Rehydration of dried alginate gel beads: Effect of the presence of gelatin and gum arabic

Abstract

This study investigates how the phase separation induced by the biopolymers gelatin and gum arabic influences the microstructure of alginate beads prepared in CaCl2 solutions and the subsequent rehydration of the air-dried beads. The extent of associative phase separation in mixture gel beads can be controlled via pH. Compared with control beads, alginate/gelatin mixture beads swelled faster at the initial stage of rehydration while slowed down at the late stage, reaching a lower equilibrium swelling ratio. The faster initial swelling kinetics can be attributed to the presence of gelatin which prevents the side-by-side aggregation of egg-box junctions. This conclusion was confirmed using wide angle X-ray diffraction (WAXD) measurements. The lower equilibrium swelling ratio was due to the gelatin network restricting alginate from further swelling. This was evidenced by temperature dependence swelling experiments and comparison with alginate/gum arabic beads where no additional network was formed on top of the alginate network. The varying of pH, correspondingly the change of phase separation extent, had a significant influence on the rehydration of mixture gel beads. The best rehydratability was observed at higher pHs where no phase separation occurred and the components were homogenously mixed. With decreasing pH, the associative phase separation between alginate and gelatin was promoted, and led to local over-concentration of alginate, which gave rise to poor rehydratability.