Edible coatings enhance the microbial safety and extend the shelf life of cooked shell eggs.

Coating the surface of eggs can seal the porous shell surface and limit the penetration of microorganisms into the interior of the eggs. Moreover, such coatings can provide a barrier that would control gas and moisture exchange into and out of the eggs. By controlling the penetration of gas and moisture, you could extend the shelf life of the product.

The intent of scientists at Oregon State University was to evaluate the antibacterial efficacy of coatings against L. monocytogenes and S. enteritidis on hard-boiled eggs. They also wanted to see what effect the coatings would have on egg quality.

In experiments, hard-boiled eggs were coated with chitosan-lysozyme, whey protein isolate (WPI) or a commercial egg wash substitute pan coating. Then they were challenged with L. monocytogenes or S. enteritidis at 104 CFU per g. The samples were stored for four weeks at 10 C.

Investigators also conducted two non-challenge studies. These involved coated shell-on eggs packaged in plastic containers, or peeled eggs that had been coated and vacuum-packaged. The chitosan-lysozyme composite coating offered antimicrobial control against S. enteritidis on the shell-on eggs, but was not effective in inhibiting the growth of L. monocytogenes.

At the end of the four-week storage period, the number of S. enteritidis on the chitosan-lysozyme coated eggs was about 4 [log.sub.10] CFU per g less than the number of the bacteria on the controls. The coatings reduced the population of coliforms and total plate counts, and completely inhibited mold growth during 10 weeks of storage.

The coatings also reduced the amount of weight loss experienced by the eggs: 4.1% to 4.8% for the coated eggs, compared with 7.5% for the uncoated ones at the end of the 10-week storage period. The pH of chitosan-lysozyme-coated eggs remained stable throughout the storage period, while it increased in the control eggs from pH 7.6 to pH 8.6.

Further information. Mark Daeschel, Department of Food Science and Technology, Oregon State University, 100 Wiegand Hall, Corvallis, OR 97331; phone: 541-737-3131; fax: 541-737-1877; email: mark.daeschel@oregonstate.edu.

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