The pH of bovine mammary secretions transiently drops at calving (to approximately pH 6.4), then increases over several days to pH 6.6 to 6.9 [206] , which is the pH characteristic of mature milk. Therefore, bovine colostrum is slightly more acidic than mature milk. Studies of isolated immunoglobulin stability over a pH range indicate that bovine IgG isolated from milk is stable for several hours at 37 °C when in pH 6-7, however stability is significantly reduced at pH ≤ 3 and ≥10 [207, 208] . The negative effect of pH on IgG stability, even in the range of 4.5-6.5, is enhanced under elevated temperature conditions [209, 210] . The use of a multiple emulsion to encapsulate milk IgG may increase stability of the protein against extreme acidic or alkali conditions, as well as against proteolytic degradation [211] . However, emulsification by homogenization may reduce the residual IgG content of the emulsion product [211] , probably as a result of high shear forces [208] . Ultrasonic treatment of isolated IgG also decreases residual IgG content [208] .