Growth potential of Clostridium perfringens in heated (75°C) ready-to-eat foods kept at temperatures between 20°C and 65°C was evaluated. It was examined at which temperatures the foods could be kept, without increasing the level of C. perfringens with more than 1 log cfu/g, over a period of three hours with varying characteristics such as pH, NaCl and cooling constant. Theoretical cooling constants were estimated at different locations in a small and large food (meatball and liver paste) using a variety of realistic heat transfer coefficients (5-500 W∙m-2∙K-1) in a simulation software. Based on this, time/temperature profiles were simulated and the growth of C. perfringens was predicted using Combase Perfringens Predictor. Growth was predicted at pH 6 or 6.5 in combination with 0 – 3 % NaCl at temperatures between 20 and 65°C. Cooling constants varied between 0.2 h-1 and 19 h-1 and differed significantly within the food – especially in the large food type – indicating that it is not sufficient to evaluate growth of C. perfringens in the centre of the food. Moreover, it was found that keeping ready to-eat-foods at temperatures above 52°C, having NaCl ≥3.0 % or pH ≤ 5.5 ensured that growth of C. perfringens was below 1 log cfu/g during a three-hour-storage regardless of the other parameters. For ready-to-eat foods where this is not the case, two tables (pH = 6.0 and pH = 6.5) was created showing which temperatures the foods can be kept at, dependent on the cooling constant.
2013 Congress of the Danish Microbiological Society, 2013