The effects of casein, κ-carrageenan and sugars (sucrose or sucralose) concentrations on the mechanical properties of gels acidified by glucono-δ-lactone (GDL) were investigated. Three experimental designs were employed to determine the formulations, and the results were analyzed using response surface regression and analysis of variance. Casein/carragenan gels were stronger than single compound gels, probably because of the strong synergism between the polymers, especially at low casein concentrations. Increased casein concentrations resulted in softer and more brittle gels, which can be explained by the excluded-volume effects. The presence of sucrose shifted this thermodynamic incompatibility indicating that higher protein concentrations were required. Moreover, gels containing sucrose showed the highest stress at rupture values and had lower influence of polymer concentrations. Conversely, gels containing sucralose showed the lowest values of stress at rupture, indicating that this co-solute, even in small proportions, decreased the polysaccharide contribution to the formation of a gel network.