Effect of Chitosan-Sodium Caseinate Complex Layer Formation at Oil-Water Interface on the Crystallization Behavior of Oil Droplets in Oil-in-Water Emulsions

Oil-in-water (O/W) emulsions containing palm oil or trimyristin as the oil phase were prepared using a membrane emulsification method. A polyelectrolyte complex layer composed of chitosan (CHI) and sodium caseinate (SC) was formed on the droplet surfaces, and its effect on oil droplet crystallization was investigated. The crystallization behavior of the oil droplets under isothermal conditions was observed using polarizing light microscopy, which revealed that the O/W emulsions with the CHI-SC complex layer exhibited slower crystal formation than those without the complex. Small-angle X-ray scattering (SAXS) analysis showed that α-form crystals were initially generated and gradually transformed into β′-form crystals, which then gradually increased during isothermal incubation. Comparison of polarizing microscopy and SAXS results indicated that the CHI-SC complex layer delayed the crystallization of oil droplets, particularly during the initial α-crystal formation stage. Similar effects were observed in emulsions containing trimyristin droplets, suggesting that the CHI-SC complex layer suppresses α-crystal formation regardless of the fatty acid composition of the triacylglycerols.