Size-controlled whey protein microgels enable tunable gelation in low-oil Pickering emulsions: Role of particle size and concentration

Although many formulations have been developed to stabilize low-oil Pickering emulsions, it remains challenging to define how particle design enables the transition from a flowable emulsion to an emulsion gel. In this study, submicron-scale spherical whey protein microgels (WPMs) with tunable sizes were produced from water-in-water emulsions via a low-energy protein–polysaccharide phase-separation route. Microgels with mean sizes of ∼200 nm, ∼500 nm, and ∼1 μm were obtained. Their potential as structural building blocks for low-oil Pickering systems was then evaluated. At a WPM concentration of 4.5 wt%, all WPM-stabilized low-oil emulsions showed minimal or no creaming during 28 days of storage. However, their rheological behavior was strongly dependent on microgel size. WPM ∼1 μm formed highly viscous, structured emulsions with gel-like characteristics, whereas WPM ∼200 nm produced more flowable emulsions with higher mobility. The stability and structuring of these systems were governed by the coupled contributions of WPMs at the oil–water interface and in the bulk phase. Larger WPMs, especially WPM ∼1 μm , exhibited lower electrostatic repulsion and more viscoelastic interfacial films. Meanwhile, their aggregation in the continuous phase promoted particle bridging and the formation of a percolated network, thereby driving the transition toward a Pickering emulsion gel and markedly enhancing system viscoelasticity. These results show that WPM size controls interfacial stabilization and bulk network formation , providing a practical route to tune low-oil Pickering systems from flowable emulsions to thick, gel-like emulsions.