Lysozyme- and nisin-containing films control bacteria on salmon.

Cold-smoked salmon is a ready-to-eat (RTE) product normally purchased in a vacuum-packed system. It has a shelf life of three to five weeks at refrigerated temperatures.

A major concern of smoked fish processors involves the contamination of their products with L. monocytogenes or Salmonella species. Scientists at Louisiana State University wanted to determine the feasibility of using oyster lysozyme in various antimicrobial coatings to enhance the preservation of cold-smoked salmon and minimize the growth of bacteria on the product.

Smoked salmon samples were cut into 1-g pieces and inoculated with broth cultures of L. monocytogenes and S. anatum. Then the pieces were dipped into calcium alginate, zein or agar coatings containing 160 g per ml of oyster lysozyme or hen egg white lysozyme, both with or without nisin at 1000 IU per g. The treated samples were allowed to air-dry for 20 minutes and were refrigerated at 4 C.

The scientists determined bacterial counts at various intervals up to 35 days. The investigators found that S. anatum counts declined by 1.82 log CFU per g when oyster lysozyme was incorporated into calcium alginate film, as compared to the non-coated salmon on day one. However, S. anatum counts were only reduced by 0.97 and 0.4 log CFU per g when smoked salmon samples were coated with zein or agar coatings containing oyster lysozyme, respectively, on the first day.

Calcium alginate coatings containing nisin and oyster lysozyme reduced levels of L. monocytogenes and S. anatum by 2.75 log CFU per g and by 2.25 log CFU per g, respectively, by day 35. There was no significant difference between the coatings containing oyster lysozyme and hen egg white lysozyme in reducing the bacterial counts.

It appears that calcium alginate edible film was the most effective coating for retaining the antimicrobial activity of nisin, oyster lysozyme or hen egg white lysozyme against L. monocytogenes and S. anatum throughout the 35-day test period.

Further information. Marlene Janes, Department of Food Science, Louisiana State University, LSU AgCenter, 111 Food Science Building, LSU Campus, LA 70894; phone: [phone]; fax: [phone]; email: [e-mail].

In this issue ... Smoked fish processors are concerned about the contamination of their products by bacteria. So, scientists examined the feasibility of using oyster lysozyme in antimicrobial coatings to improve the preservation of cold-smoked salmon. Reduce the potential for foodborne pathogens to grow both inside eggs and on the eggshell surface by using cooler water to wash shell eggs during a second washing. See how a variety of hurdles can be used to replace thermal sterilization.