Phycocyanin–chitooligosaccharide interactions drive the formation of blue soft wheat starch gels with modified digestibility: Linking multiscale structure to functional performance

Designing starch-based soft gels with visual functionality and modulated digestibility is important for developing texture-modified foods. In this study, blue wheat starch composite gels were constructed by incorporating phycocyanin (Phy, 5% and 10%) and chitooligosaccharide (COS, 2.5% and 5%), and their formation, multiscale structure, physicochemical properties, and in vitro digestibility were systematically investigated. Phy imparted a blue to blue-green appearance to the gels, while COS further modulated their color characteristics. Phy and COS reduced pasting viscosity and viscosity rebuilding and promoted the transition from a dense, starch-dominated gel network toward a looser and more heterogeneous composite structure. Structural and thermal analyses revealed reduced short-range order, relative crystallinity, and gelatinization enthalpy, accompanied by weakened viscoelasticity and lower textural strength. The incorporation of Phy and COS also redistributed the digestible starch fractions, with increased RDS and decreased SDS and RS observed in several composite formulations. Molecular docking suggested that starch-derived glucan chains and COS could potentially recognize partially overlapping regions on the Phy surface, providing a possible molecular basis for local component association and subsequent structural reorganization. Overall, these findings demonstrate that Phy and COS regulate wheat starch gel properties through formulation-dependent structural reorganization, providing a basis for designing visually distinctive and soft-textured starch-based composite gels with modulated digestion profile.