Thermal properties of whey protein aggregates

Aggregation of 10% whey protein solution was induced by addition of calcium salt, acidification, or proteolysis at 45 degrees C. Effects of the preaggregation on thermal properties of whey proteins were examined by differential scanning calorimetry. The different types of aggregates had three common effects: I) one endothermic peak, representing denaturation of whey protein aggregates, instead of two endothermic peaks representing alpha- lactalbumin and beta-lactoglobulin in the control; 2) a narrower range (similar to 10 degrees C) of denaturation temperature than the control (similar to 20 degrees C); and 3) significantly greater enthalpy values (similar to 4 J/g) than the control (<2 J/g). Denaturation temperatures (TD, To) of the aggregates were also different from those of alpha-lactalbumin (67 degrees C) and beta-lactoglobulin (76 degrees C) of the control. Aggregates induced by calcium salt (similar to 74 degrees C) and protease (similar to 73 degrees C) had intermediate denaturation temperatures. The pK-induced aggregates had high denaturation temperatures (80 to 91 degrees C) at low pH (3.5 to 5.7). An exothermic peak was detected during calcium salt- or protease-induced aggregation of whey proteins at 45 degrees C. Thus, the preaggregation changed thermal properties of whey proteins. This information on thermal properties of the aggregates may help in the design of appropriate heat processing for the application and manufacture of whey protein products.