R amalina Lichens and Their Major Metabolites as Possible Natural Antioxidant and Antimicrobial Agents

Abstract

Three lichen species of Ramalina (R. farinacea, R. fastigiata and R. fraxinea) were examined. Evernic, fumarprotocetraric, lecanoric, stictic and usnic acid levels were determined by high performance liquid chromatography-diode array detection. Acetone, methanol and ethanol were used to examine the efficiencies of different solvent systems for the extraction of lichen acids. The total phenol contents in the extracts were determined by the Folin–Ciocalteu method. The antioxidant capacities were determined by the ABTS (2,2′-azino-bis[3-ethylbenzothiazoline-6-sulphonic acid]) method. The methanol extracts of the Ramalina species showed the highest antioxidant capacities. Broth microdilution testing was performed to determine the minimum inhibitory concentration (MIC) of the methanol extracts of the three Ramalina species. The MIC values of all extracts ranged from 64 to 512 μg/mL for all bacterial strains tested in this study. Practical Applications Lichens and their natural products are used worldwide for decorations, brewing and distilling, food, fodder, spice and natural remedies, and in the perfume and dying industries. Lichens produce a large number of phenolic compounds, such as depsides, depsidones and dibenzofurans. Lichens with antioxidant activity have increased abilities to scavenge toxic-free radicals due to their phenolic groups. In recent years, many lichen substances have been found to have several biological activities. This article evaluates the antimicrobial and antioxidant activities and lichen acids of three Ramalina species. This is the first study to determine the stictic acid level in a R. farinacea extract and fumarprotocetraric acid and lecanoric acid levels in an R. fastigiata extract. The results of this study will contribute significantly to current knowledge regarding the utility of antimicrobial and antioxidant materials.