Combination of analytical and microbiological techniques to study the antimicrobial activity of a new active food packaging containing cinnamon or oregano against E. coli and S. aureus

Abstract

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.

Exposure of Escherichia coli ATCC 12806 to Sublethal Concentrations of Food-Grade Biocides Influences Its Ability To Form Biofilm, Resistance to Antimicrobials, and Ultrastructure

“…Coagulated cytoplasmic material was observed near the cell wall of treated E. coli. This coagulated material is thought to be a precipitate of abnormal proteins or denatured membrane (58,59). The treated cells also showed numerous breaks in the cell membranes.…”

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“…From the result of research by Becerril et al, 2007 26 showed that the cinnamaldehyde in the broth dilution method were less efficient than in the vapour diffusion assay. Previous reports indicated the rapid inhibitions of energy metabolism of some tested organism upon the exposure of bactericidal concentration of cinnamaldehyde 27 . Also Cinnamaldehyde produced significant inhibitory effect when used alone without combination of others antimicrobial substances 28 , further indicating that strong antimicrobial effect against various microorganism that tested by MIC.…”

Fabrication of an antimicrobial active packaging and its effect on the growth of Pseudomonas and aerobic mesophilic bacteria in chicken

“…Several articles have reported the use of antimicrobial agents to formulate antimicrobial packaging [6,[13][14][15][16][17][18]. Essential oils and their components have antimicrobial properties against microorganisms (including Gram-positive and Gram-negative bacteria) [13,14,16,[19][20][21][22][23][24]. The use of essential oils (e.g., cinnamon, oregano, clove, eucalyptus, lavender, lemongrass, lemon, lime, orange, peppermint, basil, wintergreen and thyme) as antimicrobial agents, in vitro and in foodstuffs, has been reported in several studies [13,16,[20][21][22][23][24][25][26].…”

“…Essential oils and their components have antimicrobial properties against microorganisms (including Gram-positive and Gram-negative bacteria) [13,14,16,[19][20][21][22][23][24]. The use of essential oils (e.g., cinnamon, oregano, clove, eucalyptus, lavender, lemongrass, lemon, lime, orange, peppermint, basil, wintergreen and thyme) as antimicrobial agents, in vitro and in foodstuffs, has been reported in several studies [13,16,[20][21][22][23][24][25][26]. The FDA has categorized clove oil as generally recognized as safe (GRAS) for use in dental cement and as a food additive (CFR 184.1257).…”