Encapsulation of BSA/alginate water-in-water emulsions by polyelectrolyte complexation

Water-in-Water (W/W) emulsions were prepared in aqueous mixtures of an anionic polyelectrolyte (sodium alginate, NaAlg), with a globular protein (bovine serum albumin, BSA). This combination showed phase separation at two different intervals of pH, and their phase behavior was studied. BSA-in-alginate emulsions were obtained and dropped into Ca2+, Fe3+ or chitosan solutions, forming capsules with diameters around 2-4 mm, by ionic complexation of sodium alginate, located in the continuous phase of the emulsions. The results showed a strong dependence on the cation or polycation. Capsules prepared with Ca(2+ )were not robust and collapsed during freeze-drying, while Fe3+ induced the gelation of the interior of capsules, even at short (5 min) contact time. Better results were obtained when encapsulating with chitosan and applying longer immersion times. In these capsules, the liquid interior contained well-preserved BSA-in-alginate emulsions droplets, identical to the initial emulsions before encapsulating. Freeze-dried spherical capsules prepared with alginate/Fe3+ or alginate/chitosan shells had smooth surfaces, and a highly porous interior, templated by the presence of W/W emulsion droplets.