Abstract: In this study,the separation rule and the enrichment feasibility of nanofiltration was explored to separate rosmarinic acid from low concentration ethanol-aqueous solution.The experiment showed that ethanol concentration had influences on the membrane flux and the rejection of rosmarinic acid.In order to ensure the separation efficiency and rejection,the optimal conditions were optimized by response surface method of quadratic regression model,and the results were 0.41 μg/mL for rosmarinic acid concentration,20% for ethanol concentration and 450 Da for molecular weight cut-off.Under these conditions,the rejection of rosmarinic acid was 93.81%,which was close to the predicted values.These results indicated the quadratic polynomial mathematical model built by Design-Expert software was accurate and feasible and the optimized concentrate process was stable and reliable.In addition,the results showed that nanofiltration had several big advantages over the vacuum concentrate.When the nanofiltration membrane was applied in ethanol-aqueous solution for long time,the membrane fouling and swelling was not reversible.But the rejection of rosmarinic acid was stable,which suggested that the nanofiltration membrane module was of better durability.

Key words: rosmarinic acid, ethanol, nanofiltration, vacuum concentrate, durability