Time release of essential oils for packaging

In response to Antimicrobials in food packaging, Gaurav has commented on the use of essential oils as antimicrobials and antifungal agents and asked if I (or perhaps you) can suggest what kind of coating matrix can be most cost-effective for coating on paper or plastic substrates.

What he wants to do is to coat the package wall with a slow release rate to not alter the organoleptic (taste and smell) of the packaged food. Well, I am sure there are a variety of ways already worked out for the dermal patch, slow-release technology. The key word here in his question is “cost”. In principle, any current coating applied to paper and plastic substrates will be cost-effective as it is built into the cost of the existing product. Key to the successful use of any of the coatings will be the release rate of the essential oil from the coating. This, of course, will be related to the diffusion rate of the oil in the coating and the concentration.

Now, most of the essential oils will very likely have a relatively high permeation rate through some polymers and a low permeation rate through others. So the first step is to determine the relative barriers of each polymer coating to the oil of interest. A simple way is to place the oil in a bag made from or with the coating material, place some cotton with the oil in the bag and place in a jar. Set aside and smell the headspace occasionally to see how strong the smell is. Of course, you can also use diffusion instruments to do the testing. At any rate, you have to be able to control the relative rate of diffusion through the coating. Then you can add directly to the coating, but better would be to make a two-layer coating, one to hold the essential oil and the second to cover and control the diffusion.

An alternative approach is to encapsulate the essential oil into a spherical particle covered with a barrier polymer (to the oil) to control the release, or perhaps absorb into a microporous particle for incorporation into the coating to act as a source of the essential oil and let the coating control the rate of diffusion.

While this is not perhaps a direct answer to the specific question, I think you get the idea that there is no direct question for all essential oils, and what is needed is an approach to finding the right coating for any particular essential oil. This is very much the same approach to determining the best coating for flavor and aroma protection.