Self-assembly of Fu brick tea polysaccharide conjugate and chitosan quaternary ammonium salt for the synergistic stabilization of β-carotene-loaded complex emulsions with enhanced stability and bioaccessibility.

To improve the emulsifying performance of Fu brick tea polysaccharide conjugate (FBTPC) and expand its application in delivering hydrophobic bioactives, an FBTPC-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) complex emulsion system was developed. FBTPC exhibits good resistance to gastric digestion, while HACC possesses strong cationic adhesion properties. Their combination endowed the system with the dual advantages of interfacial stability and intestinal delivery. The emulsifying properties, stabilization mechanism and delivery performance of the system were systematically evaluated. The results showed that a robust lamellar interfacial network was formed between FBTPC and HACC through hydrogen bonding and electrostatic interaction. With increasing HACC content (1%-2.5%), the rheological properties and structural stability of the complex emulsions were significantly improved. Under various environmental stress conditions such as pH, ionic strength, heat treatment and long-term storage, the complex emulsions maintained stable zeta potential and particle size. Moreover, the complex emulsions effectively encapsulated β-carotene, with the encapsulation efficiency (EE) exceeding 93.09%. They also markedly improved the stability of β-carotene, retaining 92.68% after 10 h of UV light exposure and 93.61% after 14 d of storage. In vitro simulated gastrointestinal digestion studies showed that the complex emulsions with higher HACC content exhibited good stability in the gastric phase and underwent structural disassembly in the enzymatic environment of the small intestine. This process facilitated lipid hydrolysis and β-carotene release, significantly enhancing its bioaccessibility (17.16%). This study provides a promising strategy for improving the emulsification performance of FBTPC and provides valuable insight for the design of TPC-based delivery systems.