Electrochemical evaluation of the antioxidant capacity of medicinal plant micellar extracts

Medicinal plants are one of the sources of bioactive components, which extraction can provide novel substances for the drug development. The use of sonication-assisted extraction of antioxidants from medicinal plants using surfactant micellar media is developed for the first time. The surfactant nature (cationic, non-ionic, and anionic) effect was tested, and the data obtained were compared to traditional ethanolic extracts. Non-ionic surfactants are the most effective. According to coulometric titration with electrogenerated titrants (bromine and hexacyanoferrate(III) ions), Triton X-100 (10 mM) is the best extractant providing 1.7–6.5-fold higher yield of antioxidants vs. ethanol. The obtained total antioxidant capacity and ferric reducing power of the extracts indicate total content of the antioxidants of various classes and the total content of phenolic antioxidants in the sample, respectively. A two-step chronoamperometric method at the electrode modified with MnO₂ nanorods was developed for antioxidant capacity evaluation of the medicinal plant micellar extracts. The electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and voltammetry. A two-step chronoamperometry at 0.35 and 0.75 V for 50 s each allows assessment of the contribution from the antioxidants of different powers to the antioxidant capacity of the samples. Electrochemical approaches were used for screening of 24 samples of commercial medicinal plants of various species used in phytotherapy. The plant parts included bark, shoots, rhizomes and roots, leaves, herb, flowers, fruits, etc. The highest antioxidant parameters were obtained for Bergenia crassifolia (L.) Fritsch rhizomes, Vaccinium vitis-idaea L. leaves, Ledum palustre L. shoots, and Sanguisorba officinalis L. rhizomes and roots that agrees well with their phytochemical profile.