Characterization of gelatin based films modified with transglutaminase, glyoxal and formaldehyde

Protein films possess good gas barrier properties at low to intermediate relative humidity but reduced water vapor barrier properties, which limits their application. The introduction of chemical or enzymatic modifications could be an alternative to improve the cohesion properties of the polymeric matrix due to the formation of cross-linkages, thus improving the barrier characteristics and the mechanical resistance and decreasing the film solubility. The objective of this study was to evaluate and compare the effect of chemical and enzymatic modifications on the solubility, mechanical properties, barrier properties, thermal properties and morphology of gelatin-based films. The results indicated that the treatments resulted in 20% reduction in solubility for all the modified films, whereas the greatest reduction in water vapor permeability was observed for the enzymatic modified films ( congruent to 35%) as compared to the native film. The mechanical properties were only significantly affected by treatment with formaldehyde, where an increase of approximately 60% with respect to tensile strength was observed. Greater thermal stability, with an increase in the melting point, was observed for the chemically treated films, indicating a greater degree of cross-linking, as confirmed by the number of free e-amine groups remaining after the modification reactions. The morphological analyses indicated a loss of fibrillar orientation as a function of the introduction of cross-linking and the reduced percentage of renaturation of the modified films, as observed in the calorimetric assays. The results indicated that the effect of cross-linked protein films on water vapor permeability is always limited due to the inherent hydrophobic character of the protein and also on the morphology imposed by the modifications. (C) 2004 Elsevier Ltd. All rights reserved.