Pressurized liquid extraction of bioactive compounds from Parmotrema perlatum: Optimization and analysis

Parmotrema perlatum (family Parmeliaceae), also known as black stone or stone flower, is a lichen found in the Southern and Northern hemispheres and is utilized as a spice in India and China. Although it is documented that many lichen-derived substances possess a broad spectrum of bioactivity, studies on characterization and especially the recovery of bioactive components utilizing sustainable extraction technologies are relatively scarce. This study evaluated pressurized liquid extraction (PLE) as a sustainable technique for recovering lichen-specific functional components. Firstly, liquid chromatography with tandem mass spectrometry (LC-MS/MS) indicated that lichen extracts were characterized by lecanoric-, gyrophoric- and usnic acid. In that direction, a central composite design and response surface methodology was used to assess the effect of extraction parameters, including solvent (ethyl acetate-ethanol), time (15–45 min) and temperature (40–120 °C) on the recovery of the three main components, chosen as response factors. The highest concentrations for lecanoric- (ca. 350 mg gE−1 of extract), gyrophoric- (ca. 287 mg gE−1 of extract), and usnic acid (ca. 60 mg gE−1 of extract) were observed with ethyl acetate. Analysis of variance indicated that, the extraction temperature was a critical factor, with high recoveries recorded under mild conditions (40–50 °C). Furthermore, lecanoric and gyrophoric acid extraction was favoured by short extraction times, whereas usnic acid required more extended extraction periods. After numerical optimization under the selected constraints and considering all observed responses, the optimal extraction conditions were (pure ethyl acetate, 45 °C, and 24 min), under which all quadratic models were validated. Besides targeted substances, LC-MS/MS data revealed the occurrence of other depside and dibenzofuran derivatives. Conclusively, this study highlights the high efficiency of PLE in recovering rapidly fractions with high concentrations of the targeted bioactive molecules under mild conditions.