Survival of Listeria monocytogenes in three Zimbabwean fermented milk products

The growth and survival of Listeria monocytogenes was studied in traditionally fermented unpasteurized and pasteurized milk and in an industrially fermented milk marketed in Zimbabwe. Inoculated milk samples were incubated at 20 degrees C for 24 h, and then one set of samples of each type of milk was stored at ambient (20 degrees C) and a duplicate set at refrigeration (5 degrees C) temperatures for a further 96 h. The industrially fermented milk was least favorable to the survival of L. monocytogenes, followed by traditionally fermented unpasteurized milk and traditionally fermented pasteurized milk when these milks were stored at ambient temperature. A different trend was observed when the milks were stored at refrigeration temperature with traditionally fermented unpasteurized milk allowing the least survival of L. monocytogenes followed by industrially fermented milk and traditionally fermented pasteurized milk. More L. monocytogenes survived in all the three fermented milks when they were stored at refrigeration temperature than at ambient temperature.