Foam fractionation for effective recovery of resveratrol from the leaching liquor of Polygonum cuspidatum by using partially ethylated β-cyclodextrin as collector and frother

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In this work, foam fractionation has been proposed to recover resveratrol from the leaching liquor of Polygonum cuspidatum. Resveratrol is a natural polyphenol without surface activity. For achieving the adsorption of resveratrol on the gas-liquid interface, a biological surfactant of partially ethylated β-cyclodextrin (partially Eβ-CD) was prepared. First, the inclusion behavior between partially Eβ-CD and resveratrol was investigated. Resveratrol molecular could easily enter into the cavity of partially Eβ-CD from its wide rim due to the possible driving forces of charge transfer and dipole-dipole interactions. The experiments of foam properties suggested that partially Eβ-CD could decrease the surface tension of aqueous solution, thus generating stable foam. By using partially Eβ-CD as collector and frother, foam fractionation was performed. Under the suitable conditions of partially Eβ-CD concentration 0.680 g/L, loading liquid volume 250 mL, volumetric air flow rate 40 mL/min, pore diameter of gas distributor 0.45 mm and pH 4.0, the enrichment ratio and the recovery percentage of resveratrol reached 2.79 and 73.84%, respectively. The concentration of resveratrol in the foamate was as high as 0.050 g/L. This work is expected to provide a new strategy to effectively recover a non-surface-active material from its aqueous solution, and to facilitate the industrialization of foam fractionation.