Development of supercritical CO2 extraction of bioactive phytochemicals from black poplar (Populus nigra L.) buds followed by GC-MS and UHPLC-DAD-QqTOF-MS.

The supercritical CO2 (SC-CO2) extraction process of black poplar (Populus nigra L.) buds was optimized (pressure, temperature) based on the yields of major phytochemicals (volatiles and non-volatiles). The optimal settings were 30 MPa/60 °C. Major volatiles determined by GC-MS in the optimized SC-CO2 extract (mg of benzyl salicylate equivalent (BSE) per 100 g of buds) were: pinostrobin chalcone (1574.2), β-eudesmol (640.8), α-eudesmol (581.9), 2-methyl-2-butenyl-p-coumarate (289.9), pentyl-p-coumarate (457.0), γ-eudesmol (294.4), and benzyl salicylate (289.2). Partial qualitative similarity was observed between SC-CO2 extracts and corresponding hydrodistilled essential oil dominated by sesquiterpenes, but with lower yields. Major compounds (mg per 100 g of buds) identified by UHPLC-DAD-QqTOF-MS in the optimized SC-CO2 extract were: pinostrobin (751.7), pinocembrin (485.6), 3-O-pinobanksin acetate and methyl-butenyl-p-coumarate (290.2; 144.9 of pinobanksin and p-coumaric acid equivalents, respectively). SC-CO2 extraction was found useful for green, efficient and simultaneous extraction of both volatile/non-volatile, bioactive phytochemicals of poplar buds - precursors of poplar-type propolis.