Thursday, February 2, 2012
If some essential oils are anti-microbial, why aren't we using them as preservatives?
Because they aren't very good anti-microbials in the sense of being able to preserve our products. They might have some wonderful anti-microbial properties on their own - good at killing yeast or bacteria - but they don't offer enough preserving power to keep our products safe. Let's take a look at the science!
I think it's been established that some essential oils have great antimicrobial abilities. For instance, in this study about using cinnamon and clove oils to combat mold, it was found that "Levels of the oils above 250 ppm and of cinnamic aldehyde and eugenol above 200 ppm completely inhibited mold growth, or permitted only a small amount of growth that never reached secondary metabolism and never produced aflatoxins during the time of this study." This study concluded that "Both essential oils possessed significant antimicrobial effects against all microorganisms tested". This study showed that "EOs from cinnamon, allspice, and clove bud plants are compatible with the sensory characteristics of apple-based edible films. These films could extend product shelf life and reduce risk of pathogen growth on food surfaces." We know that tea tree has some antimicrobial properties. (And finally, click here for a great article on tea tree, thyme, peppermint, and rosemary as antimicrobial agents.) Rather than go on for hours, I think we can call it established that some essential oils have the potential to kill beasties!
For instance, this study exploring the antibacterial potential of Ocimum gratissimum essential oil (clove basil, which contains a lot of eugenol) found that "Liquid and semisolid formulations of the oil were designed in a variety of bases for topical antiseptic medication. The products were evaluated by agar diffusion assay against type strains and clinical isolates from boil, wound and pimples. Remarkable antibacterial effects, higher than those of commercial antiseptic products, were demonstrated at 2% Ocimum oil concentration in some bases. The properties of base into which the oil was incorporated affected its activity. It was more effective in hydrophilic bases than in lipophilic bases. Solubilization and microemulsification grossly reduced its activity." So they found that clove basil had great anti-bacterial properties, but adding it to an oil base (lipophilic base) and emulsifying it grossly reduced the activity.
And this is our problem. It isn't as simple as adding essential oils at reasonable levels in the cool down phase. We have to consider what is water soluble and what is oil soluble. We have to consider that emulsions can mess up the chemical properties of things - one of the reasons we can't make our own sunscreen - and we have to consider solubility. We have to take into consideration that our products are complicated things, and science hasn't found a way to make essential oils work as active preservatives yet!
Want to know more about the picture above? Yes, that really is a beach scene painted on a petri dish with fluorescent bacteria! - click here!