Abstract:The parameters for enzyme-assisted extraction of Lycium barbarum polysaccharides （LBP）were optimized by single-factor and orthogonal experiments.Ultrafiltration technology was used to separate the polysaccharides in the crude polysaccharide extract and allowed further in vitro characterization of antioxidant activity of each LBP fraction.The optimal parameters for enzyme-assisted extraction were determined as follows：cellulase and papain at the ratio of 1∶1.5（g/g），total enzyme amount of 2%，at pH 4.0，a solidliquid ratio of 1∶30 （g/mL），and extraction temperature of 50 ℃.Using these conditions，the polysaccharide extraction yield was found to be （7.28 ± 0.12）%.The optimal process parameters for ultrafiltration were determined to be the following：60 min time，pressure of 0.25 MPa，LBP mass concentration of 3 g/L.At these conditions，three fractions were obtained：Mw＜3.5 kDa，3.5 kDa＜Mw＜10 kDa，and Mw＞10 kDa，accounting for 52.46%，29.25%，and 16.50% of the total sugar content，respectively.The molecular weights for each of the three fractions were approximately 1 782，4 410 Da and 8 794 Da，respectively.The classification of polysaccharides resulting from ultrafiltration was further optimized.The antioxidant activity of different fractions of LBP was found to be significantly different.The fraction showing the highest antioxidant activity was Mw＞10 kDa，followed by 3.5 kDa＜Mw＜10 kDa，Mw＜3.5 kDa，and crude polysaccharide.The results presented herein showed that the antioxidant activity of LBP was closely related to its molecular weight.