SURVIVAL OF PATHOGENS IN HIGH PRESSURE PROCESSED MILK

The aim of the study was to assess the ability of pathogens metabolic repair from injury within 10 days of refrigerated storage of milk after high pressure treatment. Two pathogenic strains - Listeria monocytogenes ATCC 7644 (LM) and Escherichia coli ATCC 25922 (EC) were inoculated in ultrahigh-temperature treated (UHT) milk at concentration of about 10(7) CFU mL(-1) and treated at 400, 500, 550, and 600 MPa for 15 min with inlet temperatures 20 degrees C, and then stored at 4 +/- 2 degrees C to evaluate survival and growth of pathogens. By increasing the applied pressure, an increased rate of the pathogens' inactivation was achieved. After 10 days of storage, milk treated at 400 MPa showed growth over 3.5 log CFU mL(-1) of L. monocytogenes and 1.7 log CFU mL(-1) of E. coli. In 550 MPa and 600 MPa treated milk samples after 8 and 10 days of storage colony formation occurred (3 CFU mL(-1) (550 LM) and 2 CFU mL(-1) (550 EC, 600 LM and 600 EC)). Although high pressure treatment is effective method for reducing of pathogenic bacteria, the metabolic repair from injury of bacterial cells in milk during storage should be considered.