I.I. Koleva: New methods for the screening of antioxidants in three Sideritis species

Promotor: Prof.dr. Ae. de Groot
Co-Promotor: Dr. T.A. van Beek
Co-Promotor: Dr.ir. J.P.H. Linssen

This thesis describes the rapid and robust evaluation of antioxidant activity of complex mixtures e.g. plant extracts. The study was directed to establish the best screening and isolation procedures for components with antioxidative properties to ensure the development of an "algorithm" for studying natural antioxidants. Three different screening methods were used. Three plants from the genus Sideritis grown in Bulgaria served as test species. The strengths and limitations of each method were illustrated. A novel hyphenated method (HPLC-DPPH) to rapidly and selectively pinpoint individual antioxidants in complex mixtures was developed. The use of the alternative ABTS"+ radical cation as in on-line version made the method more sensitive. The instrumental set-up and physico-chemical parameters of both methods were studied. The methods were successful for both qualitative and quantitative measurements. A range of flavonoid, phenylpropanoid and iridoid glycosides were isolated among them three novel compounds. Preliminary studies by the headspace GC method were applied to investigate how Sideritis extracts and pure components would behave in real systems, applying rosmarinic acid and BHT as standards.

Title thesis: New methods for the screening of antioxidants in three Sideritis species