Inactivation of bacteriophages by thermal and high-pressure treatment

Dairy companies commonly experience fermentation failures due to bacteriophages that are spread mainly by milk, whey or air. Heat or high-pressure treatment may potentially reduce the phage titre, but further knowledge about the inactivation kinetics is desirable. Inactivation experiments were carried out with the commonly occurring lactococcal phages P001 and P008. Phage suspensions in calcium-enriched M17-broth were heated at 55-80 °C, or high-pressure treated at up to 600 MPa. Kinetic analysis showed that the order of inactivation reaction was above 1; thus, inactivation kinetics were approximated by a non-linear regression model. The Arrhenius parameters, rate constant, kp,T, and activation energy, EA (for heat treatments), and the volume of activation, ΔV# (for pressure treatments) were calculated. Both measured and calculated results indicate that phage P008 was the more heat- and pressure-resistant of the two. By combining the results from heat and pressure inactivations, a pressure-temperature diagram for phage P008 was established.