Properties of partially denatured whey protein products: Viscoelastic properties

Abstract

Partially denatured whey protein products (PDWPC's) can be classified based on the viscoelastic properties of their solutions. Strain sweeps show that PDWPC-A and –B and microparticulated WPC (MPWPC) with compact, spherical aggregated particles exhibit a strong strain overshoot. PDWPC-C and –D, on the other hand, which have open, elongated porous particles show a weak strain overshoot. The concentration dependence of the elastic modulus G′ in the linear viscoelastic region has a biphasic power law dependence with concentration for all protein products studied, except for WPC where G′ is independent of protein concentration. Frequency sweeps suggest that MPWC solutions form a strong physical gel at all concentrations above 14% (w/w). PDWPC-A and –B form weak gels over the same concentration range. PDWPC-C and –D also form weak gels at 14% protein (w/w) but strong physical gels at higher concentrations. The frequency dependence of G′ and G″ for all aggregated proteins show a power law dependence indicating fractal type structures. For all solutions above a critical concentration, the fractal dimensions span the range 1.6–2.3, indicating a range of gel network structures from open and diffuse to compact and dense. Adherence to the empirical Cox-Merz rule was observed in PDWPC-A, -C and –D at concentrations of 14 and 16% (w/w) protein, suggesting liquid-like behaviour. At higher protein concentrations the deviations from the Cox-Merz rule suggest more pronounced elasticity in the structure. For PDWPC-B, the behaviour is complex, with deviation from the Cox-Merz rule at low frequencies/shear rates, but correspondence at higher frequencies/shear rates at all concentrations. This indicates a frequency-dependent change from liquid-like behaviour over long timescale deformations, to a solid-like behaviour at short timescale deformations. MPWPC solutions of all concentrations do not follow the Cox-Merz rule, suggesting solid-like behaviour. The PDWPCs exhibit a complex rheological behaviour which suggests they could be versatile thickening, texturizing and fat replacement ingredients that will offer food manufacturers greater control over the texture of formulated fluid foods.