Antioxidant efficiency of Beech (Fagus sylvatica L.) bark polyphenols assessed by chemometric methods

Beech (Fagus sylvatica L.) is a common industrial wood species. Its bark is mostly regarded as a by-product, however it is an abundant source of antioxidant polyphenols worthwile to extract and to utilize for various purposes. Hitherto, it has been unknown which polyphenols are primarily responsible for the antioxidant properties. The objective of the present study was to implement chemometric methods for the identification of the compounds which are mostly responsible for antioxidant effects. With this knowledge extraction can be optimized, antioxidant properties can be enhanced. Earlier published data on the polyphenolic composition and antioxidant properties of altogether 26 extract solutions were evaluated in the present study. Antioxidant capacity of the extracts was determined with DPPH (2,2-diphenyl-1-picrylhydrazyl), ARTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and FRAP (ferric reducing ability of plasma) assays. Relative concentrations of polyphenols were measured with high-performance liquid chromatography/tandem mass spectrometry by means of MRM (multiple reaction monitoring) peak areas. Chemometric methods involved correlation analysis, factor analysis and cluster analysis. A scoring system was applied for the evaluation of chemometric results. The five overall most efficient antioxidants in beech bark were found to be (+)-Catechin > Procyanidin B dimer 2 > Unidentified 5 > (-)-Epicatechin > Coniferin isomer 2 compounds. Isomers of Procyanidin B dimers and C timers were shown to have different antioxidant efficiency. Significant DPPH prooxidant effects of Coniferin isomer 1 and Syringic acid-di-O-hexoside 1 were reported. The presented evaluation could be used for the assessment of the antioxidant efficiency of compounds in other plant extracts, too.