Unveiling the mechanism for improving the structural, functional and interfacial properties of casein via ultrasound-assisted enzymatic glycosylation and the effect on high internal phase emulsions as curcumin delivery vehicles.

Increasing research attention has been focused on biopolymer-based particles for stabilizing high internal phase emulsions (HIPEs), owing to their outstanding biocompatibility and biodegradability, rencently. In this study, a transglutaminase-induced sodium caseinate (SC)-carboxymethyl chitosan (CMCS) covalent complex (SC-CMCS) was prepared, the effect of different mass ratios (3:1, 2:1, 1:1, 1:2, 1:3) and ultrasonic pretreatment times (400 W, 0, 10, 20, and 40 min) of SC before conjugation on the structural and functional characterization, as well as the modification effect on curcumin-loaded HIPEs were systematically investigated. Key parameters including grafting degree, FTIR spectra, fluorescence spectra, surface hydrophobicity, emulsifying properties, foaming properties, interfacial properties, lipid oxidative stability, curcumin encapsulation efficiency, and in vitro digestive behavior of HIPEs were determined. The results showed that the optimal mass ratio of SC to CMCS was 3:1. After 10 min of ultrasonic pretreatment, the glycosylated SC exhibited increased hydrophobicity, elevated fluorescence intensity, reduced particle size, and the highest solubility. Its interfacial properties were enhanced as evidenced by reduced interfacial tension and an elevated diffusion rate (Kdiff). This improved interfacial performance enabled the glycosylated SC to adsorb more effectively at the oil-water interface, thus enhancing emulsion stability. HIPEs prepared using this modified casein featured a dense three-dimensional network structure, excellent resistance to lipid oxidation, and notably enhanced protective effects on curcumin. Specifically, their curcumin encapsulation efficiency reached 93.24%. These results indicate that HIPEs stabilized by enzymatically glycosylated casein have great potential as highly efficient delivery systems for functional food applications, particularly for hydrophobic bioactive compound delivery.