Strecker Degradation Of Amino Acids Research Articles

Discovery of nitrogenous derivatives of dihydromyricetin in cell culture medium

AbstractDihydromyricetin (DMY) is a health‐beneficial flavanonol in the family of flavonoids, extracted from Ampelopsis grossedentata (Hand.‐Mazz.) W. Wang. When investigating the stability of DMY in Dulbecco's modified Eagle's medium (DMEM) solution at 37°C by LC‐MS/MS, four nitrogenous derivatives of DMY were found except for the previously known dimers, oxidized products, and ring‐cleavage products of DMY. Compound 1 (N‐DMY) was identified to be 4′‐amino (NH2)‐DMY based on MS and NMR data. The formation mechanism of N‐DMY was thought to include two steps. First, the pyrogallol moiety on the ring B of DMY was prone to be oxidized to quinone. Second, quinone might further participate in the Strecker degradation of amino acids in DMEM to form N‐DMY and corresponding aldehydes. Correspondingly, compounds 2–4 might be formed by the Strecker degradation reaction of amino acids in DMEM with quinones from the oxidation of DMY dimers and DMY ring‐cleavage products. Consistent with the formation mechanism, it was observed that flavonoids with a catechol or pyrogallol moiety readily form their nitrogenous derivatives during the incubation in DMEM at 37°C, which might be because catechol or pyrogallol are easily oxidized to quinones. In addition, the nitrogenous derivatives of flavonoids may have a potential to participate in the metabolism of flavonoids during in vitro and in vivo experiments. Therefore, flavonoid nitrogenous derivatives may play a significant role in the actual effects of flavonoids, which need to be further investigated in the future.

Reactions of Quinones-Mechanisms, Structures, and Prospects for Food Research.

Oxidation of plant phenolics leads to quinones, which are unstable intermediates that may react with nucleophiles. Quinones play an important role in the enzymatic browning of fruits and vegetables and may form covalent adducts with amino acids, peptides, and proteins. These reactions may alter both the physicochemical and immunological properties of food proteins. Quinones trap odoriferous compounds and contribute to the formation of aroma compounds through Strecker degradation of amino acids. Oxidative dimerization of chlorogenic acids in the presence of amino acids leads to the formation of green benzacridines, which are a promising alternative to chlorophylls as food colorants.

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

A camphor-derived sulfonimine with a conjugated carbonyl group, oxoimine 1 (O2SNC10H13O), reacts with amino acids (glycine, L-alanine, L-phenylalanine, L-leucine) to form a compound O2SNC10H13NC10H14NSO2 (2) which was characterized by spectroscopic means (MS and NMR) and supported by DFT calculations. The product, a single diastereoisomer, contains two oxoimine units connected by a –N= bridge, and thus has a structural analogy to the colored product Ruhemann´s purple obtained by the ninhydrin reaction with amino acids. A plausible reaction mechanism that involves zwitterions, a Strecker degradation of an intermediate imine and water-catalyzed tautomerizations was developed by means of DFT calculations on potential transition states.

Antagonism between lipid-derived reactive carbonyls and phenolic compounds in the Strecker degradation of amino acids

The Strecker-type degradation of phenylalanine in the presence of 2-pentanal and phenolic compounds was studied to investigate possible interactions that either promote or inhibit the formation of Strecker aldehydes in food products. Phenylacetaldehyde formation was promoted by 2-pentenal and also by o- and p-diphenols, but not by m-diphenols. This is consequence of the ability of phenolic compounds to be converted into reactive carbonyls and produce the Strecker degradation of the amino acid. When 2-pentenal and phenolic compounds were simultaneously present, an antagonism among them was observed. This antagonism is suggested to be a consequence of the ability of phenolic compounds to either react with both 2-pentenal and phenylacetaldehyde, or compete with other carbonyl compounds for the amino acids, a function that is determined by their structure. All these results suggest that carbonyl–phenol reactions may be used to modulate flavor formation produced in food products by lipid-derived reactive carbonyls.

Contribution of Phenolic Compounds to Food Flavors: Strecker-Type Degradation of Amines and Amino Acids Produced by o- and p-Diphenols

The ability of 20 phenolic derivatives to produce the Strecker-type degradation of phenylalanine and phenylglycine methyl ester was studied to investigate both the direct degradation of amino acids and amines by phenolic compounds in the absence of added oxidants and the effect of the number and positions of hydroxyl groups in the aromatic ring of the phenolic compound in relation to its ability to produce carbonyl derivatives from amino compounds. The obtained results showed that polyphenols can produce the Strecker degradation of amino acids and amines in the absence of added oxidants. The only requisite for producing the reaction is the presence of two hydroxyl groups in ortho or para positions. However, the presence of two hydroxyl groups in meta position in an additional aromatic ring can inhibit the Strecker-degrading ability of the hydroxyl groups in ortho or para positions. A reaction pathway that explains all of these findings is proposed. In addition, the effect of reaction conditions on the obtained reaction yields was studied. Activation energies (Ea) for phenylacetaldehyde formation from phenylalanine in the presence of hydroquinone, 1,2,4-trihydroxybenzene, and benzoquinone were 32.9, 31.5, and 28.8 kJ/mol, respectively.

Maillard reaction and lipid peroxidation contribute to non‐enzymatic browning in krill‐based products: A model study on proposed mechanisms

The main objective of this study was to further investigate whether the occurrence of Strecker degradation in krill‐based products is due to the presence of N‐Acetylglucosamine (amino sugar derived from krill exoskeleton) or lipid‐derived carbonyls. A simple model system comprising amino acids was incubated at 60°C for 0, 3, 9, and 24 h with five selected lipid‐derived carbonyls or five Strecker‐derived volatiles or an amino sugar. The presence of both amino sugar and lipid‐derived carbonyls (especially α,β‐unsaturated aldehydes) caused non‐enzymatic browning reactions: (i) pyrrole formation; (ii) browning development; and (iii) Strecker degradation of amino acids, with a faster reaction rate by amino sugar. In addition, the presence of a high level of Strecker degradation products might enhance pyrrole formation.Practical applications: This work provides information about the Strecker degradation of amino acids induced by amino sugar (N‐Acetylglucosamine) and lipid‐derived carbonyl compounds, and the increase of pyrrole formation is ascribed to the presence of a high level of Strecker degradation products. The obtained knowledge from this fundamental study explains the occurrence of Strecker degradation in krill products especially after enzymatic treatment due to the increased level of amino acids, lipid oxidation products and amino sugar derived from krill shell. This information is not only applicable to krill matrix but also to similar matrices from other food systems.Non‐enzymatic browning reactions, especially Strecker degradation of amino acids in krill‐based products during their thermal treatment, are induced either through Maillard reaction due to the presence of amino sugar derived from krill exoskeleton or through the lipid peroxidation pathway due to the presence of unsaturated aldehydes derived from lipid oxidation.

Intermediate role of α-keto acids in the formation of Strecker aldehydes

The ability of α-keto acids to covert amino acids into Strecker aldehydes was investigated in an attempt to both identify new pathways for Strecker degradation, and analyse the role of α-keto acids as intermediate compounds in the formation of Strecker aldehydes by oxidised lipids. The results obtained indicated that phenylalanine was converted into phenylacetaldehyde to a significant extent by all α-keto acids assayed; glyoxylic acid being the most reactive α-keto acid for this reaction. It has been proposed that the reaction occurs by formation of an imine between the keto group of the α-keto acid, and the amino group of the amino acid. This then undergoes an electronic rearrangement with the loss of carbon dioxide to produce a new imine. This final imine is the origin of both the Strecker aldehyde and the amino acid from which the α-keto acid is derived. When glycine was incubated in the presence of 4,5-epoxy-2-decenal, the amino acid was converted into glyoxylic acid, and this α-keto acid was then able to convert phenylalanine into phenylacetaldehyde. All these results suggest that Strecker aldehydes can be produced by amino acid degradation initiated by different reactive carbonyl compounds, included those coming from amino acids and proteins. In addition, α-keto acids may act as intermediates for the Strecker degradation of amino acids by oxidised lipids.

Short communication: Evidence for methylglyoxal-mediated browning of Parmesan cheese during low temperature storage

Brown pigmentation can occasionally form in Parmesan cheese during the ripening process, creating an unappealing appearance and associated off-flavors. The browning reactions proceed at refrigerated temperatures and in the relative absence of reducing sugar, contrary to typical Maillard browning. Residual sugars, lipid oxidation products, byproducts of fermentation, and (or) enzymes may react with primary amines in cheese to form brown pigmentation and concomitantly generate volatile compounds unique to each of these reactions. Determining the volatile profiles provides a means of understanding the potential substrates involved and causative reaction pathways. This work is divided into 2 segments. The first portion characterized the pigmentation and the browning index of Parmesan cheeses with and without extensive browning. The second phase examined the volatile character of the cheeses using gas chromatography-mass spectrometry. Various pyrazines, such as 2,3,5-trimethylpyrazine and 3,5-diethyl-2-methylpyrazine, were found in the brown cheeses but were not present in the white samples. The formation of pyrazines is proposed to result from the spontaneous condensation of aminoacetone. Aminoacetone can be formed by the Strecker degradation of amino acids with methylglyoxal, the latter a byproduct of sugar fermentation. Evidence is provided to support a browning pathway mediated by the production of methylglyoxal in Parmesan cheese.

Model Studies on the Degradation of Phenylalanine Initiated by Lipid Hydroperoxides and Their Secondary and Tertiary Oxidation Products

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.

Homocysteine Toxicity in Connective Tissue: Theories, Old and New

Hyperhomocysteinemia causes connective tissue pathology. Several theories on the mechanism of homocysteine toxicity in connective tissue are reviewed briefly. A possible new mechanism was revealed recently in the discovery of a reaction in which homocysteine thiolactone is converted to mercaptopropionaldehyde. The reaction is the Strecker degradation of amino acids in which ninhydrin is replaced by the structurally similar dehydroascorbic acid. The reaction may occur in vivo and may be pathogenic to connective tissue in four ways: (1) the reaction may deplete ascorbic acid that is required for collagen synthesis, (2) the mercaptoaldehyde product may interfere with collagen synthesis, (3) the mercaptoaldehyde may cause abnormal cross-linking of collagen molecules, and (4) the mercaptoaldehyde may attach to collagen molecules rendering them antigenic and triggering an autoimmune response.

Strecker-type Degradation of Phenylalanine by Methyl 9,10-Epoxy-13-oxo-11-octadecenoate and Methyl 12,13-Epoxy-9-oxo-11-octadecenoate

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.

Strecker-type Degradation Produced by the Lipid Oxidation Products 4,5-Epoxy-2-Alkenals

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.

Volatile compounds on the surface and within Iberian dry-cured loin

The profile of volatile compounds from external and internal areas of Iberian dry-cured loin was studied by headspace solid-phase microextraction. Higher levels of 16 volatile compounds (hexane, decane, 3-methylbutanal, several sulphur compounds and some aromatic hydrocarbons) were detected in the outer part of the loins. These differences could be owing to several factors, such as greater exposure to oxygen and dehydration conditions in the surface of the product, which favour oxidation reactions and Strecker degradation of amino acids. Moreover, the addition of spices on the surface and the proximity of a mould layer growing on the surface of the product could also contribute to the higher levels of these compounds on the external layer. However, other sulphur compounds coming from spices showed similar levels on the surface and within the loins. This different behaviour could be a consequence of different diffusion rates depending on the features of the compound and the matrix.

Comparison of simultaneous distillation extraction (SDE) and solid‐phase microextraction (SPME) for the analysis of volatile compounds in dry‐cured ham

AbstractSimultaneous distillation extraction (SDE) and solid‐phase microextraction (SPME) using a carboxen/polydimethylsiloxane fibre were compared for their effectiveness in the extraction of volatile compounds from dry‐cured ham samples. A higher number of compounds was detected using SPME owing to the use of a solvent delay time in the GC‐MS analysis of SDE extracts. SPME was more efficient in extracting low molecular weight and high volatility compounds, while SDE was able to extract compounds with low volatilities that were not extracted using SPME. Both techniques satisfactorily extracted most volatiles previously highlighted as odour‐active compounds in dry‐cured ham. However, the ratio between some compounds from lipid oxidation and those from degradation of amino acids was much lower in SDE extracts than with SPME, which could be a consequence of the development of Strecker degradation of amino acids during distillation in SDE owing to the high temperatures used. Similarly, diunsaturated aldehydes detected in SDE extracts were absent using SPME, probably owing to oxidation of polyunsaturated fatty acids in SDE as a consequence of the temperature during extraction. Copyright © 2004 Society of Chemical Industry

Reductones participate in redox reactions during amine-catalyzed sugar degradation

The term Maillard reaction stands as a synonym for the complicated reaction pathways of reducing sugars with amines [1]. Within this context, redox reactions represent a relatively new and by far an unclarified aspect. α-Oxoenediol and α-oxoeneaminol structures are potential reaction partners with major influence on the final product spectrum. Only recently, we succeeded in synthesizing 1-deoxyglucosone (1-DG) as a major representative of these so-called reductones [2]. 1-DG formation during the degradation of hexoses is explained via enolization of the Amadori product and cleavage of the amine. If, alternatively, the hydroxy function at C-4 is eliminated, 1-amino-1,4-dideoxyglucosone (1-A-1,4-DG) will be formed.1-DG is reduced during the Strecker degradation of amino acids to result in 1-deoxyfructose/1-deoxypsicose (1-DF). These sugars are then degraded via enolization and dehydration to 1,4-dideoxyglucosone (1,4-DG). Alternatively, the formation of 1,4-DG can also be explained by an intermolecular redox reaction of two molecules of 1-DG to give 1-DF, degrading to 1,4-DG, and a tricarbonyl compound. After synthesis of all participating structures, monitoring of incubations of glucose, 1-DG, and 1-DF with various amines lead to confirmation of the proposed reaction pathways.1-A-1,4-DG is of special interest, as it still incorporates the amine in contrast to most other reactive Maillard intermediates so far elucidated. Second, as an aminoreductone, 1-A-1,4-DG boasts a highly electron-rich moiety and therefore has to be judged as extremely reactive. In spite of this potential importance, so far only very limited information has been published, based exclusively on sugar–alkylamine reaction systems [3]. To gain further insight into the importance of 1-A-1,4-DG, we synthesized the quinoxaline–lysine derivative in a 6-step procedure as an authentic reference material. The structure was unequivocally identified and quantitated in incubations of Nα-t-BOC-lysine with glucose and maltose, and during the degradation of the respective Amadori products in presence of o-phenylenediamine. In addition, for the first time the formation of protein-bound 1-A-1,4-DG was monitored after enzymatic hydrolysis. Above formation pathway suggests the parallel synthesis of both 1-DG and 1-A-1,4-DG. However, our results show that the ratio of both structures is highly dependent on the quality of respective substituents at C-1 and C-4 as leaving groups. In glucose incubations at 50 °C, only trace amounts of 1-A-1,4-DG were formed. In contrast, maltose reaction mixtures lead to formation of significant quantities [4].

New Device for Direct Extraction of Volatiles in Solid Samples Using SPME

A new device that allows extraction of volatiles from solid materials by SPME, avoiding preparation of the sample, was designed and tested in two different food products. Volatiles from dry-cured ham and canned liver sausage were analyzed by headspace SPME (HS SPME) and by using a new device that protects the SPME fiber in the core of the solid material. Volatile profiles generated by using both methods of extraction were very similar in both products. Compounds that have been previously highlighted as quality markers, such as products from oxidative degradation of lipids, products from Strecker degradation of amino acids, or terpenes, were satisfactorily extracted by SPME coupled to the device for direct extraction. In addition, by using this method no laboratory contaminants were extracted, whereas some major laboratory solvents were presented in the chromatogram using the HS SPME method. However, coefficients of variation were higher when performing the direct sampling procedure. This new device appears to have potential as a simple method for extracting volatiles in solid materials while at the same time avoiding taking samples.

Minor Strecker degradation products of phenylalanine and phenylglycine

Phenylalanine (Phe) was oxidized with either potassium peroxodisulfate or glyoxal. Volatile reaction products were isolated and analyzed by GC/FID and GC/MS. Nonvolatile products were derivatized with diazomethane and analyzed by the same methods. Under the experimental reaction conditions (equimolar ratio of reactants, 100 °C, 1 h), the decomposed amount of amino acid was 28% (glyoxal) and to 74% (peroxodisulfate), respectively. Sixteen volatile compounds having their origin in the amino acid molecule were detected and identified. The major compound was phenylacetaldehyde (208 mg/peroxodisulfate, 11 mg/glyoxal), followed by bibenzyl, benzaldehyde, and benzyl alcohol. Other products were present in concentrations lower then 0.1 mg. For comparison, the lower homologue of Phe, phenylglycine, was oxidized under the same conditions. Analogously, 21% (glyoxal) and 65% (peroxodisulfate) of this amino acid decomposed, predominantly to benzaldehyde (242 mg/peroxodisulfate, 95 mg/glyoxal). A minor decomposition product was benzoic acid (2.9 mg), other ten products arose at levels lower then 0.1 mg. The formation of minor oxidation products during Strecker degradation of amino acids suggests the importance of radical reactions. In systems comprising glyoxal, ten heterocyclic compounds arose as minor products (3-furancarbaldehyde, 5-methyl-2-furancarbaldehyde, 2-pyrrolcarbaldehyde, 3-phenylpyridine, pyrazine, methyl-, ethyl-, vinyl-, and 2-phenylethylpyrazine).

The influence of the pH value on the formation of Strecker aldehydes in low moisture model systems and in plant powders

Strecker aldehydes are regularly found in the low boiling point fraction of volatile compounds of processed plant foods. They are produced via the Strecker degradation of amino acids. The formation of 3-methylbutanal (3-MB) in a glucose- and leucine-containing low moisture model system and the formation of acetaldehyde, 2-methylpropanal, 2-methylbutanal and 3-MB in plant powders showed a linear pH dependence. The formation of the Amadori rearrangement product (ARP) fructose-leucine (fru-leu) in the model system, in contrast to it's degradation, was not influenced by the pH. The formation of the 3-deoxyosone [3-deoxy-d-erythro-hexos-2-ulose (3-DH)] by degradation of fru-leu was slower at pH 7 than at pH 5 suggesting that it is either less stable at pH 7 or being formed to a lesser extent. Further experimental results suggested that enolisation and retro aldol reactions of reducing sugars also contribute to the production of Strecker aldehydes as the pH is increased, by creating α-dicarbonyl compounds. The appearance of fructose in the glucose-containing model systems indicates enolisation reactions in the course of a Maillard reaction.

The Roles of Amino Acids and Sugars in the Production of Volatile Materials in Microwave Heated Tobacco Dust Suspensions

Abstract For the first time, the role(s) of selected amino acids and sugars in the production of volatile compounds in microwave prepared heat treated tobacco suspensions (HTTS) has been unambiguously defined. The role can be expressed in two major reaction pathways: 1) Strecker degradation of amino acids and 2) amino acid/sugar Maillard-type reactions. The mechanism of the Strecker degradation was confirmed by the addition of selected 13C- labelled amino acids to the reaction suspension. The addition of the amino acid resulted in a dramatic increase in the concentration of the specific, appropriate, low molecular weight Strecker aldehyde in the headspace above the reaction suspension. The mechanism of the amino acid/sugar Maillard-type reactions was substantiated by: 1) adding a wide array of amino acids to the suspension; 2) by employing 15N-labelled amino acids; and 3) employing 13C-labelled sugars. Addition of amino acids to the suspension followed by heat treatment resulted in significant increases (2 ×) in the concentration of volatile pyrazines relative to the control. Most amino acids significantly increased the concentration of headspace pyrazines. Reactivity differences, as a function of sugars, was also demonstrated. Analysis of the headspace above suspensions incorporating 15N-labelled amino acids and 13C-labelled sugars revealed the 15N and 13C atoms to have been distributed throughout a wide array of volatile pyrazines. The distribution of the 15N atoms within the pyrazines was unique to the amino acid and the distribution of the 13C atoms was linked to the type of sugar employed. These results have documented for the first time in a heat treated tobacco formulation the mechanisms of amino acids and sugars in the production of volatile compounds which have documented intense sensory characteristics.

Volatiles from interactions of Maillard reactions and lipids

This article provides current information on the production of volatile compounds from interactions of Maillard reactions and lipids. It includes a brief introduction outlining the Maillard reactions, the Strecker degradation of amino acids, and the oxidation of lipids. It highlights those compounds derived from these reactions that could interact to form volatile flavor components during the processing or cooking of food. The article discusses results obtained from model systems involving interactions between (1) Maillard reaction products and carbonyl compounds, (2) amino acids and carbonyl compounds, (3) amino acids and derivatives of fatty acids, and (4) Maillard reaction products, triglycerides and phospholipids. The qualitative and quantitative effects that triglycerides and phospholipids have on the formation of volatile Maillard products are also discussed. Particular attention is given to those long-chain alkyl heterocyclic compounds formed during these reactions, proposed methods for their formation, and their aromas. The role that such compounds play in food flavors is discussed with reference to those volatile compounds identified in certain cooked foods, such as meat (beef, lamb, and pork), chicken, potatoes (baked, French-fried, and crisps), and beverages (coffee, tea, and cocoa).