Effect of glyceraldehyde on the kinetics of Maillard browning and inhibition by sulphite species

The kinetics of browning (A470) are reported for glyceraldehyde+glycine and glucose+glycine+glyceraldehyde mixtures ([glucose]=0–1 mol l−1; [glycine]=0–1 mol l−1; [glyceraldehyde]=0–10 mmol l−1; pH 5.5, [acetate buffer]=0.2 mol l−1 with respect to acetate ion; 55°C). In the absence of glucose the rate of reaction depends only on glyceraldehyde concentration, whereas glycine is required for colour development. The rate of browning when all 3 reactants are present is much greater than calculated as the sum of the individual glyceraldehyde+glycine and glucose+glycine reactions. This synergistic behaviour is accompanied by the removal of the induction phase normally seen for the Maillard reaction, and a browning reaction whose kinetics depend on the concentrations of all 3 reactants. The apparent dissociation constant of the hydroxysulphonate of glyceraldehyde is 6.76×10−5 mol l−1 (pH 5.5, 55°C, ionic strength≈0.2 mol l−1). Theoretical calculations suggest that the conversion of glyceraldehyde to its hydroxysulphonate could contribute to the mechanism of the inhibition of Maillard browning by sulphite species.