Abstract
AbstractUsnic acid is a unique lichen metabolite of industrial importance, widely studied to explore its pharmacological potential and valued especially as an antibacterial agent in cosmetics. Although a vast number of papers describe usnic acid extraction from various lichen species, none has so far provided an unequivocal indication of the best extraction procedure for this compound. Thus, the current study was focused on the direct comparison of three commonly used usnic acid extraction methods (heat reflux, shaking, ultrasound-assisted extractions), which were optimized using fractional factorial design. Heat reflux extraction, shaking extraction and ultrasound-assisted extraction were first optimized in a series of experiments using fractional factorial design, with respect to three parameters: the extraction time, the solvent used and the number of extraction repetitions. HPLC was employed for usnic acid quantitative analysis. The best scores for each extraction method were statistically compared and the optimal conditions were indicated. The optimal set of parameters for usnic acid was established to be a single, 60 min heat reflux extraction with acetone. This extraction scheme provided 4.25 ±0.08 mg g−1 d.w. of usnic acid, while for ultrasound-assisted and shaking extractions the amount was two- or even four times lower (2.33 ±0.17 and 0.97 ±0.08 mg g−1 d.w., respectively). The optimal procedure for usnic acid extraction described here may be suitable for effective acquisition of this compound for scientific research purposes, but also for applications in the pharmaceutical or cosmetic industries.
Highlights
Usnic acid (2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyl-1,3(2H,9bH)dibenzo-furandione) is a structurally unique, yellow, lipophilic metabolite found selectively in lichens
Quantitative analyses of usnic acid content in various lichen species have been performed using several different extraction methods. The results of these studies are difficult to compare because the analytical conditions vary substantially, often depending on the research goal, and giving inaccurate information on the real content of usnic acid in the given lichen material
A fractional factorial design was applied for the first time to study usnic acid extraction optimization
Summary
Usnic acid (2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyl-1,3(2H,9bH)dibenzo-furandione) is a structurally unique, yellow, lipophilic metabolite found selectively in lichens. Some recent reports indicate its photoprotective (Varol et al 2015) and wound healing (Pagano et al 2019) properties, when applied externally. Taken together, these attributes of usnic acid, its wide distribution in nature in significant amounts of up to 5% (Galanty et al 2019), and an easy isolation procedure (Ingolfsdottir et al 1998; Lohezic Le Devehat et al 2007; Galanty et al 2017), make this lichen metabolite an attractive subject of research
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