as a result of conformational changes, aggregation or adsorption (Skrabanja et al., 1994). There have been some reports on the stability of IgY in regard to these methods. Freezing and freeze-drying did not affect the activity of IgY unless repeated several times (Shimizu et al., 1988). However, Chansarkar (1998) showed that frozen or freeze-dried IgY resulted in some loss of antigen-binding activity and a significant drop in the solubility under the conditions of high salt and protein concentrations. The same findings were observed by Sunwoo et al. (2002). Recently, Fu et al. (2006) examined the thermal stability of IgY at various temperatures ranging between 25 and 90°C for 15 min treatment, before and after freeze-drying process. Their results indicated that freeze-dried IgY had shown a good thermal stability with no significant reduction in reactive activity except at 90°C. But this was also observed for the non freeze-dried IgY.
Yokoyama et al. (1992) analyzed some properties of IgY powders obtained by spray-drying or freeze-drying the water-soluble fraction of egg yolks from Escherichia coli immunized hens. As compared to the freeze-dried powder, the spray-dried powder did not show a significant alteration in antibody titres and yields, even when several spray-drying temperatures were tried (140 to 170°C). However, a higher moisture content of powder was observed in the powder prepared by spray-drying than by freeze-drying.