reaction mixtures heated in the presence of platinum oxide. All these results suggest that, analogously to carbohydrates, certain lipid oxidation products may degrade appropriate amino acids to their corresponding vinylogous derivatives.  相似文献   

6.
Fruits and vegetables contain naturally occurring polyphenolic compounds that can undergo enzyme-catalyzed oxidation during food preparation. Many of these compounds contain catechol (1,2-dihydroxybenzene) moieties that may be transformed into o-quinone derivatives by polyphenoloxidases and molecular oxygen. Secondary reactions of the o-quinones include the Strecker degradation of ambient amino acids to form flavor-important volatile aldehydes. The purpose of this work was to investigate the mechanism of the polyphenol/o-quinone/Strecker degradation sequence in a nonenzymic model system. By using ferricyanide ion as the oxidant in pH 7.17 phosphate buffer at 22 degrees C, caffeic acid, chlorogenic acid, (+) catechin, and (-) epicatechin were caused to react with methionine and phenylalanine to produce Strecker aldehydes methional and phenylacetaldehyde in 0.032-0.42% molar yields (0.7-10 ppm in reaction mixtures). Also, by employing l-proline methyl ester in a reaction with 4-methylcatechol, a key reaction intermediate, 4-(2'-carbomethoxy-1'-pyrrolidinyl)-5-methyl-1,2-benzoquinone (7), was isolated and tentatively identified.  相似文献   

7.
Application of aroma extract dilution analysis on the volatiles formed by reacting glucose and L-phenylalanine (30 min, 100 degrees C) revealed the Strecker aldehyde, phenylacetaldehyde (PA), and, in addition, phenylacetic acid (PAA) as the two key odorants among the volatiles formed. Quantitative measurements on alpha-dicarbonyl formation revealed that the 3-deoxyosone and glyoxal were formed as the first prominent sugar degradation products, whereas 2-oxopropanal became predominant after approximately 4 h at 100 degrees C. Among the four alpha-dicarbonyls analyzed, 2-oxopropanal proved to be the most effective in generating PA as well as PAA from phenylalanine, but the reaction parameters significantly influenced the ratio of both odorants; for example, at pH 3.0 the ratio of PA to PAA was 3:1, whereas at pH 9.0 the ratio was 1:5. Furthermore, in the presence of oxygen and copper ions the formation of the acid was further increased. 3-Deoxyosone and glucosone were found to be effective precursors of phenylacetaldehyde, but neither was very effective in acid generation. On the basis of the results, a new oxygen-dependent formation pathway of the Strecker reaction is proposed.  相似文献   

8.
Formation of flavor compounds from branched-chain alpha-keto acids in fermented foods such as cheese is believed to be mainly an enzymatic process, while the conversion of phenyl pyruvic acid, which is derived from phenylalanine, also proceeds chemically. In this research, the chemical conversion of alpha-keto acids to aldehydes with strong flavor characteristics was studied, with the main focus on the conversion of alpha-ketoisocaproic acid to the aldehyde 2-methylpropanal, and a manganese-catalyzed reaction mechanism is proposed for this conversion. The mechanism involves keto-enol tautomerism, enabling molecular oxygen to react with the beta-carbon atom of the alpha-keto acid, resulting in a peroxide. This peroxide can react in several ways, leading to unstable dioxylactone or noncyclic intermediates. These intermediates will break down into an aldehyde and oxalate or carbon oxides (CO and CO(2)). All the alpha-keto acids tested were converted at pH 5.5 and in the presence of manganese, although their conversion rates were rather diverse. This chemical reaction might provide new ways for controlling cheese flavor formation with the aim of acceleration of the ripening process or diversification of the flavor characteristics.  相似文献   

9.
The effect of lipids on the formation of the Strecker aldehyde phenylacetaldehyde during wort boiling was studied to determine the role that small changes in the lipid content of the wort have in the production of significant flavor compounds in beer. Wort was treated with 0-2.77 mmol per liter of glucose, linoleic acid, or 2,4-decadienal and heated at 60-98 degrees C for 1 h. After this time, the amount of the Strecker aldehyde phenylacetaldehyde increased in the samples treated with linoleic acid or decadienal but not in the samples treated with glucose. Thus, the amount of phenylacetaldehyde produced in the presence of linoleic acid was 1.1-2.5 times the amount of the Strecker aldehyde produced in the control wort, and this amount increased to 3.6-4.6 times when decadienal was employed. The higher reactivity of decadienal than linoleic acid for this reaction decreased with temperature and was related to the oxidation of linoleic acid that occurred to a higher extent at higher temperatures. The above results suggest that lipids can contribute to the formation of Strecker aldehydes during wort boiling and that changes in the lipid content of the wort will produce significant changes in the formation of Strecker aldehydes in addition to other well-known consequences in beer quality and yeast metabolism. On the other hand, because of the high glucose content in wort, small changes in its content are not expected to affect the amount of Strecker aldehydes produced.  相似文献   

10.
Benzaldehyde, a potent aroma chemical of bitter almond, can also be formed thermally from phenylalanine and may contribute to the formation of off-aroma. To identify the precursors involved in its generation during Maillard reaction, various model systems containing phenylalanine, phenylpyruvic acid, phenethylamine, or phenylacetaldehyde were studied in the presence and absence of moisture using oxidative and nonoxidative Py-GC-MS. Analysis of the data indicated that phenylacetaldehyde, the Strecker aldehyde of phenylalanine, is the most effective precursor and that both air and water significantly enhanced the rate of benzaldehyde formation from phenylacetaldehyde. Phenylpyruvic acid was the most efficient precursor under nonoxidative conditions. Phenethylamine, on the other hand, needed the presence of a carbonyl compound to generate benzaldehyde only under oxidative conditions. On the basis of the results obtained, a free radical initiated oxidative cleavage of the carbon-carbon double bond of the enolized phenylacetaldehyde was proposed as a possible major mechanism for benzaldehyde formation, and supporting evidence was provided through monitoring of the evolution of the benzaldehyde band from heated phenylacetaldehyde in the presence and absence of 1,1'-azobis(cyclohexanecarbonitrile) on the ATR crystal of an FTIR spectrophotometer. In the presence of the free radical initiator, the enol band of the phenylacetaldehyde centered at 1684 cm(-1) formed and increased over time, and after 18 min of heating time the benzaldehyde band centered at 1697 cm(-1) formed and increased at the expense of the enol band of phenylacetaldehyde, indicating a precursor product relationship.  相似文献   

11.
Model systems were used to study the reaction kinetics of vanillin and pentalysine, lysine, glutathione, cysteine, aspartame, or phenylalanine (molar ratio 1:1) in phosphate buffer. The buffer pH was adjusted to the pK(a)(2) of the available alpha-amino group of each amino acid or peptide. Reductions of vanillin followed first-order kinetics at 55, 65, and 75 degrees C in the presence of each of the amino acids or peptides used. The reaction rates were accelerated as the temperature increased. The rate constants were highest for pentalysine followed by lysine, phenylalanine, glutathione/cysteine, and aspartame. The reduction of phenylalanine followed first-order kinetics, whereas the formation of its reaction product followed zero-order kinetics. The activation energy (E(a)) for the reaction ranged from 5.6 to 14.5 kcal/mol.  相似文献   

12.
The reaction of methyl 13-hydroperoxyoctadeca-9,11-dienoate (MeLOOH), methyl 13-hydroperoxyoctadeca-9,11,15-trienoate (MeLnOOH), methyl 13-hydroxyoctadeca-9,11-dienoate (MeLOH), methyl 13-oxooctadeca-9,11-dienoate (MeLCO), methyl 9,10-epoxy-13-hydroxy-11-octadecenoate (MeLEPOH), and methyl 9,10-epoxy-13-oxo-11-octadecenoate (MeLEPCO) with phenylalanine was studied to determine the comparative reactivity of primary, secondary, and tertiary lipid oxidation products in the Strecker degradation of amino acids. All assayed lipids were able to degrade the amino acid to a high extent, although the lipid reactivity decreased slightly in the following order: MeLEPCO > or = MeLCO > MeLEPOH > or = MeLOH > MeLOOH approximately = MeLnOOH. These data confirmed the ability of many lipid oxidation products to degrade amino acids by a Strecker-type mechanism and suggested that, once the lipid oxidation is produced, a significant Strecker degradation of surrounding amino acids should be expected. The contribution of different competitive mechanisms to this degradation is proposed, among which the conversion of the different lipid oxidation products assayed into the most reactive MeLEPCO and the fractionation of long-chain primary and secondary lipid oxidation products into short-chain aldehydes are likely to play a major role.  相似文献   

13.
alpha-Dicarbonyls, generated by sugar degradation, catalyze the formation of the so-called Strecker aldehydes from alpha-amino acids. To check the effectiveness of Amadori compounds (suggested as important intermediates in alpha-dicarbonyl formation from carbohydrates) in Strecker aldehyde formation, the amounts of phenylacetaldehyde (PA) formed from either an aqueous solution of L-phenylalanine/glucose or the corresponding Amadori compound N-(1-deoxy-D-fructosyl-1-yl)-L-phenylalanine (ARP-Phe) were compared. The results revealed the ARP-Phe as a much more effective precursor in PA generation. On the contrary, a binary mixture of glucose/phenylalanine yielded preferentially phenylacetic acid, in particular, when reacted in the presence of oxygen and copper ions. Further model experiments gave evidence that a transition-metal-catalyzed oxidation of the ARP-Phe by air oxygen into the 2-hexosulose-(phenylalanine) imine is the key step responsible for the favored formation of phenylacetaldehyde from the Amadori compound. This mechanism might explain differences in the ratios of Strecker aldehydes and the corresponding acids depending on the structures of carbohydrate degradation products involved.  相似文献   

14.
Reactions between five humic acids extracted from soils with widely differing pedological histories and 17 amino acids commonly occurring in proteins were investigated in aqueous solutions at pH 3.0 and 6.5. The reactions were affected by: (a) nature of the humic acid: (b) pH of the system: and (c) length of contact. The principal reaction appeared to be the microbiological oxidative degradation of the amino acids leading to the formation of substantial amounts of ammonium. While there was no evidence that the humic acids per se interacted with the amino acids, they did not appear to interfere with the microbiological degradation of the amino acids.  相似文献   

15.
The reactions of 4,5-epoxy-2-decenal with octylamine, benzylamine, and 2-phenylglycine methyl ester were studied to investigate if amines may suffer a Strecker type degradation by epoxyalkenals analogously to amino acids. In addition to other reactions, the studied amines were converted into their corresponding Strecker aldehydes (octanal, benzaldehyde, and methyl 2-oxo-2-phenylacetate, respectively) to an extent that depended on the pH, the temperature, the amount of epoxyalkenal, and the amine involved. Each amine exhibited an optimum pH for the reaction, but the corresponding Strecker aldehydes were produced to a significant extent within a broad pH range. In addition, the temperature mostly influenced the reaction rate, which was increased between 6.5 and 9.5 times when the reaction was carried out at 60 degrees C than when it took place at 37 degrees C. Furthermore, Strecker aldehyde formation was linearly correlated with the amount of the epoxyalkenal present in the reaction mixture. Nevertheless, the reaction yield mostly depended on the amine involved. Thus, octylamine only produced trace amounts of octanal, benzylamine was converted into benzaldehyde with a yield of 4.3%, and 2-phenylglycine methyl ester was converted into methyl 2-oxo-2-phenylacetate with a reaction yield of 49%. All of these results suggest that suitable amines can be degraded by epoxyalkenals to their corresponding Strecker aldehydes to a significant extent.  相似文献   

16.
The interaction between glucose and essential amino acids at 100 degrees C at pH values ranging from 4.0 to 12.0 was investigated by monitoring the disappearance of glucose and amino acids as well as the appearance of brown color. Lysine was the most strongly destroyed amino acid, followed by threonine which induced very little additional browning as compared with that undergone by glucose. Around neutrality, the nonenzymatic browning followed pseudo-zero-order kinetics after a lag time, while the glucose and amino acid losses did not follow first-order kinetics at any of the pH values tested. Glucose was more strongly destroyed than all of the essential amino acids, the losses of which are really small at pH values lower than 9.0. However, glucose was less susceptible to thermal degradation in the presence of amino acids, especially at pH 8.0 with threonine and at pH 10.0 with lysine. The contribution of the caramelization reaction to the overall nonenzymatic browning above neutrality should lead to an overestimation of the Maillard reaction in foods.  相似文献   

17.
Duck eggs were pickled in 4.2% NaOH/5% NaCl solution for 20 days to prepare the traditional Chinese Pidan. The extent of racemization of compositional amino acid in egg albumen and yolk over the alkaline pickling period was investigated with micellar capillary electrophoresis (MCE) using beta-cyclodextrin as chiral selector. The racemization value of amino acids in egg albumen was in the order serine > aspartic acid > glutamic acid > phenylalanine > leucine > valine > threonine = isoleucine, whereas the order in egg yolk was aspartic acid > glutamic acid > phenylalanine > leucine > valine. Therefore, the tendency of amino acid racemization appeared to be closely related to the properties of its residual side chain, as well as the pH and alkaline treating period. Moreover, racemization of most of the amino acids was remarkably induced by the alkaline treatment during the initial pickling period.  相似文献   

18.
Compounds possessing antioxidant activity play a crucial role in delaying or preventing lipid oxidation in foods and beverages during processing and storage. Such reactions lead to loss of product quality, especially as a consequence of off-flavor formation. The aim of this study was to determine the antioxidant activity of kilned (standard) and roasted (speciality) malts in relation to phenolic compounds, sugars, amino acids, and color [assessed as European Brewing Convention units (degrees EBC) and absorbance at 420 nm]. The concentrations of sugars and amino acids decreased with the intensity of the applied heat treatment, and this was attributed to the extent of the Maillard reaction, as well as sugar caramelization, in the highly roasted malts. Proline, followed by glutamine, was the most abundant free amino/imino acid in the malt samples, except those that were highly roasted, and maltose was the most abundant sugar in all malts. Levels of total phenolic compounds decreased with heat treatment. Catechin and ferulic acid were the most abundant phenolic compounds in the majority of the malts, and amounts were highest in the kilned samples. In highly roasted malts, degradation products of ferulic acid were identified. Antioxidant activity increased with the intensity of heating, in parallel with color formation, and was significantly higher for roasted malts compared to kilned malts. In kilned malts, phenolic compounds were the main identified contributors to antioxidant activity, with Maillard reaction products also playing a role. In roasted malts, Maillard reaction products were responsible for the majority of the antioxidant activity.  相似文献   

19.
The qualitative and quantitative composition of free amino acids in a typical Finnish peat bog at various depths down to 5.3 m below the surface was studied using capillary gas chromatography and mass spectrometry. Sixteen amino acids were identified at each depth: α-alanine, β-alanine, glycine, valine, leucine, proline, isoleucine, serine, threonine, glutamic acid, aspartic acid, phenylalanine, tyrosine, γ-aminobutyric acid, ornithine and lysine. Their amounts decreased markedly at a depth of 40–100 cm. The total amount of amino acids varied between 0.6 and 5.6 g kg?1 dry matter (i.e. 0.06–0.56%) depending on the depth. The proportion of neutral amino acids was greatest at all depths studied, except at the surface layer where it ranged between 41 and 72% by mass. The acidic amino acids decreased with depth from 56 to 23% of the total. The proportion of aromatic amino acids was very small, 3.2–5.5% by mass. In samples from aerobic conditions, where the microbial production of free amino acids was the greatest, α-ala, gly, glu and asp were most abundant. In peat from anaerobic conditions, where the microbiological activity was low, the proportion of the most chemically stable amino acid was exceptionally high. This may have been because glycine was a degradation product of other amino acids or peptides. Peat type and degree of decomposition had a strong influence on the total amount of free amino acids and their qualitative composition.  相似文献   

20.
The formation of acrylamide was studied in low-moisture Maillard model systems (180 degrees C, 5 min) based on asparagine, reducing sugars, Maillard intermediates, and sugar degradation products. We show evidence that certain glycoconjugates play a major role in acrylamide formation. The N-glycosyl of asparagine generated about 2.4 mmol/mol acrylamide, compared to 0.1-0.2 mmol/mol obtained with alpha-dicarbonyls and the Amadori compound of asparagine. 3-Hydroxypropanamide, the Strecker alcohol of asparagine, generated only low amounts of acrylamide ( approximately 0.23 mmol/mol), while hydroxyacetone increased the acrylamide yields to more than 4 mmol/mol, indicating that alpha-hydroxy carbonyls are much more efficient than alpha-dicarbonyls in converting asparagine into acrylamide. The experimental results are consistent with the reaction mechanism based on (i) a Strecker type degradation of the Schiff base leading to azomethine ylides, followed by (ii) a beta-elimination reaction of the decarboxylated Amadori compound to afford acrylamide. The beta-position on both sides of the nitrogen atom is crucial. Rearrangement of the azomethine ylide to the decarboxylated Amadori compound is the key step, which is favored if the carbonyl moiety contains a hydroxyl group in beta-position to the nitrogen atom. The beta-elimination step in the amino acid moiety was demonstrated by reacting under low moisture conditions decarboxylated model Amadori compounds obtained by synthesis. The corresponding vinylogous compounds were only generated if a beta-proton was available, for example, styrene from the decarboxylated Amadori compound of phenylalanine. Therefore, it is suggested that this thermal pathway may be common to other amino acids, resulting under certain conditions in their respective vinylogous reaction products.  相似文献   

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