Development of flexible bactericidal films based on poly(lactic acid) and essential oil and its effectiveness to reduce microbial growth of refrigerated rainbow trout

The main shortcoming of poly(lactic acid) (PLA) for food packaging applications is its brittleness. The aim of this work was to evaluate the potential use of Origanum vulgare L. essential oil (OEO) in PLA-based matrices to obtain developed bio-based films with enhanced mechanical properties as well as antimicrobial performance. The PLA-essential oil composite films were more flexible than neat PLA films; so that up to 6-fold increase in the elongation-at-break values (2.82–16.78%) were acquired when 0.5% (w/w) oil was added to the polymer matrix. The addition of essential oil decreased the PLA glass transition temperature ( T g ), as the result of the polymer plasticization, and led to modification of the tensile behavior. AFM results confirmed that the PLA surface microstructure was drastically influenced in terms of roughness parameters ( R a and R q ) when OEO was added. The films’ antimicrobial activities were induced by incorporating essential oil, which were more effective against the bacteria in direct contact method than a vapor phase. However, in both of test methods, Staphylococcus aureus was the most sensitive bacterium to OEO-containing films, while Escherichia coli was the most resistant. Then, efficacy of bioactive film included with 1.5% (w/w) essential oil to reduce microbial growth of rainbow trout during chilled storage was evaluated; the results indicated that antimicrobial PLA film was effective against all the microorganisms tested in this study. These results suggest that the developed PLA films with active substance could be used in designing antimicrobial packaging materials.