Storage stability of fish gelatin films by molecular modification or direct incorporation of oxidized linoleic acid: Comparative studies

Changes in properties of films fabricated with oxidized linoleic acid (OLA)-modified gelatin (OMG) and those prepared with OLA-added gelatin (OAG) were investigated during storage for 8 weeks, in comparison to the control film (without modification or OLA addition). OMG and OAG films showed lower water-vapor permeability (WVP) throughout 8 weeks of storage (p < 0.05) compared to control gelatin films. Additionally, a slight decrease in WVP was found in control and OMG films with an increase in storage time. Regarding mechanical properties, tensile strength (TS) and elastic modulus (EM) increased during storage, while elongation at break (EAB) decreased (p < 0.05). During storage, OMG and control films showed similar appearances, with slight changes in yellowness and transparency; however, OAG films showed a marked increase in yellowness, opacity and rancid smell at week 8 of storage. These changes were associated with the increase in lipid oxidation as ascertained by significantly higher thiobarbituric acid reactive substances (TBARS) and volatile compounds observed for OAG films during storage up to 8 weeks. As a consequence, transition temperatures, including glass transition, melting and degradation temperatures of films stored at week 8 were higher than those at week 0. In addition, control and OMG films showed greater thermal stability than OAG films at week 0 and 8. Therefore, the addition of OLA had a relevant impact on the properties of fish gelatin films during extended storage, depending on the method used for OLA incorporation.