STABILITY OF BOVINE IMMUNOGLOBULINS TO THERMAL-TREATMENT AND PROCESSING

Thermal stability of bovine immunoglobulin (IgG) in model systems and in commercially processed milk products was investigated. Bovine serum IgG dissolved in either phosphate buffered saline (PBS), boiled milk or ultra high temperature (UHT) sterilized milk was heated at temperat ures ranging from 62.7 degrees C to 80 degrees C. The D-values ranged from 90, 200 and 170 s at 80 degrees C to 25.5, 27.2 and 32.8 min at 7 2 degrees C for IgG in PBS, boiled milk and UHT milk, respectively. Th ese results suggest slightly greater thermal stability of IgG in milk than in phosphate buffer. IgG content was not changed after 30 min at 62.7 degrees C, nor by holding for 24 h at either ambient temperature or 4 degrees C. Over the temperature range from 72 degrees to 80 degre es C, z-values were 6.7, 8.9 and 8.5 degrees C, and energies of activa tion were 353.5, 258.2 and 298.5 kJ mol(-1) for thermal destruction of bovine serum IgG in PBS, boiled milk and UHT milk, respectively. Thes e findings in model systems suggest that commercial pasteurization pro cesses should not result in complete destruction of IgG. Comparison of IgG content in raw milks and corresponding HTST-pasteurized milks of varying fat content indicated 59-76% retention after pasteurization, w ith no apparent effect by either homogenization, skimming or standardi zation to 1 or 2% fat levels. The IgG contents and specific antibody a ctivity against lipopolysaccharide fractions of live bacteria were det ermined for several commercially processed milk products. HTST-pasteur ized milks, reconstituted skim milk powder and whey from cheddar chees e production all showed high levels of IgG and specific antibody activ ity. However, canned evaporated milk and ultra high temperature (UHT) sterilized milk had little or no IgG. This study demonstrates the depe ndence of bovine IgG stability in milk products on severity of thermal treatment used in various commercial processes.