Green extraction of poplar type propolis: ultrasonic extraction parameters and optimization via response surface methodology

Optimizing the extraction of natural products is an important step to obtain products rich in bioactive compounds with less energy use and costs. The aim of this study was to optimize the ultrasonic extraction process of poplar type propolis with natural deep eutectic solvent (NADES) citric acid:1,2-propanediol 1:4 (CAPD 1:4). Based on preliminary experiments, the extraction parameters solvent to solid ratio, temperature, and time were found to have a strong positive effect on the extraction of phenolic compounds, and they were further optimized by response surface methodology (RSM) via the Box-Behnken design (BBD). Solvent to solid ratio of 30 mL/g, ultrasonication time of 39 min and temperature of 65 °C were determined as optimum conditions for the highest values of total phenolic content (TPC, 290.35 mg/g), total flavones and flavonols content (TFC, 89.48 mg/g) and radical scavenging activity (31.89%RSA). The optimized extract was analyzed by gas chromatography-mass spectrometry (GC-MS) and a high relative content of valuable propolis constituents was found such as pinocembrin, 3-acetylpinobanksin, chrysin, galangin and phenethyl caffeate (CAPE). The results provide knowledge about optimal conditions for the development of a greener extract of poplar type propolis rich in valuable bioactive compounds with potential application in cosmetic, nutraceutical and pharmaceutical industries.