Bioactive Phytocompound Profiling and the Evaluation of Antioxidant, Antihyperglycemic, and Antimicrobial Activities of Medicinal Plants from Serbian Traditional Medicine

Medicinal plants represent an important source of bioactive compounds whose composition and biological activity are strongly influenced by geographical origin and extraction conditions. In this study, six medicinal plants traditionally used in south-eastern Serbia (Galium verum, Filipendula vulgaris, Lythrum salicaria, Sideritis montana, Teucrium chamaedrys, and Teucrium montanum) were investigated for their phytochemical composition and antioxidant, antihyperglycemic, and antimicrobial activities. Aqueous and 40% ethanol extracts were prepared and analyzed for total phenolic content (TPC) and total flavonoid content (TFC), followed by HPLC-DAD profiling of individual polyphenolic compounds. Antioxidant activity was assessed using DPPH, ABTS, and reducing power assays, antihyperglycemic activity by α-glucosidase inhibition, and antimicrobial activity by the microdilution method against selected bacterial and fungal strains. L. salicaria exhibited the highest TPC (113.56–119.09 mg GAE/g DW), while F. vulgaris showed the highest TFC (65.74–66.31 mg RE/g DW). HPLC analysis revealed notable levels of ferulic acid in L. salicaria ethanol extract (39.12 mg/g DW), as well as rutin, luteolin, and myricetin in several species. Ethanol extracts generally demonstrated stronger antioxidant activity, with L. salicaria showing the highest DPPH (378.60 µM TE/g) and reducing power (684.06 µM TE/g), while its aqueous extract exhibited the highest ABTS activity (3621.93 µM TE/g). Strong antihyperglycemic activity was observed for F. vulgaris extracts (100% α-glucosidase inhibition). Antimicrobial assays revealed higher sensitivity of Gram-positive bacteria, particularly Listeria monocytogenes and Staphylococcus aureus, with F. vulgaris and L. salicaria extracts showing the strongest effects. These findings highlight the significant influence of plant species and extraction solvent on bioactivity and support the potential of selected Serbian medicinal plants as sources of multifunctional natural bioactive compounds.