Extraction of lichen bioactive compounds using volatile natural deep eutectic solvents and comparative analytical approaches

Abstract

Lichens are a source of bioactive secondary metabolites with different pharmacological activities. However, these metabolites are challenging regarding their extraction. The presented study aims to optimise the extraction methods of key compounds (depsidones and depsides) from Hypogymnia physodes (L.) Nyl. and additional species of lichens using traditional and advanced extraction methods. The comparative analysis included the evaluation of accelerated solvent extraction (ASE), maceration method of extraction, and using of volatile natural deep eutectic solvents (VNADES), as well as the type of solvent, ratio, duration and temperature of extraction on the yield of the main lichen metabolites (physodalic and physodic acids, 3-hydroxyphysodic acid, atranorin, and chloroatranorin). The combination of ASE with acetone was found to be the most selective method for lichen acid extraction, reducing both solvent consumption and processing time. As a green extraction approach, the use of VNADES was evaluated for yield. The following extraction parameters using VNADES were developed to maximise metabolite extraction: menthol/camphor ratio (1.5:1), liquid/solid ratio (100:1, volume/mass), temperature of extraction (40 °C), time of extraction (30 min). A comparison of different extraction drying methods showed the effectiveness of rotary evaporation as a cost-effective and rapid alternative to lyophilisation, preserving bioactive compounds from degradation.