Purpose: The ability of C. perfringens to germinate and grow in ten commercially prepared beef, pork and poultry barbeque products was assessed.
Methods: Each product was inoculated with a cocktail of three strains of heat-activated C. perfringens spores to achieve ca. 2 log (low) or 4 log (high) inoculum levels, vacuum packaged, and cooled exponentially from 54.4 to 7.2 °C in 6, 9, 12, 15, 18 or 21 h, to simulate abusive cooling from the prescribed cooling time of 6.5 h. Total germinated C. perfringens population was determined after plating on tryptose sulfite cycloserine agar and incubating the plates anaerobically at 37 °C for 48 h. Also, C. perfringens growth from spores was assessed at an isothermal temperature of 44 °C.
Results: The pH of the products ranged from 4.74 to 6.35. No growth was observed in products with pH ranging from 4.74 to 5.17, both during exponential abusive cooling periods of up to 21 h and during storage for 21 h at 44 °C. While less than 1 log growth of C. perfringens from spores was observed in the pH 5.63 product cooled exponentially from 54.4 to 7.2 °C in 15 h or less, product with pH 6.35 supported growth even during 6 h cooling.
Significance: These challenge tests demonstrate that pH adjustment of the barbeque products to pH ≤5.63 inhibit C. perfringens spore germination and outgrowth during extended cooling periods from 54.4 to 7.2 °C in up to 15 h, while safe cooling for products with homogeneous, lower pH can be substantially longer.