Contribution of protein microgels, protein molecules, and polysaccharides to the emulsifying behaviors of core/shell whey protein-alginate microgel systems

The mixtures of proteins and polysaccharides are often used in stabilizing food emulsion systems and biopolymer microgels have gained increasing research interest for emulsion stabilization. When a mixture of whey protein and alginate solution was heated for 15 min at 90 °C at pH 7, a core/shell whey protein-alginate microgel system was formed consisting of protein microgel (M), unconverted protein molecule (P), and alginate (A). This system can stabilize oil-in-water emulsion with long-term stability and strong texture. In this present study, the individual contributions of protein microgel, protein molecule and polysaccharide and their combinations (M + P, M + A, P + A, and M + P + A) to the emulsion properties and texture were investigated. While the protein microgel itself could not be well adsorbed at the oil droplet surface, the presence of alginate decreased the water contact angle of protein microgel from ∼107° to ∼90°, enabling the protein microgel adsorption at the water/oil (w/o) interface to form stable Pickering emulsions. In the tri-component system containing protein molecule, protein microgel and alginate, the w/o interfacial layer was dominated by protein molecules, while the protein microgels were distributed in the continuous phase. The jamming effect brought by the protein microgel between the oil droplets effectively prevented flocculation and coalescence, leading to super stable emulsions. Varying alginate or microgel content can provide a convenient strategy to modify the rheological properties and texture of the emulsions. Especially for the emulsions prepared from the tri-component system, increasing protein microgel content will make 30% oil emulsions show similar rheological and flow behavior to emulsions containing 50% oil. This result demonstrates that the protein microgel system has the potential for applications in preparing "low fat" emulsion-based food formulations with a comparable texture to that of full-fat counterparts.