The antimicrobial effect of thyme essential oil, nisin and their combination against Escherichia coli O157 : H7 in minced beef during refrigerated storage

The antimicrobial effect of thyme essential oil (EO) at supplementation levels of 0.3%, 0.6% or 0.9%, nisin at 500 or 1000 IU/g, and their combination, on Escherichia coli O157:H7 was examined in both tryptic soy broth (TSB) and minced beef meat. EO at 0.3% possessed a weak antibacterial activity against the pathogen in TSB, whereas at 0.9% showed unacceptable organoleptic properties in minced meat. Thus, only the level of 0.6% of EO was further examined against the pathogens in minced meat. Treatment of minced beef meat with EO at 0.6%) showed an inhibitory activity against E coli O157:H7 during storage at 10 degrees C, but not at 4 degrees C. Treatment of minced beef meat or TSB with nisin at 500 or 1000 IU/g did not show any antibacterial activity against E coli O157:H7. The combination of EO at 0.6% and nisin at 500 or 1000 IU/g showed an additive effect against the pathogen, which was higher during storage at 10 degrees C than at 4 degrees C. (C) 2007 Elsevier Ltd. All rights reserved.