Casein gel particles as novel soft Pickering stabilizers: The emulsifying property and packing behaviour at the oil-water interface

Abstract

The aim of this study was to create food-grade soft gel particles that stabilize oil-in-water emulsions. The gel particles were prepared by covalently crosslinking the protein network within the self-associated casein sub-micelles (CN-GP) or calcium-induced casein micelles (CN-Ca-GP) with genipin. The mean diameters of CN-GP and CN-Ca-GP were 17.6 ± 2.9 nm and 113.5 ± 1.4 nm, respectively. From the atomic force microscopy images, it can be found the height of the two particles on the mica plate surface were significantly smaller than their width, indicating both the CN-GP and CN-Ca-GP were soft particles. Their ability to stabilize the oil droplets against creaming, coalescence and flocculation was assessed with Turbiscan analysis, droplet size determination and microscopy observation. For comparison, sodium caseinate (CN) was used as the control. The microscopy observation suggested the oil droplets stabilized by CN exhibited obvious flocculation, whereas the oil droplets stabilized by CN-GP or CN-Ca-GP were quite stable against flocculation. Turbiscan analysis showed the emulsions stabilized by CN-GP or CN-Ca-GP exhibited higher stability against creaming than the emulsions stabilized by CN. The droplet size determination indicated no significant changes in the average size of the oil droplets stabilized by CN-GP or CN-Ca-GP during 30 days’ storage, whereas significant increase in the average size of the oil droplets stabilized by CN can be observed during the storage. Cryo-scanning electron microscopy images suggested the CN-GP or CN-Ca-GP can be closely packed and deformed at the interfaces of the oil droplets. Overall, casein gel particles offer promising prospects in food emulsion-based products.