The antimicrobial activity of twelve natural extracts was tested against two fish spoilage bacteria (Pseudomonas
fluorescens and Aeromonas hydrophila/caviae) and Listeria innocua, in order to assess their potential utilization in
the preservation and safety of minimally processed fish products. After a screening of the active extracts by agar
diffusion and vapour diffusion methods, oregano and thyme essential oils and citrus extract were selected. The
minimum inhibitory concentration (MIC) of the selected extracts was determined by disc diffusion method
against target bacteria and at two temperatures: bacteria's optimal growth temperature (30 °C or 37 °C) and refrigeration
temperature (4 °C). Due to its better solubility, lack of odour and greater inhibitory effect
obtained against L. innocua at refrigerated temperature, citrus extract was selected and incorporated
at 1% (v/v) into different biopolymer film forming solutions (gelatin, methyl cellulose and their blend
50:50 w/w). The antimicrobial activity of the developed films was then evaluated, just after preparation
of the films and after one month of storage at 43±3% relative humidity and 24±3 °C. Regardless of the
biopolymer matrix, all the developed films showed antimicrobial activity against the target bacteria. The
most sensitive bacterium towards active films was L. innocua while P. fluorescens appeared as the most
resistant one, in accordance with the previously performed antimicrobial tests for pure extracts. The differences
in activity of the films between the tested two temperatures were not significant except for
L. innocua, for which three times higher inhibition diameters were observed at refrigerated temperature.
The inhibitory effectiveness of the films against the tested strains was maintained regardless of the biopolymer
matrix for at least one month. Therefore, these edible films show potential for their future use
in fresh fish fillets preservation.