Reduction of Listeria monocytogenes and Escherichia coli O157:H7 numbers on vacuum-packaged fresh beef treated with nisin or nisin combined with EDTA.

Nisin or nisin combined with EDTA was used to treat fresh beef. Beef cubes (2.5 by 2.5 by 2.5 cm) that were inoculated with approximately 7 log CFU/ml of Listeria monocytogenes Scott A or Escherichia coli O157:H7 505 B were dipped in the following solutions: (i) H2O, (ii) HCl, (iii) nisin, (iv) EDTA, or (v) nisin combined with EDTA, respectively, for 10 min each, with an exception of one set of control beef samples without treatment. Beef samples were then drip-dried for 15 min, vacuum packaged, and stored at 4 degrees C for up to 30 days. The pH on beef after different treatments was not a key factor in preventing bacterial growth. Treatment with nisin or with nisin combined with EDTA reduced the population of L. monocytogenes by 2.01 and 0.99 log CFU/cm2 as compared to the control, respectively, under the conditions of vacuum package and storage at 4 degrees C for up to 30 days. However, the effect of nisin and nisin combined with EDTA against E. coli O157:H7 505 B was marginal at 1.02 log CFU/cm2 and 0.8 log CFU/cm2 reductions, respectively.