Properties of deamidated gluten films enzymatically cross-linked

Films were prepared at neutral pH from deamidated gluten by casting with or without enzymatic treatment by transglutaminase in the presence of various concentrations of diamines added to the film-forming solution. Variation i n the glycerol/deamidated gluten ratio from 0.2 to 0.5 had a major effect o n the film mechanical properties, which is characteristic of a plasticizing effect;; A ratio of 0.35, producing a tensile strength of 1.14 +/- 0.12 MP a and an elongation at break of 376 +/- 62%, was chosen for most of the enz ymatic modifications. The action of transglutaminase with or without the ad dition of external diamines induced a simultaneous increase in tensile stre ngth and elongation at break of the films but tended to decrease the contac t angle between the film surface and a water droplet. The presence of diami nes in the film solution affected the elongation at break more than the ten sile strength of the films. These diamines, able to react at their two extr emities, probably acted as spacers between gluten proteins. The decrease in solubility was related to the formation of high molecular weight polymers in the film. The film properties were unaffected by the type of diamine add ed as secondary substrate in the transglutaminase reaction.