Sara Burt talks with
ScienceWatch.com 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
Article: Essential oils: their antibacterial
properties and potential applications in foods - a
Journal: INT J FOOD MICROBIOL, 94 (3): 223-253 AUG 1
Addresses: Univ Utrecht, Fac Vet Med, Dept Publ Hlth &
Food Safety, POB 80175, NL-3508 TD Utrecht,
Univ Utrecht, Fac Vet Med, Dept Publ Hlth & Food
Safety, NL-3508 TD Utrecht, Netherlands.
Listen to a podcast by Sara Burt
discussing this research.
Why do you think your paper is highly
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
Does it describe a new discovery, methodology, or synthesis of
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
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
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
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
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.