Changes in functionality of whey protein and micellar casein after high pressure – low temperature treatments

• Whey protein isolate and micellar casein dispersions were pressure treated at sub-zero temperature conditions (HPLT).
• Caseins formed fibrillar aggregates with shear thickening effect after HPLT treatments.
• Foams prepared from HPLT treated whey proteins showed increased stability.
• Emulsion stability was negatively affected by all pressure treatments but effect was less pronounced for HPLT treatments.

Changes in functional properties of micellar caseins (MC) and whey proteins (WPI) due to high pressure – low temperature (HPLT) treatments were investigated and compared to changes induced via high pressure treatments at room temperature (HP). Single whey protein solutions, micellar casein dispersions and two mixtures (micellar caseins:whey proteins weight mixing ratios 80:20 and 20:80) were treated at a concentration of 2% (w/w) and at two different pH values (7.0 and 5.8). Oscillating pendant drop and shear experiments were performed to identify changes in the rheological behavior at the air/water interface and in bulk, respectively. Foaming and emulsification experiments were conducted to investigate further impacts on the functional behavior. Both, HPLT and HP treatments led to a decreased emulsion stability for emulsions from WPI solutions independent from the treatment pH, while the foam stability was increased for these samples. In comparison, the changes for MC dispersions exhibited the same tendency but less pronounced. HPLT treatments of MC rich samples always led to the formation of a few very large flocs which had a major influence on the functional behavior. The rheological behavior of these samples changed from a Newtonian to a shear-thickening behavior. The elastic part of the surface dilatational modulus was increased for a pure WPI solution after HPLT and HP treatments while the viscous part remained unaffected. However, changes in functional properties highly depended on the sample composition and results for mixtures differ from those for pure dispersions.

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