Multi-stage recovery of phytochemicals from buckwheat (Fagopyrum esculentum Moench) flowers by supercritical fluid and pressurized liquid extraction methods

Supercritical fluid extraction with carbon dioxide and co-solvent ethanol (SFE CO2/ET) and pressurized liquid extraction (PLE) with the increasing polarity solvents, hexane (HX), acetone (AC), ethanol/water (ET/W) and water (W) were applied for recovery of bioactive substances from buckwheat (Fagopyrum esculentum) flowers (BWF). The products obtained were evaluated for their antioxidant capacity and phytochemical composition. Extract yields varied from 1.78 to 35.6% with the highest values for ET/W (21.7-35.6%), while the total yields were in the range of 37.02-64.05%. Comparing total phenolic content (TPC) and radical scavenging capacity in ABTS assay W extracts were weaker antioxidants than AC and ET/W extracts, while ORAC was in the range of 672-2114 tunol Trolox equivalents/g. The highest total TPC and TEAC was obtained using PLE at 140 degrees C, while the highest ORAC value was obtained using SFE CO2/PLE combination. Antioxidant activity indicators of solid plant substances were followed during extraction by using QUENCHER method. Lipophilic fractions were weaker antioxidants although they contained high concentrations of tocopherols, up to 392 mu g/g dry weight of extract (DWE). Seven phytochemicals were quantified in BWF, rutin being the major constituent (70-110 mg/g DWE) followed by quercitrin (6.4-88.0 mg/g DWE) and citric acid (0.31-31.3 mg/g DWE). Extracts increased the oxidative stability of rapeseed oil and emulsion in Oxipres and Rancimat assays. High pressure fractionation schemes have never been applied to BWF previously: as a result new promising fractions have been obtained, which may serve as a good platform for the development of new industrial products.