Individual and combined effect of nisin (N) and potassium sorbate (KS), supported in tapioca starch edible
films, on Listeria innocua and Zygosaccharomyces bailii, as well as the effect of antimicrobials on some
physical and mechanical properties, were studied.
Results obtained showed that the starch films containing N or N/KS yielded a clear inhibition zone around
the film, showing antimicrobial diffusion to the solid medium. The barrier assay showed that films without
antimicrobials or individuals one allowed the Listeria growth. On the contrary, films containing N/KS
showed a bacteriostatic effect. In the presence of Z. bailii, teasted films allowed the yeasts growth. However,
N/KS films showed a final yeast count of 1.3 log cycle lower than the film without antimicrobials.
Regarding mechanical properties, individual or combined antimicrobials exerted a plasticizing effect in
comparison with films without preservatives. It was observed a decrease of tensile stress to around 0.62 MPa
and an increase of the elongation at break until 3.2, being N/KS films the most extensible. The solubility in
water was higher, 25-36%, when antimicrobials were incorporated. Contrarily, water vapor permeability
(WVP) was not affected by antimicrobials presence and it was determined a average value of 1.44 x 10-9 g /
Pa m s. Color attributes showed a slight darkness for antimicrobial films as was established by an increase of
YI and b* values. Combined N/KS films displayed the highest YI (13.6) and b* (7.1) parameters.
These results revealed that the antimicrobial film developed could act as an active packaging being a hurdle
against microorganisms present in food systems and to act as a barrier to further product contamination. The
films with combined preservatives presented the best perfomance. It must be remark that, despite the
antimicrobial agents modified the physical and mechanical properties of the films, they maintained a suitable
behaviour as a packaging material.