Stabilization of oil continuous emulsions with colloidal particles from water-insoluble plant proteins

Emulsions stabilized by surface active particles are becoming an attractive alternative to conventional surfactant-stabilized emulsions. Biobased, environmentally friendly, and edible particles are particularly interesting for applications in foods, agriculture, and consumer products. Previously, water insoluble proteins such as prolamins have been only used as a platform for stabilization of water continuous emulsions. In this paper, we investigate the ability of zein particles to stabilize oil continuous emulsions. We synthesized and used zein particles in the form of (i) an aqueous, or (ii) an oil suspension. Aqueous suspensions of zein particles resulted in water-in-oil (w/o) emulsions that were generally stable for more than an hour, with up to 30 vol% water as the dispersed phase. Cryo-SEM images show that only a small fraction of zein particles are adsorbed at the oil-water interface as Pickering stabilizers. Adding an oil soluble surfactant (lecithin) prior to emulsification with zein particles in an aqueous suspension promoted the formation of oil-continuous emulsion with phase inversion point at 40 vol% of water. Zein particles suspended in oil produced less stable emulsions, which showed reversible phase inversion attributed to the electrostatic repulsion of hydrophilic protein loops above their isoelectric point. Our results show that zein particles act as a predominantly hydrophilic stabilizer that requires control prior to emulsification to form w/o emulsions. These emulsions, however, have only a limited stability. (c) 2018 Elsevier Ltd. All rights reserved.