Influence of Weak and Covalent Bonds on Formation and Hydrolysis of Gelatin Networks

The relative influence of physical and chemical bonds to overall gel properties are explored in gelatin gels. Physical, chemical, chemical−physical, and physical−chemical gels are obtained by cooling the protein solution and/or by transglutaminase reaction. Each type of network is characterized by rheology and polarimetry. It is shown that the overall properties as well as the dynamics inside the gels are dependent upon the order of formation and on the relative amount of triple helices and covalent bonds. Enzyme hydrolysis of covalent gels is slower than that of physical gels, as confirmed by the kinetics of helix release and degradation. A scheme is proposed to explain the results at both the physicochemical and the molecular levels.