Antigen‐binding and protein G‐binding abilities of immunoglobulin G in hyperimmunized cow's milk treated under various conditions

Skim milk and whey prepared from milk secreted by cows that had been injected with bacteria were kept under various conditions, and the antigen‐binding and protein G‐binding abilities of immunoglobulin G (IgG) in the milk samples were investigated. More than 85% of the original antigen‐binding and protein G‐binding abilities remained when the skim milk was heated at 63°C for 60 min or kept at a pH range of 4–10 for 24 h at 37°C. Both of the high abilities were maintained on pepsin treatment above pH 4 and intestinal proteinase treatments. Little antigen‐binding and protein G‐binding abilities decreased upon storage of the powdered skim milk for 12 months at room temperature. In contrast, at least half, and more than 70% of their respective abilities, were lost upon incubation at pH 2 in the absence and presence of pepsin, respectively, for 1 h at 37°C. These results suggest that most of the biological activities of the Fab‐region and Fc‐region of bovine milk IgG can be maintained during processing or storage, and both of the inactivation degrees mainly depend on the stomach condition after oral ingestion of the IgG preparation.