Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2005
Publication Date: 12/1/2005
Citation: Sanchez-Plata, M.X., Amezquita, A., Blankenship, E., Burson, D.E., Juneja, V.K., Thippareddi, H. 2005. Predictive model for growth of clostridium perfringens in roast beef during cooling and inhibition of spore germination and outgrowth by salts of organic acids. Journal of Food Protection. Vol.68(12):2594-2605. Interpretive Summary: One of the most common types of food poisoning in the United States is caused by the bacterium, Clostridium perfringens. Illnesses have been traditionally associated with inadequate cooling practices in retail food service operations. Thus, there was a need to determine the time and temperature for cooked meat products to remain pathogen-free and provide vital data for performing risk assessment on cooked meat. We developed a model that can be used to predict the growth of C. perfringens at temperatures relevant to the cooling of cooked products. The predictive model will be of immediate use to the retail food service operations and regulatory agencies to aid with the disposition of products subject to cooling deviations and therefore, ensure the safety of the cooked foods.
Technical Abstract: Germination and outgrowth of Clostridium perfringens spores in roast beef during chilling was studied following simulated cooling schedules normally used in the processed meat industry. Beef top rounds were formulated to contain a marinade (finished product concentrations of salt, 1%; potassium tetrapyrophosphate, 0.2%; and starch, 0.2%), ground and mixed with antimicrobials [sodium lactate (SL) and SL plus sodium diacetate (SD), 2.5%; buffered sodium citrate (BSC) and BSC plus SD, 1.3%]. The ground product was inoculated with a three-strain cocktail of C. perfringens spores (NCTC 8238, 8239 and ATCC 10388), mixed, vacuum packaged, heat shocked for 20 min at 75ºC and chilled exponentially from 54.5 to 7.2ºC in 9, 12, 15, 18 or 21 h. C. perfringens populations (total and spore) were enumerated after heat shock, during chilling and during storage for up to 60 days at 10ºC using Tryptose-Sulfite-Cycloserine (TSC) agar. C. perfringens spores were able to germinate and grow in roast beef (control, without any antimicrobials) from an initial population of ca. 3.1 log10 CFU/g by 2.00, 3.44, 4.04, 4.86 and 5.72 log10 CFU/g subsequent to 9, 12, 15, 18 and 21 h exponential chill rates, respectively. A predictive model was developed to describe sigmoidal C. perfringens growth curves during cooling of roast beef from 54.5 to 7.2ºC within 9, 12, 15, 18 and 21 h. Addition of antimicrobials prevented germination and outgrowth of C. perfringens, regardless of the chill times. However, C. perfringens spores could be recovered from samples containing organic acid salts that were stored up to 60 days at 10ºC. Extension of chilling time for greater than or equal to 9 h resulted in greater than 1 log10 CFU/g growth of C. perfringens under anaerobic conditions in roast beef. Organic acid salts inhibited outgrowth of C. perfringens spores during chilling of roast beef when extended chill rates were followed. While C. perfringens spore germination is inhibited by the antimicrobials, this in itself may introduce another hazard when such products are incorporated into new products, such as soups, chili, etc. that do not contain these antimicrobials, and thus allow spore germination and outgrowth if temperature abused.