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Department of Food Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5
ABSTRACT
Several factors affecting thermal stability of the proteins present in whey were studied over 2.5 to 6.5 pH range using differential scanning calorimetry and heat-induced precipitation. Heating whey at 95°C for 5 min above pH 3.8 to 3.9 produced extensive protein coagulation. When the same heat treatment was applied below pH 3.7, protein precipitation was prevented; however, protein denaturation still occurred in various whey protein fractions. The highest denaturation temperature for an acid whey protein concentrate prepared by ultrafiltration was 88°C at pH 3.5, while for an isolated ß-lactoglobulin preparation the highest denaturation temperature, obtained also at pH 3.5, was 81.9°C. Presence of milk sugars (lactose, glucose, and galactose) appeared to increase the resistance of ß-lactoglobulin to thermal denaturation. Heat stability of 
-lactalbumin was lower at pH 3.5 than in the pH 6.5 to 4.5 range; at all pH denaturation temperatures of -lactalbumin (61.5 to 58.6°C) were lower than those for ß-lactoglobulin or two serum albumin preparations. Sample of serum albumin containing 1.0 to 1.3 mol of fatty acids/mol of albumin showed substantially higher denaturation temperatures than an essentially fatty acid free preparation. Thermal behavior of an ultrafiltration whey protein concentrate appears to be controlled by the dominating ß-lactoglobulin fraction.
1 Present address: Department of Food Science, University of Guelph, Guelph, Ontario, N1G 2W1.
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