Preparation and characterization of gelatin films by transglutaminase cross-linking combined with ethanol precipitation or Hofmeister effect

Abstract

In this study, the gelatin films were prepared by dehydration with ethanol precipitation or Hofmeister effect via absolute ethanol or saturated (NH4)2SO4 solution after transglutaminase (TG) cross-linking. The prepared gelatin films remained the integrity after heat treatments (boiling or high-temperature sterilization), and had a low water vapor permeability (WVP) due to TG cross-linking. Ethanol precipitation improved the mechanical, water barrier (water solubility) and visual sensory (color difference and transparency) properties of the gelatin films especially at a high gelatin concentration, which was due to the increase of hydrogen bonding and triple helix content, and ethanol decolorization effect, respectively. The tensile strength (TS) and elongation at break (EAB) were increased by 155.28% and 72.73% than in oven-dried gelatin film (15% gelatin concentration). The results of thermo-gravimetric analysis (TGA) and thermal shrinkage suggested the enhanced thermal stability of films induced by ethanol precipitation due to more orderly internal structure. Although mechanical properties and thermal shrinkage of gelatin films could also be improved by Hofmeister effect, the (NH4)2SO4 migrated to films after dehydration, especially at a low gelatin concentration, which limits the application of this method. The present results indicated that TG cross-linking combined with ethanol precipitation can serve as an effective method to obtain gelatin films with good thermal stability and mechanical, visual sensory and water barrier properties.