Spontaneous formation of protein microcapsules using water-in-water emulsions stabilized by protein microgels.

Protein microgels tend to adsorb at the surface of dispersed droplets in water-in-water (W/W) emulsions. It was hypothesized that suspensions of stable protein microcapsules (MC) can be produced by spontaneous crosslinking of the microgels at the interface in a process akin so-called cold gelation. Rapeseed or whey protein microgels added to W/W emulsions formed by mixing polyethylene oxide (PEO) and Dextran (DEX) adsorbed at the W/W interface. The rapeseed protein microgels were found to spontaneously crosslink and formed MC suspensions that were stable to dilution and washing. The size of the MC was monitored using confocal laser scanning microscopy and could be tuned between a few µm and a few tens of µm by varying the volume fraction of the dispersed phase or the protein concentration. After washing, the MC remained stable between pH 4 and pH 9 as well as after addition of 0.1 M NaCl. In order to form stable MC with whey protein microgels it was necessary to add a very small amount of cationic napin, thereby reducing electrostatic repulsion.