Properties of films from fish gelatin prepared by molecular modification and direct addition of oxidized linoleic acid

Films prepared from fish gelatin molecularly modified via covalent attachment with oxidized linoleic acid (OLA) so called "modified gelatin (MG)" and those added with OLA (G + OLA) at various levels (10-50%, w/w, of protein) were characterized, in comparison to control film (without modification or addition with OLA). Films from MG and G + OLA had lower elastic modulus (EM), tensile strength (TS) and water-vapor permeability (WVP) but higher elongation at break (EAB) and yellowness (b*-value), as compared to control film (p < 0.05). MG film had lower WVP than G + OLA film containing OLA up to 30% (p < 0.05). Moreover, MG film possessed higher transparency and much lower yellowness without rancid smell, compared to the G + OLA films. The control and MG films exhibited similar smooth and homogenous surface and cross-section, while G + OLA films showed rough surface with distributed oil droplets. FTIR and DSC analyses revealed that incorporation of OLA via either molecular modification or direct addition to gelatin led to the decrease of gelatin-gelatin interactions and structure order. In addition, both MG and G + OLA films exhibited lower glass-transition (T-g), melting transition (T-m) and degradation (T-d) temperatures than the control film. Therefore, the incorporation of OLA by molecular modification and direct addition to gelatin could improve flexibility and water-vapor barrier property of gelatin-based films but slightly decrease thermal stability.