Reductions of Listeria innocua and Brochothrix thermosphacta on beef following nisin spray treatments and vacuum packaging

Sections of UV sterilized lean and adipose tissues from the surfaces of post-rigor (24 h post-mortem) beef carcasses were inoculated with Brochothrix thermosphacta or Listeria innocua to obtain approximately 4.50 log₁₀ cfu cm^-2 and subjected to spray treatments with sterile water or nisin (5000 AU ml^-1). Untreated and spray treated samples were vacuum- packaged, and incubated at 4°C for up to 4 weeks. Bacterial populations from untreated vacuum-packaged tissues and spray treated, vacuum- packaged tissues were enumerated on non-selective and selective media at 0, 7, 14, 21 or 28 days. Nisin spray treatments of lean and adipose vacuum- packaged tissues reduced the numbers of L. innocua up to 2.83 log₁₀ cfu cm^-2. Additionally, nisin sprays and vacuum packaging effectively suppressed L. innocua during the 4-week incubation such that the remaining bacteria did not grow to the same level as untreated or water-treated, vacuum- packaged tissues. Nisin spray treatments and vacuum packaging of lean and adipose tissues reduced B. thermosphacta to undetectable levels. Data from this study demonstrate that nisin spray treatments followed by vacuum packaging under refrigerated conditions could increase the shelf life by suppressing or inhibiting the growth of undesirable bacteria present on fresh beef.