Time dependent gelling properties of cuboid alginate gels made by external gelation method: Effects of alginate-CaCl2 solution ratios and pH

Abstract

This study investigated the gel strength and syneresis of cuboid alginate gels (2 × 2x1.4 cm) using 2% Na-alginate solutions as a function of gelling time, CaCl2 solution concentrations (0.05 M - 0.20 M) and pH (4−11) in an external gelation method. This study also investigated the effects of providing a limited or excess amount of calcium ions needed to completely cross-link the alginate chains by altering the ratio between alginate and CaCl2 solutions. For comparison purpose, the gelling time and syneresis of alginate beads (2.5–3.0 mm in diameter) were also studied. The results showed that an increase in the CaCl2 concentration resulted in a faster gelling time, increased gel strength and higher degree of syneresis. Meanwhile, an increase in pH of the alginate and CaCl2 solutions resulted in the decrease of gel strength and the degree of syneresis. In the presence of excess CaCl2, the gels would reach the same equilibrium degree of syneresis (∼39%) after a certain gelling time, regardless of CaCl2 concentration. It was also observed that the degree of syneresis gradually increased from the start of gelation until a stable point was reached which corresponds to the end of gelation. This trend of syneresis was observed in both cuboid gels and spherical gel beads although stabilisation of syneresis occurred sooner in the gel beads (<2 h) compared to cuboid gels (>5 h). Since the smaller gel beads exhibited syneresis phenomena similar to that of large cuboid gels, it can be inferred that micron size gels may exhibit similar behaviour.