Effect of dynamic heat treatment on the physical properties of whey protein foams

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied with the aim of determining the optimal temperature for the production of heat-induced aggregates dedicated to foaming. The native protein solutions (2% w/v WPI; 50 mM NaCl) at neutral pH were heat-treated using a tubular heat exchanger between 70 °C and 100 °C. Protein denaturation and aggregation were followed by micro-differential scanning calorimetry, size exclusion chromatography, laser diffraction and dynamic light scattering. The protein solutions were whipped using a kitchen mixer to produce foams. Foam overrun, stability against drainage, texture and bubble size distribution were measured. Experimental results showed that overrun slightly decreased with an increase of the temperature used to treat proteins, whereas foam rigidity was improved at the same time. An optimal temperature of thermal treatment was found at 80 °C for stability against drainage. Quantitative analyses showed that the formation of approximately 10% soluble aggregates in the WPI sample before whipping maintained a good level of overrun, lead to an increased stability against drainage and to an improved rigidity for whey protein foams. Conversely, they revealed that an increase of temperature above 80 °C before foaming did not improve anymore the functional properties of the proteins.