The outbreak of Escherichia coli O157:H7 linked with dry-cured salami in late 1994 prompted regulatory action that required manufacturers of fermented products to demonstrate a 5-log unit reduction in counts of this pathogen during processing. Therefore, pepperoni batter (75% pork:25% beef with a fat content of ca. 32%) was inoculated with a pediococcal starter culture and a five-strain mixture of E. coli O157:H7 (≥2 × 107 CFU/g) and stuffed into 55-mm diameter fibrous casings 47 cm in length. The viability of the pathogen was monitored before stuffing, after fermentation, after thermal processing, and/or after drying. Chubs were fermented at 96°F (36°C) and 85% relative humidity (RH) to pH ≤ 5.0 and then dried at 55°F (13°C) and 65% RH to a moisture/protein ratio of ≤1.6:1 (modified method 6 process). Counts of the pathogen decreased about 1.2 log units after fermentation and drying. In subsequent experiments, heating chubs after fermentation to internal temperatures of 145°F (63°C) instantaneous or 128°F (53°C) for 60 min resulted in a ≥5-log unit decrease in numbers of strain O157:H7 without visibly affecting the texture or appearance of the product. These data revealed that a traditional nonthermal, process for pepperoni was only sufficient to eliminate relatively low levels (ca. 2 log CFU/g) of E. coli O157:H7, whereas heating to internal temperatures of 145°F (63°C) instantaneous or 128°F (53°C) for 60 min delivered a 5 to 6 log unit reduction in counts of the pathogen in pepperoni.
The fate of Escherichia coli O157:H7 was monitored in salami during conditioning of batter, fermentation and drying of sticks, and storage of slices. The raw batter (75% pork: 25% beef, wt/wt, fat content about 20%) was inoculated with a pediococcal starter culture (about 10(8) CFU/g) and a five-strain cocktail of E. coli O157:H7 ( > or = 2 x 10(7) CFU/g) and stuffed into 104-mm diameter fibrous casings. After being refrigerated at 4 degrees C or being tempered at 13 degrees C, frozen at -20 degrees C, and thawed at 4 degrees C, or being frozen at -20 degrees C, and thawed at 4 degrees C, the inoculated batter was fermented at 24 degrees C and 90% relative humidity (RH) to pH < or = 4.8, dried at 13 degrees C and 65% RH to a moisture/protein ratio of < or = 1.9:1, and then stored at 4 or 21 degrees C under air or vacuum. For salami sticks sampled immediately after drying, appreciable differences were evident among the various batter-conditioning treatments; pathogen numbers were reduced from original levels by 2.1, 1.6, or 1.1 log10 units when batter was tempered, frozen, and thawed, frozen and thawed, or refrigerated, respectively. Similarly, regardless of storage temperature or atmosphere, within 7 days salami slices cut from sticks prepared from batter that was tempered, frozen, and thawed (2.7- to 4.9-log10-unit reduction) or frozen and thawed (2.3- to 4.8-log10-unit reduction) displayed a greater impact on pathogen numbers than slices cut from sticks prepared from batter that was refrigerated (1.6- to 3.1-log10-unit reduction). The effects of batter conditioning notwithstanding, a greater reduction in levels of E. coli O157:H7 was observed when slices were stored at 21 degrees C compared to otherwise similar slices stored at 4 degrees C. After storage for 60 days the pathogen was only detected by enrichment in slices stored at 21 degrees C, whereas pathogen levels ranged from 1.4 to 4.5 log10 CFU/g in slices stored at 4 degrees C. Differences related to storage atmosphere were first observed after slices were stored for 21 days. Such differences were more readily demonstrable after 60 and 90 days, with pathogen numbers for treatments that were statistically different ranging from 0.6- to 1.5-log10 units higher on slices stored under vacuum than in air. These data emphasize the need to implement multiple barriers to appreciably reduce numbers of E. coli O157:H7 in salami.
Pepperoni batter was prepared with fat contents of about 15, 20, and 32% (wt/wt) and inoculated with a pediococcal starter culture and > or = 2.0 x 10(7) CFU/g of a five-strain inoculum of Escherichia coli O157:H7. The batter was fermented at 96 degrees F (ca. 36 degrees C and 85% relative humidity (RH) to pH < or = 4.8 and then dried at 55 degrees F (ca. 13 degrees C) and 65% RH to a moisture/protein ratio of < or = 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 > or = 5.56 and > or = 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 < or = 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.
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