Phase transitions during high pressure treatment of frozen carrot juice and influence on Escherichia coli inactivation

- Phase transition in frozen carrot juice was evaluated under HP at room temperature.
- Transition to Ice III was observed at pressures above 350 MPa.
- Special container was used to maintain frozen conditions during treatment.
- Enhanced inactivation of E. coli was demonstrated in frozen carrot juice.
- Substrate state, phase transition and pressure level influenced inactivation.

Influence of high pressure (HP) treatment (200-400 MPa; 0-10 min) on phase transition behavior of frozen carrot juice and the resulting influence on the inactivation kinetics of Escherichia coli ATCC 25922 were evaluated. Experiments were carried out in a specially designed container to prevent heat exchange from the environment, except for the compression heating and decompression cooling. Solid to solid and solid to liquid transitions were recognized during HP treatment. Transition to Ice-III was observed from the temperature-pressure profiles when the application pressure was >350 MPa. Inactivation of E. coli in frozen carrot juice followed the first order kinetics with D values between 2.62 and 2.12 min at 300-400 MPa pressure levels, much shorter than those observed in unfrozen carrot juice. The combination of frozen state, phase transition status and pressure level likely contributed to the better inactivation of E. coli in frozen carrot juice.