DIFFERENTIAL SCANNING CALORIMETRIC STUDY OF DIFFERENT GENETIC-VARIANTS OF BETA-LACTOGLOBULIN

The onset temperatures, denaturation temperatures, and temperatures at width of half-peak height of beta-lactoglobulins AA, BB, and AB were compared using differential scanning calorimetry. Heat stability of the different phenotypes of beta-lactoglobulin was variable, depending on the pH and composition of buffer. At pH 6.80, denaturation temperatures of beta-lactoglobulin BB were 3.0, 3.3, and 5.5-degrees-C higher than those of the AA variant in Jenness-Koops, sodium phosphate, and sodium or potassium phosphate buffers, respectively. Although beta-lactoglobulin AB had denaturation temperatures similar to those of AA type in the first two buffers, its denaturation temperature was lowest at 73.4-degrees-C in the last buffer system. Beta-Lactoglobulin AB was the most stable in water and piperazine-N,N'-bis-(ethanesulfonic acid), and similar denaturation temperatures were obtained for beta-lactoglobulins AA and BB in these solvents. The cooperativity of the transition process was also associated with the genetic types of beta-lactoglobulin. In a 1:1 mixture of beta-lactoglobulin and kappa-casein, kappa-casein BB and AB lowered both the onset and denaturation temperatures of beta-lactoglobulin. In contrast, kappa-casein AA slightly raised the transition temperatures of beta-lactoglobulin.