Inactivation of lactococcal bacteriophages in liquid media using dynamic high pressure

Abstract

Abstract Phosphate buffered saline, whey permeate (WP), and milk containing lactococcal bacteriophages c2, sk1 and ul36 (members of the phage species c2, 936, and P335 respectively) were submitted to dynamic high-pressure (DHP) treatments using a laboratory device. Bacteriophage inactivation was evaluated at 25°C, 100 and 200 MPa and 1, 3 or 5 passes. Inactivation was proportional to both pressure and number of passes. In buffer, a maximum inactivation of 5 log cycles was obtained with 200 MPa after 5 passes while the lowest inactivation was obtained with 100 MPa and 1 pass. Lactococcal bacteriophages were more resistant to DHP when spiked in milk and WP with maximum reductions of 2, 2.5 and 3 log cycles for c2, sk1 and ul36 respectively. Bacteriophage inactivation depended also on initial phage concentration. The highest reduction was obtained when the phage load did not exceed 10 4 PFU mL −1 . Heating milk or WP to 50°C prior to DHP treatment did not enhance inactivation. DHP thus seems to be an effective non-thermal method for significant inactivation of lactococcal bacteriophages.