Use of nisin in ice cream and effect on the survival of Listeria monocytogenes

The survival characteristics of Listeria monocytogenes V7 were investigated in a full fat (10% fat) and reduced fat (3%) ice cream. The effect of nisin on the survival of Listeria monocytogenes in the ice creams was also evaluated. Ice cream mixes varying in composition were manufactured and inoculated with L. monocytogenes, passed through a ''soft serve'' freezer and then frozen at -18 degrees C for up to 3 months. Samples were removed from storage throughout the three months, thawed, and then plated on Listeria-selective agar. In the samples that did not contain nisin, no reduction in the cell population was observed throughout manufacture and frozen storage. When nisin was present in the ice cream, a significant reduction in the cell population (P < .05) was observed. At the end of 3 months of frozen storage, no Listeria cells were detected in the 3% fat ice cream containing nisin. The effect of nisin on Listeria cells was decreased somewhat in the higher fat ice cream but this decrease was not significant over the 3 month storage. The stability of nisin in the ice cream remained constant throughout storage at -18 degrees C.