Effect of hydrocolloid and minerals content on the mechanical properties of gels

The mechanical behavior of agar, carrageenan and alginate gels was evaluated for a wide range of gum and setting agent concentrations as well as for different gel preparation methods. Two types of gel were defined based on their mode of mechanical response to a change in the concentration of the gel-forming components. The first type, which includes alginate set with glucono-D-lactone and carrageenan gels, is characterized by a maximum in the value of yield stress and of the deformability modulus at a certain gum and setting agent concentration. This phenomenon is attributed to the trend of formation of aggregates, at high reactants (gum and setting agent) concentration, rather than a strong gel having a uniform matrix of high density of cross-linkage bonds. Although on both sides of the maximum point one may get gels of apparently the same yield stress, these gels still differ in other aspects such as brittleness and extent of mechanical syneresis. The second type of gel, which includes agar and alginate set by a slow diffusion of calcium ions, is characterized by an increase in gel strength the higher the, gum concentration.