Bulk and Interfacial\nBehavior of Potato Protein-Based\nMicrogels

This study aims to understand the bulk and interfacial\nperformance\nof potato protein microgels. Potato protein (PoP) was used to produce\nmicrogels of submicrometer diameter via a top-down approach of thermal\ncross-linking followed by high-shear homogenization of the bulk gel.\nBulk “parent” gels were formed at protein concentrations\n[PoP] = 5–18 wt %, which subsequently varied in their bulk\nshear elastic modulus (<i>G</i>′) by several orders\nof magnitude (1–100 kPa), <i>G</i>′ increasing\nwith increasing [PoP]. The PoP microgels (PoPM) formed from these\nparent gels had diameters varying between 100 and 300 nm (size increasing\nwith increasing <i>G</i>′ and [PoP]), as observed\nvia dynamic light scattering and atomic force microscopy (AFM) of\nPoPM adsorbed onto silicon. Interfacial rheology (interfacial shear\nstorage and loss moduli, <i>G</i><sub><i>i</i></sub>′ and <i>G</i><sub><i>i</i></sub>″) and interfacial tension (γ) of adsorbed films of\nPoP (i.e., nonheated PoP) and PoPM (both at tetradecane–water\ninterfaces) were also studied, as well as the bulk rheology of the\nPoPM dispersions. The results showed that PoPM dispersions (at 50\nvol %) had significantly higher bulk viscosity and shear thinning\nproperties compared to the nonmicrogelled PoP at the same overall\n[PoP], but the bulk rheological behavior was in sharp contrast to\nthe interfacial rheological performance, where <i>G</i><sub><i>i</i></sub>′ and <i>G</i><sub><i>i</i></sub>″ of PoP were higher than for any of the PoPM.\nThis suggests that the deformability and size of the microgels were\nkey in determining the interfacial rheology of the PoPM. These findings\nmay be attributed to the limited capacity for “unfolding”\nand lateral interactions of the larger PoPM at the interface, which\nare presumed to be stiffer due to their production from the strongest\nPoP gels. Our study further confirmed that heating and cooling the\nadsorbed films of PoPM after their adsorption showed little change,\nhighlighting that hydrogen bonding was limited between the microgel\nparticles.