Effect of pH and high pressure at sub-zero temperature on the viability of some bacteria

Abstract

The objective of this study was to investigate the viability of Escherichia coli and Staphylococcus aureus in apple juice after treatment with high pressure at sub-zero temperature and during subsequent storage at 5 and 20 °C. The viability of E. coli and S. aureus cells suspended in the apple juice with a pH of 3.8 did not decrease considerably after pressure treatment at 193 MPa and−20 °C. However, viability losses occurred during storage of samples after pressure treatment. Living cells of both strains were not detected in pressurized samples of apple juice stored for 10 days at 20°C. The lethal effect was lower when the samples after pressure treatment were incubated at refrigerated temperature; the number of E. coli and S. aureus decreased by 6 log cycles when the juice was stored for 10 days at 5 °C.

Keywords:

• high pressure
• sub-zero temperature
• inactivation of microorganisms
• pH

Acknowledgements

The authors express their gratitude to Professor Zdzisław E. Sikorski for the suggestions in making the final draft of this manuscript.