Abstract: This work aims to establish a new technology of purifying lysozyme from egg white based on the combination of polyethylene glycol（PEG）precipitation and aqueous two-phase extraction. The results showed that 98.1% of non-lysozyme proteins were removed by the precipitation when PEG 4000 was added into pretreated egg white until its mass fraction reached 16%. Then,the supernatant of PEG precipitation was collected and mixed with saturated（NH₄）₂SO₄ solution until the mass fraction of this salt reached 4.32%. Therefore,the aqueous two-phase system of PEG/（NH₄）₂SO₄ was established and most of lysozyme could be transferred into the top phase. It was found that 96.34% of the freeze-dried top phase was lysozyme,and the rest was PEG 4000,no any other proteins existed. The recovery rate and the specific activity of lysozyme were 70.2% and 25 000 U/mg,respectively. In conclusion,this purification technology was simple,accurate,safe and reliable,and could be used for large-scale production of lysozyme.

Key words: polyethylene glycol 4000, precipitation, aqueous two-phase extraction, lysozyme