Rheological behaviour of whey protein concentrate and λ-carrageenan aqueous mixtures

Steady-state and oscillatory tests of whey protein concentrate (WPC) (2.0–32.0% (w/w) of total solids), λ- Carrageenan (λ-C) (0.1–2.0% (w/w)), mixtures of 2.0–25.0% (w/w) WPC +1.0% (w/w) λ-C and mixtures of WPC/λ-C ratio 8:1, 16:1 and 32:1 were investigated. Both WPC and λ-C solutions showed shear-thinning behaviour and the 32.0% (w/w) WPC solution also exhibited thixotropy. Both kinds of mixtures exhibited shear-thinning behaviour, the 15.0–25.0% WPC+1.0% λ-C and the different WPC/λ-C ratio mixtures showing thixotropy. Besides, the mixture apparent viscosities were appreciably higher than the protein apparent viscosity+polymer apparent viscosity. While all solutions behaved as viscoelastic fluids at the concentrations studied, the mixtures of ratio 8:1; 16:1and 32:1 behaved as high entanglement structures or weak gels, since the moduli were practically parallel, G′ being equal or higher than G″ throughout the frequency range. Besides, the moduli values were appreciably higher than those of the WPC and λ-C solutions. The comparison of apparent and complex viscosities confirmed the viscous nature of the dispersions as well as the weak gel properties of the mixtures.