Finally, it can be observed that, on the contrary to formic acid,
oregano essential oil seems to exert a greater antimicrobial effect
on A. niger after being incorporated into the bioplastic. E. coli and
C. kefyr are the most resistant microorganism under the action of
oregano essential oil at 5 wt.% OEO and for the EW matrix.
Interestingly, essential oil may also inhibit the growth of microorganisms
even if it is not in direct contact with them, by promoting
the formation of an antimicrobial atmosphere within the container.
Thus, the antimicrobial activity of an oregano oil-containing bioplastic
sample placed under the Petri dish lid is illustrated in
Fig. 1c. This outcome may be of relevant importance in the development
of matrix for non-contact food preservation. For the sake of
comparison, the antimicrobial activity of OEO-free LDPE is also
shown in Fig. 1c. As seen, no antimicrobial activity was found