Biopolymer hydrogels based on polysaccharide and protein: Interactions with anthocyanins and bioactive compounds in...

Hydrogel-based materials derived from biological macromolecules have emerged as promising platforms for multifunctional food packaging. This review critically examines how the molecular structures of major biopolymers, including chitosan, alginate, starch, cellulose derivatives, gelatin, casein, and related polysaccharides and proteins, influence the active and intelligent functions of hydrogel packaging systems. Structural characteristics such as monomer composition, charge distribution, degree of substitution, and chain conformation are linked to crosslinking mechanisms, network topology, swelling behavior, and the resulting mechanical and barrier properties. The interactions of these hydrogels with bioactive agents, including essential oils, polyphenols, antimicrobial peptides, metal nanoparticles, and natural colorants, are discussed, with emphasis on hydrogen bonding, electrostatic interactions, hydrophobic association, and coordination bonding that govern encapsulation, stabilization, and controlled release. Particular attention is given to anthocyanin-incorporated hydrogels, where the pigment microenvironment and binding interactions regulate pH sensitivity, halochromic behavior, and color stability. Structure-function relationships are further explored by relating macromolecular composition and crosslink density to transport mechanisms, stimuli responsiveness, and correlations between colorimetric changes and spoilage indicators such as microbial growth and total volatile basic nitrogen. Recent advances in hybrid and nanocomposite hydrogels, including nanocellulose-reinforced, metal-organic framework-containing, and peptide self-assembled systems, are also highlighted. Finally, key challenges involving pigment stability, the balance between biodegradability and mechanical strength, and large-scale production are discussed, along with future directions for designing robust, sustainable, and stimuli-responsive hydrogel-based packaging systems.