Co-stabilization mechanisms of solid particles and soluble compounds in hybrid Pickering emulsions stabilized by unrefined apple pomace powder

Abstract

Vegetal by-product powders, such as apple pomace powder, represent an efficient green alternative to conventional emulsifiers to stabilize oil-in-water Pickering emulsions. The natural material being used without purification, its multiple components shall impact differently the emulsion stability and interact with each other. These effects might be either synergic, competitive, or both depending on their ratio. Herein, the co-stabilizing effects of the apple pomace compounds on Pickering emulsions were explored from microscopic to macroscopic scales. The apple pomace powder was first fragmented into several fractions which were characterized (particle sizes, shape and wettability, oil-water surface activity). Emulsions were then prepared by varying the stabilizing material composition using the different fractions obtained from the apple powder. Emulsions properties (droplet size, rheological properties) and stability were monitored over a month. The key role of solid particles in the surface activity of the apple pomace powder was shown by interfacial tension measurements. All particle-stabilized emulsions were stable against coalescence during storage despite high droplet diameters (up to 80 μm) and low surface coverage. Soluble matter and particles show a synergic behavior to stabilize oil-in-water emulsions. The soluble matter drives droplet size whereas insoluble cellulosic particles are responsible for emulsion stability by both Pickering adsorption to the oil droplet and oil droplet trapping in a three-dimensional network. This study provides new insights into the understanding of natural powders stabilizing mechanisms that may lead to a better prediction of the potential of vegetal by-products as stabilizing agents from their chemical composition.