Physicochemical studies of heat -denatured whey protein functionality
The physicochemical effects of pH, temperature, ionic strength and ingredient interaction on the formation of heat-denatured whey proteins and their resulting aggregation and gelation were investigated. Results were interpreted based on the molecular interactions that exist between protein molecules.
Aggregation was dependent on protein concentration, pH, heat time and heat temperature. Optimal conditions for production of heat-denatured whey for use as a cold-set gelation ingredient were identified as 10 wt%, pH 7 and 75 to 85°C for 10 to 30 minutes, dependent on desired gel time and rheological properties. Whey protein aggregates were further characterized using Ultrasonic Attenuation Spectroscopy (UAS). UAS proved to be a valuable method for the investigation of molecular relaxation and scattering mechanisms in whey proteins.
Electrostatic interactions proved crucial to cold-set gel network formation. Gel texture and optical properties were closely related to mineral content and type, with divalent cations inducing gelation via charge shielding and cross-linking, thereby reducing the amount of added salt necessary.
Aggregation of heat-denatured whey proteins exhibited a concentration-dependent sensitivity to sucrose addition. Below 8 wt% sucrose network formation was retarded, as detected by suppression of rheological properties. This was attributed to the viscosity contribution by sucrose to the continuous phase, thereby reducing aggregate collision frequency. Above 8 wt%, the trend was reversed due to preferential dehydration of the protein molecules that encouraged protein-protein interaction.
The addition of xanthan to a cold-set gelation system increased its textural properties. This was due to phase separation of the xanthan and heat-denatured whey proteins that resulted due to thermodynamic incompatibility. Excluded volume effects increased the effective concentrations of both biopolymers accounting for their resulting synergism.
Finally, heat-denatured whey protein was added to an emulsion stabilized by non-ionic surfactant (Tween 20). Addition of salt caused aggregation of the proteins and was found to be dependent on protein and mineral concentration. A gel network formed around the non-interactive oil droplets to produce a thickened emulsion.