Evaluation of the antimicrobial activity of sodium alginate films integrated with cinnamon essential oil and citric acid on sliced cooked ham

Bio-based antimicrobial films have been developed using sodium alginate and 6 wt% of cinnamon essential oil (CEO) as a volatile antimicrobial substance and 4 and 6 wt% of citric acid (CA) as a non-volatile antimicrobial substance. Antimicrobial activity of the films was tested in in vitro tests against Escherichia coli and Listeria innocua by disc diffusion or vapour diffusion assay. Sodium alginate films containing CA exhibited a zone of inhibition between 30.86 ± 2.55 and 45.87 ± 1.90 against E. coli and L. innocua in the disc diffusion assays. Films containing CEO also showed significant antimicrobial activities in the vapour diffusion assays that resulted in a log reduction of 5.3 for E. coli and 3.2 for L. innocua after 6 days. Antimicrobial activities of all films were also tested against L. innocua on sliced cooked ham. Films containing CEO did not prevent the growth of L. innocua inoculated on ham. On the other hand, sodium alginate films with CA fully inhibited the growth of L. innocua on ham during storage at 7.5 C for 12 days resulting in a bacterial count below the detection limit after 12 days. The addition of antimicrobial substances in sodium alginate films resulted in a slight colour change (but significant) and reduced the tensile strength of the films significantly. Adding CA to sodium alginate films increased the moisture content (from 24.81% to 35.41–48.02%) as well as the elongation at break (from 11.3% to 22.6–33.2%) of the films.