Melanoidins flavours

The Amadori compound may be degraded via either of two pathways, depending on pH, to a variety of active alcohol, carbonyl and dicarbonyl compounds and ultimately to brown-coloured polymers called melanoidins (Figure 2.31). Many of the intermediates are (off-) flavoured. The dicarbonyls can react with amino acids via the Strecker degradation pathway (Figure 2.32) to yield another family of highly flavoured compounds. 

The properties of the melanoidin complexes depend upon the nature of the amino compound and sugar from which they are prepared. They have characteristic flavours no doubt due, in part, to the relevant aldehydes. For example, the melanoidin from ammonia has been described as bitter [24], that from glycine reminiscent of bread crust [24] or beers [25] and that from... 

The importance of Strecker degradation is mainly in the formation of reactive and often sensory active aldehydes and ammonia (free or bound in reactive a-amino carbonyl compounds). Strecker aldehydes, together with a-amino carbonyl compounds, contribute significantly to the formation of many heterocyclic compounds (which are important flavour-active components of processed foods) and the brown pigments melanoidins. Aldoses simultaneously produce the corresponding 2-deoxyaldoses or 1-amino-1-deoxyalditols and 2-oxoacids. 

Following the formation of the deoxyketosyl derivative, the reactions leading to the formation of the brown pigments or melanoidins (Fig. 3) are not well defined. These reactions, however, are responsible for numerous flavours and odours, possibly for toxicity, and for a further reduction in protein nutritive value via destruction of amino acids and reduced digestibility. There are thought to be three main pathways in the advanced Maillard reaction. 

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