The use of natural essential oils as antimicrobial solutions in paper packaging. Part II

We have assessed the antimicrobial, vapor-phase activity of the following natural essential oils (EOs) when used in paraffin-based “active coatings” for paper packaging materials intended to come into contact with foods: clove (Sygzium aromaticum), cinnamon (Cinnamomum zeylanicum), and oregano (Origanum vulgare) EOs, and cinnamaldehyde-enriched cinnamon EO. To our knowledge, this is the first time that such an approach has been presented for consideration by the scientific community.The potential utility of the active paper manufactured using the paraffin coatings was tested in assays with several common fungal and bacterial contaminants of foods. In these assays, the fortified cinnamon EO paraffin coating totally inhibited Candida albicans, Aspergillus flavus, and Eurotium repens, and provided significant activity against both Penicillium nalgiovense and Penicillium roqueforti. These results are very promising, since foods that are often packaged with this type of material include fruit and vegetables that are more frequently spoiled by fungi than other agents. In contrast, no inhibition of the tested Gram-positive bacteria (Bacillus cereus, Listeria monocytogenes, Enterococcus faecalis, and Staphylococcus aureus) was observed, and the only active coatings that showed inhibitory activity against Gram-negative bacteria were the enriched cinnamon EO (which significantly inhibited the highly relevant organisms Salmonella cholerasuis, Escherichia coli, Yersinia enterocolitica, and Pseudomonas aeruginosa) and to a lesser extent, oregano EO.Preliminary analysis of the atmospheres generated by the active coatings by single drop microextraction (SDME) followed by gas chromatography–mass spectrometry (GC–MS) showed that there were significant differences amongst them, which were consistent with known differences in the compositions of the EOs. The percentage of EO added to the coatings, but not the thickness of the coatings, was found to have a significant influence on their antimicrobial activities. Probable reasons for this difference are discussed.The shelf-life of the packaging manufactured using the fortified cinnamon EO was evaluated against C. albicans and A. flavus, and it was found to retain its total inhibitory activity over the whole, 71-day test period. Finally, the efficacy of the coatings was tested in trials with two varieties of strawberries. Complete protection was obtained during 7 days storage in a fridge at 4 °C, during which no visible fungal contamination developed and there were no apparent visible or organoleptic changes in the strawberries.