Flavonol quantification and stability of phenolics in fermented extracts from fresh Betula pendula leaves

An HPLC method, which allows reliable quantitation of flavonols and other phenolics in birch leaf extracts, was developed and validated. The method was applied to study the bioconversion of flavonols in fermented aqueous extracts. Almost 100% of the flavonols were converted during the 12 months observation period. The generated phenolics as well as consecutive conversion products were identified by HPLC–DAD, LC–MS and GC–MS techniques.