Maillard deoxyosone

HjO / pH - 5) are 2- and 3-mercaptopropionic-, furan-, and thiophene carboxylic acids, which amount to 40 to 80 % of the volatile Maillard products. The furan- and thiophene carboxylic acids are formed via 3-deoxyosone and the mercaptoacids via 1-deoxyosone (Figure 6). By dehydration, addition of H 0 (or by Strecker degradation of Cys) and reduction of the carbonyl group, furfuryl-mercaptan (the impact component of roasted coffee) results. 2-Hydroxymethyl-4-thiolanone, which may be formed by the same route, was identified for the first... 

The furanic aldehydes 5-(hydroxy-methyl)furfural and 2-furaldehyde, systematically present in the toasted wood, can be formed by the thermal degradation of 3-deoxyosone during sugar pyrolysis or Maillard reactions (27). They could also be formed from glyceraldehyde, coming from degradation of DDMP, by condensation with subsequent elimination of water or formaldehyde (24). 

As expected, pentoses react similarly to hexoses in the Maillard reaction, with the formation of 1- and 3-deoxyosones. However, the initial two-carbon fragment formed from the reaction of xylose with alanine is not the glycolal-dehyde expected from retro-aldolisation of the Amadori rearrangement product, but glyoxal, for reasons which are not clear. ... 

The reaction products of the Maillard reaction, such as l-amino-l-deoxy-2-ketose (Amadori product) or 2-amino-2-deoxyaldose (Heyns product), do not contribute to flavor directly but they are important precursors of flavor compounds [48]. These thermally unstable compounds undergo dehydration and deamination reactions to give numerous rearrangement and degradation products. The thermal degradation of such intermediates is responsible for the formation of volatile compounds that impart the characteristic burnt odor and flavor to various food products. For example, at temperatures above 100 C, enolization products (such as l-amino-2,3-enediol and 3-deoxyosone) yield, upon further dehydration, furfural from a pentose and 5-hydroxy methylfurfural and 5-meth-ylfurfural from a hexose [2]. 

F. Hayase, Recent development of 3-deoxyosone related Maillard reaction products, Food Sci. Technol. Res., 6 (2000) 79-86. 

Amadori products are only intermediates formed in the course of the Maillard reaction. In spite of their limited stability, these products can be used under certain conditions as an analytical indicator of the extent of the heat treatment of food. Unlike the acidic (pH <3) and alkaline (pH >8) sugar degradation reactions, the Amadori compounds are degraded to 1-, 3-, and 4-deoxydicarbonyl compounds (deoxyosones) in the pH range 4-7. As reactive a-dicarbonyl compounds, they yield many secondary products. Formulas 4.54. 57 summarize the degradation reactions starting with the Amadori compound. 

The stable secondary products of the Maillard reaction, that are isolated from many different reaction mixtures and have known structures, can be generally assigned to a definite deoxyosone by a series of plausible reaction steps (enolization, elimination of water, retroaldol cleavage, substitution of an amino function for a hydroxy function etc.). 

The reactions between a-dicarbonyl compounds, like the deoxyosones obtained in the Maillard reaction, and amino acids are classed under the term Strecker reaction. This reaction leads to the formation of aldehydes (Strecker aldehydes), CO2 and a-aminoketones on oxidative decarboxylation of the a-amino acids (Formula 4.88). It occurs in foods at higher concentrations of free amino acids and under more drastic reaction conditions, e. g., at higher temperatures or under pressure. 

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