Survival and death of Listeria monocytogenes on cooked bacon at three storage temperatures

摘要

Survival of Listeria monocytogenes on cooked bacon cubes (a_w 0.910 ± 0.080), strips (a_w 0.726 ± 0.054), and bits (a_w 0.620 ± 0.038) was determined during a 25 week storage period at -20,4.4, and 22℃. Selective enrichment and subsequent enzyme-linked fluorescent antibody (ELFA) detection were used to asses survival on samples inoculated at ca. 1 -log_(10) CFU/g (LI). Samples inoculated at ca. 5.5-log_(10) CFU/g (HI) were analyzed over time by direct plating on modified Oxford medium (MOX). The Baranyi model was fitted to the inactivation curves of HI samples using the DMFit program. At -20 ℃, a decline of about 1 -log_(10) CFU/g occurred on all HI cooked bacon types by 14 weeks, although most LI samples remained positive by the ELFA detection method for 25 weeks. At 4.4 and 22 ℃, some strips and bits LI samples were negative for the pathogen within 3 weeks, and >1.5 log_(10) CFU/g reductions occurred on HI strips and bits by 8 weeks. Reductions on cubes at refrigeration and ambient temperature were ca. 0.5 log_(10) CFU/g, and cubes remained positive on LI samples for 25 weeks. Rate parameter estimates indicated that the population declined fastest on strips and bits at 22℃ compared to all other product and temperature combinations. This study demonstrates that cooked bacon does not support the growth L. monocytogenes and that the pathogen gradually dies off during storage.