. Materials and methods
2.1. Preparation of L. monocytogenes Scott A culture
Stock cultures of L. monocytogenes Scott A were
maintained on tryptic soy agar plus 0.6% yeast extract
(TSAYE) (Difco Laboratories, Detroit, MI) at 4 jC and
monthly transferred onto a freshly made TSAYE plate
during the experimental period. For growth, a loopful of
L. monocytogenes was transferred from a TSAYE plate to
tubes of tryptic soy broth plus 0.6% yeast extract (TSBYE)
(Difco). The TSBYE culture was then incubated at 37 jC
for 18 h to stationary phase. The cells were harvested by
centrifugation at 2400g for 15 min, washed with sodium
phosphate buffer (0.1 M, pH 7.0), and resuspended in UHT
whole milk (pH 6.7) to give approximately 2109 CFU/
ml. All samples were inoculated 2 h before treatment to
allow cells to acclimatize. One ml of un-inoculated milk
was transferred onto TSAYE plates and incubated at 37 jC
for 3 days to make sure that the milk samples were sterile