Effect of High Hydrostatic Pressure on Escherichia coli and Pseudomonas fluorescens Strains in Ovine Milk

Ovine milk that had been standardized to 6% fat was inoculated with Escherichia coli 405 CECT and Pseudomonas fluorescens 378 CECT at a rate of 106 and 107 cfu/ml, respectively, and treated with high hydrostatic pressure. Treatments consisted of combinations of pressure (300, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50°C), and time (5, 10, and 15 min). Inactivation (>6 log cfu/ml) of both strains was observed at 50°C for all pressures and treatment times. A similar level of inactivation occurred at >450 MPa and 25°C for E. coli and at >400 MPa and 10°C for P. fluorescens. Destruction was lowest at 10°C for E. coli and at 25°C for P. fluorescens. The test strain of E. coli was more baroresistent than was the P. fluorescens strain.