Differential Scanning Calorimetric Study of Different Genetic Variants of β-Lactoglobulin

Abstract

The onset temperatures, denaturation temperatures, and temperatures at width of half-peak height of J3-laetoglobulins AA, BB, and AB were compared using differential scanning calorimetry. Heat stability of the different phenotypes of 13lactoglobulin was variable, depending on the pH and composition of buffer. At pH 6.80, denaturation temperatures of 13-lactoglobulin BB were 3.0, 3.3, and 5SC higher than those of the AA variant in Jenness-Koops, sodium phosphate, and sodium or potassiwn phosphate buffers, respectively. Although l3-lactoglobulin AB had denaturation temperatures similar to those of AA type in the first two buffers, its denaturation temperature was lowest at 73.4C in the last buffer system. I3-Lactoglobulin AB was the most stable in water and piperazine-N,N'-bis-(ethanesulfonic acid), and similar denaturation temperatures were obtained for J3lactoglobulins AA and BB in these solvents. The cooperativity of the transition process was also associated with the genetic types of j3-lactoglobulin. In a 1: 1 mixture of 13-lactoglobulin and lC-casein, lC-casein BB and AB lowered both the onset and denaturation temperatures of 13-1actoglobulin. In contrast, lC-casein AA slightly raised the transition temperatures of l3-lactoglobulin.