Nature is a source of substances with vastly different properties. It is therefore no wonder that for many years man has found – and still finds – interesting substances in nature – some of which have found their way to cosmetics. For example, many medicines are or are inspired by substances from nature. In cosmetics, natural substances are gradually gaining a more and more prominent place.
PLANT EXTRACTS IN SKINCARE
EXTRACTIONS IN COSMETICS
Nature has developed properties which often are very useful and can be difficult to obtain in other ways. As examples, plants contain many interesting antioxidants, anti-inflammatory substances, antimicrobials, cleansing, exfoliating, barrier-building and moisturizing substances. An example is Rooibos, with the Latin name Aspalathus Linearis: Extracts of this plant can have significant antioxidant and antibacterial properties, which can benefit impure skin. Another good example is the well-known medicinal plant chamomile, with the Latin name Anthemis Nobilis, where the flower heads are often used to extract substances with e.g. anti-inflammatory properties. Two of the interesting active ingredients from chamomile are Chamazulene and α-Bisabolol. A third example could be the extract of the fig cactus, Opuntia Ficus-indica, which has good moisturizing and antioxidant properties. Of course, animals can also make interesting substances. For example, bees from which we get honey and beeswax, fish from which you can extract moisture-retaining collagen and silkworms, from which we get silk and thereof you can extract certain proteins with interesting moisturizing properties for skin and hair. A way to obtain desired substances from nature is with different extraction processes.
EXTRACTION AND EXTRACTION PROCESSES
Extraction is the process of separating or extracting something from where it was originally – in a matrix. There are many extraction techniques and many different areas where they are used – for example at home in the kitchen, in hospitals, at treatment plants, in companies such as those producing food, medicines and raw materials for other industries and many other places. Extraction has historically been of great importance.
Extraction methods can be divided into several different types and in different ways. An overall division can be to distinguish between whether the matrix from which you want to extract something is in solid form or liquid form. In the same way, you can also divide according to whether the extraction agent used is in solid form, liquid form or gaseous form. Thus, in general, the types are liquid / liquid extraction, solid / liquid extraction, solid / gas extraction or liquid / solid extraction.
In the following, some different extraction techniques, such as those used for the extraction of plant materials, will be presented.
Maceration is a relatively simple solid / liquid extraction technique in which the material to be extracted is soaked in the solvent at room temperature for a minimum of 3 days with regular stirring, and then filtered. This technique is used e.g. in winemaking (the first fermentation process).
You can use various solvents which are liquid at room temperature in maceration. Typically, a lot of solvent is used in this technique, but in return the process is gentle on heat-sensitive substances in the plant material.
Infusion is also a simple technique in which the solvent, which is often water, is cold or hot (boiling point) or somewhere in between. The extraction time is usually in minutes followed by filtration and often the ratio of the material to the solvent will be fixed. As an example: Tea brewing is infusion. This technique produces substances which dissolve relatively quickly in the solvent (depending on the extraction time and temperature).
There is a very similar technique called “digestion” where you heat the solvent a little during the extraction, whereby you extract more substances from the material.
In decoction, water is often used at the boiling point as solvent. The ratio of material to solvent (e.g. 1: 4) and the extraction time (typically in minutes) are usually fixed. In some cases, the extract is boiled during the extraction so that the amount of solvent is reduced, whereby the resulting extract is concentrated before being filtered. This technique is used for some types of coffee brewing. In relation to maceration and infusion, you also get a little more oil-soluble substances out of the material. The technique is not suitable for heat-labile substances.
Percolation is somewhat similar to the previous techniques, but here you let the solvent penetrate through a layer of the material from which you want to extract substances. Often a funnel-shaped equipment is used in which you place the material, which may be moistened with the solvent first for some time before pouring the cold or hot solvent over and letting it penetrate slowly (in some cases you let them draw some time before the funnel opens at the bottom and the extract drips out). This technique is known, for example, from coffee brewing.
HOT CONTINUOUS (REFLUX) EXTRACTION – SOXHLET
This extraction technique usually uses a special closed equipment called a “Soxhlet” (named after the inventor, Franz von Soxhlet), where the finely divided material to be extracted is placed in a special container while the solvent is in a flask below. The solvent is heated during stirring so that its vapors rise upwards in the Soxhlet, condense on in a cooling tube and drip into the container with the material where the extraction takes place. When this container becomes full, the extraction liquid is passed down into the flask and thus this reflux process continues a number of times. This process uses less solvent compared to the techniques described above but is not suitable for heat-labile substances. You can use different solvents for this technique – and this will determine the composition of the final extract. The technique is used, for example, in laboratory studies of environmental samples and food.
PRESSURIZED LIQUID EXTRACTION
This technique is also called accelerated solvent extraction and is, as the name suggests, extraction with a solvent in liquid form under high pressure (typically 50-100 Atm) – and heated so that the solvent remains in liquid form. It is a relatively fast and efficient extraction method, and the amount of solvent is relatively low. The solvent can be, for example, ethanol and water.
SUPERCRITICAL FLUID EXTRACTION
This technique is among the newer techniques, where instead of a solvent that is in liquid form under normal pressure and temperature, a solvent is used which will normally be in gaseous form but via a combination of higher pressure and temperature (depending on the gas’ critical point) it comes in a supercritical liquid form, which has a high density and properties that are somewhat similar to liquid and gas. It provides special extraction properties that can be adjusted with pressure and temperature. The most common solvent is CO2, which is obtained in supercritical fluid form at a pressure above 73 Atm and a temperature above 31 ° C. It is thus suitable for extracting heat-sensitive substances such as some fragrant oils. Other advantages are that CO2 is a safe substance, cheap, not harmful to the environment and the solvent (CO2) can be easily removed, so you have your extract without solvent after the extraction. However, CO2 has some limitations (like other solvents) in terms of which substances it can extract – it is primarily the more lipophilic substances that are extracted. This can be remedied a bit by adding small amounts of some other substances to CO2 such as ethanol. This technique is used, for example, to reduce the caffeine content of coffee and to certain plant extracts, such as essential oils and oleoresins.
ULTRASOUND, MICROWAVE AND ENZYME-ASSISTED EXTRACTION TECHNIQUES
You can increase the yield of the extraction process by “adding” different techniques:
With ultrasound (Sonication) an ultrasonic frequency between 20 and 2000 kHz is added to the extraction, which e.g. increases the permeability of the cell walls in the material and thus facilitates the release of substances from the material so that the extraction time can be shortened and less solvent must be used. A disadvantage of ultrasound is that it can alter some natural substances so that free radicals are produced.
With microwaves, heat is generated by interacting with polar substances such as water, which increases the extraction yield in less time and reduces solvent consumption. It is not suitable for heat-labile substances and the heating process is not completely evenly distributed during the extraction.
Enzymes can help to break down, for example, cell walls and membranes in the material and thus facilitate the release of substances from the material.
These techniques are used primarily to extract volatile substances such as essential oils. There are slightly different techniques, but basically it involves using hot water or water vapor or vapors from other solvents to extract substances from the material. The volatile substances come into gaseous form in the closed container and condense together with the solvent into a liquid. This liquid can afterwards be separated into the two components. One will often try to keep the temperature as low as possible as many volatile substances from plants are sensitive to temperature. Steam distillation is the most common technique for extracting essential oils.
By pressing, (typically) oils are simply squeezed out of the glands in which the plant produces them. Not all plant materials are suitable for this technique, and it is usually not quite as efficient as solvent extraction. In order to optimize the utilization of the plant material, you therefore often choose to make an “extra” extraction with solvent, so that you can extract more of the desired substances.
The pressing process is usually used for fresh plant material, without the use of solvent (plant material will contain liquid) and can be hot or cold – for example, the technique is used for cold-pressed olive oil. One type of essential oil that is typically produced by pressing is citrus peel essential oils.
- Zhang, QW., Lin, LG. & Ye, WC. Techniques for extraction and isolation of natural products: a comprehensive review. Chinese Medicine 13, 20 (2018)
- Azwanida, NN. A Review on the Extraction Methods Use in Medicinal Plants, Principle, Strength and Limitation. Medicinal and Aromatic plants 4 (2015): 1-6
- Patel, K., Panchal, N., Ingle, P., Review of Extraction Techniques – Extraction Methods: Microwave, Ultrasonic, Pressurized Fluid, Soxhlet Extraction, Etc. International Journal of Advanced Research in Chemical Science 2019, 6(3): 06-21
- Handa, S. S., Khanuja, S. P. S., Longo, G. & Rakesh, D. D. (2008). Extraction Technologies for Medicinal and Aromatic Plants. United Nations Industrial Development Organization and the International Centre for Science and High Technology
- Berkem website. Plant Extraction: the heart of Berkem’s trade. Lokaliseret 3. Juli 2021: https://www.berkem.com/en/expertise-en/plant-extraction