http://naturalingredient.org/wp/wp-content/uploads/Burt_Essential_Oils_A_Review_2004.pdf

Essential oils: their antibacterial properties and potential applications in foods--a review.

The volatile oils of black pepper [Piper nigrum L. (Piperaceae)], clove [Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae)], geranium [Pelargonium graveolens L'Herit (Geraniaceae)], nutmeg [Myristica fragrans Houtt. (Myristicaceae), oregano [Origanum vulgare ssp. hirtum (Link) Letsw. (Lamiaceae)] and thyme [Thymus vulgaris L. (Lamiaceae)] were assessed for antibacterial activity against 25 different genera of bacteria. These included animal and plant pathogens, food poisoning and spoilage bacteria. The volatile oils exhibited considerable inhibitory effects against all the organisms under test while their major components demonstrated various degrees of growth inhibition.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2000.00969.x

Antimicrobial agents from plants: antibacterial activity of plant volatile oils.

The antimicrobial activity of plant oils and extracts has been recognized for many years. However, few investigations have compared large numbers of oils and extracts using methods that are directly comparable. In the present study, 52 plant oils and extracts were investigated for activity against Acinetobacter baumanii, Aeromonas veronii biogroup sobria, Candida albicans, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serotype typhimurium, Serratia marcescens and Staphylococcus aureus, using an agar dilution method. Lemongrass, oregano and bay inhibited all organisms at concentrations of ≤ 2.0% (v/v). Six oils did not inhibit any organisms at the highest concentration, which was 2.0% (v/v) oil for apricot kernel, evening primrose, macadamia, pumpkin, sage and sweet almond. Variable activity was recorded for the remaining oils. Twenty of the plant oils and extracts were investigated, using a broth microdilution method, for activity against C. albicans, Staph. aureus and E. coli. The lowest minimum inhibitory concentrations were 0.03% (v/v) thyme oil against C. albicans and E. coli and 0.008% (v/v) vetiver oil against Staph. aureus. These results support the notion that plant essential oils and extracts may have a role as pharmaceuticals and preservatives.

Antimicrobial activity of essential oils and other plant extracts

Mechanisms of membrane toxicity of hydrocarbons.

Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds’ mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.

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Essential oils in food preservation: mode of action, synergies, and interactions with food matrix components.

The essential oil composition of Cananga odorata, Boswellia thurifera, Cymbopogon citratus, Marjorana hortensis, Ocimum basilicum, Rosmarinus officinalis, Cinnamomum zeylanicum and Citrus limon was analysed by GC and GC–MS, and their antimicrobial and antioxidant activity tested. Twenty-five different genera of bacteria and one fungal species were used in this study as test organisms. These included animal and plant pathogens, food poisoning and spoilage bacteria and the spoilage fungus Aspergillus niger. The volatile oils exhibited considerable inhibitory effect against all the tested organisms. The oils also demonstrated antioxidant capacities, comparable with α-tocopherol and butylated hydroxytoluene (BHT). The method adopted in this study was the modified thiobarbituric acid reactive species (TBARS) assay. The antioxidant activity was carried out under different conditions by using egg yolk and rat liver in the absence and presence of the radical inducer 2,2′-azobis (2-amidinopropane) dihydrochloride (ABAP). © 1998 John Wiley & Sons, Ltd.

Antimicrobial and antioxidant properties of some commercial essential oils

Ninety-three different commercial essential oils were screened for activity against 20 Listeria monocytogenes strains in vitro and the results correlated against the actual chemical composition of each oil. There was a substantial difference in the activity between different essential oils as expected, but there was also a difference in activity between different samples of the same essential oil. Strong anti-Listeria activity was often correlated with essential oils containing a high percentage of monoterpenes, eugenol, cinnamaldehyde, thymol, and sometimes with citronellol, limonene and geraniol. However, as there was often no correlation between the anti-Listeria activity and the main chemical components, it is possible that either there is a more complex relationship with the chemical composition (which includes the minor components) or that substantial adulteration had occurred in some essential oil samples. The possible use of a number of essential oils in a dual role as flavours and antimicrobials is discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.1997.00153.x

Bioactivity of selected plant essential oils against listeria monocytogenes

The essential oils obtained from five commercial samples of Sicilian aromatic plants, laurel, sage, oregano, rosemary and coriander were analyzed by GC/MS and assayed for their antibacterial, antifungal and antioxidant activities Twenty-five different genera of bacteria and one fungal species were used in this study as test organisms The oils showed a high degree of inhibition against all the microorganisms tested The highest and broadest activity was shown by the oil of oregano, while the oil of sage was the least effective The antioxidant activity of the oils was measured by the modified Thiobarbituric Acid Reactive Species (TBARS) assay, using egg yolk and rat liver as oxidable substrate, in absence and in presence of the radical inducer 2,2'-azobis (2-amidinopropane) dihydrochloride (ABAP) The activities were compared with those of α-tocopherol and 2,6-di-tert-butyl-4-methylphenol (BHT, butylated hydroxytoluene) The oils showed different effectiveness, the oregano oil being endowed with

Chemical Composition, Antimicrobial and Antioxidative Activity of Laurel, Sage, Rosemary, Oregano and Coriander Essential Oils

In order to establish the value of the use of biological activities as accessory criteria (in conjunction with gas chromatography, but in the absence of enantiomeric analysis) for establishing the authenticity of essential oils, the biological activities of 105 commercial essential oils were investigated against 25 species of bacteria, 20 strains of Listeria monocytogenes, and three filamentous fungi; their antioxidant action was also determined and all the results were related to the actual chemical composition of the oils as determined by gas chromatography The results showed some relationship between the major components and some bioactivities There was a negative correlation between 1,8-cineole content and antifungal activity There was, however, great variability between the biological action of different samples of individual oils and groups of oils under the same general name, eg lavender, eucalyptus or chamomile, which was reflected in differences in chemical composition, The results suggest that, although the biological activities are not all related to the main components, any significant blending, rectification and adulteration of commercial oils can be monitored by their biological activities The use of essential oils named simply as ‘chamomile’ or ‘eucalyptus’, or any commercial oil which has been adulterated, cannot be justifiably used in treating medical conditions unless it can be shown that the action is non-specific and independent of the chemical composition © 1998 John Wiley & Sons, Ltd

Stanley G. Deans

Papers

Antimicrobial agents from plants: antibacterial activity of plant volatile oils.

Antimicrobial and antioxidant properties of some commercial essential oils

Bioactivity of selected plant essential oils against listeria monocytogenes

Chemical Composition, Antimicrobial and Antioxidative Activity of Laurel, Sage, Rosemary, Oregano and Coriander Essential Oils

Relationship between bioactivity and chemical composition of commercial essential oils