Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 1998
Publication Date: N/A
Interpretive Summary: A plastic material containing a foodgrade preservative was created. Prior to refrigeration or freezing, red meat is routinely vacuum packaged in plastic bags. More than 90% of red meat subprimals that leave packing plants are vacuum packaged. Estimates from 1983 are that approximately 25 million pounds of meat were lost to spoilage, representing a loss of approximately 40 million dollars per year. Outbreaks and recalls of meat lead to more losses. Following the packaging process, no other antimicrobial intervention is utilized other than refrigeration. Vacuum packaging helps to preserve the meat and enhance shelflife by suppressing rancidity, desiccation and microbial growth. We have demonstrated that a foodgrade antimicrobial compound, nisin, can be incorporated into a plastic and used in vacuum packaging beef and retain its antimicrobial activity. The addition of an antimicrobial to the plastic actually inhibits surface bacterial growth. Our study showed that meat packaged with the bacteriocin (nisin)-containing plastic had significantly lower numbers of spoilage bacteria compared to an untreated control. Nisin is a bacteriocin made by the cheese starter bacterium Lactococcus lactis and inhibits some other bacteria. In the USA, nisin has approval for inclusion in some cheese and egg products. Nisin, and other bacteriocins, are generally heat resistant and are broken down in the human gut; thus they are attractive as natural preservatives. Demonstrating that nisin is still active even after incorporation into a plastic may allow other bacteriocins to be included in plastic formulations to inhibit a wide range of bacteria.
Technical Abstract: The bacteriocin, nisin, was incorporated into a polyethylene based plastic film and retained activity against the indicator bacteria Lactobacillus helveticus and Brochothrix thermosphacta. Beef carcass surface tissue sections (BCT) topically inoculated with the psychrotrophic spoilage bacterium B. thermosphacta were vacuum packaged both with and without wrapping with the nisin impregnated plastic and held at 4 deg C. An initial reduction of 2 log10 cycles of B. thermosphacta was observed with nisin-impregnated wrapped BCT within the first two days of storage. After 20 days of refrigerated storage, B. thermosphacta populations from nisin impregnated plastic wrapped samples were significantly less than (P<0.05) control vacuum packaged samples; log10 5.8 vs. 7.2 CFU per cm**2 respectively. Temperature abuse was simulated by shifting inoculated packs from 4 deg C (after 2 days) to 12 deg C. Again, by 20 days, the B. thermosphacta populations of treated samples wrapped with nisin impregnated plastic were significantly less than (P<0.05) control vacuum packaged samples; log10 3.6 vs. 6.3 CFU per cm**2 respectively. This work highlights the potential for incorporating antimicrobial peptides with a wider and different range of inhibitory activity directly into plastics of different properties for use in controlling food spoilage as well as preservation to enhance product microbial safety.