VIABILITY OF ESCHERICHIA-COLI O157-H7 IN FERMENTED SEMIDRY LOW-TEMPERATURE-COOKED BEEF SUMMER SAUSAGE

The population of inoculated Escherichia coli 0157:H7 was monitored du ring the manufacture and storage of a semidry beef summer sausage proc essed by fermentation and cooking at a low temperature by heating to a n internal temperature of 130 degrees F (54 degrees C). The all-beef b atter (11% fat and nonmeat ingredients) was inoculated with the commer cial starter culture Pediococcus acidilactici HP (greater than or equa l to 8.6 log CFU/g of batter) and a five-strain mixture of E. coli 015 7:H7 (greater than or equal to 7 log CFU/g) and then hand stuffed into 2.5-inch (64-mm) diameter fibrous casings. The sausages were fermente d at an initial temperature of 85 degrees F (29 degrees C) to a final temperature of 105 degrees F (41 degrees C) over ca. 13 h at 80% relat ive humidity (RH) to pH 4.6 or pH 5.0. After fermentation to pH 4.6, t he internal temperature of the chubs was raised to 130 degrees F (54 d egrees C) instantaneous over 3.6 h at 60% RH. After fermentation to pH 5.0, the internal temperature of the chubs was raised to 130 degrees F (54 degrees C) over 3.6 h at 60% RH and the chubs were maintained un der these conditions for 0, 30, or 60 min. The chubs were cold water s howered for 15 min and then chilled at 39 degrees F (4 degrees C) for 6 h before being vacuum packaged and stored at 39 degrees F (4 degrees C) or 77 degrees F (25 degrees C) for 7 days. Regardless of the targe t pH, fermentation alone resulted in only a 1.39-log CFU/g decrease in pathogen numbers. However, fermentation to pH 4.6 and heating to an i nternal temperature of 130 degrees F (54 degrees C) instantaneous redu ced counts of E. coli 0157:H7 by greater than or equal to 7.0 log unit s to below detection levels (<10 CFU/g). Pathogen numbers remained bel ow levels detectable by direct plating, but viable E. coli 0157:H7 cel ls were recovered by enrichment of samples during sausage storage at e ither refrigeration or abuse temperatures. In contrast, fermentation t o pH 5.0 and heating to an internal temperature of 130 degrees F (54 d egrees C) instantaneous resulted in a 3.2-log-unit decrease in counts of E. coli 0157:H7. No appreciable reductions in pathogen numbers were observed thereafter following storage at either 39 degrees F (4 degre es C) or 77 degrees F (25 degrees C) for 7 days. Fermentation to pH 5. 0 and heating to an internal temperature of 130 degrees F (54 degrees C) instantaneous followed by holding for 30 or 60 min resulted in abou t a 5- or 7-log reduction, respectively, in pathogen numbers. For chub s held for 30 min at 130 degrees F (54 degrees C), pathogen numbers de creased to 2.02 and <1.0 log CFU/g at 39 degrees F (4 degrees C) and 7 7 degrees F (25 degrees C), respectively, after 7 days; viable cells w ere only observed by enrichment after storage at 77 degrees F (25 degr ees C). For chubs held for 60 min at 130 degrees F (54 degrees C), pat hogen numbers remained below levels detectable by direct plating, but viable cells were recoverable by enrichment after 7 days at both stora ge temperatures. These data will be useful guidelines to manufacturers for developing processing conditions to further ensure the safety of this category of fermented sausages relative to food-borne pathogens s uch as serotype 0157:H7 strains of E. coli.