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Many people are familiar with St. John’s wort oil and its characteristic deep red colour. Numerous manufacturers offer this oil, which is used for neuralgia, rheumatism, lumbago and sprains. With its calming, analgesic and wound-healing properties, it not only helps with cracked skin and skin irritations where the skin is reddened, but also with minor burns.
The red oil is very easy to make at home. To do this you need a plant oil, such as olive or peanut oil, and fresh St. John’s wort (Hypericum perforatum). You can find the bright yellow flower growing along the roadside in June, usually in areas of full sunlight. Traditionally, flowering St. John’s wort is finely chopped and steeped in plant oil for four weeks in transparent glass jars placed in direct sunlight. During this time, the components of the St. John’s wort seep into the oil and the initially greenish-yellow blend turns red. After pressing the plant parts, the oil is ready.
How can you tell the quality of the oil?
This was the very question asked by WALA, which uses the red oil in its WALA Medicines and Dr. Hauschka Skin Care products. Miriam Heinrich, then a PhD student in the WALA Department of Phytochemical Research, wrote her thesis on the subject. She carried out her research together with her colleagues at WALA. Prof. Rolf Daniels from the Institute of Pharmaceutical Sciences at Eberhard Karls University in Tübingen provided scientific support for her PhD.1
First, the team had to develop a method that enabled the quality of the oil to be determined reliably and, to use the scientific term, reproducibly. With the help of UHPLC technology, the researchers were able to identify the key ingredients of the red oil. UHPLC stands for ultra high performance liquid chromatography. This process enables the components in liquids to be separated and precisely quantified – i.e., the exact quantities of each ingredient to be determined. Using spectrophotometric measurements, the research group was also able to characterise the shades of red and the colour intensity of the St. John’s wort oil. A spectrophotometer measures how much light passes through a liquid and the spectral proportion of light that is absorbed by the liquid.
Using UHPLC separation, the researchers were able to identify up to 25 different constituents in the fresh plant material. In the traditional production of this oil, these substances – which are secondary plant metabolites known as phytochemicals – are transferred into the oil extract in varying quantities. They include antioxidant flavonoids and other phenolic compounds that are similar to hypericin. The latter are what gives the oil its red colour and are apparently responsible for the antidepressant effect of St. John’s wort. The greater the quantities of these compounds, the higher the quality of the oil.
Can the quality and colour of the oil be optimised?
In a second step, the research group looked into the manufacturing method of this oil and found that the temperature and light conditions under which the oil extract matures for four weeks strongly influence the quality of the oil.1 In addition, a follow-up study proved that the type of plant oil used is decisive for the result.2 Peanut, soy, almond, sunflower, maize germ, macadamia, olive, jojoba and sesame oil were all used for the extract. The colour and components of the finished product varied depending on the oil used. These research results will allow for the optimisation of St. John’s wort oil production in the future.
The researchers also discovered something extraordinary. Hypericin was not traceable in the oil extract, only derivatives – i.e., similar molecules derived from it. However, the exact characterisation of these derivatives was not possible. It is therefore impossible to say which combination of substances is ultimately responsible for the oil’s distinctive red colour. St. John’s wort still keeps its secret to this today.
1 Heinrich M, Daniels R, Stintzing FC, Kammerer DR. “Comprehensive phytochemical characterization of St. John’s wort (Hypericum perforatum L.) oil macerates obtained by different extraction protocols via analytical tools applicable in routine control.” Pharmazie 2017; 72:131–138.
2 Heinrich M, Vikuk V, Daniels R, Stintzing FC, Kammerer DR. “Characterization of Hypericum perforatum L. (St. John’s wort) macerates prepared with different fatty oils upon processing and storage.” Phytochemistry Letters 2017; 20:470-480.