Interaction-Induced Characterization of Animal-Based Protein-Polysaccharide Composite Hydrogels: A Review

The molecular interactivities between proteins and polysaccharides exhibit a profound role in characteristics of binary hydrogels. The binary gels were characterized from the major aspects; molecular behavior, microstructure, texture, rheology, water-holding capacity (WHC), and swelling ratio (SR). Despite previous articles claiming the electrostatic interactions to be the main driving forces of gelation, it was shown that gelation of animal-derived proteins and polysaccharides are totally in line with hydrogen and hydrophobic forces. Polysaccharides unfold proteins, evidenced by increased surface hydrophobicity and fluorescence quenching. Polysaccharides modify both secondary and tertiary structures of proteins by facilitating the transition of α-helix to β-sheet along with all-gauche conformation to trans-gauche-gauche. The π-π stacking causes enhanced adhesiveness, elasticity, gel strength, springiness, resistance to fracture, WHC, and SR. Increased specific surface area and surface active energy enhance the gelation properties. Both excessive total polymer concentrations and hydrophobic interactions weaken the structure. Polysaccharide addition enhanced the gel tendency toward water, so WHC and SR increased. However, excess protein reduction abruptly reduced them. Therefore, a threshold was known for protein/polysaccharide mass ratio. In common, polysaccharide made the structure harder than single protein gel.