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The aim of this work was to evaluate the bactericidal efficacy of ultrahigh-pressure homogenization (UHPH) against Listeria innocua ATCC 33090 inoculated into milk and orange juice. We also intended to study the effect of inlet temperature on the lethality and production of sublethal injuries in this microorganism and its ability to survive, repair, and grow in refrigerated storage after UHPH treatment. Samples of ultrahigh-temperature whole milk and ultrahigh-temperature orange juice inoculated at a concentration of approximately 7.0 log (CFU per milliliter) were immediately pressurized at 300 MPa on the primary homogenizing valve and at 30 MPa on the secondary valve, with inlet temperatures of 6.0 +/- 1.0 degrees C and 20 +/- 1.0 degrees C. L. innocua viable counts and injured cells were measured 2 h after UHPH treatment and after 3, 6, and 9 days of storage at 4 degrees C for milk and after 3, 6, 9, 12, 15, 18, and 21 days of storage at 4 degrees C for orange juice. Both the inlet temperature and the food matrix influenced significantly (P < 0.05) the inactivation of L. innocua, which was higher in whole milk at the 20 degrees C inlet temperature. The UHPH treatment caused few or no sublethal injuries in L. innocua. During storage at 4 degrees C after treatments, counts increased by approximately 2 logarithmic units from day 0 to 9 in whole milk, whereas in orange juice counts diminished by approximately 2.5 logarithmic units from day 0 to 18.

The aim of this work was to evaluate the efficacy of ultrahigh-pressure homogenization (UHPH) for inactivation and/or sublethal injury of two strains of Escherichia coli (O58:H21 ATCC 10536 and O157:H7 CCUG 44857) inoculated into orange juice (pH 3.6). The effects of orange juice inlet temperature (6 and 20 degrees C) on the lethality values and the capacity of these strains for survival, repair, and growth during refrigerated storage after UHPH treatment also was evaluated. Samples of orange juice that had been treated with ultrahigh temperatures were inoculated with E. coli in the stationary phase of growth until a final concentration of approximately 7.0 log CFU/ml was reached. These samples were then treated for one cycle with a double-valve UHPH machine, with 300 MPa at the primary homogenizing valve and 30 MPa at the secondary valve. Counts of viable and injured bacterial cells were obtained for samples taken 2 h after UHPH treatment and after 3, 6, 9, 12, 15, 18, 21, 27, and 33 days of storage at 4 degrees C. The inlet temperature and the strain type both influenced significantly (P < 0.05) the lethality effect on E. coli, which was higher when the inlet temperature was 20 degrees C. No sublethal injuries were detected after any treatment. The changes in viable counts over time for both strains in pressurized and control samples were similar. The viable counts remained high from day 0 to day 18 and then tended to decrease. After 27 days of storage at 4 degrees C, E. coli O157: H7 was more resistant in orange juice samples pressurized at inlet temperatures of 6 and 20 degrees C, with viable counts of 3.41 and 3.20 log CFU/ml, respectively.

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