Concentration of biologically active compounds extracted from Sideritis ssp. L. by nanofiltration

▶ High concentration effect of biologically active compound by nanofiltration. ▶ Concentrated extracts by nanofiltration preserve their high antioxidant activity. ▶ Concentrated extracts can be used as a source of concentrated biologically active material. ▶ The separation of flavonoids from phenols with lower molecular weight is found possible at MWCO > 400 Da. In the present study experimental results on the nanofiltration of ethanolic extracts from Sideritis ssp. L. are reported, regarding polyphenols and flavonoids concentration and solvent reuse. Three membranes, resistant to organic solvents, have been used: Starmem™ 240 (polyimide), Duramem™ 300 and Duramem™ 500 (both of them modified polyimide). The dependence of the membrane rejection on its MWCO is presented. The separation of flavonoids from phenols with lower molecular weight is found possible at MWCO > 400 Da. A decrease of the flux is observed at permeate to feed volume ratio of about 0.58, thus indicating the existence of a critical concentration, independent of the feed volume and MWCO of the membranes used. The membrane behaviour during nanofiltration has been characterised by ESEM and ATR-FTIR. Concentrations of active compounds up to 3–4 times higher have been obtained in the retentates. The extracts concentrated by nanofiltration preserve their high antioxidant activity. Further dilution of the retentates displays a logarithmic concentration dependence of the radical scavenging activity. The experiments have proved the possibility for permeate use for extraction instead of ethanol, thus essentially reducing the volume of the solvent.