Characterisation of Polyphenol-Containing Extracts from Stachys mucronata and Evaluation of Their Antiradical...

Background: The aromatic plant Stachys mucronata (Lamiaceae) is endemic to the island of Crete (southern Greece), but as opposed to other native Greek members of this family, this species has never been investigated in the past with regard to its polyphenolic composition and antioxidant potency. Methods: Aerial parts of S. mucronata were exhaustively extracted and partly fractionated through partition, using n-butanol and dichloromethane. Results: Following an initial examination, which consisted of estimating the total polyphenol content and the antiradical activity, the n-butanol extract was found to be by far the richest in polyphenols, exhibiting much stronger antiradical activity compared with the dichloromethane counterpart. On this basis, the n-butanol extract was analysed by liquid chromatography-diode array-mass spectrometry, to tentatively characterise the principal polyphenolic components, which were shown to be flavonol but mainly flavone derivatives. Conclusions: The most potent radical-scavenging compounds were detected in the n-butanol fraction of the extracts, suggesting that the most active antioxidants in S. mucronate are relatively polar. The analyses suggested the major constituents to be derivatives of the flavone luteolin, accompanied by apigenin analogues, as well as flavonol glycosides and chlorogenate conjugates.