Antimicrobial nanocomposite films made of poly(lactic acid)-cellulose nanocrystals (PLA-CNC) in food applications-part B: effect of oregano essential oil release on the inactivation of Listeria monocytogenes in mixed vegetables

Antimicrobial nanocomposite films containing oregano essential oil (EO) were prepared by solvent casting. Film matrix was composed of supramolecular poly(lactic acid)-cellulose nanocrystals (PLA-CNC) nanocomposite. Bioactive PLA-CNC-oregano films were prepared by incorporating oregano EO as an antimicrobial agent. Resulting films were then converted into packaging applied on mixed vegetables as a food model and stored for 14 days at 4 A degrees C to determine their antimicrobial capacity against Listeria monocytogenes, their physico-chemical/structural properties and their total phenols (TP) release during storage, in order to evaluate the effect of oregano EO. It was observed the addition of oregano EO did not affect the water vapor permeability (WVP) of films, but increased their elongation at break (Eb) and reduced their tensile strength (TS) and tensile modulus (TM) at day 0. However, TS, TM, Eb and WVP values of control and bioactive films were increased slightly after 14 days of storage. FTIR analysis allowed characterizing the molecular interactions of oregano EO with PLA-CNC matrix via the identification and interpretation of their respective vibration bands. Microbiological analysis of mixed vegetables inoculated with L. monocytogenes (3 log CFU g(-1)) indicated that PLA-CNC-oregano films induced a quasi-total inhibition of bacteria in vegetables at day 14 and therefore demonstrated a strong antimicrobial capacity in situ. The percentage of TP release from bioactive films was determined by Folin-Ciocalteu's method and results showed that TP release increased continuously from day 0 to day 14, up to 16.6 % at day 14. These results allowed demonstrating the strong antimicrobial capacity of PLA-CNC-oregano films for food packaging applications in vegetable produce.