Death of enterohemorrhagic Escherichia coli O157:H7 in real mayonnaise and reduced-calorie mayonnaise dressing as influenced by initial population and storage temperature.

This study was undertaken to determine the survivability of low-density populations (10(0) and 10(2) CFU/g) of enterohemorrhagic Escherichia coli O157:H7 inoculated into real mayonnaise and reduced-calorie mayonnaise dressing and stored at 20 and 30 degrees C, temperatures within the range used for normal commercial mayonnaise distribution and storage. Inactivation patterns at 5 degrees C and inactivation of high-inoculum populations (10(6) CFU/g) were also determined. The pathogen did not grow in either mayonnaise formulation, regardless of the inoculum level or storage temperature. Increases in storage temperature from 5 to 20 degrees C and from 20 to 30 degrees C resulted in dramatic increases in the rate of inactivation. Populations of E. coli O157:H7 in the reduced-calorie and real formulations inoculated with a population of 0.23 to 0.29 log10 CFU/g and held at 30 degrees C were reduced to undetectable levels within 1 and 2 days, respectively; viable cells were not detected after 1 day at 20 degrees C. In mayonnaise containing an initial population of 2.23 log10 CFU/g, viable cells were not detected after 4 days at 30 degrees C or 7 days at 20 degrees C; tolerance was greater in real mayonnaise than in reduced-calorie mayonnaise dressing stored at 5 degrees C. The tolerance of E. coli O157:H7 inoculated at the highest population density (6.23 log 10 CFU/g) was less in reduced-calorie mayonnaise dressing than in real mayonnaise at all storage temperatures. In reduced-calorie mayonnaise dressing and real mayonnaise initially containing 2.23 log10 CFU/g, levels were undetectable after 28 and 58 days at 5 degrees C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)