Thermoresistance of Listeria monocytogenes in milk I. Death and sublethal injury at various temperatures
1998
Karakolev, R. (Rajonen Veterinaren Institut , Veliko T"rnovo (Bulgaria))
The thermoresistance of 5 strains L. monocytogenes in skim milk at 55, 60, 63, 65, 68 and 70 degree C were studied. At different heating temperatures a different period of devitalization of L. monocytogenes strains is needed. The F-values (for the 6576 strain which displays lower thermoresistance, and for the 579 strains which displays the highest thermoresistance are from 68,3 to 111 min at 55 degree C, from 8,5 to 17 min at 60 degree C, from 2,51 to 6,27 min at 63 degree C, from 0,99 to 2,7 min at 65 degree C, from o,31 to 1,04 min at 68 degree C and from 0,14 to 0,49 min at 70 degree C. The period (in min) for a 90% reduction (D-values) of the number of microorganisms (for the 6576 strain and for the 579 strains respectively) are from 11,98 to 19,47 min at 55 degree C, from 0.17 to 0.45 min at 65 degree C and from 0,025 to 0,088 min at 70 degree C. At each included in tests L. monocytogenes strains was needed from 5,6 to 6,4 degree C in order to go through a logarithmic cycle.
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