Effects of polyols on gelation kinetics, gel hardness, and drying properties of alginates subjected to internal gelation

This study investigates the influence of polyols (glycerol, sorbitol, mannitol and isomalt) on thickening of sodium alginate solutions, hardness and drying kinetics of calcium alginate gels and their glass transition temperature (Tg) after drying. Two alginate samples with 30% and 63% guluronate were used to prepare gels by internal gelation based on release of calcium ions from CaCO₃ by hydrolysis of glucono-delta-lactone. The lag period, determined from viscosity-time plots, for the low-G alginate was about 13 min less than that for the high-G alginate. Presence of polyols did not influence the lag period values. The hardness value for high-G gels was about 100 g greater than that of low-G gels. Addition of isomalt resulted in gels with higher hardness values compared to other polyols. Presence of polyols had a significant effect on residual moisture and Tg of alginate films. Initial drying rates were the same for all samples but gels containing glycerol had high residual moisture (∼3.5 g/100 g) and produced very flexible films, whereas mannitol containing samples had low moisture (∼0.2 g/100 g) and produced brittle films. Tg of the films varied from −88 °C to 35 °C and decreased upon polyol addition.