Note: Ultra High Hydrostatic Pressure Inactivation of Escherichia Coli in Milk,and Orange and Peach Juices

Abstract

Inactivation of Escherichia coli by high hydrostatic pressure (UHHP) was determined in broth, milk and orange and peach juices inoculated with the bacteria. HHP ranged from 200 to 700 MPa at 25 C and different treatment times. No cell growth occurred in broth after 60, 25, 15, 10 and 7 min at 300, 400, 500, 600 and 700 MPa, respectively. Reduction of aerobic bacteria in milk and peach juice were 3.08 and 6.07 log units after 15 min at 400 MPa, respectively, while all bacterial cells were inactivated in orange juice. Sterilisation of raw milk contaminated with E. coli occurred at 600 MPa for 30 min, while peach and orange juices needed 12 and 10 min, respectively. The injury of cells in broth at 300 MPa ranged from 8.8 to 100% depending on magnitude of pressure and treated time. In general, inactivation of aerobic bacteria and E. coli was enhanced significantly (P<0.01) by increasing the pressure.