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CO2 extraction – an effective way to get the most out of plant processing by-products!

As large amounts of medicinal and aromatic plants are being processed, mountains of by-products are piling up – quite literally. After the steam distillation process of chamomile (Matricaria), tons of biomass remain. Until this moment, the biomass has been used as digestate. By-products are also created during the cultivation of plant biomass in bioreactors (in vitro). Although the amounts of such by-products are small, very often the mass of by-products is still rich in various active compounds and valuable substances.

In order to extract active ingredients from the by-product biomass, SIA “Field and Forest” together with partners SIA “Alternative plants” and the Institute of Environmental Solutionscarries out the project “A biorefinery approach for the development of bioactive cosmetic ingredients from by-products of medicinal plant processing and plant cell cultivation”. During the project, the biologically active substances are obtained from the by-products of the processing of chamomile (Matricaria) and the by-products of the in vitro cultivation of dragonhead (Dracocephalum), gooseberry (Ribes) and juniper (Juniperus) biomass. Our researchers have identified supercritical CO2 extraction as the most successful and environmentally friendly way to extract active ingredients from the by-product biomass. In order to understand the extraction process, the essence of the specific method and the main advantages, we invited the head of the chemistry laboratory of the Institute of Environmental Solutions, Dr. Ilva Nakurte and SIA “Field and Forest” researcher and product development specialist Liene Kienkas to an interview with us.

Tell us why you chose to work with the supercritical CO2 extraction method?

Ilva Nakurte: The Institute of Environmental Solutions, in cooperation with SIA “Field and Forest”, has accumulated vast experience in the multi-stage extraction processes of medicinal and aromatic plants. We have knowledge of the solvents that must be used to extract certain active substances. However, many of the solvents are harmful and even toxic – so extra work is required to reduce the amount of residual solvents in the final product. This, in turn, requires additional testing and is more costly. In contrast, the COextraction method is much less harmful to the environment, as no toxic solvents are used and the CO gas itself does not have to be specifically separated from the final product after the extraction process. In addition, the method is also quite effective, because we can obtain a “cocktail” of various active substances, from which it is easy to further extract the compounds of interest.

Liene Kienkas: CO2 extraction is a great addition to the extraction technology cycle. By steam distillation, we can obtain volatile compounds from biomass. Using water extraction, water-soluble compounds are obtained. In turn, COextraction allows to obtain a wide range of lipophilic compounds from biomass. By combining these extraction methods, we can get the full use of the plant and the by-products are 100% recycled.

 

Supercritical CO2 extractor. Image: IES.

Supercritical CO2 extractor. Image: IES.

What are the conclusions after first tests of supercritical CO2 extraction method?

IN: Firstly, the hypothesis that by-products of medicinal and aromatic plant processing and biomass cultivation contain valuable and potentially cosmetic active compounds, has been confirmed. We are pleased that using this extraction method we have obtained a number of compounds which, in the context of these plants, have been described in the scientific literature but which we had not yet encountered. The biological activity of identified and potentially useful compounds is tested in the laboratory of our project partners “Alternative Plants”. You can read more about these tests in an interview with “Alternative Plants” researchers Anna Ramata-Stunda and Mārtiņš Borodušķis. Tested substances show good results, such as hight antiradical and photoprotective activity. As for the by-products of biomass cultivation, they contain substances that are highy demanded in the cosmetic ingredient production industry, such as rosemary acid, caffeic acid and chlorogenic acid.

What is the working principle of CO2 extraction?

LK: The basic principle is the same for any extraction process – just as similar dissolves similar, similar extracts similar. We use liquefied CO2 in the extractor and, by changing the pressure and temperature, ensure the transition of CO2 to the supercritical phase and its complete recirculation at the end of the process. In supercritical phase, COhas properties of both gas and liquid. Like gas, CO2 is able to enter microscopic cells and expel active substances. But the solving properties of aupercritical CO2 are as strong as those of a substance in the liquid phase. By changing the pressure, temperature and cosolvent, we can carry out a targeted extraction process.

How to prepare samples for supercritical CO2 extraction?

LK: Biomass must be dry. The surface area of the sample must be as large as possible, so the biomass must be finely ground. We are currently looking for the best technological solution for the preparation of biomass cultivation by-products. These by-products are gel-like and must be dried either by lyophilization or under particularly gentle conventional drying conditions before extraction.

Addition of crushed dried chamomile (Matricaria) petal powder to the extractor tank. Image: IES.

Addition of crushed dried chamomile (Matricaria) petal powder to the extractor tank. Image: IES.

You mentioned that CO2 extraction allows to obtain a wide range of different compounds and substances. Can you list the main classes of substances?

IN: The range is broad! We can obtain vitamins, sugars, amino acids, flavonoids, polyphenols, tannins, saponins, lignins, terpenes, essential oils. Also proteins, minerals and other compounds also enter the extract.

Chamomile (Matricaria) by-product extracts obtained with a CO2 extractor. Image: NRA.

Chamomile (Matricaria) by-product extracts obtained with a CO2 extractor. Image: IES.

What are the advantages of this extraction method? Does the method have any drawbacks?

LK: The main advantage of the method is that the solvent is environmentally friendly. It leaves no residue in the extracted product and does not need to be removed from the product after the extraction process – CO2 is recycled back into the extraction system. The extraction is efficient, and of course the advantage is that we can extract different compounds with one solvent!

In terms of drawbacks, we see that scalability of the process could be challenging. If the extraction is for commercial purposes, dozens of reactors would have to be purchased and operated at the same time due to the limited capacity of the reactor tanks. Both the purchase and maintenance of the equipment  would be very costly. Ensuring low moisture content of by-products biomass is also rather difficult.

Generally, supercritical CO2 extraction is a process that requires continuous learning – as we work with different types of biomass, the result will always be different for the same parameters. The researcher must get to know the extraction equipment thoroughly, so that they you can quickly figure out which settings will be the right ones to “squeeze out” the desired miz of compounds from the biomass!

Research “A biorefinery approach for the development of bioactive cosmetic ingredients from by-products of medicinal plant processing and plant cell cultivation” (1.1.1.1/19/A/075) is developed as a part of the European Regional Development Fund programme 1 .1.1.1 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 on the project here.