Effects and mechanisms of ultrasound-assisted emulsification treatment on the curcumin delivery and digestive properties of myofibrillar protein-carboxymethyl cellulose complex emulsion gel

Different emulsion gel systems are widely applied to deliver functional ingredients. The effects and mechanisms of ultrasound-assisted emulsification (UAE) treatment and carboxymethyl cellulose (CMC) modifying the curcumin delivery properties and in vitro digestibility of the myofibrillar protein (MP)-soybean oil emulsion gels were investigated. The rheological properties, droplet size, protein and CMC distribution, ultrastructure, surface hydrophobicity, sulfhydryl groups, and zeta potential of emulsion gels were also measured. Results indicate that UAE treatment and CMC addition both improved curcumin encapsulation and protection efficiency in MP emulsion gel, especially for the UAE combined with CMC (UAE-CMC) treatment which encapsulation efficiency, protection efficiency, the release rate, and bioaccessibility of curcumin increased from 86.75 % to 97.67 %, 44.85 % to 68.85 %, 18.44 % to 41.78 %, and 28.68 % to 44.93 % respectively. The protein digestibility during the gastric stage was decreased after the CMC addition and UAE treatment, and the protein digestibility during the intestinal stage was reduced after the CMC addition. The fatty acid release rate was increased after CMC addition and UAE treatment. Apparent viscosity, storage modulus, and loss modulus were decreased after CMC addition while increased after UAE and UAE-CMC treatment especially the storage modulus increased from 0.26 Pa to 41 Pa after UAE-CMC treatment. The oil size was decreased, the protein and CMC concentration around the oil was increased, and a denser and uniform emulsion gel network structure was formed after UAE treatment. The surface hydrophobicity, free SH groups, and absolute zeta potential were increased after UAE treatment. The UAE-CMC treatment could strengthen the MP emulsion gel structure and decrease the oil size to increase the curcumin delivery properties, and hydrophobic and electrostatic interaction might be essential forces to maintain the emulsion gel.