Turbulence-dependent reversible liquid-gel transition of micellar casein-stabilised emulsions

Gel-like emulsions formed with colloidal particles have attracted great attention in various research fields, with studies on food applications surging in an effort to discover new food-grade particle stabilisers that can replace chemical emulsifiers and stabilisers. Turbulence-induced emulsion gels (TIEGs) have recently been reported as a novel means of producing stable gel-like food emulsions. Here we investigate the ability to alternate between liquid and gel-like textures for emulsions stabilised by bovine casein micelles. We describe a reversible emulsion textural transition between free-flowing liquids and semi-solid gels, controlled solely by the application of rotor-stator mixing and high-intensity low-frequency ultrasound (HILF-US), respectively. Rheological and microstructural analyses of the emulsions were performed over five treatment cycles, revealing the importance of the droplet close packing at the submicron level, unique to HILF-US. The amino acid content of the casein was not altered by sonochemical effects. However, the overall secondary structure of the casein protein changed during TIEG formation due to resulting interfacial associations. In-vitro digestion results showed that the initial emulsion texture did not alter protein digestibility. However, TIEG emulsions had smaller droplets that were more stable during digestion. The outcomes aim to deepen the understanding of turbulent-induced emulsion gel formation and advance knowledge on emulsion textural manipulation for food applications.