Effect of salt concentration and composition on the rheological and mechanical properties of k/i-carrageenan gels: optimization using response surface methodology

Abstract

Carrageenans are sulphated polysaccharides of red seaweed used as gelling, thickening and stabilizing agents by the food industry. Particularly, κ/ι-carrageenan gels show unique properties and have received increased interest in recent years. Gelation occurs in the presence of cations, typically potassium in κ- and calcium in ι-carrageenan. The aims of this study were to 1) analyse the effect of cation concentration and composition on the rheology, texture and syneresis of food grade κ/ι-carrageenan gels, and 2) optimize the structural properties of these gels. Response surface methodology (RSM), small composite design(SCD) was used to evaluate the effects of three factors (carrageenan concentration, salt concentration, and KCl fraction in a mixture of KCl and CaCl2) on the following responses: elastic modulus at 1 Hz (G?), hardness (H), rupture strength (R) and syneresis (S). Regression analyses indicated that the quadratic model was the most appropriate to explain all responses. Carrageenan concentration positively affected G?, H and R, while salt concentration negatively influenced these responses, indicating that highercarrageenan and lower salt concentrations improved gel firmness. Higher KCl fractions also resulted in increased H and R. Syneresis was reduced with the increase of carrageenan concentration and KCl fraction, while it was augmented by high salt concentrations. To optimize the structural properties of the gels, G?, H and R were maximized and S was minimized, achieving a global desirability of 0.895 with the following combination of factors: carrageenan concentration = 1.74% (w/w), salt concentration = 0.07M and KCl / (KCl + CaCl2) = 0.85.