Pressure-induced inactivation of bacteria through pressure-assisted thawing using a thermal buffer zone.

- To maintain Isothermal conditions in samples, it was necessary to use thermal buffer.
- Pressure-assisted thawing with thermal buffer achieved high levels of microbial inactivation; around 6-log reduction.
- High inactivation rates took place at the thermal plateau under constant pressure.
- The longer the thermal plateau, the higher the level of microbial inactivation.

Effect of thermal buffer zone was examined on the microbial inactivation through a pressure-assisted thawing. A plastic bag of bacterial suspension enclosed with a thermal buffer zone was frozen at − 50 °C, and treated for 20 min with a pressure-assisted thawing in water of 4 °C. A reduction of 8-log cycle was obtained at 200 MPa for the stationary growth phase cells of Escherichia coli that was suspended in 1% skim milk and enclosed with wheat flour/water paste and two polytetrafluoroethylene plates. When 100% ethanol was used as a thermal buffer and the samples were pressured at 194 MPa in 1% skim milk, levels of E. coli and Listeria monocytogenes were reduced by 6-log cycle and 7-log cycle, respectively. Staphylococcus aureus decreased by 4-log cycle.Industrial relevanceThis work will contribute to new developments in the pressure processing of foods, since the use of a thermal buffer zone in pressure-assisted thawing was very effective in enhancing the level of pressure-induced microbial inactivation.