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 Ca2+ 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.

The present work was mainly financed by the Spanish Ministry of Science and Innovation (CTQ2017S-84998-P), with support from Generalitat de Catalunya (2017SGR1778). In addition, we also acknowledge the “Grupo de Nanotecnología Farmacéutica”, of the Faculty of Pharmacy and Food Sciences, at the University of Barcelona (UB), that forms an R&D Associated Unit (“Unidad Asociada”) to CSIC. J.E also greatly thank Carlos Rodríguez-Abreu (IQAC-CSIC, Barcelona, Spain), Allan Mackie and Josep Bonet (URV, Tarragona, Spain), Maria J. Garcia-Celma (UB, Barcelona, Spain) and Andeaa Pasc (UL, Nancy, France), for useful discussions.

Peer reviewed