Inhibitor-Assisted High-Pressure Inactivation of Bacteria in Skim Milk

The combined inactivation effects of high hydrostatic pressure (HHP) and antimicrobial compounds (potassium sorbate and epsilon-polylysine [epsilon-PL]) on 4 different bacterial strains present in skim milk and the effect of these treatments on milk quality were investigated in this study. HHP treatment at 500 MPa for 5 min reduced the populations of Escherichia coli, Salmonella enterica Typhimurium, Listeria monocytogenes, and Staphylococcus aureus from 6.5 log colony-forming units (CFUs) or higher to less than 1 log CFU/ mL. Compared to HHP alone, HHP with potassium or epsilon-PL resulted in significantly higher reductions in the bacterial counts. After 5 min of treatment with HHP (500 MPa) and e-PL (2 mg/mL), no growth of E. coli, S. enterica Typhimurium, or L. monocytogenes in skim milk was observed during 15 d of refrigerated storage (4 +/- 1 degrees C). Scanning electron microscopy analysis revealed that the synergistic treatments caused more serious damage to the bacterial cell walls. Quality assessments of the treated samples indicated that the combined treatments did not influence the color, the turbidity, the concentrations of -SH group of the proteins, or the in vitro digestion patterns of the milk. This study demonstrates that HHP with potassium or e-PL may be useful in the processing of milk or milk-containing foods.