Stromal Protein from Jumbo Squid as a Natural Emulsifier for Cinnamon Essential Oil Emulsions: Effects of High-Intensity Ultrasound on Physicochemical Properties and Antioxidant Activity

Marine stromal proteins represent a promising but underexplored source of natural emulsifiers for developing functional emulsions. This study investigated the effects of high-intensity ultrasound (HIU) on the physicochemical characteristics, interfacial properties, and antioxidant performance of emulsions formulated with stromal protein extracted from Dosidicus gigas mantle and cinnamon essential oil. Sonication time (0, 3, 5, and 10 min) and amplitude (40, 70, and 100%) were evaluated. The physicochemical and colloidal properties of the emulsions were evaluated through oil-holding capacity (OHC), particle size, polydispersity index (PDI), zeta potential, and rheological behavior. At the same time, antioxidant performance was determined using DPPH, ABTS, FRAP, and erythrocyte hemolysis inhibition assays. HIU markedly improved the physicochemical properties of the emulsions. The Z-average droplet diameter of the emulsions ranged from 195.3 ± 1.5 to 368.7 ± 4.0 nm. The treatment at 5 min and 70% amplitude produced the smallest droplets (195.3 ± 1.5 nm), corresponding to an approximately 27% reduction compared with the untreated emulsion (268.7 ± 4.6 nm), as well as the lowest PDI (0.215 ± 0.026) and a zeta potential of −15.8 ± 0.4 mV. Ultrasound also improved oil retention and enhanced antioxidant performance, although the magnitude of the response depended on the assay employed. The emulsions inhibited AAPH-induced erythrocyte hemolysis by approximately 77–95%, with the highest inhibition observed after treatment for 10 min at 40% amplitude. Overall, HIU enhanced the interfacial functionality of squid stromal proteins, supporting their potential application as natural emulsifiers in protein-based antioxidant delivery systems.