Abstract: Extraction temperature and glycerol content are the critical factors affecting gelatin film properties. In the present study, chum salmon (Oncorhynchus keta) skin gelatin was extracted at different temperatures (40, 50, 60, 70, 80 and 90 ℃), and the effect of glycerol content (1.1, 1.2 and 1.5 g/100 mL) on gelatin film properties including thickness, mechanical properties, color, optical properties, microstructure and infrared absorption characteristics was explored. Results indicated that films of gelatin extracted at 40, 50 and 60 ℃ showed higher thickness than films of gelatin extracted at 70, 80 and 90 ℃ (P < 0.05). Mechanical analysis showed that tensile strength (TS) of films of gelatin extracted at 50 and 60 ℃ was higher than that of films of gelatin extracted at 70, 80 and 90 ℃ (P < 0.05). Elongation at break (EAB) of films with 1.5 g/100 mL glycerol increased with the increase of gelatin extraction temperature (P < 0.05). TS of films prepared from gelatin extracted at 50, 70 and 80 ℃ declined with the increase of glycerol content (P < 0.05). The a* value of films increased with the increase of gelatin extraction temperature (P < 0.05). Water vapor permeability (WVP) showed an increase with the increase of extraction temperature and glycerol content (P < 0.05). The light transmittance of films were 0.00% at wavelengths of 200 and 280 nm and 46.53%–74.57% in the range of 350–800 nm. The light transmittance of films prepared from gelatin extracted at 60 ℃ was lower than that of films prepared from gelatin extracted at 40 and 50 ℃ (P < 0.05). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis demonstrated that gelatin films exhibited the characteristic absorption regions of gelatin, including amide I, II and III bands and amide A and B bands. Among them, amide A shifted to lower wavelength with the increase of extraction temperature and its amplitude increased with increase of glycerol content. Scanning electronic microscopy showed no distinct crack or gaps on the surface and cross section of films. The results indicated that extraction temperature had a significant impact on mechanical properties, WVP and color of gelatin films. However, glycerol content only affected mechanical properties and WVP. Thus, the properties of films prepared from chum salmon skin gelatin can be improved by optimizing gelatin extraction temperature and glycerol content.

Key words: fish skin, gelatin film, glycerol, temperature, mechanical properties, microstructure