Thermal behavior of collagen crosslinked with tannic acid under microwave heating

With the aim at assessment of thermal stabilities of collagen crosslinked with tannic acid under microwave, some thermo-analysis methods have been employed to analyze the properties of the crosslinked product. Meanwhile, for getting some information about the non-thermal effect of microwave on the process, microwave heating with simultaneous cooling (MHSC) method was adopted and compared with water bath heating. The thermal decomposition of the collagen material was characterized by the mass-loss ratio with thermo-gravimetry/derivative thermo-gravimetry curves recorded in nitrogen flow. The crosslinked collagen under MHSC exhibited a higher peak temperature and a lower degree of thermo-oxidative decomposition. The thermal denaturation of the material was determined by the differential scanning calorimetry (DSC) analysis in nitrogen flow. DSC curves showed that microwave gave a higher denaturation temperature and enthalpy, which increased about 3.9 °C and 73.0 J g−1, respectively. The hydrothermal stability of the product was evaluated using the method of micro hot table in glycerol–water condition. The results showed that the shrinkage temperature increased about 3.5 °C under MHSC. In result, microwave gave a higher thermal and hydrothermal stability of the crosslinked collagen, which could be attributed to a stronger bonding of the collagen with tannic acid as a result of microwave non-thermal effect. The results presented here may lay a foundation for the application of microwave in vegetable tanning.