Development and characterization of high internal phase emulsions for lycopene encapsulation with safflower seed meal globulin modified via ultrasound, heating and pH-shifting

This study investigated the synergistic effect of ultrasound in combination with pH-shifting and heating modification on the physicochemical properties, structural characteristics, and emulsifying performance of safflower seed meal globulins (SMG). Furthermore, the efficacy of the modified protein (UHA-SMG) as a natural emulsifier was evaluated for preparing lycopene (LYC)-loaded high internal phase emulsions (HIPEs). Under the suitable modification conditions (ultrasonic power: 500 W, ultrasonic time: 5 min, temperature: 70 °C, pH: 9.0), UHA-SMG exhibited improved physicochemical properties, including altered micromorphology, reduced particle size and interfacial tension, as well as enhanced zeta-potential, surface hydrophobicity, wettability, and solubility. Structural characterization via far-UV circular dichroism, UV-Vis spectroscopy, and fluorescence spectroscopy indicated that the modification altered the secondary and tertiary structures of SMG, as evidenced by a rise in α-helical content and the redistribution of internal hydrophobic groups and aromatic amino acids. At a concentration of 2.0% (w/v), UHA-SMG successfully stabilized oil-in-water HIPEs with an internal phase volume of 75%. These HIPEs demonstrated typical shear-thinning behavior, gel-like rheological characteristics (G' > G''), and excellent stability against centrifugation, heating, and long-term storage. For LYC encapsulation, the HIPEs formulated with 2.0% (w/v) UHA-SMG achieved a high encapsulation efficiency of 96.39 ± 1.34% and provided markedly enhanced stability of LYC against UV irradiation, thermal degradation, and storage compared to free LYC. In summary, the synergistic triple-modification strategy (ultrasound, heating, and pH-shifting) significantly enhanced the functionality of SMG, rendering it a promising candidate as a bio-based stabilizer for HIPEs with considerable potential in lipophilic bioactive ingredient delivery systems.