THERMAL KINETICS OF STREPTOCOCCUS-FAECIUM IN NUTRIENT BROTH SOUS VIDE PRODUCTS UNDER PASTEURIZATION CONDITIONS

There is current major interest in the microbiological aspects and safety of chilled foods such as sous vide. Thermal kinetics for a target microorganism, Streptococcus faecium, was performed and is described in this paper. An E-20 S. faecium was tested for heat resistance in cooked meat nutrient broth. Known cell concentrations were inoculated into ampoules containing the heating medium and exposed to various heating temperatures (60-85C). Swival curves for the recovered S. faecium cells were constructed. The D-values calculated from the logarithm of number of survivors versus time plot were 22.53, 4.47, 1.11, 0.61, 0.29, 0.20 min for 60, 65, 70, 75, 80, 85C, respectively. The z-value obtained from 60-85C was 12.4C; however when only 60-75C was considered, the z-value obtained was 9.4C. Pasteurization values (P-v) calculated for a 13D reduction of S. faecium at 65 and 75C based on the above kinetics and heat penetration data under sous vide processing conditions compared favorably with experimental values in both nutrient broth and in sous vide spaghetti with meat sauce and mackerel with rice products. Using D-values of a heat resistant representative, S, faecium E-20 as a basis, parameters for pasteurization that effectively eliminate vegetative nonspore forming bacteria may be developed. However, the variation in z-values suggest that their usefulness in determining pasteurization process parameters should be carefully considered.