Effect of sugars on the rheological properties of acid caseinate-stabilized emulsion gels

Rheological properties of sweetened acid-induced caseinate-stabilized emulsion gels (30% v/v n-tetradecane) and the corresponding acid-induced caseinate gels have been investigated. Emulsions were typically prepared with sodium caseinate (1.4% w/v) as emulsifier and with added sucrose (0–66% w/v) or a mixture of sucrose+glucose (76% w/v) present in the aqueous phase. The development of a three-dimensional network, following slow acidification on addition of glucono-δ-lactone granules (0.3 g GDL/g protein), was followed through the resulting increase in the small-deformation shear moduli (G′ and G″) at 25°C. Sugar concentrations greater than 60% w/v led to larger emulsion droplets. Added sugar was found to reduce the gelation time and increase substantially the elastic modulus of these emulsion gels and protein gels, especially at high sugar/protein ratio. Sugar was found also to affect the large-deformation rheology, promoting strain-weakening behavior and a shorter linear regime. Emulsion gels of high sugar content showed the typically expected behavior on changing oil volume fraction or protein content. Overall, the findings are consistent with an enhancement in the strength of the protein–protein interactions in the presence of sugars.