Biorefining of goldenrod (Solidago virgaurea L.) leaves by supercritical fluid and pressurized liquid extraction and evaluation of antioxidant properties and main phytochemicals in the fractions and plant material

Supercritical carbon dioxide (SFE-CO2) and pressurized liquid extraction (PLE) with increasing polarity solvents were applied for biorefining goldenrod (Solidago virgaurea) into fractions. Extract yields varied from 2.40 to 28.9% (dry weight); the total yields were 42.87-63.79%. The highest content of phenolics and trolox equivalent antioxidant capacity was obtained using PLE at 140 °C, while the highest oxygen radical absorbance capacity (ORAC) value was obtained using the combination of SFE-CO2/PLE. Antioxidant activity indicators of solid plant substances gradually decreased during extraction as measured by QUENCHER method. α-Tocopherol was the major tocol in lipophilic extracts (61.4-134 µg/g). Ten phytochemicals were quantified: the concentration of quercitrin was 50.7-94.1 mg/g followed by hyperoside, 33.8-70.1 mg/g dry extract weight. PLE fractions increased the oxidative stability of rapeseed oil and emulsion in Oxipres and Rancimat assays. Multistep SFE-CO2/PLE processes were demonstrated to be effective for producing high added value functional ingredients from goldenrod leaves.