Survival of Escherichia coli O157:H7 during storage in pressure-treated orange juice.
The effect of a high-pressure treatment on the survival of a pressure-resistant strain of Escherichia coli O157:H7 (NCTC 12079) in orange juice during storage at 3 degrees C was investigated over the pH range of 3.4 to 5.0. The pH of shelf-stable orange juice was adjusted to 3.4, 3.6, 3.9, 4.5, and 5.0 and inoculated with 10(8) CFU ml(-1) of E. coli O157:H7. The orange juice was then pressure treated at 400 MPa for 1 min at 10 degrees C or was held at ambient pressure (as a control). Surviving E. coli O157:H7 cells were enumerated at 1-day intervals during a storage period of 25 days at 3 degrees C. Survival of E. coli O157:H7 during storage was dependent on the pH of the orange juice. The application of high pressure prior to storage significantly increased the susceptibility of E. coli O157:H7 to high acidity. For example, after pressure treatment, the time required for a 5-log decrease in cell numbers was reduced from 13 to 3 days at pH 3.4, from 16 to 6 days at pH 3.6, and from >25 to 8 days at pH 3.9. It is evident that the use of high-pressure processing of orange juice in order to increase the juice's shelf-life and to inactivate pathogens has the added advantage that it sensitizes E. coli O157:H7 to the high acid conditions found in orange juice, which results in the survival of significantly fewer E. coli O157:H7 during subsequent refrigerated storage.
Linton
M
M
Food Science Division (Food Microbiology), Department of Agriculture for Northern Ireland, Belfast. mlinton@alpha1.dani.gov.uk
McClements
J M
JM
Patterson
M F
MF
D004926:Escherichia coli / Q000472:pathogenicity*; D005516:Food Microbiology; D005519:Food Preservation; D005638:Fruit / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D011312:Pressure; D013696:Temperature; D013997:Time Factors