Study of combined effects of glycerol and transglutaminase on properties of gelatin films

Gelatin films plasticized with different glycerol contents (0-40%) were cross-linked using transglutaminase (TGase). Unmodified films were prepared as controls. Cross-linking degree of the films decreased linearly with increasing glycerol content, resulting in an increase in water solubility. Glycerol increased the mobility and free volume of the gelatin film matrix as observed by differential scanning calorimetry, thus increasing the moisture content and thickness. Tensile strength and Young's modulus had a negative linear correlation with glycerol content, with no significant differences between TGase-modified and unmodified films (p > 0.05). However, TGase-modified films showed a 294% and 187% relative increase in elongation at break and toughness, respectively, in comparison with controls at 30% glycerol content (p < 0.05). X-ray diffraction and circular dichroism spectroscopy both showed a linear decrease in triple-helix content as glycerol content increased, and TGase-modified films had lower triple helix contents. Also, the second derivative of FTIR spectra showed that TGase-modified films had increased single alpha-helix structures, but decreased disordered coil structures. In addition, SEM results indicated that TGase-modified films had more smooth and compact microstructures, especially at high glycerol contents (30-40%). (C) 2016 Elsevier Ltd. All rights reserved.