The May edition of the Journal of Food Protection evaluates the efficacy of ultrahigh-pressure homogenization for inactivation and/or sublethal injury of two strains of E. coli inoculated into orange juice.
Samples of orange juice that had been treated with ultrahigh temperatures were inoculated with E. coli in the stationary phase of growth and then treated for one cycle with a double-valve UHPH machine.
Counts of viable and injured bacterial cells were obtained for samples taken 2 hours after UHPH treatment and after 3, 6, 9, 12, 15, 18, 21, 27, and 33 days of storage at 4 degrees Celsius.
The inlet temperature and the strain type both influenced significantly the lethality effect on E. coli, which was higher when the inlet temperature was 20 degrees Celsius.
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 Celsius, E. coli O157: H7 was more resistant in orange juice samples pressurized at inlet temperatures of 6 and 20 degrees Celsius.