The underlying mechanism between emulsification stability and in vitro digestion in golden pompano (Trachinotus ovatus) myofibrillar protein-fish oil oleogel emulsion under ultrasonic treatments

Fish oil contains rich EPA and DHA, but their low absorption rate and bioavailability in the gastrointestinal tract limit their physiological activity. Ultrasonic treatments can modify the spatial structure of myofibrillar proteins and influence their function. The microstructure, viscoelastic properties, spatial conformation, size and charge, interfacial characteristics were investigated in the emulsions with fish oil oleogels to clarify the mechanism between emulsification stability and lipid digestion by ultrasonic treatment. The results showed that ultrasonic-treated (120 s or 150 W) fish myofibrillar protein had higher interfacial protein concentration and formed the more stable interfacial adsorption layer to wrap the fish oil oleogel with higher viscoelastic properties. The surface charge density was affected by adsorbed proteins, and higher interfacial adsorption capacity enhanced electrostatic repulsion and reduced the size. CLSM images also indicated that the droplet distribution was more uniform with smaller particle size. The increase in β-sheets facilitated interfacial adsorption and emulsion stability, and hydrophobic force and disulfide bonds promoted the interactions between myofibrillar protein and fish oil oleogel. In the stomach, the demulsification and flocculation occurred, and β-sheets increased along with hydrophobic forces and disulfide bonds, facilitating flocculation and aggregation as well as the increase in particle size. The electrostatic repulsion and spatial conformation altered the hydrolysis degree. In the intestine, the decreasing β-sheets, hydrophobic force and disulfide bonds were conducive to the adsorption of bile salts and lipase/colipase. Hence, ultrasonic treatments simultaneously enhanced emulsion stability and lipid digestion.