Abstract:A three-tiered membrane filtration method， combining ultrafiltration， nanofiltration， and reverse osmosis， was used to enrich small molecular antioxidant components from Rosa roxburghii Tratt with water as the solvent. The appropriate ultrafiltration membrane was selected from polyethylene membranes with five different molecular weight cut-offs. With the polysaccharide permeation rate， vitamin C（VC） permeation rate，and membrane flux as indicators， response surface methodology and single factor experiments were employed to optimize the ultrafiltration parameters. The nanofiltration membrane was screened with the tyrosinase inhibition rate， DPPH radical scavenging activity， and ABTS+ radical scavenging activity as indicators， and nanofiltration parameters were optimized by single factor experiments. Finally， the nanofiltration permeate was concentrated with the reverse osmosis membrane to prepare the small molecular antioxidant extract rich in VC. The chemical composition of the extract was analyzed by liquid chromatography-tandem mass spectrometry （LCMS/MS）， and the VC content was determined by high-performance liquid chromatography （HPLC）， on the basis of which the impacts of membrane separation on active components were studied. The results showed that the optimized conditions were a combination of a 5 kDa ultrafiltration membrane， a 500 Da nanofiltration membrane， and a reverse osmosis membrane. The ultrafiltration parameters were dilution of R. roxburghii juice by 20 times， transmembrane pressure of 0.4 MPa， filtration volume of 6 L， and flushing once. The nanofiltration parameters were pressure of 0.8 MPa and three flushes. After concentration by the reverse osmosis membrane，the highest yield of VC was 88.90%， and the small molecular natural products with antioxidant activity were obtained after freeze-drying.