Stable protein microcapsules by crosslinking protein particles in water in water emulsions

Abstract

In the past protein microcapsules have been made using oil in water emulsions. Usage of such microcapsules in all aqueous systems requires removal of the oil which is difficult and tedious to do fully. Here we present two methods to obtain stable protein microcapsules directly in all aqueous systems, which in addition allows capturing of water soluble ingredients during preparation. One method consisted of adding protein microgels to a water in water (W/W) emulsion formed by droplets of a phase rich in pullulan dispersed in a phase rich in amylopectin (AMP). The microgels adsorbed at the interface forming a monolayer. Physical bonds were formed between the microgels after reducing their net charge density by adding HCl or GDL. Covalent bonds were formed by adding the enzyme transglutaminase. Microcapsules could be formed in both cases, but only covalently bonded capsules resisted dilution for extended times, increasing the pH and heating. The second method involved an aqueous three phase system in which one phase (dextran) formed a layer around droplets of a second phase (poly(ethylene oxide)) dispersed in a continuous third phase (AMP). Protein microgels partitioned preferentially to the dextran phase and were physically or covalently crosslinked in the same manner. Also with this second method only covalently bonded microcapsules resisted dilution for extended times, increasing the pH, and heating. With this second method microcapsules shells with controlled thickness could be formed rendering these microcapsules more resistant to deformation.