Inhibit L. monocytogenes using coating containing nisin.

Antimicrobial additives have been incorporated successfully into foods for many years. The scientific literature provides evidence that some of these additives also may be effective as indirect additives that are incorporated into food packaging systems.

Antimicrobial food packaging systems are directed toward reducing surface contamination on processed, prepared products, such as sliced meats and hot dogs. Such packaging materials are not meant to be substitutes for good sanitation practices, but should enhance the safety of a product as an additional hurdle against the growth of pathogenic or spoilage microorganisms.

Researchers at Clemson University have focused on the development, characterization and testing of a packaging film that contains nisin. As you know, nisin is a GRAS substance which is particularly effective for inhibiting Gram-negative bacteria. The scientists' studies have shown that nisin can be released from the coating matrix when tested in a peptone solution using an assay. Once a nisin coating formulation was established by the researchers, they used it to coat the inside surface of barrier bags that would contain individual hot dogs inoculated with a five-strain cocktail of L. monocytogenes--5 log CFU per package. Four different levels of nisin were used in the study. The hot dogs were vacuum packaged, stored at refrigeration temperature and sampled periodically for up to 60 days.

Packaging films coated with a cellulose-based solution containing 10,000 IU per mL and 7,500 IU per mL of nisin significantly decreased L. monocytogenes populations on the surface of hot dogs by greater than 2 log CFU per package throughout the 60-day study. The scientists observed similar results for hot dogs packaged in films coated with 2,500 IU per mL of nisin. L. monocytogenes populations were approximately 4 log CFU per package after 60 days of refrigerated storage from plate counts on tryptic soy and modified oxford agars.

Further information. Kay Cooksey, Department of Packaging Science, Clemson University, B-228 Poole Agricultural Center, Box 340370, Clemson, SC 29634; phone: [phone]; fax: [phone]; email: [e-mail].