Physical, mechanical and antibacterial properties of alginate film: Effect of the crosslinking degree and oregano essential oil concentration

Alginate films with different degrees of crosslinking obtained by internal gelation, and alginate films incorporated with oregano essential oil (OEO) were prepared. The impact of the degree of crosslinking caused by the use of calcium carbonate as crosslinking agent and the incorporation of OEO into the alginate films on their antibacterial, optical, mechanical, microstructural and water vapour barrier properties was evaluated. An increase in the degree of crosslinking produced alginate films that were significantly thicker (0.031–0.038 mm) and stronger (51.9–52.9 MPa) but less elastic (2.3%) than those non-crosslinked films (0.029 mm; 39.7 MPa; 4.4%). The water vapour permeability (WVP) of the films decreased significantly only with the highest level of crosslinking. The incorporation of OEO in alginate films affected significantly their physical properties. Thickness and percent elongation at break of the films were increased by the addition of OEO (0.036–0.042 mm and 2.7–3.7%), while the tensile strength and water vapour permeability decreased (31.1–55.5 MPa and 2.7–3.0 × 10−9 g/m s Pa). Films incorporated with OEO were more effective against Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes) than Gram-negative bacteria (Escherichia coli and Salmonella Enteritidis). A minimum concentration of 1.0% of OEO was necessary to ensure their antibacterial efficacy.