Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 1995
Publication Date: N/A
Interpretive Summary: Nisin, a naturally occurring, antimicrobial protein associated with cheese making, was investigated as a means of killing bacteria attached to vacuum packaged beef. Brochothrix thermosphacta and Listeria innocua were inoculated onto individual pieces of lean and fat beef. Nisin or water was sprayed onto the pieces of beef. The pieces were vacuum packaged and stored under refrigeration for up to one month. Beef that was sprayed with nisin, vacuum packaged, and stored did not have as much Listeria innocua growth as the untreated or water sprayed beef after four weeks. No growth of Brochothrix thermosphacta was detected on nisin sprayed beef after four weeks under refrigeration, when compared to untreated or water sprayed beef. This study demonstrates that spray washing with nisin followed by vacuum packaging effectively reduces bacterial populations on beef.
Sections of U.V. sterilized lean and adipose tissues from the surfaces of post rigor (24 h post mortem) beef carcasses were inoculated with Brochothrix thermosphacta (BT) or Listeria innocua (LI) to obtain approximately 4.50 log**10 CFU/cm**2 and subjected to spray treatments with sterile water or nisin (5000 AU/ml). Untreated and spray treated samples were vacuum packaged, and incubated at 4 deg C for up to 4 weeks. Bacterial populations from untreated, vacuum packaged tissues and spray treated, vacuum packaged tissues were enumerated on nonselective and selective media at 0, 7, 14, 21, or 28 days. Nisin spray treatments of lean and adipose vacuum packaged tissues reduced LI up to 2.83 log**10 CFU/cm**2. Additionally, nisin sprays and vacuum packaged effectively suppressed LI during the four 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 BT to undetectable levels. Data from this study are the first demonstration that nisin spray treatments followed by vacuum packaging under refrigerated conditions could increase the shelf life by suppressing or prohibiting the growth of undesirable bacteria present on fresh beef.