Chitosan-polysaccharide composite carriers under in vitro digestion: Classification, gastrointestinal behavior, and bioaccessibility implications-A review.

Chitosan-polysaccharide composites should be evaluated as gastrointestinally responsive structures rather than as generic encapsulation matrices. We organize food-relevant systems into four architectures: interfacial multilayers, hydrogel and microgel networks, particulate carriers, and hierarchical hybrids. Within this framework, we examine how material attributes, carrier structure, cargo properties, and digestion protocols govern protection, structural reorganization, release, bioaccessibility, and probiotic viability. The evidence shows that high retention, encapsulation efficiency, or mucoadhesion alone does not predict effective delivery. Performance depends on whether the carrier changes at the appropriate digestive stage. It must also transfer the cargo to a relevant endpoint. Examples include a mixed-micellar fraction, an uptake-related readout, controlled intestinal release, and viable-cell recovery. In probiotic systems, complexed or spatially separated chitosan can provide protection, whereas freely accessible cationic chains may reduce viability. Reported transitions include gastric consolidation, intestinal swelling or interfacial displacement, and relaxation of multilevel barriers, but the evidence does not support one universal sequence for all formulations. Comparison remains limited by incomplete material specifications, reliance on static digestion models, inconsistent endpoint definitions, weak quantitative comparability, and sparse validation in food matrices or after digestion. We therefore propose an evidence-bounded framework that links architecture to digestive function and endpoint selection.