Abstract: In recent years, yolk antibody has become a hot research in immunology due to their no cross reaction and strong specificity. Studies have shown that IgY isolated from egg yolk can prevent or cure digestive or respiratory-related diseases, but there is still lack of industrial processes suitable for mass production. The existing purification methods are mainly divided into precipitation, chromatography and ultrafiltration method, with their own advantages and disadvantages. Among them, precipitation method is the most potential method to be applied in quantitative production; however, the precipitation method often cannot achieve both potency and yield. In this study, the yolk stock solution isolated from eggs produced by hens immunized with inactivated Newcastle disease virus was selected and tested by polyethylene glycol concentration gradient extraction. The results showed that the continuous purification of 3.5%, 8.0% and 12.0% were the best. In addition, the obtained yolk stock solution was almost without egg white after the separation of egg yolk and egg white by physical separation method, which eliminated the effects of protein and lipid in egg white on purification. The yolk antibody obtained through physical separation and three consecutive purification can reach purity of about 80% by BCA and SDS-PAGE tests, and the average titer was 2¹³ using a hemagglutination inhibition test. And this study showed that IgY extract can be stored at -20 ℃ for more than one year after dialysis with buffer. The present study showed that the optimized purification method guarantees both potency and yield, and the test process is simple and of low cost, which lays the foundation for the research and development of industrialized production method of yolk antibody purification.

Key words: IgY, protein purification, polyethylene gly, avian pneumo-encephalitis virus, blood coagulation test and hemagglutination inhibition test