Time-dependent evolution of properties of fish gelatin edible films enriched with carvacrol during storage

The temporal stability of the physicochemical, antibacterial and antioxidant properties of fish gelatin (FG) films plasticized by glycerol (20% w/w) and supplemented with carvacrol (CRV) obtained by casting and stored at 65% RH and 25 degrees C, was investigated over 15 days. The level of CRV incorporated into FG film was determined from minimum inhibitory concentration (MIC) values against E. coli and S. aureus. The incorporation of 0.6% w/v CRV reduced the moisture content (MC), and water vapor permeability (WVP) while kept invariable the tensile and light barrier properties, compared to the control. Additionally, CRV increased the in vitro antibacterial and antioxidant effectiveness of films. Upon storage, the sustained loss of moisture and glycerol provoked the drop of MC and WVP values of both films. Control film became stiffer and less stretchable while the active film remained mechanically time-stable. Such difference was ascribed to the increased contribution of triple helical structures in the control, as revealed by ATR-FTIR and XRD. Antibacterial effectiveness (based on disc diffusion assay) decayed from 3.1 +/- 0.1 and 2.7 +/- 0.3 cm for E. coli and S. aureus, respectively, to undetectable levels for both pathogens. Antioxidant power in terms of radical scavenging activity (RSA) declined to about 2.74 % of the initial value, in line with the decline of CRV level up to 13 % of its initial concentration. Overall this study proves the significance of assessing the stability of the properties of edible films before proposing any technical application.