Covalent ternary complexes for improved curcumin delivery: Role of dicaffeoylquinic acid isomers and conjugation sequence with β-lactoglobulin and hyaluronic acid

Protein-based complexes are critical for enhancing food functionality, particularly owing to the synergistic effects of ternary covalent complexes containing proteins, polysaccharides, and polyphenols. This study investigated the formation mechanism, structural characteristics, and functional properties of ternary covalent complexes composed of β-lactoglobulin (β-Lg), hyaluronic acid (HA), and three dicaffeoylquinic acid (DCQA) isomers (3,5-DCQA, 3,4-DCQA, and 4,5-DCQA); the complexes were prepared using different addition sequences. These complexes exhibited reduced surface hydrophobicity, altered secondary structures, and enhanced thermal stability. They showed significantly better antioxidant activities and emulsifying properties in comparison with native β-Lg. The protein-polysaccharide-polyphenol sequence yielded more stable and compact structures with higher polyphenol binding capacity. Subsequently, the protein-polysaccharide-polyphenol complexes were used to encapsulate curcumin (Cur), and it yielded encapsulation efficiencies up to 76.14 % (β-Lg-HA-3,4-DCQA-Cur), which was significantly higher than the encapsulation efficiency of native β-Lg-Cur (36.35 %). These complexes also improved the physical stability and antioxidant activity of Cur under adverse conditions. These findings highlight the critical roles of the addition sequence and polyphenol structure in modulating the functionality of protein-based complexes, and offer promising strategies for enhancing the delivery of bioactive compounds in food applications.