Effect of transglutaminase and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide on the solubility of fish gelatin–chitosan films

The possibility of decreasing the water solubility of the films made from fish gelatin and chitosan by modification with TGase was investigated. The effectiveness of enzymatic treatment was also compared with chemical crosslinking using EDC. The treatment of the components with TGase in concentration of 0.2 mg/ml of the film-forming solution limited the solubility of the films at 25 °C from 65% to 28% at pH 6 and from 96% to 37% at pH 3. After 15 min of heating at 100 °C, the modified films were soluble in 23% at pH 6 and in 41% at pH 3. Further decrease of the solubility of the fish gelatin–chitosan films was achieved when enzymatic modification was conducted in the presence of 5–10 mM DTT; the solubility was about twice lower than that without DTT at both studied temperatures and pH values. Generally, the composite films modified with EDC in concentration of 30 mM were distinctly less soluble than films made from the components modified with TGase in the presence of DTT.