Formation by Maillard reaction

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... 

Figure 6. Mechanisms of Sotoion formation by Maillard reaction (21).

N, S and 0 heterocyclic compounds, along with noncyclic sulfur compounds and hydrocarbons, are predominant in "meaty" flavor volatiles. The mechanisms of heterocyclic formation by Maillard and pyrolysis reactions have been reviewed by Vemin and Parkanyi (57) and the Maillard reaction itself is a recurring subject of review (58). Since other speakers contributing to this volume will discuss these aspects of meat flavor, they will not be repeated in this presentation. 

Figure 15. Formation of volatile compounds with toasty aromas by Maillard reactions between sugar molecules and amino acid residues when wood is heated...

This is an essential class for the formation of aroma compounds, mainly by caramelization of the low-molecular-weight sugars and by Maillard reaction with the amino acids (see Section 3.1). 

Tressl R. (1981) Formation of aroma compounds by Maillard reaction. 9th Int. Colloq. Chem. Coffee (London, 16-20.6.1980) (ASIC, 1981), 55-76. 

Saccharomyces cerevisiae was cultivated with potato protein liquor (PPL) and glucose (starch hydrolysate) as substrate. Before the start of the cultivation PPL was sterilized at various temperatures between 80 and 120 °C for different periods between 5 s and 30 min [27]. The foaminess of PPL was very low before the sterilization. The foaminess increased with the temperature and time during sterilization and, at 120 °C and 30 min, 2 was enlarged by a factor of 2x10. This effect is due to the denaturation of proteins [4] and the formation of Maillard reactions between reducing sugars and amino adds [28]. 

After the different industrial steps of fractionation and refining, the starch obtained exhibits some traces of lipids, gluten and phosphate. These co-products may affect the properties of the starch - e g. by the formation of lipid complexes, or by Maillard reactions (with gluten) at the processing stage [XIE 12]. 

The corrosive effects to be considered (mainly simple corrosion of metals) are, as would be expected from the edible nature of foodstuffs which are not excessively either acidic or basic but which may contain sulphur, less severe than those often encountered with inedible materials containing reactive substances. The importance of corrosive efiects where foodstuffs are concerned lies not so much in the action of the foodstuffs on the metal involved as in the resultant metal contamination of the foodstuff itself, which may give rise to off-flavours, in the acceleration of other undesirable changes (by the Maillard reaction for example), and in the possible formation of toxic metallic salts. Metal ions generally have threshold values of content for incipient taste effect in different liquid foodstuffs. Except in the case of the manufacture of fruit juices and pickles, process plant failure through corrosion must be rare. Nevertheless all foodstuffs, particularly liquid ones, should be regarded as potentially corrosive and capable of metal pick-up which may be undesirable. 

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...

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