Rheological and structural properties of sodium caseinate as influenced by locust bean gum and -carrageenan

The interactions between sodium caseinate and polysaccharide were investigated by choosing both neutral (locust bean gum) and anionic polysaccharides (kappa-carrageenan). The linear and non-linear rheological properties, zeta-potential and structures of the sodium caseinate/gum mixtures were evaluated. The mixtures all displayed shear-thinning phenomenon, and the increase of either locust bean gum or kappa-carrageenan content led to the increase of storage (G') and loss (G") moduli. The large amplitude oscillation shear (LAOS) test and Fourier transform have been successfully used to detect the slight rheological differences caused by microstructure changes. Increasing levels of kappa-carrageenan led to critical strain decreased of the mixture, but not for locust bean gum. The sodium caseinate/locust bean gum mixtures behaved as "hard gel", while the sodium caseinate/kappa-carrageenan mixtures behaved as "soft gel" in Fourier-transform rheology. Changes in viscoelasticity under large strain were illustrated using elastic and viscous Lissajous curves, which were correlated to the micro structural change within the network of the mixtures. The zeta-potential values were significantly decreased in the presence of kappa-carrageenan, while the addition of locust bean gum had no significant influence. Phase separation was found more dominant to change the structure than the protein network formation in the sodium caseinate/locust bean gum mixtures. However, protein network formation was the factor to dominate the structure forming of sodium caseinate/kappa-carrageenan mixtures with electrostatic forces and hydrogen bonding.