Content and Dynamics of Polyphenols in Betula spp. Leaves Naturally Growing in Estonia

The seasonal variation in the chemical composition and chemosystematics of the leaves of Betula pendula Roth. ,B. pubescens Ehrh., B. humilis Schrank and B. nana L. (Betulaceae), growing naturally in Estonia, and in B. pendula buds was studied. Polyphenols were analyzed by HPLC and HPLC-MS/MS. Hyperoside (423-3724 µg/g), myricetin glucuronide (106-1696 µg/g), quercetin glucuronide (206-1435 µg/g), myricetin glucoside (89-1197 µg/g), quercitrin (53-578 µg/g), and kaempferol glucuronide (77-342 µg/g) were found to be the main flavonoids in the birch leaves studied. The content of flavonoids in buds was lower than in leaves. The moderate correlations between the contents of the main polyphenols in the compared birch species were determined: B. pendula showed correlations with B. pubescens and with B. humilis. The seasonal variation of polyphenols was specific for each birch species, and no general tendency was observed. The presence of coumaric acid O-hexoside is not typical to B. nana and the content of some polyphenols can indicate the collecting time of plant material.