In September, I attended the 48th International Symposium on Essential Oils (ISEO2017), organised by the University of Pécs, Hungary. Pécs is the 5th largest Hungarian city with a rich history and beautiful architecture, located in the middle of the fields near Croatian border and only a few hours drive from Ljubljana where I live.
ISEO is an annual symposium which attracts not only researchers from all over the world but also industry representatives from different fields connected with essential oils. 152 participants from 32 countries gathered this year, including the initiator of the first event in 1969, Dr Jan Karlsen (Oslo, Norway).
The symposium doesn’t focus on a specific theme each year but covers a broad range of topics on plant volatiles. We had an opportunity to attend 30 lectures and 105 poster presentations on the variability of plant volatiles and their ecological functions, cultivation and postharvest of aromatic plants and biological activity of essential oils. Also, new trends in the production, analysis, toxicology, nanotechnology, regulation and trade of essential oils were introduced.
HOME USE OF ESSENTIAL OILS
At the symposium, I presented a poster – the results of an online survey about the habits of essential oil home use in Slovenia.
When I searched the literature, I was surprised to find that we know very little about which essential oils we use most often, how do we use them and for what purposes, or where do we get information about them (a notable exception is a French study by Nicolas Dornic and co-workers from 2016). So I decided to do my research and presented the results at the symposium. The results do not represent a global pattern as they are based on a country-specific sample, but it’s a start.
As the poster doesn’t cover everything, I made an extended version of the survey with more results, available for download. Here are some of the results:
The survey was received well by other attendees. They were mostly surprised as they realised we don’t have this sort of information, and we agreed it would be useful to have more data. Many found it interesting that frankincense is the third most popular essential oil and that soles seem to be the second most popular site of application. I wasn’t surprised at all 🙂
If you come from aromatherapy scene, ISEO may not be the most exciting event for you, as it brings together the whole diversity of essential oil research – of which therapeutic application is only a small part. You may be surprised how broad this field actually is.
What were the research trends this year? Antimicrobial activity and analytics for sure – from new cutting-edge analytical methods to analyses of the composition of e-liquids, volatiles in black and green tea, passion fruit and many medicinal plants, including some unusual ones such as liverworts.
To my slight disappointment (and in contrast to previous editions of the symposium), there were no reports on the pharmacology of essential oils. However, most lectures were interesting, and I enjoyed the event very much. I’ll summarise some of the most relevant presentations.
The first plenary lecture, titled Biological properties of essentials oils, presented by Dr Ana Cristina Figueiredo (Lisboa, Portugal), was one of my favourites. I was looking forward to her presentation not only because it seemed relevant to my work, but also because I remember her as an excellent lecturer from the symposium on medicinal plants that we organised in Slovenia in 2009.
In her lecture, Dr Figueiredo made a concise overview of essential oils’ diverse and often overlapping modes of action. One of her main messages was the importance of having a critical stance towards evaluating research studies. It is challenging to make straightforward conclusions on biological activity, as studies differ from one another significantly in many parameters, and are therefore rarely comparable. Also, direct contact (in vitro) assays do not necessarily reproduce the response in real life situations and should be used only as an orientation for in vivo and clinical studies.
She also stressed the importance of being aware that essential oils only partially reflect the plants’ volatile profile, and that different extraction methods produce distinct profiles of compounds, which should be considered when interpreting research data.
In the second part of the lecture, Dr Figueiredo presented a case study of essential oils’ nematocidal activity against a parasitic pine nematode. This nematode is widespread in Portugal. It can rapidly destroy a tree and can reduce the yield of Pinus pinaster for more than 60%.
The research group tried to identify the most appropriate essential oil for treating infected trees. Only three essential oils from 84 tested on the nematodes were chosen for testing in a co-culture of the nematode with pine seedlings: Ruta graveolens, Satureja montana and Thymbra capitata. However, Satureja montana (winter savory) was excluded from the experiment because it was toxic to the pine. In this case, the line between killing a pathogen without killing their host is very thin.
Dr Sandy Van Vuuren (Johannesburg, South Africa) presented a comprehensive in vitro study on antimicrobial activity of commercial EOs against two bacterial species most often associated with acne (Propionibacterium acnes and Staphylococcus epidermidis) and identified most potent constituents.
They also tested antimicrobial activity of pairs of essential oils, combinations of essential oil and carrier oil and combinations of essential oils with commercial formulations, looking for potential synergies. We already know that synergies are not present per se in every mixture and predictable, and this was confirmed by Dr Van Vuuren’s research.
From over 400 tested pairs of essential oils, only 4% worked synergistically against acne-associated bacteria, while 41% combinations did not show any antimicrobial activity. Similarly, from 276 combinations of essential oil with a carrier oil, only 2% worked synergistically, while 64% did not show antimicrobial activity and in 34% cases effects were additive.
Some examples of synergistic pairs were myrrh and ylang EOs, lavender and sage lavandifolia EOs, calendula carrier oil and bergamot EO, avocado carrier oil and sandalwood EO. In the next research phase, the group plans to test specific formulations on human subjects.
Interestingly, some essential oils (such as tea tree or patchouli) showed antagonistic activity when combined with commercial acne preparations. If you use conventional preparations for acne, it may not be a good idea to combine them with essential oil.
For more information on this subject, you can read a comprehensive study (Orchard and Van Vuuren 2017) on the use of essential oils as skin antimicrobials.
A lecture by Dr Toni Kutchan (St. Louis, United States) pointed to an entirely different avenue of plant volatiles research. She presented the possibilities for bioengineering of camelina (Camelina sativa), a low-input crop plant, to synthesise high-value compounds for the industrial and pharmacological application. Camelina is a plant Dr Kutcher’s team studies as a possible chemical factory for the production of terpene rich oilseed. Terpenes have a high energy value, and the oilseed could be used as an airplane fuel. The field experiment already showed some promising results.
One of the keynote speakers was Dr Éva Németh-Zámboriné (Budapest, Hungary). The title of her lecture was provoking: Shall we stress the plants to produce more volatiles? Indeed, it’s a widespread assumption that plants growing in a stressed environment produce more volatiles and other secondary metabolites. But the answer is more complicated than we thought. Dr Németh-Zámboriné focused her talk on water stress and presented a few studies with variable results.
One hypothesis is that under the water stress, as the stomata close down, the metabolism directs more towards the synthesis of secondary metabolites, instead of photosynthesis (primary metabolism).
However, many biological and ecological parameters affect the production of volatiles, including intensity and duration of stress and plants’ acclimatisation to it. The latter is an important factor to consider because a stressor can affect plants at the beginning of the exposure, but after a while, its effect may diminish.
In the majority of research studies, the content of essential oil is evaluated only in terms of the yield (mL EO/100g dry mass), without consideration of the change of biomass. Although the yield of stressed plants is often higher, the total amount of essential oil produced may be lower due to a smaller increase in biomass.
Even if taking all of those factors into account, we cannot make general conclusions about the effect of stress on the content of volatiles due to enormous variability of plants. Every species and even subspecies or chemotypes may respond differently.
Did we smell anything? Well, yes, but not much. The only presentation which included smelling (a pheromone and beta-ionone) was a plenary lecture by Dr Jérôme Golebiowski (Nice, France). First, he explained the mechanism of smelling in great detail and then presented some of the results from his lab.
Did you know that human evolution resulted in a loss of almost 50% of olfactory receptors? But we can compensate for this reduction by our intelligence. Or, that we have olfactory receptors outside our nose? They are located almost everywhere in our body, for example in the skin, liver, tongue, kidneys, heart, sperm cells, and so on. They may respond to the same molecules as the receptors in our nose, but we don’t actually “smell” with them – they seem to have various physiological and developmental functions.
Another interesting fact Dr Golebiowski mentioned was that reading a short text out loud in the presence of an odour – regardless of whether it is pleasant or not – is faster and more precise than reading in an odourless situation.
Dr Jérémie Topin (Nice, France) had a lecture about olfactory adaptation: what its significance is and what are the regularities behind it. Olfactory adaptation is a short-term loss of sensitivity to an odour, which occurs at the level of olfactory receptors as well as in the brain. It enables us to detect new odours in our olfactory environment. If we continuously smelled everything we’re exposed to, it would be too difficult to recognise small changes.
In an experiment, they compared adaptation and recovery times between complete essential oils and isolated constituents. Isolates exerted faster adaptation and longer recovery time, compared to essential oils. This seems logical, as concentrations of individual constituents are lower in essential oil and therefore habituation is less likely to occur.
I may add here that adaptation and recovery time also depends on the size of the molecule (bigger molecules tend to saturate our nose faster and for a longer period) and can vary from a few seconds to a few minutes. Recovery time usually takes longer than adaptation – and in case you’re wondering, coffee beans don’t have anything to do with it.
Three lectures were devoted to the use of essential oils as food preservatives. Several essential oils and single constituents can significantly improve the shelf life of fresh foods such as cheese, strawberries, chicken breasts and sausages, in concentrations small enough not to affect their organoleptic properties.
Another research avenue in the food industry is the development of active smart packaging, where essential oils or single constituents are incorporated into packaging materials, without getting into direct contact with food. A third option is to encapsulate active constituents into nanoparticles for slow release (e.g., in the transport of citrus fruits).
Other lectures were mostly about the diversity of plant volatiles and new analytical and methodological approaches, such as kits to determine allergens in cosmetic products or efficient antibacterial screening of essential oil vapour.
Posters covered a similar range of topics but were mostly more specific. Unfortunately, I missed half of them as they were exhibited on the same day as mine.
At the end of the symposium, Dr Karlsen made excellent conclusive remarks. He pointed out that essential oils represent only a part of plant volatiles, much of which is lost or modified during harvest and distillation. We should stop thinking exclusively in terms of an essential oil and start talking about the whole volatile profile (the volatilome). Moreover, research should go beyond chemical analysis and routine antimicrobial screening, and focus instead on a more meaningful, biologically oriented interpretation of analytical data. I couldn’t agree more!
When I was driving back home, I was thinking about the talks I had with the researchers. I asked many of them if they use essential oils at home. It didn’t surprise me that the majority don’t think much about essential oils outside their labs: they either don’t want additional exposure or are just not into “this aromatherapy thing”.
We need to understand that essential oil research is a very diverse field with different aims and applications, of which therapeutic use is only a small part. While basic research is fundamental to any science, the challenge is to convey more research into the applicative setting (e.g., human trials).
One step towards bridging that gap is to have a better overview of what problems people face and what they do with their essential oils at home. That’s what motivated me in the first place to conduct the survey. I encourage you to perform a similar enquiry for your region or a country. The more information we have, the better. I will be glad to help as I learned a lot from my survey and am aware of things that could be improved.
Another and more important step is a close cooperation between essential oil researchers, aromatherapists, medical professionals and research funding bodies. This way, more quality information would be available to everyone, and research studies could be conducted in a way that would better translate into real-life situations. The recent Phyt’Arom congress in Grasse is an excellent example of the advancement in the field.
Photos: Tamás Thaler (with permission) and Pixabay