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Antimicrobial active packaging has emerged as an effective technology to reduce microbial growth in food products increasing both their shelf-life and microbial safety for the consumer while maintaining their quality and sensorial properties. In the last years, a great effort has been made to develop more efficient, long-lasting and eco-friendly antimicrobial materials by improving the performance of the incorporated antimicrobial substances. With this purpose, more effective antimicrobial compounds of natural origin such as bacteriocins, bacteriophages and essential oils have been preferred over synthetic ones and new encapsulation strategies such as emulsions, core-shell nanofibres, cyclodextrins and liposomes among others, have been applied in order to protect these antimicrobials from degradation or volatilization while trying to enable a more controlled release and sustained antimicrobial action. On that account, this article provides an overview of the types of antimicrobials agents used and the most recent trends on the strategies used to encapsulate the antimicrobial agents for their stable inclusion in the packaging materials. Moreover, a thorough discussion regarding the benefits of each encapsulation technology as well as their application in food products is presented.

The aim of this work is the optimization and application of a group of analytical and microbiological techniques in the study of the activity of essential oils (EOs) incorporated in a new antimicrobial packaging material and the research in depth of the interaction between the microbial cells and the individual compounds present in the active material. For this purpose the antimicrobial activity of the active packaging containing cinnamon or oregano was evaluated against E. coli and S. aureus. The vapour phase activity and the direct contact between the antimicrobial agents themselves, or once incorporated in the packaging material, and the microbial cells have been studied. The direct contact was studied using a broth dilution method. The vapour phase was evaluated by using a new method which involves the use of a filter disk containing the EOs. Furthermore, the kill time assay was used to determine the exposure time for the maximum efficiency in packaging, and transmission electron microscopy was used to investigate the antimicrobial activity and the possible mechanism of action against E. coli and S. aureus. Finally, the compounds absorbed by cells were identified. The results showed that the techniques used provide relevant information about the antibacterial activity of cinnamon and oregano in direct contact as well as in the vapour phase. The antimicrobial packaging showed a fast efficiency which supports its likely application as a food packaging material. Bacteria treated with EOs exhibit a wide range of significant abnormalities; these include formation of blebs, coagulation of cytoplasmatic constituents, collapse of the cell structure and lack of cytoplasmatic material. Some of these observations are correlated to the ability of some of these substances to disrupt envelop structure, especially the inner membrane. After an extraction from dead cells, cinnamaldehyde was detected by GC-MS in E. coli exposed to the active packaging containing cinnamon.

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Essential oils (EOs) are excellent antimicrobial agents sometimes used in active food packaging. This work studies the susceptibility of 48 clinical isolates and 12 reference strains of Gram-negative bacilli to oregano essential oil, cinnamon essential oil, and combinations of both. Furthermore, the tendency of the clinical isolates to develop resistance to these EOs and to different antibiotics after sequential oregano or cinnamon exposure was studied. For this purpose, antibiotic susceptibility (through disk diffusion assays and minimum inhibitory concentration [MIC] determination) and oregano and cinnamon susceptibility (through MIC and minimum bactericidal concentration [MBC] determination) were compared after 50 passages in the presence or absence of subinhibitory concentrations of oregano and cinnamon essential oils. The results showed that all strains were susceptible to both EOs and their combination independently of the antibiotic resistance profile. In addition, neither synergistic nor antagonistic effects were observed between oregano and cinnamon essential oils at the concentrations tested. After the sequential exposure to both EOs, only Serratia marcescens, Morganella morganii, and Proteus mirabilis treated with oregano changed their antibiotic resistance profile and/or increased their resistance to this EO. However, the changes in antibiotic and oregano resistance were not related.

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