The Phenolic Composition of Centaurea cyanus L. Flower Extracts: Antioxidant, Antimicrobial, and Fibroblast Biocompatibility of a Phenolic-Rich Ethanolic Extract

Six Centaurea cyanus L. flower extract variants were prepared using methanol, ethanol or water as a solvent; in each case, the material was either defatted with chloroform or not. The phytochemical profile of all obtained extracts was analyzed qualitatively and quantitatively using UPLC-PDA-Q/TOF-MS. In total, 35 phenolic compounds were detected, including flavonols, flavones, anthocyanins, phenolic acids and their derivatives, as well as an N-p-coumaroyl spermidine derivative; some compounds were identified using authentic standards, while others were tentatively identified based on chromatography and mass spectrometry data. The defatted ethanolic extract showed the highest total quantified phenolic content (42.18 mg/g DW), with the predominant constituents being apigenin derivatives, particularly apigenin-O-hexoside-O-glucuronide and apigenin-3-O-glucoside-(6″-acetyl)glucoside. The extract exhibited notably high antioxidant capacity, viz. DPPH (240.34 µmol TE/g), ABTS (170.53 µmol TE/g), and FRAP (189.93 µmol TE/g), and moderate antimicrobial activity, particularly against E. coli (MIC 0.5 mg/mL). The extract did not exhibit any cytotoxic effect toward L929 or Hs68 fibroblasts in vitro at concentrations up to 5 mg/mL. These findings indicate that the phenolic-rich ethanolic extract demonstrated both antioxidant and antimicrobial activities while also being non-cytotoxic against fibroblasts within the tested concentration range; as such, it may be suitable for dermatological and cosmetic formulations.