Effects of pH on antioxidant and prooxidant properties of common medicinal herbs
Bayliak, Maria M. | Burdyliuk, Nadia I. | Lushchak, Volodymyr I.
Background: We studied in vitro and vivo antioxidant and prooxidant abilities of aqueous extracts from Rosa canina L., Rhodiola rosea L., Hypericum perforatum L., and Gentiana lutea L. Methodology: Total antioxidant capacity was measured by four assays (phosphomolybdate method, Fe³+-reducing activity, ABTS•⁺ scavenging, H₂O₂ scavenging). Prooxidant activity was estimated by H₂O₂ production. Yeast viability in the presence of H₂O₂ and/or plant extracts was determined by plating or by counting live cells’ number. Results: Plant extracts differed in the total phenolic content (R. canina > R. rosea > H. perforatum > G. lutea) which clearly correlated with their ABTS•⁺ scavenging activity (R² = 0.963). H₂O₂ scavenging activity was not clearly associated with plant phenol levels and was significantly higher in acidic, than in alkaline medium. In line with this, plant extracts effectively protected yeast S. cereviasiae against H₂O₂ and stimulated reproductive ability of yeast cells at acidic but not at alkaline pH. At alkaline pH, plant extracts produced certain amounts of H₂O₂ which were related to their phenolic content. Conclusion: The antioxidant activity of plant extracts is decreased at alkaline pH with an increase in the prooxidant activity. It reduces protective capacity of plant extracts against oxidative and other stresses in vivo.
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