Effects of mechanism of gelation on physical, mechanical and antibacterial properties of alginate films with oregano essential oil incorporated

Alginate films with different degrees of crosslinking obtained by internal and external gelation method and alginate films incorporated with oregano essential oil were prepared. The effect of mechanism of gelation and the incorporation of oregano essential oil on their optical, mechanical, antibacterial, microstructural and water vapor barrier properties were evaluated. The films subjected to external gelation process were characterized as thicker, stronger, slightly more permeable to water vapour and substantially less elastic than films subjected to internal gelation. The incorporation of oregano essential oil in alginate films led to the formation of more flexible, less rigid and less transparent films with a slight decrease in their water vapour permeability. Films incorporated with oregano essential oil were slightly more effective against Gram-positive bacteria (S. aureus and L. monocytogenes) than Gram negative bacteria (E. coli and S. Enteritidis). A minimum concentration of 1.0% of oregano essential oil was necessary to ensure their antibacterial efficacy.