Rheological properties of fine-stranded whey protein isolate gels

The rheological and fracture properties of fine stranded WPI gels were determined over a range of shear strain rates (0.014–0.69 s−1). All gels had the highest fracture strain when deformed at a strain rate of 0.014 s−1. Fracture stress was relatively constant over all strain rates. These effects were observed at all protein concentrations and suggest a link with molecular or network relaxations. The apparent modulus (stress/strain at any level of strain) exhibited decreasing or linear behavior at low to moderate strains, followed by non-linear strain-hardening behavior at higher strains. As strain rate increased, the gels displayed increased non-linear behavior. The strain where the modulus switched from linear to non-linear behavior decreased as protein concentration or strain rate was increased. Therefore, both strain rate and protein concentration affect the large-strain viscoelastic behavior of WPI gels during deformation and fracture. This observation suggests a link with the molecular relaxation processes occurring in the gel network.