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

¹ Department of Animal Science, Macdonald College of McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, PQ, Canada H9X 1C0
² Food Research Centre, Agriculture Canada, Ottawa, ON, Canada K1A 0C6

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

Key Words: ßbeta;-lactoglobulin • genetic variants • differential scanning calorimetry

Submitted on August 1, 1990
Accepted on February 25, 1991