Abstract: The present study was conducted to improve the membrane properties of silver carp skin gelatin and dissect the mechanism involved by examination of protein structure. The gel strength, viscosity and mechanical properties of silver carp skin gelatin extracted by three extraction methods (acid extraction, hot water extraction and enzymatic extraction) were comparatively studied. Then the enzymatically prepared gelatin was modified with transglutaminase (TG), and the amino acid composition was determined and compared with that of a commercial product and that of the unmodified gelatin. At the same time, circular dichroism (CD) spectroscopy and infrared (IR) spectroscopy were employed to estimate the secondary and tertiary structure, and IR spectroscopy and atomic force microscopy (AFM) were employed to examine the change of protein structure before and after TG addition. The results showed that the enzymatically prepared gelatin had the highest viscosity and strongest gel strength. Its membrane had the strongest mechanical properties and lowest water vapor permeability. Furthermore, after TG modification, its tensile strength and elongation at break were increased significantly to levels equivalent to those of type A pigskin gelatin membrane, accompanied by a decrease in water vapor permeability. CD and IR spectra showed that, compared with the samples prepared by two other methods, the enzymatically obtained gelatin had higher α-helix content and lower random coil content and thus retained more hydrogen bonds between gelatin chains. After TG modification, the –NH2 group in gelatin was changed to –NH–, consequently improving the interaction between peptide chains. The results of AFM showed that the surface microstructure of the modified gelatin membrane was more even and compact. A positive correlation existed between the α-helix content and mechanical properties of the gelatin membrane. In conclusion, pepsin-assisted extraction combined with TG modification is an effective method to improve the membrane properties of gelatin.

Key words: silver carp, gelatin, modification, film performance