Kinetic modelling of the formation of sulphur-containing flavour components during heat-treatment of milk

Multiresponse modelling was used to construct a mechanistic model for the changes in volatile sulphur components and protein-bound sulphydryl groups in skimmed and semi-skimmed milk, subjected to a broad range of heat-treatments. The model yielded an acceptable fit for all measured components: hydrogen sulphide, methanethiol, dimethyl sulphide, dimethyl disulphide and carbonyl sulphide, and in addition protein-bound masked-SH, free-SH and S–S bonds. However, this acceptable fit was obtained only if the model contained not previously described reactions of carbonyl sulphide and dimethyl sulphide into unknown components X and Y. The model could be used to calculate reference reaction rate constants and activation energies in skimmed milk and 1.5% fat milk with fair accuracy. Constants and energies were different for the two milk types, showing that formation and/or release of volatiles is very product specific. A formation/degradation kinetic model was used to describe the change in cooked flavour. Formation and disappearance of cooked flavour correlated well with that of methanethiol, and activation energies were similar.