Stanley G. Deans

Antimicrobial and antioxidant properties of some commercial essential oils

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).

Relationship between bioactivity and chemical composition of commercial 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, e.g. 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.

Evaluation in vitro of plant essential oils as natural antioxidants

ABSTRACT Five essential oils, geranium, monarda, nutmeg, oregano and thyme, were evaluated for their antioxidant properties at final concentrations of 0.75 ppm to 100 ppm. Thiobarbituric acid reactive substances (TBARS) were measured in three avian assay systems based on egg yolk, one-day old chicken livers and muscle from mature chickens. All the oils demonstrated extensive antioxidant capacities. The egg yolk TBARS assay showed monarda, nutmeg and thyme essential oils to be the most effective while the chick liver assay revealed nutmeg oil to be the most active. The chicken muscle assay demonstrated equal activity for the oils of monarda, nutmeg, oregano and thyme. Based on this assay technique, oils demonstrating the most effective antioxidant capacities will be chosen for feeding trials to demonstrate their effectiveness in vivo upon polyunsaturated fatty acid (PUFA) metabolism during vital periods of the lifespan, in particular, the foetal/neonate and aging periods.

Effect of thyme oil and thymol dietary supplementation on the antioxidant status and fatty acid composition of the ageing rat brain

The present study measured changes in antioxidant enzyme activity in, and the phospholipid fatty acid composition of the ageing rat brain and tested whether dietary supplementation with thyme oil or thymol could provide beneficial effects. There were significant declines in superoxide dismutase (EC 1.15.1.1) and glutathione peroxidase (EC 1.11.1.9) activities and the total antioxidant status in the untreated rats with age, while thyme-oil- and thymol-fed rats maintained significantly higher antioxidant enzyme activities and total antioxidant status. The proportions of 18:2n-6, 20:1n-9, 22:4n-6 and 22:5n-3 in the brain phospholipids resulting from all three dietary treatments were significantly higher in 28-month-old rats than in 7-month-old rats. Only 20:1n-9 levels in 28-month-old thyme-oil- and thymol-treated rats were significantly higher than in the age-matched control. The proportion of 22:6n-3 in brain phospholipids, which declined with age in control rats, was also significantly higher in rats given either supplement. This latter finding is particularly important as optimum levels of 22:6n-3 are required for normal brain function. These results highlight the potential benefit of thyme oil as a dietary antioxidant.

Antibacterial activity of summer savory (Satureja hortensis L) essential oil and its constituents

SummaryThe essential oil distilled from summer savory (Satureja hortensis) consists of over forty different components. Ten bacterial genera, including some of public health significance, were tested against a number of the predominant constituents in the oil, along with oils from different geographical locations (France, Hungary and Spain). Whole oils distilled from plants grown at different periods of the Scottish season were also tested against five of the test organisms. The constituents of summer savory essential oil which were most inhibitory to bacterial growth were: carvacrol, 1,8-cineole, eugenol, beta-humulene, linalool, beta-pinene, alpha-terpineol and thymol.

In vitro evaluation of antioxidant activity of essential oils and their components

Clove and nutmeg essential oils were analysed by GC and GC–MS. These oils, together with 16–18 components found to be present, were tested for antioxidant properties at final concentrations of 0.05–2.5×104 ppm in an egg yolk-based thiobarbituric acid reactive substances (TBARS) assay and also undiluted in a β-carotene agar diffusion assay. Both the essential oils and the components tested in the TBARS assay demonstrated some degree of antioxidant activity. Only the clove oil, the nutmeg oil, eugenol and terpinolene demonstrated any ability to inhibit the oxidative bleaching of the β-carotene agar. The ability of the oil components to inhibit malondialdehyde formation, and therefore lipid peroxidation, in the TBARS assay, yet apparently to possess no activity in the β-carotene agar diffusion assay, demonstrates the importance in the screening of plant material for bioactivity of using a bank of assays in vitro before assigning bioactivities. By using a number of assays, not only should the number of false positives and negatives be greatly reduced, but evidence pertaining to the mechanism of action may be obtained. Copyright

Antibacterial and antioxidant properties of Mediterranean aromatic plants

Abstract Eleven aromatic plants (lavender, thyme, winter savory, rosemary, sage, peppermint, chanomile, Roman chamomile, French tarragon, bitter and sweet fennel), typical of the Mediterranean area, were grown in Northern Italy and their essential oils obtained by steam distillation. The distilled oils were analysed for their antibacterial activities against 25 microorganisms and also for any antioxidant properties. The chemical composition of the essential oils was related to their effectiveness. Thyme and winter savory oils exhibited the greatest inhibition against the growth of all the tested organisms possibly due to the high content of thymol and carvacrol respectively. The Roman chamomile oil exhibited the highest antioxidant activity.

In Vitro Antioxidant Activity of a Number of Plant Essential Oils and Phytoconstituents

Abstract The antioxidant capacity of the synthetic antioxidants BHA, BHT, pyrogallol and α-tocopherol, the essential oils from black pepper, clove, geranium, melissa, nutmeg, oregano and thyme and 33 phytoconstituents were assessed in vitro, using an antioxidant assay. All die compounds demonstrated antioxidant capacity superior to the water soluble α-tocopherol analogue Trolox with the exception of the essential oil melissa and the phytoconstituents aromadendrene, myrcene and nerol. Clove, oregano and thyme were exceptionally potent in this assay, comparable with the activities of both BHA and pyrogallol. Eugenol, carvacrol, and thymol similarly demonstrated an equivalent degree of activity. These phytoconstituents are the major components present in clove, oregano and thyme essential oils, respectively.

Pharmacological and antimicrobial studies on different tea‐tree oils (Melaleuca alternifolia, Leptospermum scoparium or Manuka and Kunzea ericoides or Kanuka), originating in Australia and New Zealand

Three different species of Myrtaceae growing in Australia and New Zealand are known as ‘Tea‐tree’: the Australian Tea tree (Melaleuca alternifolia), the New Zealand Manuka (Leptospermum scoparium) and Kanuka (Kunzea ericoides). All three essential oils are used by aromatherapists, although only Melaleuca has been tested for toxicity, and its antimicrobial effects studied. The pharmacology and antimicrobial activity of the three ‘tea‐tree’ oils was determined using guinea‐pig ileum, skeletal muscle (chick biventer muscle and the rat phrenic nerve diaphragm) and also rat uterus in vitro. Differences were shown between the three essential oils in their action on smooth muscle: Manuka had a spasmolytic action, while Kanuka and Melaleuca had an initial spasmogenic action. Using the diaphragm, Manuka and Melaleuca decreased the tension and caused a delayed contracture; Kanuka had no activity at the same concentration. The action on chick biventer muscle was, however, similar for all three oils, as was the action on the uterus, where they caused a decrease in the force of the spontaneous contractions. The latter action suggests caution in the use of these essential oils during childbirth, as cessation of contractions could put the baby, and mother, at risk. The comparative antimicrobial activity showed greater differences between different samples of Manuka and Kanuka than Melaleuca samples. The antifungal activity of Kanuka was inversely proportional to its strong antibacterial activity, whilst Manuka displayed a stronger antifungal effect, though not as potent as Melaleuca. The antioxidant activity of Manuka samples was more consistent than that of Kanuka, while Melaleuca showed no activity. The variability in the Manuka and Kanuka essential oils suggests caution in their usage, as does the fact that the oils have not been tested for toxicity.

Dietary supplementation of thyme (Thymus vulgaris L.) essential oil during the lifetime of the rat: its effects on the antioxidant status in liver, kidney and heart tissues.

This study aimed not only to identify age-related changes in certain antioxidant systems, but to assess whether dietary supplementation of thyme oil could address the unfavourable antioxidant-pro-oxidant balance that occurs with age. The present study has shown that there were significant declines in the superoxide dismutase activities in the liver and heart of old rats, although kidney showed no decline. Liver glutathione peroxidase (GSHPx) activity was found to have increased significantly in old rats, while a significant decrease was observed in kidney. Heart GSHPX activity was not found to differ significantly between young and old rats. There were also significant declines in the total antioxidant status in each tissue examined. A general feature of these various antioxidant parameters measured was that their activities remained higher in rats whose diets were supplemented with thyme oil, suggesting that they retained a more favourable antioxidant capacity during their life span.