Molecular and structural characteristics of cod gelatin films modified with EDC and TGase

Cod gelatin films before and after cross-linking of gelatin with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) or transglutaminase (TGase) have been characterized by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) analysis. For comparison, a film prepared from unmodified pig gelatin has been also analysed. The difference spectra showed that cod gelatin during the film formation involved first of all water-to-amide hydrogen bonds, and the film from pig gelatin contained water-to-amide, amide-to-amide and water-to-water hydrogen bonds. A higher number of hydrogen bonds in the structure of the film from pig gelatin contributed to much better recovering of the helical structure in this film than in the film from cod gelatin, as the peaks at about 1663 cm−1 in the amide I band and at about 1537 cm−1 in the amide II band in the second-derivative spectra revealed. The recovered helical structure, in turn, resulted in a significantly higher melting enthalpy value in the case of the film from the pig gelatin. After modification of cod gelatin with EDC or TGase, the inter-chain cross-linkages formed in the films led to the conformation of gelatin with no indications of helical ordering. An increase of melting temperature of gelatin films by 7 °C on EDC and by 10 °C on the TGase modifications was related to the formation of covalent cross-links, and a decrease of glass temperature by 28 °C and 7 °C on EDC and TGase cross-linking, respectively, demonstrated the plasticizing effect of water.