Sugar-Amino Acid Browning Polymers

Although a maximum rate of formation of pyrazines occurred at approximately aw 0.75 in the NFEM sanples in this study, one cannot assume that this would be the case in all types of foods or reaction systems. Addition of glycerol and hydrophilic polymers to sugar/amino acid systems has been demonstrated to shift the aw at which visible browning will occur (29, 34). It is more likely that the rate of pyrazine formation increases up to a maximum at an intermediate aw range and then decreases again, but not necessarily at aw 0.75. 

The browning reaction can be defined as the sequence of events that begins with the reaction of the amino group of amino acids, peptides, or proteins with a glycosidic hydroxyl group of sugars the sequence terminates with the formation of brown nitrogenous polymers or melanoidins (Ellis 1959). 

Possible Chemical Nature of the Sugar-amine Fluorophore In sugar-amine browning, the relative amount of the fluorophore is usually low. Adhikari and Tappel found 130 pmoles per mole of glucose based on an assumption of an amino-imino-propene moiety (11). The relative amount of acid reducing power is usually much higher (28). But of course it cannot be assumed, no matter how simple the system, that the polymer-bound fluorophore and reducing power reside in the same molecule. 

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