Viability of Escherichia coli O157:H7 in salami following conditioning of batter, fermentation and drying of sticks, and storage of slices

Abstract

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.