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

¹ Unit of Food Technology, Faculty of Veterinary, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain

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.

Key Words: hydrostatic pressure • Escherichia coli • Pseudomonas fluorescens • ovine milk

Submitted on October 30, 1995
Accepted on May 6, 1997

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