Abstract: Lipoxygenase(LOX) can catalyze oxygenation of the(Z,Z)-1,4-pentadiene moiety of polyunsaturated fatty acids into enantiomeric hydroperoxide fatty acids with(Z,E)-conjugated diene moiety.In this paper,several methods were used for extracting LOX from defatted soybean powder,and LOX activity was measured.Experiment results show that the total enzyme activity 6.71×10⁷ U/10 g(defatted soybean flour) obtained by water-leaching is the highest with corresponding specific enzyme activity 8.61×10⁵ U/mL(enzyme preparation).The loss of enzyme activity is more than 1/2 after two salting-out steps or coprecipitation process.Specific activity of LOX 9.42×107 (U/g)(powdered enzyme) obtained by alkali-dissolving and acid-leaching followed by two salting-out steps is the highest of all.Free LOX loses 79% of its activity sharply at room temperature after 7 days, indicating that low storage temperatures to maintain high enzyme activity is preferred.At pH value 9,LOX exhibits the highest enzyme activity.Addition of some salts,sugar,polyol or organic electrolytes,especially EDTA-Na₂ can increase the storage stability and thermostability of LOX.By addition of 1%(mass ratio) EDTA-Na₂,the activity of LOX was kept 80% of the original after 42 day,and only 6% activity was lost by heat treatment at 50℃ for 60 min.

Key words: soybean lipoxygenase, extraction, enzyme activity