Chemical Profiling of Essential Oils and Evaluation of Enzyme Inhibition, Antioxidant, and Antimicrobial Activities in Both Methanol Extract and Essential Oils of Centaurea oltensis

The phytochemical composition and biological activities of Centaurea oltensis, an endemic species in Türkiye, were studied. GC–MS/FID analysis identified 128 compounds representing 99.2% of the EO, with decanoic acid (15.1%), α-pinene (7.9%), and sabinyl acetate (5.4%) as the principal constituents. GC–MS/FID analysis identified 128 compounds representing 99.2% of the essential oil (EO), with decanoic acid (15.1%), α-pinene (7.9%), and sabinyl acetate (5.4%) as the principal constituents. LC–MS/MS analysis of the methanol extract (ME) revealed high concentrations of ferulic acid (2410 µg/g dw) and chlorogenic acid (1170 µg/g dw), together with caffeic, salicylic, and 4-hydroxybenzoic acids. The ME exhibited potent carbonic anhydrase-II inhibition (IC₅₀ = 0.028 µg/mL) and significant α-glucosidase inhibition (IC₅₀ = 0.255 mg/mL). The EO showed strong acetylcholinesterase and butyrylcholinesterase inhibitory activities, with IC₅₀ values of 0.0145 µg/mL and 0.204 µg/mL, respectively. Antioxidant assays, including DPPH, ABTS, and FRAP, demonstrated superior activity of the ME, correlating with its higher phenolic and flavonoid contents. The EO displayed remarkable antibacterial activity against Staphylococcus aureus (MIC = 0.02 mg/mL) and moderate antifungal activity against Candida albicans. Overall, C. oltensis demonstrated considerable chemical diversity and promising antioxidant, antimicrobial, neuroprotective, and enzyme inhibitory potential for future pharmacological and therapeutic applications.