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Sara Burt talks with and answers a few questions about this month's Fast Moving Front in the field of Agricultural Sciences. The author has also sent along images of their work.
Article: Essential oils: their antibacterial properties and potential applications in foods - a review
Authors: Burt, S
Journal: INT J FOOD MICROBIOL, 94 (3): 223-253 AUG 1 2004
Addresses: Univ Utrecht, Fac Vet Med, Dept Publ Hlth & Food Safety, POB 80175, NL-3508 TD Utrecht, Netherlands.
Univ Utrecht, Fac Vet Med, Dept Publ Hlth & Food Safety, NL-3508 TD Utrecht, Netherlands.
This is a Podcast Interview Listen to a podcast by Sara Burt discussing this research.

Why do you think your paper is highly cited?

The topic of plant essential oils is interesting to researchers in the fields of food science, animal nutrition, and medical research and the interest is due to the chemical properties of the phenolic substances that the oils contain. I think that's partly why my review has delivered so many citations. It also fits in with the current "back to nature" trends in life science research.

Does it describe a new discovery, methodology, or synthesis of knowledge?

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My review bundled the current knowledge on the antibacterial properties of edible volatile oils (essential oils) obtained from plants. It summarized the known facts on concentrations required to inhibit growth of pathogenic bacteria and/or to reduce numbers of viable cells both in vitro and in food models. In addition to that, I included information on the historical uses of these oils and explained, for example, why they are called "essential."

At the end of the article, I indicated the safety and legal aspects which would need to be addressed if these oils were to be used in greater amounts than they are at present. There is still much that is unknown about the mode of action of certain plant oil constituents, and this is where I think the focus of the research is now needed.

Would you summarize the significance of your paper in layman's terms?

The paper provided an overview of the results of research on the ability of plant essential oils to inhibit and kill harmful bacteria, both in laboratory tests and in food. It presented the results of studies in a form which enabled other scientists to compare the performance of different essential oils and to see which ones were most promising for further research and development.

Although there are several research groups around the world working with plant extracts and volatile oils, they have different specialisms. Some focus on plants that grow in their region of the world; others use a particular method of extracting the chemical substance from the plant—gas extraction, methanolic extraction, or obtaining the substance by crushing the plant.

Most groups are interested in developing the antibacterial or antifungal properties for the improvement of human health. It was useful to present a systematic overview of the data on antibacterial properties of edible essential oils, so other workers in the field could draw information from it. Generally, oregano, clove, and thyme oils were the most active against bacteria that cause food poisoning.

How did you become involved in this research and were there any particular problems encountered along the way?

Another aspect of essential oils is their ability to support or strengthen the actions of other antibacterials, such as antibiotics.

As a food scientist planning a Ph.D. project, I was looking for an area of food microbiology research that had veterinary health significance (zoonotic pathogens) and where there was still much to be discovered. Apart from small practical problems which everyone has, the only real problem encountered was one of choice; so many interesting results come out of the experiments that we have had trouble deciding which aspect should first be subject to further examination.

Where do you see your research leading in the future?

Joint research with biochemists and molecular biologists has already begun and we have published five papers on this topic since the review article discussed here. We are presently examining the mechanism by which the main antibacterial component of oregano oil (carvacrol) inhibits the development of normal bacterial cells. We want to find out to what extent this reduces their ability to infect humans and animals. This "interdisciplinary" research is particularly enjoyable because you learn new techniques from the scientists from other disciplines.

At the moment, we are looking at the changes in bacteria at very low concentrations of essential oils. Low concentrations mean smaller flavor and aroma changes in food or feed, lower costs, and can still bring about significant disadvantages to the bacteria.

Another aspect of essential oils is their ability to support or strengthen the actions of other antibacterials, such as antibiotics. This synergy could lead to even more applications.

Accompanying photos show how oregano oil can prevent bacteria from developing "flagella," which the bacteria use for swimming. We think this makes it more difficult for the bacteria to colonize the gut of people and animals and we are currently working to examine this effect.

Do you foresee any social or political implications for your research?

Only the intrinsic limitations of the oils and a few practical obstacles are expected. I hope that our research will eventually lead to the development of substances useful in preventing or treating bacterial infections in people and/or in animals.

Sara A. Burt, Ph. D.
Institute for Risk Assessment Sciences (IRAS)
Division of Veterinary Public Health
University of Utrecht
Utrecht, The Netherlands

Keywords: plant essential oils, food science, animal nutrition, phenolic substances, antibacterial properties, edible volatile oils, pathogenic bacteria, plant oil constituents, plant extracts, volatile oils, methanolic extraction, oregano oil (carvacrol), clove oil, thyme oil, zoonotic pathogens, antibacterials, antibiotics, flagella.


2008 : May 2008 - Fast Moving Fronts : Sara Burt