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 Maillard reaction was investigated using aqueous model systems. The reaction mixtures consisted of four amino acids, glycine, lysine, cysteine and methionine, heated individually with ribose at five pH values between 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 decreased as the pH was raised. Nitrogen-containing compounds, such as pyrazines were detected at higher pHs, with the lysine model system producing the largest quantities of nitrogen-containing heterocyclic compounds. The major products of the methionine systems were dimethyl disulphide 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 large number of sulphur-containing compounds, including 2-methyl-3-furanthiol, a compound with a strong meaty aroma, whose formation was greatly favoured by lower pH.