Usnic 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.

中文翻译：

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使用部分因子设计优化松萝酸提取条件

松萝酸是一种具有工业重要性的独特地衣代谢物，广泛研究以探索其药理潜力，尤其是作为化妆品中的抗菌剂。尽管大量论文描述了从各种地衣物种中提取松萝酸，但迄今为止没有一篇文章明确指出该化合物的最佳提取程序。因此，目前的研究重点是直接比较三种常用的松萝酸提取方法（热回流、摇动、超声辅助提取），这些方法使用部分因子设计进行了优化。热回流提取、振荡提取和超声辅助提取首先在使用部分因子设计的一系列实验中针对三个参数进行了优化：提取时间、使用的溶剂和提取重复次数。HPLC用于松萝酸定量分析。对每种提取方法的最佳分数进行统计比较，并指出最佳条件。松萝酸的最佳参数集被确定为用丙酮进行 60 分钟的热回流萃取。该提取方案提供 4.25 ±0.08 mg g-1松萝酸的 dw，而对于超声辅助和摇动提取，其量要低两倍甚至四倍（2.33 ±0.17 和 0.97 ±0.08 mg g-1dw，分别）。此处描述的松萝酸提取的最佳程序可能适用于有效获取该化合物以用于科学研究目的，也适用于制药或化妆品行业的应用。