Purpose: This recent study investigated effects of elevated hydrostatic pressure on cell reduction and inactivation rates of L. monocytogenes at 4 and 55°C.
Methods: Various times (zero to 10 minutes) and intensity levels (zero to 380 MPa) of elevated hydrostatic pressure were investigated for inactivation of L. monocytogenes inoculated into phosphate buffered saline with target population of 7.5 log CFU/ml. Temperature was monitored, and maintained at 4 or 55°C by a circulating water bath with a stainless steel water jacket surrounding the chamber. The experiment was conducted in two biologically independent repetitions, as blocking factors of a randomized complete block design, containing three repetitions per time/temperature/pressure within each block. Experimental data was analyzed by the SAS GLM procedure using Tukey- and Dunnett-adjusted ANOVA. The inactivation Kmax and D-values were calculated using best-fitted (maximum R2) model obtained by GInaFiT software.
Results: At 380 MPa (zero to 10 minutes), a D-value of 2.81 min and inactivation Kmax of 1.60±0.41/min were observed at 4°C. At 55°C, these values were 1.59 and 3.94±0.96, respectively. At 4°C, the pathogen was reduced (P<0.05) by 3.84, 2.44, and 1.05 log CFU/ml after exposure to 10 minutes of hydrostatic pressure at 380, 310, and 240 MPa, respectively. These reductions (P<0.05) were >7.13, 6.36, and 4.53 for 10-minute treatments at 55°C, respectively. Treatments below two minutes were less efficacious (P≥0.05) against the pathogen in the vast majority of the tested time, temperature, and pressure combinations.
Significance: Results of this study could be incorporated as part of a risk assessment modeling and predictive microbiology for reducing the public health burden of listeriosis.