Pasteurization of milk: The heat inactivation kinetics of milk-borne dairy pathogens under commercial-type conditions of turbulent flow

Abstract

This is the first study to report kinetic data on the survival of a range of significant milk-borne pathogens under commercial-type pasteurization conditions. The most heat-resistant strain of each of the milk-borne pathogens Staphylococcus aureus, Yersinia enterocolitica, pathogenic Escherichia coli, Cronobacter sakazakii (formerly known as Enterobacter sakazakii), Listeria monocytogenes, and Salmonella was selected to obtain the worst-case scenario in heat inactivation trials using a pilot-plant-scale pasteurizer. Initially, approximately 30 of each species were screened using a submerged coil unit. Then, UHT milk was inoculated with the most heat-resistant pathogens at ~10(7)/mL and heat treated in a pilot-plant-scale pasteurizer under commercial-type conditions of turbulent flow for 15s over a temperature range from 56 to 66°C and at 72°C. Survivors were enumerated on nonselective media chosen for the highest efficiency of plating of heat-damaged bacteria of each of the chosen strains. The mean log(10) reductions and temperatures of inactivation of the 6 pathogens during a 15-s treatment were Staph. aureus >6.7 at 66.5°C, Y. enterocolitica >6.8 at 62.5°C, pathogenic E. coli >6.8 at 65°C, C. sakazakii >6.7 at 67.5°C, L. monocytogenes >6.9 at 65.5°C, and Salmonella ser. Typhimurium >6.9 at 61.5°C. The kinetic data from these experiments will be used by the New Zealand Ministry of Agriculture and Forestry to populate the quantitative risk assessment model being developed to investigate the risks to New Zealand consumers from pasteurized, compared with nonpasteurized, milk and milk products.

Safety characterization of Yersinia enterocolitica strains isolated from raw milk in Western Algeria

“…This study suggests that minor changes in the temperature of the milk treatment will greatly influence the survival of Y. enterocolitica and that mild temperatures are sufficient for the elimination of this microorganism as compared to others such as Mycobacterium avium subsp. paratuberculosis, Coxiella burnetii and bacterial spores (Pearce et al, 2012). Augmenting the temperature from 55 to 60°C would r e d u c e the D values 1.6 fold, a time-temperature combination of 0.85 min at 60°C is required to achieve one log reduction in Y. enterocolitica, the equivalent time at 65°C was 0.62 min.…”

The Hurdle Approach–A Holistic Concept for Controlling Food Safety Risks Associated With Pathogenic Bacterial Contamination of Leafy Green Vegetables. A Review

“…For milk, an example of a foodstuff with high microbial burden, the key hurdles are pasteurization, cool storage and protection against cross-contamination. pasteurization of milk (72°C for 15 s) can reduce the bacterial load by around 7 log 10 units for L. monocytogenes, Salmonella Typhimurium , and pathogenic E. coli (Pearce et al, 2012). However, pasteurization is not an option for fresh leafy greens.…”

Listeria monocytogenes contamination in dairy plants: evaluation of Listeria monocytogenes environmental contamination in two cheese-making plants using sheeps milk

“…The prevalence of positive raw milk samples ranges between 3.0 and 6.5% (Vitas et al, 2004;AlTahiri et al, 2008), with estimated most probable concentration of 0.1 colony forming units/mL (Meyer-Broseta et al, 2003). The application of thermisation and pasteurisation processes in sheep milk cheese-making plants results in a 3 to 6 log reduction of the number of viable L. monocytogenes cells present in raw milk (ICMSF, 1996;Pearce et al, 2012). Therefore, the presence of L. monocytogenes in dairy products is mainly ascribed to a postprocess contamination originating from the processing environment (Tompkin, 2002;Unnerstad et al, 1996).…”