Inactivation of Listeria monocytogenes by high hydrostatic pressure: effects and interactions of treatment variables studied by analysis of variance

High hydrostatic pressure is regarded as possible alternative method for fo od preservation. One of the primary considerations for industrial applicati ons is the ability of this method to eradicate pathogenic micro-organisms. This study subjected L. monocytogenes suspensions, in a phosphate buffer (p H 7.0) or in a citrate phosphate buffer (pH 5.6), to high hydrostatic press ure treatments relative to the following variables: pressure (200-600 MPa) treatment time (3, 10 and 20 min), temperature (4, 20 and 40 degrees C) and the pH of the suspension medium (5.6 and 7.0). An optimal design of 40 run s was obtained using the Fedorov algorithm and responses were studied by an alysis of variance in terms of cell survival on plate count agar. Efficienc y was determined by log(10) comparisons of the numbers of live cells before and after treatment. A statistically significant relationship was found be tween the four variables considered (pressure, pH, treatment time and tempe rature), their interactions (treatment time vs pressure, pH vs treatment ti me, pH vs pressure, pressure vs temperature, treatment time vs temperature) and the inactivation of L. monocytogenes. R-squared statistical analysis i ndicated that the linear model used accounted for more than 98.5% of the va riability in the inactivation of L. monocytogenes. (C) 2000 Academic Press.