Marjoram showed the highest antimicrobial activity out of six EOs on three foodborne pathogens.
Antimicrobial biodegradable films and coatings have potential to delay microbial spoilage of food and reduce the risk of contamination by pathogenic microorganisms, said Abdollahi et al.
However, use has been limited due to their inherent water sensitivity and poor water resistance.
This can be tackled by nanometer-sized particles in the biopolymer material, which reinforce the packaging properties compared with pure biopolymer.
Two step study
In the first step, antibacterial effects of clove, coriander, caraway, marjoram, cinnamon, and cumin essential oils were studied against E.coli, Staphylococcus aureus, and Listeria monocytogenes by agar diffusion assay.
In the next study, the three most potent essential oils were incorporated into alginate/clay nanocomposite films at several concentrations (0.5, 1.0, and 1.5% w/v).
Cumin essential oil was least effective against the three studied pathogens and E.coli showed the most resistance.
The antibacterial effectiveness of the prepared films against E. coli, S. aureus, and L. monocytogenes was studied during 12 days. The antibacterial activity of the essential oils was maintained when incorporated into the nanocomposite film.
Storage time VS effectiveness
As storage time increased the film effectiveness decreased because of the evaporation of the compounds responsible for antimicrobial activity and/or by the migration of EO components into the agar medium.
Films with 1.5% marjoram decreased the numbers of L. monocytogenes, E. coli, and S. aureus populations with respect to the control up to 6.33, 4.52, and 5.80 log, respectively.
Technologies including electron beam, thermal processing, acidified sodium chlorite, lactic acid bacteria, antimicrobial ice, freezing, irradiation, and high pressure have been investigated to eliminate pathogenic microorganisms on food.
However, some cannot be applied to food products and some have negative effects on quality, so novel ways need to be found to reduce or eliminate food-related microorganisms throughout the shelf life of food products, said the researchers.
Source: Food Control Volume 36, Issue 1, February 2014, Pages 1–7
Online ahead of print, doi: 10.1016/j.foodcont.2013.07.037
“Antimicrobial activity of alginate/clay nanocomposite films enriched with essential oils against three common foodborne pathogens”
Authors: Mehdi Alboofetileh, Masoud Rezaei, Hedayat Hosseini, Mehdi Abdollahi