Survival of Escherichia coli O157:H7 in full- and reduced-fat pepperoni after manufacture of sticks, storage of slices at 4 degrees C or 21 degrees C under air and vacuum, and baking of slices on frozen pizza at 135, 191 and 246 degrees C

Pepperoni batter was prepared with fat contents of about 15, 20, and 32% (wt/wt) and inoculated with a pediococcal starter culture and greater than or equal to 2.0 X 10(7) CFU/g of a five-strain inoculation of Escherichia coli O157:H7. The batter was fermented at 96 degrees F (ca. 36 degrees C) and 85% relative humidity (RH) to pH less than or equal to 4.8 and then dried at 55 degrees F (ca. 13 degrees C) and 65% RH to a moisture/protein ratio of less than or equal to 1.6:1. For storage, slices were packaged under air or vacuum and stored at 39 degrees F (ca. 4 degrees C) and 70 degrees F (ca. 21 degrees C). For baking, frozen slices were placed on retail frozen cheese pizzas that were subsequently baked at 275 degrees F (ca. 135 degrees C), 375 degrees F (ca. 191 degrees C), or 475 degrees F (ca. 246 degrees C) for 0 to 20 min. Appreciable differences related to fat levels were observed after drying; pathogen numbers decreased by 1.04, 1.31 and 1.62 log10 units in sticks prepared from batter at initial fat levels of 15, 20, and 32%, respectively. During storage, the temperature rather than the atmosphere had the greater effect on pathogen numbers, with similar viability observed among the three fat levels tested. At 70 degrees F (ca. 21 degrees C), compared to original levels, pathogen numbers decreased by greater than or equal to 5.56 and greater than or equal to 4.53 log10 units within 14 days in slices stored under air and vacuum, respectively, whereas at 39 degrees F (ca. 4 degrees C) numbers decreased by less than or equal to 2.43 log10 CFU/g after 60 days of storage under either atmosphere. Baking, as expected, resulted in greater reductions in pathogen numbers as the temperature and/or time of baking increased. However, it was still possible to recover the pathogen by enrichment after baking frozen slices on frozen pizza at 475 degrees F (ca. 246 degrees C) for 10 min or at 375 degrees F (ca. 191 degrees C) for 15 min. The calculated D values for all three temperatures tested increased as the fat content of the batter increased from 15 to 20 to 32%. The present study confirmed that fermentation and drying were sufficient to reduce levels of E. coli O157:H7 in pepperoni sticks by <2.0 log10 CFU/g. Storage of slices for at least 14 days at ambient temperature under air resulted in a >5.5-log10-unit total reduction of the pathogen. Baking slices on frozen pizza for at least 15 min at 475 degrees F (ca. 246 degrees C) or 20 min at 375 degrees F (ca. 191 degrees C) was necessary to reduce pathogen numbers to below detection by both direct plating and enrichment.