Viability of Escherichia coli O157:H7 during manufacturing and storage of a fermented, semidry soudjouk-style sausage

Abstract

Soudjouk-style batter was inoculated with a five-strain mixture of Escherichia coli O157:H7 at about 7.6 log10 CFU/g in each of two trials. The sticks were fermented and dried at 22°C and 50% relative humidity (RH) for 3 days and then at 9°C and 40% RH for 18 h. After being flattened to about 1.25 cm, the sticks were conditioned at 38°C and 70% RH or at 22°C and 50% RH for about 3 days. After the latter conditioning treatment, sticks either were cooked to an internal temperature of 63°C or received no heat treatment. Final mean pH values after conditioning at 22°C and 50% RH for soudjouk manufactured with a starter culture and dextrose (1.0%) and for soudjouk manufactured without a starter culture were about 4.9 and 6.0, respectively. For soudjouk produced with a starter culture, pathogen numbers were reduced by 4.53 and 0.88 log10 CFU/g after conditioning at 38°C and 70% RH and at 22°C and 50% RH, respectively. For soudjouk produced via natural fermentation, pathogen numbers were reduced by 1.39 and 0.09 log10 CFU/g after conditioning at 38°C and 70% RH and at 22°C and 50% RH, respectively. Cooking reduced pathogen numbers to below the levels detectable by direct plating (<1.0 log10 CFU/g) and by enrichment for soudjouk produced with a starter culture and also reduced pathogen numbers by 6.28 log10 CFU/g for soudjouk produced via natural fermentation. However, cooking also resulted in an unacceptable product. In general, the reduction in pathogen numbers achieved by storage at ambient temperature (25°C) was greater than that achieved by storage at cooler temperatures (4 and 15°C), particularly for soudjouk prepared with a starter culture (for which a final pH value of 4.8 and a 6.4-log10 reduction were obtained after 21 days at 25°C) rather than for that prepared without a starter culture (for which a final pH value of 6.1 and a 2.6-log10 reduction were obtained after 21 days at 25°C). These results indicate that naturally fermented old-country-type sausage may allow the survival of E. coli O157:H7 in the absence of controlled fermentation, postfermentation cooking, and/or an ambient-storage processing step.