Abstract: The saponins were extracted from Eucalyptus grandis x E. urophylla by water. Effects of extraction temperature, extraction time and ratios of liquid to solid on extraction yield of saponins were studied. The crude extract saponins were purified by three different methods. The results showed that the optimum extraction conditions were as follows: extraction temperature 61.81 ℃, extraction time 5.02 h, liquid-solid ratio 20.09:1. Under these conditions, the extraction yield of crude saponins was 5.51%. The macroporous resin adsorption combined with acetone precipitation method could refine the saponins for improving the purity from 16.22% to 50.35%. The antioxidant activities of crude saponins, the purified saponins by macroporous resin and the purified saponins by macroporous resin adsorption combined with acetone precipitation were studied by three different systems. The results demonstrated that the maximum scavenging rates of three samples for DPPH radical were 83.02%, 84.20% and 85.62%, respectively; for hydrogen peroxide were 80.10%, 55.02% and 48.21%, respectively; and for superoxide anion radical were 16.62%, 13.43% and 10.01%, respectively.

Key words: Eucalyptus grandis x E. urophylla, saponins, extraction, antioxidant activity