Method for Use of a Differential Scanning Calorimeter for Determination of Bacterial Thermal Death Times

A differential scanning calorimeter was used as an accurately controlled method of heat-treating suspensions of Staphylococcus aureus strains S6 and MF31 in 0.85% saline. D-values obtained at 52, 55, 60 and 65°C were 23.6, 9.4, 0.6 and 0.09 min, respectively, for strain S6, and 22.9, 5.0, 0.4 and 0.9 min, respectively, for MF31. Resulting thermal death time plots were linear; z-values were 5.1°C for S6 and 5.3°C for MF31. This method has potential application in milk and other liquid food systems to simulate high-temperature, short-time heat treatments. One trial of heating strain MF31 at 65°C in whole milk and in milk concentrated 1.35 × (fat basis) by ultrafiltration and l.36 × by reverse osmosis showed an increase in average D-values from 8.6 s in the whole milk to 9.2 s in the ultrafiltered milk and 10.5 s in the reverse osmosis-concentrated milk. The difference in D-values between the whole milk and the reverse osmosis-concentrated milk was significant.