Methionine thermal degradation

Under the conditions corresponding to the roasting of coffee, serine, threonine, and sucrose yield various substituted pyridines (51), furans, and furanones (52). Thirty-three pyridine derivatives were identified by Baltes and co-workers (51), Recently, 3-methylthiomethylpyridine was identified as one of the products of thermal degradation of the glucose-methionine Amadori intermediates (53). 

Two patents (42-43) claim the contribution to meatlike flavors made by thiamine when it is present in the standard pyrolytic mixture. Arnold et al. (44) have reported on the volatile flavor compounds produced by the thermal degradation of thiamine alone. It is generally agreed that the presence of methionine, the other sulfur-containing amino acid in the flavor-developing mixture, produces negative and/or undesirable results. However, one patent (45) specifies methionine in a standard Maillard procedure, and no cysteine. 

Most of the original patents referring to meat flavors utilizing Maillard technology vere claimed by Unilever (48-52 56,57). More recent patents are involved with the production of meat-like flavors. While a majority of patents are concerned vith cysteine, cystine, or methionine as the sulfur source, others claim alternatives such as mercaptoacetaldehyde, mercaptoalkamines, etc. Several patents (53,54), declare the contribution to meat-like flavors produced from thiamine in the Maillard reaction. Alternately, a technical report describes the volatile flavor compounds produced by the thermal degradation of thiamine alone (55). 

It has been identified in the products of thermal degradation of cysteine and xylose in tributyrin (Ledl and Severin, 1973). It was found in a heated cysteine/glucose model system by Sheldon et al (1986) and in serine/threonine/sucrose model systems (as well as in coffee) by Baltes and Bochmann (1987a). Silwar and Tressl (1989) studied a model reaction involving heating cysteine and methionine with 2-furaldehyde (1.63) under roasting conditions and they found that an important part of the aldehyde is reduced to furfuryl alcohol. 

The thermal generation of flavor is a very essential process for the "taste" of many different foodstuffs, e.g. cocoa, coffee, bread, meat. The resulting aromas are formed through non-enzymatic reactions mainly with carbohydrates, lipids, amino acids (proteins), and vitamins under the influence of heat. Thiamin (vitamin B ) and the amino acids, cysteine and methionine, belong to those food constituents which act as flavor precursors in thermal reactions. The role of thiamin as a potent flavor precursor is related to its chemical structure which consists of a thiazole as well as a pyrimidine moiety. The thermal degradation of this heterocyclic constituent leads to very reactive intermediates which are able to react directly to highly odoriferous flavor compounds or with degradation products of amino acids or carbohydrates. 

In Figure 13 various degradation compounds of the thermal reaction of thiamin and methionine are presented. Fortunately, we were able to identify most of the main volatile compounds. The then unknown structures in our previous paper [77, Figure 6A] with numbers (29) and (31) correspond to numbers 3 and 7 above. Two other main compounds, 2-(2-hydroxyethyl)-3-methyl-4-(methylthiomethyl)thiophene 19 (42) and 2-(2-methylthioethyl)-3-methyl-4-formylthiophene 20 (41), which account for approximately 1% and 0.6% (relative GC area) were numbered in [77, Figure 6A] as (42) and (41). Their H-NMR and mass spectra are depicted in... 

Sugar degradation products were determined as benzimidazole derivatives after reaction with o-phenylenediamine. More than 120 amino-acid specific Maillard products have been isolated and identified from the reaction of L-proline, hydixn roline, < teine and methionine with monosaccharides at 150° for 1-1.5 h, in connection with studies of thermally generated aromas. Proline derived components were important constituents of bread, malt and beer, and cysteine and methionine derived components were predominant in roasted coffee and meat flavours. The effects of temperature, pH, and the relative concentration of rhamnose and proline on the quantity of specific volatiles produced in the Maillard reaction of these substrates have been studied, and the data have been analysed 1 computer methodology. The glucosylated cyclopentenone (44) was one of the products of decomposition of the Amadori product 1-deoxy-l-piperidino-maltulose in warm water. ... 

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