Maillard reaction scheme

Scheme 12.1 Initial steps in the Maillard reaction showing the formation of an Amadori compound...

Hydrogen sulphide is a key intermediate in the formation of many heterocyclic sulphur compounds. It is produced from cysteine by hydrolysis or by Strecker degradation ammonia, acetaldehyde and mercaptoacetaldehyde are also formed (Scheme 12.4). All of these are reactive compounds, providing an important source of reactants for a wide range of flavour compounds. Scheme 12.6 summarises the reactions between hydrogen sulphide and other simple intermediates formed in other parts of the Maillard reaction. 

Scheme 12.6 The formation of heterocyclic aroma compounds from the reaction of hydrogen sulphide with intermediates of the Maillard reaction...

The routes involved in the formation of the various furan sulphides and disulphides involve the interaction of hydrogen sulphide with dicarbonyls, furanones and furfurals. Possible pathways are shown in Scheme 12.8. Furanthiols have been found in heated model systems containing hydrogen sulphide or cysteine with pentoses [56-58]. 2-Methyl-3-furanthiol has also been found as a major product in the reaction of 4-hydroxy-5-methyl-3(2H)-furanone with hydrogen sulphide or cysteine [21, 59]. This furanone is formed in the Maillard reaction of pentoses alternatively it has been suggested that it may be produced by the dephosphorylation and dehydration of ribose phosphate, and that this may be a route to its formation in cooked meat [21, 60]. 

Scheme 12.8 Routes for the formation of furanthiols, sulphides and disulphides in the Maillard reaction...

Methionine can be obtained from enzymatic protein hydrolysates or from petrochemical sources. To a lesser extent than cysteine, it is a raw material in Maillard reactions for the preparation of process flavours and it can also be utilised as a precursor for the chemical preparation of the sulfide methional, which is an important flavour constituent for potato, malt, seafood and many other flavours. Methional can be reduced to methionol, which can be esterified with organic acids to, for instance, methionyl acetate and methionyl butyrate, which are useful compounds for pineapple and other fruit flavours (Scheme 13.16). 

It is of importance to investigate the relation of free radical formation to formation of the main intermediates in the generally accepted scheme of the Maillard reaction (1), especially in connection with the potential route b mentioned above. 

A summary of the Maillard Reaction 1s given 1n Scheme 1 (4). The first step Involves the condensation between the carbonyl group of a reducing sugar, and the free amino group of an amino acid or peptide to produce a N-glycosylamine or fructosylamine. These... 

It is worth noting that Mauron7 calls the three stages Early, Advanced, and Final Maillard reactions, respectively. The way these reactions fit together is outlined in Scheme 1.1. The final products of nonenzymic browning are called melanoidins to distinguish them from the melanins produced by enzymic browning. Theoretically, the distinction is clear however, in practice, it is very difficult to classify the dark-brown products formed in foods, since they tend to be very complex mixtures and are chemically relatively intractable. 

Scheme 2.3 Maillard reactions the two major pathways from Amadori compounds to melanoidins (based on Hodge213)...

Colour formation, which lies well beyond the early-stage Maillard reaction, has been described by Wedzicha and Leong118 by the following scheme (DH = deoxy-hexosone) ... 

Jousse et al.130 have surveyed the data available on the kinetics of aroma formation by the Maillard reaction and have assembled a simplified, but broadly based, kinetic scheme, as outlined in Scheme 3.3. 

F. Jousse, T. Jongen, W. Agterof, S. Russell, and P. Braat, Simplified kinetic scheme of flavor formation by the Maillard reaction, J. Food Sci., 2002, 67, 2534-2542. 

As illustrated in O Scheme 65, 33 reacts with an amine to give an imine 326 that isomerizes into an aminoketose 327 (Amadori product), existing as an equilibrium mixture of cyclic hemi-acetals, whereas 40 affords, by way of 328, the hexosamine derivatives 329 and 330 (Heyns products), also in cyclic form The Amadori-He)ms compounds index Amadori-Heyns com-pounds % are at the head of the complex sequences of the Maillard reaction. The crystal structure of the Amadori product 331 between 33 and glycine has been determined more than three decades after the first proposal of its structure. Alternative preparations and X-ray analyses of Heyns products 332 and 333 have been reported [273,274]. 

In 1953 Hodge [22] published a scheme giving an excellent overview of the complexity of the Maillard reaction. Fig. 3.18 shows a more simplified scheme of the Maillard reaction. 

Figure 1 Scheme for the binding of protein with polysaccharide through Maillard reaction (a) and the binding mode (b). Dotted areas indicate protein molecules, and branched solid circles represent polysaccharide molecules. (From Ref. 25.)... 

The Maillard reaction has been named after the French chemist Louis Camile Maillard who first described it. Hodge [169] developed the first coherent scheme in 1953. This first scheme has been modified by Martins et al. [5] (Figure 11.8). The mechanism of the reaction is taught to occur at seven steps (A-G) with three main steps as initial, intermediate, and final stage ... 

Dehydration of the carbohydrate portion in fiuctosamines probably proceeds through a series of enolic intermediates (Scheme 31), whieh eventually tautomerize into a-dicarbonyl stractures such as 60, 62, and 63, or cycUze into 2-furoylmethyl-amines (61) and many other heterocyclic derivatives. One of the major products of D-fructosamine degradation that occurs through the 1,2-enoUzation pathway is 3-deoxy-D-e 7 /jro-hexos-2-ulose (60), which is regarded as one of the most important intermediates in the Maillard reaction both in foods and in vivo ... 

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