Growth of Listeria monocytogenes on vacuum-packaged horsemeat for human consumption.

In order to investigate the likelihood of Listeria monocytogenes (serotype 4b, ATCC 19115) growth on vacuum-packaged horsemeat at refrigeration temperature, fourteen horsemeat surface/volume homogeneous 150 g weight pieces were superficially inoculated with serotype 4b L. monocytogenes and vacuum packaged. The samples were stored at 4±1 °C. Two pieces (one for pH determination and one for L. monocytogenes counts) were examined at days 0, 7, 14, 21, 28, 35 and 42. Surface pH did not show significant variations during the experiment. The average L. monocytogenes initial contamination level was 1.77log(10) CFU/g. A lag phase of 7 days was recorded. The exponential growth rate between day 7 to day 35 was 0.125log(10) CFU/day, corresponding to 3.51log(10) CFU/g in 28 days. At the end of the experiment the mean L. monocytogenes log(10) CFU/g was 5.78.