Inactivation of Escherichia coli O157:H7 in packaged ground beef by allyl isothiocyanate

Abstract

Commercial allyl isothiocyanate (AIT) was examined for its ability to reduce numbers of Escherichia coli O157:H7 inoculated in fresh ground beef packaged under nitrogen and stored refrigerated or frozen. A five-strain cocktail of E. coli O157:H7 containing 3 or 6 log 10 cfu/g was inoculated into 100 g ground beef and formed into 10×1-cm patties. A 10-cm diameter filter paper disk treated with AIT suspended in sterile corn oil was placed on top of a single patty. One patty and paper disk were placed in a bag of Nylon/EVOH/PE with O 2 permeability of 2.3 cm 3 m −2 24 h atm at 23 °C. The bags were back-flushed with 100% nitrogen, heat-sealed and stored at 10, 4 and −18 °C for 8, 21 or 35 days, respectively. During storage, the AIT levels in the package headspaces were determined by gas liquid chromatography, and mesophilic bacteria and E. coli O157:H7 were counted. The mesophilic aerobic bacteria in ground beef patties were largely unaffected by the addition of AIT. At an initial population of 3 log 10 cfu/g, E. coli O157:H7 was reduced by AIT to undetectable levels after 18 days at 4 °C or 10 days at −18 °C. In samples inoculated with 6 log 10 cfu/g, a >3 log 10 reduction of E. coli O157:H7 was observed after 21 days at 4 °C, while a 1 log 10 reduction was observed after 8 and 35 days at 10 and −18 °C, respectively. The final AIT concentrations in the headspaces after storage at 10, 4, and −18 °C were 444, 456, and 112 μg/ml at 8, 21, and 35 days, respectively. Results showed that AIT can substantially reduce numbers of E. coli O157:H7 in fresh ground beef during refrigerated or frozen storage.