The Effect of Heat& Cold on The L.monocytogenes in the Milk Ghazi M. Al-Khatib,Mohammed J.Alwan and Nagham M. Al-Jebouri

Abstract

The influence of heat and cold on the L.monocytogenes in the milk
In order to know the thermal resistance of L.monocytogenesin the
contaminated milk, 40gram of powder milk was dissolved in 400ml
of heated water.The milk solution was sealed in 40 test tubes 10 ml
in each one.these test tubes were divided into 6 groups ,10test tubes
in each the 1st,2nd group &5 test tubes in each the 3rd ,4th ,5th ,6th
groups,then all the test tubes were inoculated with
L.monocytogenes &incubation for 24hrs at 37c.the samples of the
1st &2nd group were dipped in awater bath at tempreture 63c for
30minute &72c for 1-5.5 minute respectively .also the samples of
3rd &4th groups were dipped in awater bath at 72c for 6minute. Test
tubes of 1st ,3rd ,5th groups were kept in 4c for variable times while
samples of 4th ,6th group were exposured to - 18c for 12days. The
results showed no bacterial isolates immediately after heat
treatment in all the milk samples of 1st .3rd &4th groups but some
isolates were seen after enrichment at 4c&- 18c L.monocytogenes
was isolate from all samples of 2nd ,5th &6th groups. The results
suugest that cold enrichment play role in repair the thermally
injured cells of L.monocytogenes&these organisms surviveve
thermal treatment.