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Since the early history of mankind there have been pictorial and written references about the use of incense, be it for religious-ritual purposes, as a remedy or as a spice. Already in ancient times, starting from today's Oman, the “Incense Trade Road” has been established, via which the precious goods were distributed further north and west and brought indescribable wealth to the neighbouring countries. Outside of the Arabian Peninsula, however, frankincense is also found in eastern Africa and India. The best-known types of incense are the "Indian incense", that is obtained from Boswellia serrata ROXB. (Burseraceae) is obtained, as well as the very high priced “Arabian incense”, which derives from B. sacra FLÜCK. Other species occur mainly in East Africa, for example in Ethiopia ["Ethiopian frankincense", B. papyrifera (DELILE ex CAILL.) HOCHST].
The problem is that the high-priced varieties are often blended with inferior varieties, mostly from East Africa. Even if there is no approved (registered) medicinal product based on frankincense in Germany, internal consumption for medical purposes is heavily advertised on the Internet, mostly with questionable promises of salvation. There are quite a few pharmacological studies that deal with the health-promoting effects of frankincense, mostly an anti-inflammatory effect. However, there is currently a lack of meaningful clinical studies.
Because of the widespread use of incense-containing medicines and dietary supplements, both the American USP and the European Pharmacopoeia felt compelled to establish monographs on Indian incense (B. serrata; Olibanum indicum). On closer inspection, however, these monographs appear inadequate. In addition, extracts of dubious quality are often produced and marketed.
In cooperation with the company Floradex in Oßmannstedt / Thuringia, high-quality ethanol-based extracts were initially developed, which, in addition to incense samples from various sources, were included in these studies, with a focus on the analytical investigations of the high-quality "Arabian incense", B. sacra. The overriding goal was to develop suggestions for improving the existing pharmacopoeia monographs.
The preparation of the samples for physico-chemical analysis turned out to be problematic. Approx. 50% of frankincense consists of mostly polymeric, swellable materials, which hardly dissolve in alcohols, but in some cases, it can significantly interfere with the chromatographic analysis. To avoid these problems, an efficient extraction method and simple sample preparation were developed. A Soxhlet extraction with subsequent separation of the acidic components by solvent-extracting twice is suitable. This method works particularly well with B. sacra.
In the second step, the TLC separation was reworked to identify the materials. It was found that even with different mobile phases, extensive separation of the triterpene acids was difficult to achieve. An acidic solvent, combined with a two-fold, short development on HPTLC plates, and with an evaluation at UV 254 nm followed by the development with anisaldehyde reagent, proved to be the most favourable. This method is clearly superior to the current pharmacopoeia monographs, as many of the value-determining triterpenic acids can be identified separately.
The revision of the HPLC method turned out to be a major challenge. Of the approx. 20 triterpene acids that occur in significant amounts in frankincense, only two keto-boswellic acids are considered, which also only make up a small proportion in terms of quantity (approx. 1-3%, based on the raw material). First of all, very time-consuming experiments attempted to derivatize the acid function or the alcohol function of the triterpenic acids either via an ester bond or an acid amide bond with an aromatic ring system that can be detected without problems at UV 254 nm and higher. Unfortunately, due to the complexity of the samples, this venture proved unsuccessful. In contrast, the attempts to find a suitable internal standard (β-glycyrrhetinic acid) and the quantitative determination of other substances using response factors were successful.
A total of 11 frankincense samples (extracts plus raw materials) were processed comprehensively and many unresolved questions about chromatographic analysis could be clarified. On this basis, suggestions for the improvement of the existing pharmacopoeia monographs could be made.