Determination of covalent cross-linker efficacy of gelatin strands using calorimetric analyses of the gel state

This study assesses the efficiency of the chemical cross-linking in gelatin, when utilising two different cross-linking reagents. A new method using micro-calorimetry was developed to use the energy involved in renaturation of the protein for probing the efficiency of the cross-linking reaction. The enthalpy of renaturation upon cooling was measured for two different types of cross-linkers, viz. glutaraldehyde and transglutaminase. Gelatin is a polymer with the ability to form a physical thermo-reversible network. When cross-linking reactions occur within the gelatin gel, covalent bonds are generated. This in turn creates a second network locked in place by chemical bonds. Therefore two different types of networks coexist. Heat flow measurement at different levels of cross-linking reagent thus permits the measurement of the reduction in enthalpy of gelation as the cross-linking reaction progresses. By introducing the concept of effective concentration, the enthalpy data can be directly related to the degree of cross-linking through an empirical model. This concept emphasizes two different mechanisms taking into consideration the cross-linkers transglutaminase and glutaraldehyde. A mechanism for the polymerisation of glutaraldehyde is proposed.