In vitro bioactivity of novel chitosan bionanocomposites incorporated with different essential oils

Abstract

Essential oils (EOs) can be obtained from a variety of crops and are rich in bioactive compounds (such as phenolic compounds, terpenes), which confer them biological activities (antimicrobial and antioxidant), and when incorporated into polymers, may enhance packaging activity. Therefore, the aim of this work was to develop bionanocomposites based on chitosan/montmorillonite incorporated with two different essential oils, rosemary (Rosmarinus officinalis L.) and ginger (Zingiber officinale Rosc), and to evaluate their antimicrobial and antioxidant properties via in vitro assays. Chitosan films were produced by casting, and the mechanical reinforcement, sodium montmorillonite (MMT), was tested at the rates of 0% or 2.5% (w/w chitosan). The proportion of rosemary EO (REO) or ginger EO (GEO) incorporated were 0.5%, 1% and 2% (v/v). Films without EO and MMT were used as control. The active compounds release process was monitored by migration assays in three food simulants (ethanol 50%, ethanol 10% and distilled water), and total phenolic compounds and their antioxidant activity was measured in the simulant over time. Diffusion coefficient (D) was also calculated. The films were tested in terms of their antimicrobial activity by viable cell colony count (CFU) method against five pathogenic foodborne bacteria (gram-positive, Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus, and gram-negative, Escherichia coli, Pseudomonas aeruginosa). The type of EO, the presence of MMT and the simulant used interfered in the amount of phenolic compounds released from the films. Films incorporated with GEO presented superior D values, and the release process was accelerated in more hydrophobic simulants (ethanol 50%). Montmorillonite hindered the release of active compounds from films incorporated with REO while facilitated the migration from GEO incorporated films. Part of the antioxidant activity of the migrants was preserved after the migration process, however no significantly differences were observed in the percentage of scavenging among different films. Incorporation of REO improved the antimicrobial activity of chitosan towards E. coli (at a rate of 1%) and E. faecalis (at a rate of 0.5% and with MMT). Incorporation of GEO (at a rate of 2% and with MMT) improved the antimicrobial activity of chitosan towards E. faecalis and S. aureus. Both EO’s, at all rates tested, improved significantly the antimicrobial activity of chitosan towards L. monocytogenes (achieving a maximum of log reduction of 7.7). The highest log reduction was obtained in films with 2% of GEO + MMT against Staphylococcus aureus (7.9). These novel bionanocomposites demonstrated potential as a coating to preserve food products, especially lipid food products.