Antimicrobial Olive Leaf Gelatin films for enhancing the quality of cold-smoked Salmon

Olive leaf was evaluated as antimicrobial/antioxidant ingredient in edible films intended for cold-smoked fish preservation. Olive leaf powder (OLP) and its water/ethanol extract (OLE) were previously tested against Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica. Antimicrobial and antioxidant capacity, color and water vapor permeability (WVP) of OLE-gelatin films (0, 1.88, 3.75 and 5.63% w/w) were determined. OLP and OLE showed antibacterial activity against L. monocytogenes in agar diffusion tests, and non-effect was observed on E. coli and S. enterica. Antimicrobial and antioxidant activities of the films increased with increasing OLE concentration in their formulations. Film lightness was not significantly affected by OLE. In contrast, a* decreased and b* increased with increasing OLE concentration. Addition of 3.75 and 5.63% of OLE also increased WVP of the films. A film formulation with 5.63% OLE was considered optimal for further tests against L. monocytogenes in inoculated cold-smoked salmon. The films significantly reduced the growth of this pathogen on the fish over storage.