USE OF NISIN IN ICE-CREAM AND EFFECT ON THE SURVIVAL OF LISTERIA-MONOCYTOGENES

The survival characteristics of Listeria monocytogenes V7 were investi gated in a full fat (10% fat) and reduced fat (3%) ice cream. The effe ct of nisin on the survival of Listeria monocytogenes in the ice cream s was also evaluated. Ice cream mixes varying in composition were manu factured 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 n ot contain nisin, no reduction in the cell population was observed thr oughout manufacture and frozen storage. When nisin was present in the ice cream, a significant reduction in the cell population (P < .05) wa s observed. At the end of 3 months of frozen storage, no Listeria cell s were detected in the 3% fat ice cream containing nisin. The effect o f 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.