Liquid phase and microwave-assisted extractions for multi-component phenolic pattern determination of five Romanian Galium species coupled with bioassays

Background: Galium is a plant rich of iridoid glycosides, flavonoids, anthraquinones and small amount of essential oils and vitamin C. Recent works showed the antibacterial, antifungal, antiparasitic, and antioxidant activity of representatives of this plant genus. Methods: For the determination of multi-component phenolic pattern, liquid phase microextraction procedures were applied combined with HPLC-PDA instrument configuration in five Galium species aerial parts (G. verum, G. album, G. rivale, G. pseudoaristatum, and G. purpureum). Dispersive Liquid–Liquid MicroExtraction (DLLME) with NaCl and NAtural Deep Eutectic Solvent (NADES) medium and Ultrasound-Assisted (UA)-DLLME with β-cyclodextrin medium were optimized. Results: The optimal DLLME conditions were found to be: 10 mg of the sample, 10% NaCl, 15% NADES or 1% β-cyclodextrin as extraction solvent – 400 μL of ethyl acetate as dispersive solvent – 300 μL of ethanol, vortex time – 30 s, extraction time – 1 min, centrifugation at 12000 x g for 5 min. Conclusions: These results were compared with microwave-assisted extraction procedures. G. purpureum and G. verum extracts showed the highest total phenolic and flavonoid content, respectively. The most potent extract in terms of antioxidant capacity was obtained from G. purpureum, whereas the extract obtained from G. album exhibited the strongest inhibitory effect against tyrosinase.