Tailoring physical properties of transglutaminase-modified gelatin films by varying drying temperature

Abstract

Transglutaminase (TGase)-modified gelatin films containing different levels of physical and chemical networks were prepared by drying films above or below gelation temperature of gelatin. Differences in protein network structure were observed by optical microscopy analysis in freeze-dried film-forming solutions. The relative amount of triple helices decreased when drying temperature increased as observed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The addition of TGase slightly inhibited triple helix formation. TGase-modified films exhibited stronger mechanical properties than blank films, and the highest tensile strength was observed in films dried close to the gelation temperature (25 °C) and the highest elongation at break above it (35 °C). TGase modification enhanced the water resistance and thermal stability of gelatin films by decreasing the water solubility, increasing the glass transition temperature and degradation temperature, respectively, which was further enhanced with increasing drying temperature. The cross-section (SEM) and surface (AFM) microstructure of gelatin films with TGase both appeared more compact and smooth, and improved when temperature increased. The results obtained show that drying temperature may be used to tailor the physical properties of TGase-modified gelatin films for specific applications.