Abstract
Triterpene compounds like betulin, betulinic acid, erythrodiol, oleanolic acid and lupeol are known for many pharmacological effects. All these substances are found in the outer bark of birch. Apart from its pharmacological effects, birch bark extract can be used to stabilise semisolid systems. Normally, birch bark extract is produced for this purpose by extraction with organic solvents. Employing supercritical fluid technology, our aim was to develop a birch bark dry extract suitable for stabilisation of lipophilic gels with improved properties while avoiding the use of toxic solvents. With supercritical carbon dioxide, three different particle formation methods from supercritical solutions have been tested. First, particle deposition was performed from a supercritical solution in an expansion chamber. Second, the Rapid Expansion of Supercritical Solutions (RESS) method was used for particle generation. Third, a modified RESS-procedure, forming the particles directly into the thereby gelated liquid, was developed. All three methods gave yields from 1% to 5.8%, depending on the techniques employed. The triterpene composition of the three extracts was comparable: all three gave more stable oleogels compared to the use of an extract obtained by organic solvent extraction. Characterizing the rheological behaviour of these gels, a faster gelling effect was seen together with a lower concentration of the extract required for the gel formation with the supercritical fluid (SCF)-extracts. This confirms the superiority of the supercritical fluid produced extracts with regard to the oleogel forming properties.
Highlights
For over two hundred years, birch bark and its pentacyclic triterpene constituents such as betulin (BE), lupeol (LU), betulinic acid (BA), oleanolic acid (OA) and erythrodiol (ER) have been a subject of research [1,2]
Extraction yield related to initial amount of birch bark [%]
Performing the Rapid Expansion of Supercritical Solutions (RESS) method, the mass flow had to be limited to 1.53 ± 0.09 kg/h to
Summary
For over two hundred years, birch bark and its pentacyclic triterpene constituents such as betulin (BE), lupeol (LU), betulinic acid (BA), oleanolic acid (OA) and erythrodiol (ER) have been a subject of research [1,2]. In 1788, betulin was the first of these triterpenoids to be isolated from the outer bark of birch by sublimation [3]. The physicochemical properties of these substances and the extraction from birch bark have been reinvestigated several times [1,2,4]. During the last fifteen years, several pharmacological effects have been discovered for these triterpenoids (Table 1).
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