Microalgae protein-carboxymethyl chitosan complexes assembled via hydrogen bonding and hydrophobic interactions for enhanced emulsion stability and retarded lipid digestion.

Microalgal protein (MP) is a sustainable food resource that is nutritionally rich and environmentally friendly, but it has poor structural stability and limited emulsifying capacity, restricting its application in complex food systems. This study investigated the potential of MP-carboxymethyl chitosan (CMCS) complexes to stabilize emulsions under environmental stress. MP-CMCS complexes were prepared and structurally characterized, followed by evaluation of their stability and functionality in emulsion systems. Curcumin encapsulation and the rate of lipid digestion under simulated gastrointestinal conditions were also examined. Results showed that CMCS effectively formed MP-CMCS complexes. At a ratio of MP: CMCS = 9: 1 and pH 12, the complexes exhibited uniform microstructures with fewer pores and enhanced interfacial properties. Emulsions stabilized by the complexes maintained stable droplet sizes even at 70% oil content, tolerated salt concentrations up to 200 mM NaCl. During simulated digestion, MP-CMCS emulsions released approximately 12% less free fatty acids than MP emulsions, indicating slower lipolysis and improved bioactive retention. Curcumin encapsulation efficiency reached 78%, with higher retention and bioaccessibility. These functional improvements are attributed to hydrogen-bonded, interfacial networks, and steric reinforcement via hydrophobic anchoring, whereas pH primarily modulates protein conformation and interfacial hydration. This study provides a strategy to overcome the processing limitations of MP, promote its high-value utilization, and expand its application in the development of functional foods.