Ionic Diffusion in Spherified Calcium Alginate Gels: A Laboratory Experiment

Dilute water solutions of sodium alginate are used in molecular cooking and the dairy industry as thickening and gelling agents and also as edible films. Typically, they are obtained from brown algae or seaweeds and form stable gels in the presence of calcium ions. Calcium alginate gels can be easily prepared in the form of small solid spheres by dropping, with a syringe or a pipette, the sodium alginate solution into a water bath of calcium ions (“direct method”). After rinsing the calcium alginate spheres, fully or just partially jellified, their external pH can be easily regulated using ordinary acid and/or basic solutions. The chapter describes in detail the various steps of the procedure adopted for the preparation of calcium alginate spheres and for detecting the diffusion of protonated water inside them by observing the colour change of a suitable pH indicator contained in the spheres.