The characterization of fucoidan‑sodium caseinate electrostatic complexes with application for pH-triggered release: Microstructure and digestive behavior

This study was aimed at enhancing the stability of the medium internal phase emulsion by modulating the electrostatic interaction between fucoidan (FUC) and sodium caseinate (NaCS). Firstly, the macro and microstructure of FUC-NaCS electrostatic complexes with the mass ratio of ranged from 0.01: 2 to 4: 2 were examined at pH 3.0. As the concentration of FUC increased, the complexes transformed a soluble state to phase separation and then returned to the homogeneous state, with the turbidity and particle size initially increasing and then decreasing. The zeta potential of the complexes gradually declined, and the zero-point was corresponding to the phase separation region where the ratio of FUC-NaCS was around 0.75: 2. The microstructure by TEM and SEM demonstrated that the NaCS particles were bonded to the FUC cross-linking chain network via electrostatic interaction to form self-assembling complexes. Subsequently, the simulated digestion results suggested that the FUC-NaCS complexes could delay the hydrolysis of NaCS and displayed greater stability in gastric environments. Based on the above results, the FUC-NaCS complexes were utilized to emulsify and stabilize medium chain triglycerides (MCT). The droplets of the FUC-NaCS emulsion at 4: 2 was more dispersed with a smaller diameter, and also exhibited superior stability during stomach digestion and concurrently high digestibility during intestinal digestion, making FUC-NaCS complexes a potential choice for pH-triggered release of emulsions, especially in gastrointestinal environment.