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 log(10) 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 log(10) 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 off. 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 log(10) CFU/g, levels were undetectable after 28 and 58 days at 5 degrees C, respectively. When E. coli O157:H7 was inoculated at a population of 6.23 log(10) CFU/g, it was not detected in reduced calorie-mayonnaise dressing held at 5 degrees C after 58 days and was approaching undetectable levels in real mayonnaise after 93 days. The pathogen clearly dues not survive in real mayonnaise or reduced-calorie mayonnaise dressing commercially prepared with good manufacturing practices, and the rate of inactivation is most rapid at temperatures at which commercially processed mayonnaise is distributed and stored.