Optimization of pressurized ethanol extraction for efficient recovery of hyperoside and other valuable polar antioxidant-rich extracts from Betula pendula Roth leaves

Silver birch (Betula pendula Roth) leaves, known for their long-standing uses in traditional medicine, are bioactive compound-rich by-products of the birch logging industry, abundantly available throughout the northern hemisphere. Considering the current demands for the sustainable valorization of various plant materials and their processing by-products, this study aimed to optimize pressurized ethanol extraction (PLE-EtOH) parameters in order to produce hyperoside and other valuable polar antioxidant-rich extracts from silver birch leaves. A central composite design along with response surface methodology (CCD-RSM) was used to optimize the temperature and time of PLE-EtOH for yield, total phenolic (TPC) and flavonoid (TFC) content, Trolox equivalent antioxidant capacity (TEAC) measured in oxygen radical absorbance capacity (ORAC), cupric ion reducing antioxidant capacity (CUPRAC), and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays, and hyperoside content measured by ultraperformance liquid chromatography-electrospray tandem mass spectrometry (UPLC-ESI/MS2) analysis. The optimal PLE-EtOH conditions were 86degree celsius and 39 min, which produced an extract with 32.2% yield, high TPC (97.3 mg gallic acid equivalents/g), TFC (37.3 mg quercetin equivalents/g) and proanthocyanidin (301.2 mg catechin hydrate equivalents/g) content, also strong in vitro antioxidant capacity in ORAC, CUPRAC and ABTS assays (999.3, 297.0 and 392.3 mg Trolox equivalents/g, respectively). Hyperoside (54.1 mg/g), betuloside (18.3 mg/g) and chlorogenic acid (11.5 mg/g) were the prime phenolic compounds in the PLE-EtOH extract. Additionally, a high sun protection factor (37.4 at 1 mg/mL) was determined by in vitro method for this extract. Such products from B. pendula leaves have potential cosmetical, nutraceutical, and pharmaceutical applications.