Maillard reaction amino acid Strecker degradation

Another important aspect of the Maillard reaction involves the Strecker degradation of ot-amino acids. At elevated temperatures oe-dicarbonyl compounds, such as 3-deoxy glucosone, pyruvaldehyde, glyoxal, and dihydroascorbic acid will cause the degradation of an... 

Amino acids react with carbonyl compounds, forming azomethines. If the carbonyl compound has an electron-withdrawing group, e.g., a second carbonyl group, transamination and decarboxylation occur. The reaction is known as the Strecker degradation and plays a role in food since food can be an abundant source of dicarbonyl compounds generated by the Maillard reaction (cf. 4.2.4.4.7). The aldehydes formed from amino acids Strecker aldehydes) are aroma compounds (cf. 5.3.1.1). The ninhydrin reaction is a special case of the Strecker degradation. It is an important reaction for the quantitative determination of... 

Two branches of the above reaction pathways provide active reagents for the degradation of a-amino acids to aldehydes and ketones of one less carbon atom (Strecker degradation), which is another arm of the Maillard reaction. Strecker aldehydes from these reactions are important flavor compounds (18). 

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... 

In former experiments (5) we have shown that chemical analysis for Amadori compounds (mainly consisting of fructose-glutamic acid) and isovaleralde-hyde, formed by Strecker degradation of the amino acids leucine and isoleucine, can be used for an early detection of undesirable quality changes caused by the Maillard reaction. In order to demonstrate the usefulness of these compounds as indicator substances for quality improvement of dried products, we performed drying experiments with carrots as an example of plant products. 

Table I shows that an increase of Amadori compounds occurs parallel with an increase of isovaleraldehyde formed by Strecker degradation of the amino acid leucine (18 ). It becomes evident from Table I that the flavor impression "burnt arises if certain concentrations of isovaleraldehyde are exceeded this flavor change is increased by increasing isovaleraldehyde concentrations. By this means an analytical control of undesirable sensory changes caused by the Maillard reaction in carrots is available.

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. 

The flavors produced by the Maillard reaction also vary widely. In some cases, the flavor is reminiscent of caramelization. The Strecker degradation of a-amino acids is a reaction that also significantly contributes to the formation of flavor compounds. The... 

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... 

This product is probably formed by condensation (involving the Strecker degradation of an amino acid) of pyruvaldehyde with 2,3-pentanedione (Wang et al., 1969). It is formed in the Maillard reaction of the dipeptide Ala-Asp (alanine-aspartic acid) with glucose. 

Other possible mechanisms for the formation of pyrazines during smoking are possible. For instance, leaf carbohydrates could be degraded either through pyrolysis or Maillard reactions to form a-dicarbonyl compounds, which could, in turn, react with amino acids to undergo a Strecker degradation forming... 

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. 

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