Structure and Properties of Gallic Acid Epoxy Modified Gelatin

In this study, gallic acid (GA) was used to synthesize the gallic acid epoxy (GAE) for the chemical modification of gelatin. The chemical structure, hydration properties, thermal stability, and mechanical properties of GAE modified gelatin (GAEG) were evaluated. It was found that the epoxy group of GAE reacted with the primary amine group of gelatin to form C-N bond and covalent cross-linking. The swelling ratio of GAEG in water was increased by about 5 times. With the cross-linking degree increased from 41.13% to 72.68%, the swelling ratio decreased from 7831% to 6448%. While the gelatin dissolved completely in water within 24 h, the GAEG film remained intact for 7 days, and the disintegration rate decreased significantly with the increase of cross-linking degree. The water contact angle decreased from 88.01° to 59.87° after the modification, indicating increased hydrophilicity. The reduction of dehydration rate and the increase in total dehydration ratio suggested that the water retention capacity has been improved after the modification. The denaturation temperature increased from 55.0 ℃ to 61.7 ℃, and the thermal decomposition temperature increased from 240 ℃ to 274 ℃, with a relative decrease in thermal weight loss. The modification treatment led to a slight decrease in mechanical properties. This study demonstrated that GAE improved the hydration properties and thermal stability of gelatin, contributed to the application of gelatin as water retaining agent and stabilizer in food industry.