Abstract: The optimum extraction conditions of total polyphenols from Eucalyptus grandis×E. urograndis bark via enzymolysis treatment and ultrasonic-assisted coupling extraction method and ultrasonic extraction method were investigated by using orthogonal experiment. Vitro antioxidant activities of different solvent extracts by ultrasonic extracts were studied and the ethyl acetate extract exhibited stronger antioxidant activity. Then, 11 kinds of fractions(Fr.1-Fr.11) and a purified compound (Pu1) were separated from the ethyl acetate extract by AB-8 macroporous resin. The optimum crafts for ultrasonic extraction method were 60% ethanol, ultrasonic time 50 min, ratio of material-liquid 1:12 (g:mL), ultrasonic temperature 60℃, and the yield of total polyphenols was 5.12%. The optimum crafts for enzymolysis treatment and ultrasonic-assisted coupling extraction method were 0.15 g/L enzyme concentration,enzymolysis temperature 50℃,enzymolysis time 50 min,enzyme solution pH 5.0, combining with ultrasonic extraction, the yield of total polyphenols was 6.23%. The results of radical scavenging capacity assay showed that the scavenging rates of Fr.5, Fr.6, Fr.7 and Fr.8 active fractions at 50 mg/L were greater than 60%, and they had high antioxidant activity. The IC₅₀ of the active compound Pu1 was 8.99 mg/L, less than that of Vc(10.46 mg/L), indicating significant antioxidant activities. Moreover, the phenolic content of the active fractions showed positive correlation with their antioxidant activities (R=0.944 8,P<0.000 1). The structure of compound Pu1 was characterized by UV, FT-IR, MS and NMR and the results showed that its molecular formula and molar mass were C₂₁H₂₂O₁₄ and 498, respectively, which was named as 2'-methoxy-hexadylic biphenylate-4-O-α-L-rhamnoside.

Key words: Eucalyptus grandis×E. urograndis, total polyphenolics, enzymolysis treatment, antioxidant activity