Strecker degradation of amino acid

The formation of aldehydes (flavorings) in roasting of cocoa beans, for example, is caused by Strecker degradation of amino acids. 

Several mechanisms have been reported for pyrazine formation by Maillard reactions (21,52,53). The carbon skeletons of pyrazines come from a-dicarbonyl (Strecker) compounds which can react with ammonia to produce ot-amino ketones as described by Flament, et al. (54) which condense by dehydration and oxidize to pyrazines (Figure 6), or the dicarbonyl compounds can initiate Strecker degradation of amino acids to form ot-amino ketones which are hydrolyzed to carbonyl amines, condensed and are oxidized to substituted... 

Figure 5. Formation of secondary reaction products involved in production of l-(methylthio)ethanethiol by Strecker degradation of amino acids. (Reproduced from Ref. 49. Copyright 1972, American Chemical Society.)...

Figure 2.10. Strecker degradation of amino acids and a-dicarbonyls to form heterocyclic compounds. For glycine, R = H. Reprinted with permission from Wong, J. W., and Shib-amoto, T. (1996). Geotoxicity of the Maillard reaction products. In The Maillard Reaction. Consequences for the Chemical and Life Sciences, Ikan, R., ed., John Wiley Sons, Chichester, UK, 129-159.

The identification of 49 pyrazines in heated beef and other meats has been extensively revieved (32, 43). Several mechanisms have been proposed for pyrazine formation by the Maillard reaction. Dlcarbonyl compounds can initiate Strecker degradation of amino acids to yield ot-amino ketones, vhich in turn can undergo condensations and oxidizations to form substituted pyrazines (13). 

Heterocyclic aroma compounds found in meat primarily arise from interactions between mono- and dicarbonyl compounds, H2S and ammonia. The carbonyl compounds are derived from the Maillard reaction, including Strecker degradation of amino acids, oxidation of lipids and aldolization reactions. H2S is produced by thermal degradation of sulfur amino acids and ammonia by amino acid pyrolysis. 

Chemical oxidation reactions and Strecker degradation of amino acids may also result in aldehyde formation (16). These reactions are important for the formation of acetaldehyde in baked or heated Sherries. Chemical oxidation reactions catalyzed by metal ions (Cu, Fe, Mn, Mo) can result in aldehyde production in oak aged distillates (20). Such reactions may also result in the formation of oxidation products from fatty acids released during the secondary fermentation of sparkling wines (21). 

Strecker [34] discovered that the reaction between amino acids (glycine, alanine, leucine) and the tricarbonyl compound alloxan yields CO2 and aldehydes. The Strecker degradation of amino acids occurs also with dicarbonyl compounds [35] including those that are formed in the course of the Maillard reaction, in particular deoxyglycosones and some of the smaller sugar fragments like 7 and diacetyl. Fig. 3.22 shows the reaction pathway that involves the formation of an imine 8, followed by decarboxylation and liberation of the resulting aminoketo compound and the Strecker aldehyde from the intermediate 10. Odour-active Strecker aldehydes which... 

Thiols are another key group of odor compounds in coffee, these are formed due to Strecker degradation of amino acids like mediionine to give mediional and die reaction of H2S (formed by the degradation of Cysteine) with fiiraldehydes, namely the formation of 2-furylthiol (62). 

The main reactions that lead to the formation of flavor can be listed as Maillard reactions, the Strecker degradation of amino acids, lipid oxidation and microbial and enzymatic reactions, and interactions between lipids, proteins, and carbohydrates. 

Proteins affect several sensory properties such as appearance, color, texture, and flavor. Although most proteins have little flavor, they influence perceived flavor because they may contain bound off-flavors modify flavor by selective binding produce off-flavors or act as precursors of flavors through the Strecker degradation of amino acids [79]. 

G. P. Rizzi, The Strecker degradation of amino acids Newer avenues for flavor formation, Food Rev. Int., 24 (2008) 416-435. 

Oxidation of amino acids by oxidising agents, which generates carbon dioxide, ammonia and a carbonyl compound containing one less carbon atom than the starting amino acid, is called a Strecker degradation of amino acids (Table 2.26). 

Flqure 2.43 General scheme of Strecker degradation of amino acids. 

Decarboxylation of amino acids can also proceed as a non-enzymatic reaction. Analogously to the enzyme catalysed decarboxylations, amines are formed as byproducts of the Strecker degradation of amino acids and by thermal decarboxylation of amino acids, especially of sulfur amino acids, hydroxyamino acids and aromatic amino acids. For example, thermal decarboxylation and subsequent reactions of cysteine and cystine produce ammonia... 

By retro-aldol cleavages of the 1-deoxyosone short-chain dicarbonyls like diacetyl, methylglyoxal or hydroxydiacetyl are formed which - like the deoxyosones - may participate in the Strecker degradation of amino acids, thus creating volatile flavor components 17,18). On the other hand, the 1-deoxyosone undeigoes several cyclization reactions yielding e.g. acetylfiiran, maltol, isomaltol, furaneol and 5-hydroxy-5,6-dihydromaltol (DHM) (75). 

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