Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2001
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 beef surfaces. Nisin was incorporated into different formulations of plastic (NIP) containing either polyethylene or a polyethylene oxide blend. Antimicrobial activity was tested by experimentally inoculating beef surfaces with a meat spoilage organism, Brochothrix thermosphacta, then wrapping the beef in NIP or in control plastic (without nisin) and vacuum packaging. Wrapped meat samples were tested for remaining bacterial populations after refrigerated storage of 0, 3, 7, 14, and 21 days. Two control plastics did not exhibit any antimicrobial activity against B. thermosphacta on beef. The NIP reduced B. thermosphacta on beef surfaces up to 21 days to a greater extent than the control plastic. This study demonstrates that NIP could be used to reduce undesirable bacteria on beef surfaces.
Technical Abstract: Incorporation of antimicrobial peptides such as bacteriocins into polymer films has the potential to reduce undesirable bacteria on a variety of muscle food surfaces. In this study, five different film compositions were developed, including polyethylene (PE), a PE and polyethylene oxide (70% PE and 30% PEO; PE+PEO) blend, PE and nisin (PE+nisin), PE, nisin, and EDTA (PE+nisin+EDTA), and PE+PEO with nisin (PE+PEO+nisin). Plate overlay assays were conducted with pieces of the polymer film on lawns of Brochothrix thermosphacta. Of the polymer films tested, PE, PE+PEO did not exhibit any antimicrobial activity against the bacterium; however, PE+nisin, PE+nisin+EDTA, and PE+PEO+nisin did. In a subsequent experiment, beef surfaces were experimentally inoculated with approximately 3100 cells/cm**2 of B. thermosphacta, vacuum packaged without (Untreated) or with each of the five polymer films, and held under refrigeration for 21 days. After 3 days of refrigerated storage, B. thermosphacta was reduced >90% and >99.9%, by PE+nisin and PE+nisin+EDTA respectively. By day 21 of refrigerated storage, PE+nisin and PE+nisin+EDTA reduced B. thermosphacta >90% and >99%, respectively. However, populations of B. thermosphacta were reduced >99.999% when surfaces were treated with PE+PEO+nisin. These results indicate that PE+PEO+nisin or PE+nisin+EDTA polymer films were more effective for reducing B. thermosphacta, as compared to polymer films composed of PE+nisin. Based on this information, nisin-incorporated polymer films may provide a means of controlling the growth of undesirable bacteria, thereby extending the shelf life and possibly enhancing the microbial safety of meats.