Effect of essential oils and homogenization conditions on properties of chitosan-based films

The influence of essential oil type (basil and thyme), its content and the homogenization treatment on the physical properties of chitosan-based film-forming dispersions and edible films was studied. Two homogenization treatments were applied, without (H1) and with (H2) microfluidization (MF) at 165 MPa. H2 emulsions showed the smallest particle size with the highest ζ-potential and the lowest viscosity. Composite films with essential oils were softer, less rigid and more stretchable than pure CH films. MF intensified these changes. H2 films showed micro-cracks due to the weakening of the polymer chain interaction forces when oils are present, which affected their mechanical behaviour. MF increased WVP of pure CH films while oil incorporation was only effective to reduce WVP when they were incorporated at the lowest ratio and when high pressure was used in the homogenization of the film-forming dispersion. Gloss was reduced by the essential oil addition, whereas MF tended to yield glossier films.