EFFECT OF THERMAL PROTECTANTS ON THE STABILITY OF BOVINE-MILK IMMUNOGLOBULIN-G

pH stability, thermal stability, and the effect of homogenization and ultrasonic treatment on the stability of bovine milk immunoglobulin G (IgG) in model systems was studied. Separated IgG (0.02 mg/mL) was fou nd to be unstable and susceptible to denaturation when incubated at pH <4 or >10 or thermally treated at temperature >75 degrees C. IgG in t he colostrum, on the other hand, was found to be much more stable than in whey or in PBS when thermally treated at temperatures in the range of 75-100 degrees C. The residual IgG content reduced more sharply wi th increasing heating times, and almost no IgG content was detected wh en IgG in PBS (0.15 M NaCl/0.01 M phosphate buffer, pH 7.0) was heated at 95 degrees C for 15 s, whereas the corresponding residual IgG cont ents in whey and colostrum were found to be 42 and 59%, respectively. For IgG in PBS heated at 95 OC for 15 s, addition of 5% fructose or ma ltose displayed most remarkable protection effects by raising the resi dual IgG content to 31%, followed by sucrose, lactose, glucose, and ga lactose. However, extravagant addition (>30%) to IgG in PBS led to a d ecline in residual Ige content. Addition of 0.4% glutamic acid and 2% glycine to IgG in PBS heated at 95 degrees C for 15 s also remarkably improved the residual IgG content by 13.5 and 26.7%, respectively. Gly cerol and sugar alcohol, such as sorbitol, stabilized IgG during the t hermal treatment.