A model study of Escherichia coli O157:H7 survival in fermented dry sausages—influence of inoculum preparation, inoculation procedure, and selected process parameters

Fadia Naim, Serge Messier, Linda Saucier, Gabriel Piette
Journal of Food Protection 2003, 66 (12): 2267-75
The influence of inoculum preparation, inoculation level, and inoculation procedure on Escherichia coli O157:H7 inactivation during the manufacture of fermented sausage was evaluated in a model study. Prior growth in glucose-enriched tryptone soya broth, which provided exposure to mildly acidic conditions (pH 4.8), had no effect on the later survival of E. coli O157: H7 strains 5-1 and ATCC 43894 under extremely acidic conditions (pH 2), but the same strains became sensitive to acidity after 7 days of incubation on the surface of refrigerated beef (as per the normal contamination route from slaughter to further processing). In subsequent sausage production trials, the extent of destruction observed for E. coli O157:H7 strains F-90, 5-1, and ATCC 43894 inoculated directly into the meat batter was unchanged when the inoculation level was decreased from 7.3 to 4.7 log CFU/g, but the level of inactivation was ca. 1 log higher when the surfaces of beef cuts, rather than the batter, were inoculated 7 days prior to processing. Regardless of processing conditions (fermentation to a pH of < or = 5.0 at 24 or 37 degrees C, drying at 14 degrees C to a water activity [a(w)] value of 0.91 or 0.79), strains F-90, 5-1, and ATCC 43894 showed similar survival capacities during the manufacture of sausage. A approximately 2-log reduction in pathogen numbers was generally obtained after samples were dried to an a(w) of 0.91, irrespective of fermentation temperature. The addition of a 5-day predrying holding stage at the fermentation temperature significantly (P < 0.05) increased pathogen inactivation when fermentation was carried out at 37 degrees C (but not when it was carried out at 24 degrees C). However, significant pathogen reductions (4 to 5 log CFU/g) were achieved only for extensively dried products (a(w) = 0.79).

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