Lichens are a valuable source of secondary metabolites with high antioxidant and therapeutic potential. This study evaluated the antioxidant activity of methanolic extracts from three species of the Parmeliaceae family—Parmelia discordans, Parmelia saxatilis, and Xanthoparmelia tinctina—. Antioxidant activity was determined using ORAC, FRAP and DPPH assays. The phenolic compound content was also evaluated, using the Folin-Ciocalteu assay.

Parmelia discordans showed the highest ORAC value (24.94 µmol TE/mg) and a considerable phenolic content (106.49 µg AG/mg), indicating strong radical scavenging capacity associated with phenolic metabolites. Parmelia saxatilis exhibited a balanced profile, with high ORAC activity (19.03 µmol TE/mg), relevant reducing power (FRAP = 1.029 Eq Fe²⁺/g), and strong DPPH activity (IC₅₀ = 814.42 µg/mL), together with high phenolic content (97.86 µg AG/mg). Xanthoparmelia tinctina displayed the highest reducing capacity (FRAP = 2.295 Eq Fe²⁺/g) and the most potent DPPH activity (IC₅₀ = 642.93 µg/mL), despite its low phenolic content (20.13 µg AG/mg). This finding suggests that non-phenolic compounds may play a central role in its antioxidant potential.

Additionally, methanolic extracts were tested on human neuroblastoma SH-SY5Y cells to assess their effects on cell viability, resistance to oxidative stress, and intracellular generation of reactive oxygen species (ROS). The combined biochemical and cellular data highlight complementary antioxidant strategies: phenolic-driven activity in P. discordans, a robust and balanced profile in P. saxatilis, and non-phenolic but highly effective mechanisms in X. tinctina.

These findings support lichens as promising candidates for further phytochemical and pharmacological research focused on natural antioxidant agents. Nevertheless, it is necessary to continue researching.