Protamine peptide-enhanced pectin composite gel beads for efficient gastrointestinal-responsive anthocyanin release

Pectin-calcium gels are widely used as carriers for food bioactives, but their strong dependence on Ca²⁺-mediated crosslinking creates a trade-off between structural stability and intestinal release. High Ca²⁺ levels strengthen the gel network but can hinder the release of anthocyanins, which are mainly absorbed in the small intestine, whereas reducing Ca²⁺ may compromise gel integrity. In this study, protamine peptide was incorporated into a pectin-based gel matrix to improve intestinal responsiveness while maintaining structural stability at reduced Ca²⁺ levels. Complementary zeta-potential, ITC, DSC, FTIR, and XPS analyses supported spontaneous association between pectin and protamine peptide, primarily involving electrostatic association and hydrogen bonding. These additional interactions were associated, at least in part, with the maintenance of gel integrity, and formulation 16 exhibited a hardness of 1.15 N at 0.5% Ca²⁺. The composite gel beads retained their structure under simulated gastric conditions but underwent marked disintegration in simulated intestinal fluid (SIF). Formulation 16 achieved an intestinal-phase anthocyanin release of 68.20%, more than twice that of the conventional pectin-Ca²⁺ control beads. Kinetic analysis indicated that limited gastric release was mainly governed by diffusion, whereas enhanced intestinal release resulted from the combined effects of gel disintegration and diffusion. These findings demonstrate the potential of pectin-protamine peptide gel beads as gastrointestinal-responsive carriers for anthocyanins and other food bioactives.