A comparative study on the effect of homogenization conditions on the properties of the film-forming emulsions and the resultant films.

Emulsions based on licorice essential oil (LEO) were prepared under different homogenization conditions (ultra-homogenization (U1) or U1 together with sonication (U2)). The obtained emulsions were incorporated into the carboxymethyl cellulose (CMC) film. The results showed that U2 caused significant changes in the size and the surface charge of the emulsions. Remarkable differences in the microstructure were observed between the U1 and the U2 emulsion-based films as revealed by SEM and AFM. Both emulsions reduced the rigidity and increased the flexibility of the films. The film made from the CMC alone had a water vapor permeability (WVP) of 2.66 × 10-9 g m-1 s-1 Pa-1, while the CMC film made from U2 emulsion had a WVP of 1.87 × 10-9 g m-1 s-1 Pa-1. Also, the film containing 0.0125% U1-LEO exhibited antibacterial activity on gram-positive bacteria only while the film containing 0.0125% U2-LEO demonstrated antibacterial activity on both gram-positive and gram-negative bacteria.