Maillard reaction, mechanism

The reaction pathways for the Maillard Reactions have been studied and reviewed by many researchers since Dr. Maillard s early work (4—6) These papers give a concise outline of the major chemical pathways identified in the Maillard Reaction Mechanism. In heat treated meat with nearly 75% of those volatiles generated are pyrazines derivatives (7). Those pyrazines have been found to play an important role in developing a roasted flavor in heated products. They will be discussed later. 

Whereas this study is concerned mainly with Maillard browning and nonvolatile products formed near neutral pH, a recent report by Mottram and Norbrega described the accelerating effects of phosphate and phdialate ions on the formation of flavor volatiles in a cysteine/ribose system at acidic pH (8). The catalytic activity of phosphate at acid pH suggested the involvement of dihydrogen phosphate ion in die Maillard reaction mechanism. 

Fig. 6.25. Simplified mechanism of two degradation reactions between peptides and reducing sugars occurring in solids, a) Maillard reaction between a side-chain amino (or amido) group showing the formation of an imine (Reaction a), followed by tautomerization to an enol (Reaction b) and ultimately to a ketone (Reaction c). Reaction c is known as the Amadori rearrangement (modified from [8]). b) Postulated mechanism of the reaction between a reducing sugar and a C-terminal serine. The postulated nucleophilic addition yields an hemiacetal (Reaction a) and is followed by cyclization (intramolecular condensation Reaction b). Two subsequent hydrolytic steps (Reactions c and d) yield a serine-sugar conjugate and the des-Ser-peptide...

Hydroxy-2-methyl-4//-pyran-4-one (maltol) and 2-acetyl-3-hydroxy-furan (isomaltol) are also products of the Maillard reaction. Both have a considerable history, due to their early detection in beer and breads. A mechanism based upon the pyranose form of a methyl-a-dicarbonyl inter-... 

Several other non-nitrogenous products have been identified as products of the Maillard reaction. These include butanol, butanone, butane-dione, and pentane-2,3-dione as well as dihydroxyacetone, glycer-aldehyde, and D-erythrose. Obviously, the same products are present after mild acidic or basic degradation of carbohydrates. Thus, the necessity of an amine or amino acid in the mechanism of their formation is uncertain. 

Fu MX, Wells-Knecht KJ, Blackledge JA, Lyons TJ, Thorpe SR and Baynes JW (1994) Kinetics, mechanisms, and inhibition of late stages of the Maillard reaction. Diabetes 43, 676-683. 

Glomb MA and Monnier VM (1995) Mechanism of protein modification by glyoxal and glycolaldehyde, reactive intermediates of the Maillard reaction. J Biol Chem 270, 10017-10026. 

P. de Lange (3 1 ) of the Central Institute of Food Research (Centr. Inst. Voedingonderzoek), Utrecht, Netherlands reviewed the mechanism of the Maillard reaction, though his title did not show the term. 

A New Mechanism of the Maillard Reaction Involving Sugar Fragmentation and Free Radical Formation... 

The mechanism proposed by Hodge in 1953 U) for the early stages of the Maillard reaction, involving the Amadori rearrangement as a key step, has been accepted over a quarter of a century as a most apt description. Here, we propose a new mechanism... 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

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