title: Short communication: heat resistance of Escherichia coli strains in raw milk at different subpasteurization conditions.
abstract: A commonly applied treatment of raw milk to reduce bacterial loads is the short-time application of heat at subpasteurization levels under continuous flow, generally referred to as thermization, because this method retains some of the beneficial properties of raw milk. In a previous study, Escherichia coli strains exhibiting increased thermotolerance were found, demanding investigations into their ability to survive thermization. Nine E. coli strains, including 4 Shiga toxin-producing E. coli (STEC) strains, were investigated for their reduction during a thermization treatment in raw milk using a pilot-plant pasteurizer to reflect typically applied commercial conditions. Six of the 9 E. coli strains, including the 4 STEC strains, were similarly inactivated at 60, 62.5, and 65°C, whereas increased thermotolerance was observed for 3 E. coli strains. All strains were reduced to <2 log10 at 60 and 62.5°C within 25s. At 65°C, 6 of 9 E. coli strains were reduced by at least 5 log10 after 25s, whereas at 67.5°C, such a reduction was observed for 8 strains. A much higher thermotolerance was found for E. coli strain FAM21805. For some E. coli strains, time-temperature combinations above 65°C were required to obtain a substantial reduction during a thermization treatment.
authors.affiliation: Institute for Food Safety and Hygiene, University of Zurich, 8057 Zurich, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Peng
authors.forename: J
authors.initials: J
authors.lastname: Hummerjohann
authors.forename: R
authors.initials: R
authors.lastname: Stephan
authors.forename: P
authors.initials: P
authors.lastname: Hammer
mesh_terms: D000818:Animals; D058491:Bacterial Load; D002611:Cheese / Q000382:microbiology; D004926:Escherichia coli / Q000145:classification / Q000502:physiology*; D005511:Food Handling / Q000379:methods*; D006358:Hot Temperature; D050296:Microbial Viability; D008892:Milk / Q000382:microbiology*; D061352:Pasteurization; D013045:Species Specificity