THE EFFECT OF PH ON THE FORMATION OF VOLATILE COMPOUNDS IN MEAT-RELATED MODEL SYSTEMS

The effect of small pH changes on volatile compounds produced in the M aillard reaction was investigated using aqueous model systems. The rea ction mixtures consisted of four amino acids, glycine, lysine, cystein e and methionine, heated individually with ribose at five pH values be tween 4.5 and 6.5. The colour, the overall aroma and the nature of the volatile compounds were all influenced by pH. At low pHs, 2-furfural was a major product of all the model systems, but its concentration de creased as the pH was raised. Nitrogen-containing compounds, such as p yrazines were detected at higher pHs, with the lysine model system pro ducing the largest quantities of nitrogen-containing heterocyclic comp ounds. The major products of the methionine systems were dimethyl disu lphide and 3-(methylthio)propanal and, as the pH increased, the latter compound showed a small decrease in concentration, while an increase in the disulphide was observed. The cysteine model system led to a lar ge number of sulphur-containing compounds, including 2-methyl-3-furant hiol, a compound with a strong meaty aroma, whose formation was greatl y favoured by lower pH.