Ultra-sound assisted formation of biodegradable double emulsion capsules from hen egg white

It was found that directed self-assembly of hen egg white proteins at oil-water interfaces in Pickering emulsions followed by acoustic denaturation of the proteins at the interface produces double emulsion capsules. The formation of capsules is dependent on the pH of the aqueous phase and on the concentration. At pH 5.5, the capsules are easily formed while at pH 8.5 the formation is difficult and only occurs at high concentration and in low quantity. The difference in capsule stability and interface stabilization at different pH was rationalized by competitive stabilization forces at the oil-water interface which was investigated by dynamic interfacial tension measurements. While the absolute interfacial stabilization does not differ much at different pH, when taking into account stabilization behavior of the pure buffer solutions without protein there is a significant difference. At neutral and alkaline conditions we observed that the pure buffer already stabilizes the interface which competes with the stabilization by the protein. This competitive stabilization resulted in less stable capsules formed at higher pH. Moreover, a lower pH enhances the ultra-sound assisted denaturation of the proteins, yielding an additional stabilization of the formed structures. In addition, the capsules are biodegradable. Upon digestion with trypsin, they were completely destroyed leaving behind small protein aggregates.