Impact of the Population of Spoilage Microflora on the Growth of Listeria monocytogenes on Frankfurters

Abstract

Approximately 100 CFU/cm2 of a five-strain mixture of Listeria monocytogenes was coinoculated onto frankfurters with three different concentrations (102, 104, and 106 CFU/cm2) of an undefined spoilage microflora derived from commercial frankfurters. The frankfurters were vacuum packaged and stored at 10°C for up to 48 days. The populations of L. monocyto-genes, aerobic mesophilic bacteria, lactic acid bacteria, and Enterobacteriaceae were determined at various time intervals during storage. After 14 days, the population of L. monocytogenes was highest when grown with a spoilage microflora population of 102 CFU/cm2, and this trend continued until 48 days. Throughout the entire storage period, the populations of L. monocytogenes at any concentration of inoculated spoilage microflora rarely differed by more than 0.5 log CFU/cm2, and the maximum observed difference as 1.1 log CFU/cm2 at 40 days. The growth rate of L. monocytogenes was approximately the same at all concentrations of the inoculated spoilage microflora. These results suggest that the concentration of spoilage microflora present on the original processed meat may have a slight impact on the growth of L. monocytogenes in the package.