A repelling innovation: insect repellents from the waste of essential oil production
Zero-waste - Although this phrase suggests shopping in bulk, waste-free and strictly restricting consumption, this bioeconomy concept is particularly effective when implemented in a production environment. For example, materials that have before been written off as waste are now seen as potential raw materials for the development of innovative products. At the moment, at the Institute of Environmental Solutions, we give meaningful second life to the production by-products of our partners, the leading Baltic medicinal and aromatic plant grower "Field and Forest".
IES: Please tell us what this production "waste" is and how must it be treated in order to serve as a basis for the development of botanical repellents?
Dr. Laura Pastare: These are by-products of the biorefining of essential oils. Our project partner Field and Forest provides a large amount of biomass that has been steamed during distillation. Although biomass has lost some of the valuable compounds concentrated in the essential oil and flower waters, it is still full of valuable substances - the so-called secondary metabolites.
IES: What plant biomass waste is studied? Are any of them already known to have insect repellent properties?
LP: We study extracts from three plant species that Field and Forest work with on a daily basis: chamomile (Matricaria chamomilla), caraway (Carum carvi) and pine (Pinus sylvestris). In traditional knowledge, chamomile infusions are mentioned to have insect-repelling properties. Both chamomile and the other two plants are rich in various active compounds and have great potential - why not test it out?
Chamomile and its essential oil. Photo: SIA "Field and Forest"
IES: In order to develop these botanical pesticides, you need biomass extracts. How are they obtained and analyzed?
LP: The by-product biomass extracts are prepared by the project partner Field and Forest. The extracts are obtained by varying different parameters (biomass to water ratio, temperature, duration), because the chemical composition of the final extract and the concentrations of the active compounds also vary as the extraction method is changed. The next step is the on-site chemical screening at IES. Using a microplate spectrophotometer, we determine the main classes of active substances (e.g phenols, flavanoids, tannins, saponins, etc.) and their concentrations in the extracts. Although the microplate reader does not provide information on the presence and amount of specific compounds, it has the advantage of being able to analyze a large number of samples simultaneously. Using this initial screening, we "sift through" the samples in whichthat contain the largest concentrations of compounds of chemical classes that we are interested in. After analyzing the results, we provide feedback to “Field and Forest” on which extraction methods have worked the best. The extract samples are then forwarded to insect tests and plant allelopathic tests. If green light is obtained in the tests, the extract is examined in-depth, using liquid chromatography-mass spectrometry to identify and analyze already specific chemical compounds.Microplates with samples already colored using reagents. Photo: IES
IES: What happens in the insect tests? And what - in plant allelopathic tests?
LP: Insect tests check the extract's repellency towards selected insects - peach aphid (Mizus persicae), greenhouse whitefly (Trialeurodes vaporariorum) and cabbage white (Pieris brassicae). We conclude, whether the insect's behavior or eating habits change. Tests on the allelopathic properties of plants assess how the selected plants (cabbage and cucumber seedlings) react to the spraying of the developed repellent - does the plant show no signs of stress?
Colleagues from IES will tell you more about these tests in the next news articles.
IES: How is with the scientific literature - is the development of biological repellents a popular topic? Is it easy to gain useful information for the study?
LP: This topic is researched globally, we can't say there is a lack of information. However, it should be understood that, for example, the extracts analyzed in the other studies are obtained under different conditions and using different methods. Therefore, the results are also different. Even if the resulting substance classes are similar, the proportions are likely to be different. As it is in the pharmceutical development process - it's more likely the synergy of several compounds, not the effect of a single active substance. Therefore, it is difficult to interpret and use the research already done, because it is not always known exactly what is responsible for the desired effect. There is a lot of research in the field of medicinal plants. It's like a forest where you have to cut your own path - but it's interesting!
IES: Tell us more about the planned products. How will repellents work and what pests are they designed to repel?
LP: As part of the project, we are developinged deterrents against 3 insect species: peach aphid (Myzus persicae), the greenhouse whitefly (Trialeurodes vaporariorum) and cabbage white (Pieris brassicae). Ideally, we aim to develop one universal repellent for all these insects. However, if this fails, we will develop a prototype repellent for each pest. Insect repellents that are currently available on the market operate on the basis of physical properties. For example, by creating a reflection on the leaves, which makes the plant “invisible” to the insect. Or by creating a physical barrier that prevents the insect from biting into the plant.
IES: Why is it important to determine the chemical composition of extracts?
LP: The main repellent activity of the extracts may be caused by various secondary metabolites of the plants, such as flavonoids, tannins. Flavonoids are compounds that perform various regulatory functions in plants, such as regulating growth rate, pigmentation, the plant's natural protection against pests, and other functions. Tannins are compounds whose role is to help protect the plant against fungal and bacterial infections. By obtaining extracts even from a previously distilled biomass, these active substances are transferred from the plant to the extract. By determining the presence and concentration of these groups of compounds in the extracts, we are one step closer to determining which compounds or combinations thereof are responsible for this repellent activity!
The research is a part of the project “Essential oil distillation waste streams as a potential source of sustainable plant-based repellent products” (No. Nr. 22.214.171.124/20/A/096). It is developed as a part of the European Regional Development Fund programme 126.96.36.199 measure “Support for applied research” and specific objective 1.1.1 “Improve research and innovation capacity and the ability of Latvian research institutions to attract external funding, by investing in human capital and infrastructure”.
More about the project here.