G.P.P. Kamatou

Eugenol--from the remote Maluku Islands to the international market place: a review of a remarkable and versatile molecule.

Eugenol is a major volatile constituent of clove essential oil obtained through hydrodistillation of mainly Eugenia caryophyllata (=Syzygium aromaticum) buds and leaves. It is a remarkably versatile molecule incorporated as a functional ingredient in numerous products and has found application in the pharmaceutical, agricultural, fragrance, flavour, cosmetic and various other industries. Its vast range of pharmacological activities has been well-researched and includes antimicrobial, anti-inflammatory, analgesic, anti-oxidant and anticancer activities, amongst others. In addition, it is widely used in agricultural applications to protect foods from micro-organisms during storage, which might have an effect on human health, and as a pesticide and fumigant. As a functional ingredient, it is included in many dental preparations and it has also been shown to enhance skin permeation of various drugs. Eugenol is considered safe as a food additive but due to the wide range of different applications, extensive use and availability of clove oil, it is pertinent to discuss the general toxicity with special reference to contact dermatitis. This review summarises the pharmacological, agricultural and other applications of eugenol with specific emphasis on mechanism of action as well as toxicity data.

Menthol: A simple monoterpene with remarkable biological properties

Menthol is a cyclic monoterpene alcohol which possesses well-known cooling characteristics and a residual minty smell of the oil remnants from which it was obtained. Because of these attributes it is one of the most important flavouring additives besides vanilla and citrus. Due to this reason it is used in a variety of consumer products ranging from confections such as chocolate and chewing gum to oral-care products such as toothpaste as well as in over-the-counter medicinal products for its cooling and biological effects. Its cooling effects are not exclusive to medicinal use. Approximately one quarter of the cigarettes on the market contain menthol and small amounts of menthol are even included in non-mentholated cigarettes. Natural menthol is isolated exclusively from Mentha canadensis, but can also be synthesised on industrial scale through various processes. Although menthol exists in eight stereoisomeric forms, (-)-menthol from the natural source and synthesised menthol with the same structure is the most preferred isomer. The demand for menthol is high and it was previously estimated that the worldwide use of menthol was 30-32,000 metric tonnes per annum. Menthol is not a predominant compound of the essential oils as it can only be found as a constituent of a limited number of aromatic plants. These plants are known to exhibit biological activity in vitro and in vivo such as antibacterial, antifungal, antipruritic, anticancer and analgesic effects, and are also an effective fumigant. In addition, menthol is one of the most effective terpenes used to enhance the dermal penetration of pharmaceuticals. This review summarises the chemical and biological properties of menthol and highlights its cooling effects and toxicity.

The In Vitro Antimicrobial Activity of Lavandula angustifolia Essential Oil in Combination with Other Aroma-Therapeutic Oils

The antimicrobial activity of Lavandula angustifolia essential oil was assessed in combination with 45 other oils to establish possible interactive properties. The composition of the selected essential oils was confirmed using GC-MS with a flame ionization detector. The microdilution minimum inhibitory concentration (MIC) assay was undertaken, whereby the fractional inhibitory concentration (ΣFIC) was calculated for the oil combinations. When lavender oil was assayed in 1 : 1 ratios with other oils, synergistic (26.7%), additive (48.9%), non-interactive (23.7%), and antagonistic (0.7%) interactions were observed. When investigating different ratios of the two oils in combination, the most favourable interactions were when L. angustifolia was combined with Cinnamomum zeylanicum or with Citrus sinensis, against C. albicans and S. aureus, respectively. In 1 : 1 ratios, 75.6% of the essential oils investigated showed either synergistic or additive results, lending in vitro credibility to the use of essential oil blends in aroma-therapeutic practices. Within the field of aromatherapy, essential oils are commonly employed in mixtures for the treatment of infectious diseases; however, very little evidence exists to support the use in combination. This study lends some credence to the concomitant use of essential oils blended with lavender.

The additive and synergistic antimicrobial effects of select frankincense and myrrh oils--a combination from the pharaonic pharmacopoeia.

Aims:  The in vitro antimicrobial activity of three essential oil samples of frankincense (Boswellia rivae, Boswellia neglecta and Boswellia papyrifera) and two essential oil samples of myrrh and sweet myrrh (Commiphora guidotti and Commiphora myrrha), collected from different regions of Ethiopia, was investigated independently and in combination to determine their anti‐infective properties.

An untargeted metabolomic approach in the chemotaxonomic assessment of two Salvia species as a potential source of α-bisabolol.

α-Bisabolol is a commercially important aroma chemical currently obtained from the Candeia tree (Vanillosmopsis erythropappa). Continuous unsustainable harvesting of the Candeia tree has prompted the urgent need to identify alternative crops as a source of this commercially important sesquiterpene alcohol. A chemotaxonomic assessment of two Salvia species indigenous to South Africa is presented and recommended as a potential source of α-bisabolol. The essential oil obtained by hydrodistillation of the aerial parts was analysed by gas chromatography coupled to mass spectrometry (GC-MS) and mid-infrared spectroscopy (MIRS). Orthogonal projections to latent structures-discriminant analysis (OPLS-DA) were used for multivariate classification of the oils based on GC-MS and MIRS data. Partial least squares (PLS) calibration models were developed on the MIRS data for the quantification of α-bisabolol using GC-MS as the reference method. A clear distinction between Salvia stenophylla and Salvia runcinata oils was observed using OPLS-DA on both GC-MS and MIRS data. The MIR calibration model showed high coefficient of determination (R² = 0.999) and low error of prediction (RMSEP=0.540%) for α-bisabolol content.

Constituents of Cinnamon Inhibit Bacterial Acetyl CoA Carboxylase

Cinnamon bark ( CINNAMOMUM ZEYLANICUM) is used extensively as an antimicrobial material and currently is being increasingly used in Europe by people with type II diabetes to control their glucose levels. In this paper we describe the action of cinnamon oil, its major component, TRANS-cinnamaldehyde, and an analogue, 4-hydroxy-3-methoxy- TRANS-cinnamaldehyde against bacterial acetyl-CoA carboxylase in an attempt to elucidate the mechanism of action of this well-known antimicrobial material. These natural products inhibited the carboxyltransferase component of ESCHERICHIA COLI acetyl-CoA carboxylase but had no effect on the activity of the biotin carboxylase component. The inhibition patterns indicated that these products bound to the biotin binding site of carboxyltransferase with TRANS-cinnamaldehyde having a K (i) value of 3.8 ± 0.6 mM. The inhibition of carboxyltransferase by 4-hydroxy-3-methoxy- TRANS-cinnamaldehyde was analyzed with a new assay for this enzyme based on capillary electrophoresis. These results explain, in part, the antibacterial activity of this well-known antimicrobial material.

The in vitro antimicrobial activity and chemometric modelling of 59 commercial essential oils against pathogens of dermatological relevance.

This study reports on the inhibitory concentration of 59 commercial essential oils recommended for dermatological conditions, and identifies putative compounds responsible for antimicrobial activity. Essential oils were investigated for antimicrobial activity using minimum inhibitory concentration assays. Ten essential oils were identified as having superior antimicrobial activity. The essential oil compositions were determined using gas chromatography coupled to mass spectrometry and the data analysed with the antimicrobial activity using multivariate tools. Orthogonal projections to latent structures models were created for seven of the pathogens. Eugenol was identified as the main biomarker responsible for antimicrobial activity in the majority of the essential oils. The essential oils mostly displayed noteworthy antimicrobial activity, with five oils displaying broad‐spectrum activity against the 13 tested micro‐organisms. The antimicrobial efficacies of the essential oils highlight their potential in treating dermatological infections and through chemometric modelling, bioactive volatiles have been identified.

Vibrational Spectroscopy as a Rapid Quality Control Method for Melaleuca alternifolia Cheel (Tea Tree Oil)

INTRODUCTION Tea tree oil (TTO) is an important commercial oil which has found application in the flavour, fragrance and cosmetic industries. The quality is determined by the relative concentration of its major constituents: 1,8-cineole, terpinen-4-ol, α-terpineol, α-terpinene, terpinolene, γ-terpinene and limonene. Gas chromatography coupled to mass spectrometry (GC-MS) is traditionally used for qualitative and quantitative analyses but is expensive and time consuming. OBJECTIVE To evaluate the use of vibrational spectroscopy in tandem with chemometric data analysis as a fast and low-cost alternative method for the quality control of TTO. METHODS Spectral data were acquired in both the mid-infrared (MIR) and near infrared (NIR) wavelength regions and reference data obtained using GC-MS with flame ionisation detection (FID). Principal component analysis (PCA) was used to investigate the data by observing clustering and identifying outliers. Partial least squares (PLS) multivariate calibration models were constructed for the quantification of the seven major constituents. RESULTS High correlation coefficients (R(2) ) of ≥ 0.75 were obtained for the seven major compounds and 1,8-cineole showed the best correlation coefficients for both MIR and NIR data (R(2)  = 0.97 and 0.95, respectively). Low values were obtained for the root mean square error of estimation (RMSEE) and root mean square error of prediction (RMSEP) values thereby confirming accuracy. CONCLUSION The accurate prediction of the external dataset after introduction into the models confirmed that both MIR and NIR spectroscopy are valuable methods for quantification of the major compounds of TTO when compared with the reference data obtained using GC-MS. Copyright

Quantification of Rosmarinic Acid in Salvia Species Indigenous to South Africa by HPTLC

The genus Salvia (Lamiaceae) encompasses about 900 species worldwide of which 26 are found in southern Africa. Salvia spp have several medicinal uses in South Africa such as antimicrobial, anticancer, antimalarial, and antituberculosis properties. Rosmarinic acid (RA) has been identified as one of the major molecules responsible for these various medicinal properties. Eleven Salvia species (18 samples) collected at different localities in South Africa were extracted with methanol in order to determine the level of RA present in the extracts. High-performance thin-layer chromatography (HPTLC) analysis was performed on glass silica gel 60 F254 plates developed with ethyl acetate, toluene, and formic acid (6:3:1, v/v), while a gradient of acetic acid and methanol was used for high-performance liquid chromatography-ultra violet (HPLC-UV) analysis. Densitometric quantification was performed at λ = 328 nm (the wavelength of maximum absorption of RA) by fluorescence scanning using a CAMAG TLC Scanner 3. Polynomial (HPTLC) and linear (HPLC-UV) regression analyses were used to determine the amount of RA in the extracts. The mobile phase used for HPTLC produced good separation for RA (RF = 0.42). A good polynomial regression model was obtained in the range of 200–1000 ng and peak areas with the correlation coefficient (R2) of 0.9995. The coefficient of variation (%) of intra-day and inter-day precision of RA at 400 ng per band were 1.44 and 4.48, respectively. Salvia runcinata contained the highest (145.71 mg g−1) RA content. The paired sample t-test showed no statistical significant difference in the estimation of the amount of RA in the solvent extracts using the two chromatographic techniques. The prescribed method is simple, fast, reliable, sensitive and here proposed for the routine assay of Salvia extracts containing RA.

Chemical composition and antimicrobial activity of Eucalyptus radiata leaf essential oil, sampled over a year

Abstract This study investigated the seasonal variation of the chemical composition and antimicrobial activity of Eucalyptus radiata leaf essential oil. Young and mature Eucalyptus radiata leaf material was collected monthly (January 2014 to December 2014), hydrodistilled and analyzed using GC-MS. Essential oil yields ranged from 0.14% to 4.31% (w/w). The major compounds were 1,8-cineole (65.7% ± 9.5), α-terpineol (12.8% ± 4.4) and limonene (6.5% ± 2.4). Chemometric tools were used to determine seasonal variations, which showed slight variance in E. radiata chemistry between seasons. The minimum inhibitory concentration (MIC) assay showed that the highest activity was noted against the Streptococci (0.19–2.00 mg/mL) and Lactobacillus acidophilus (0.19–1.75 mg/mL). The activity of the E. radiata leaf essential oil is dependent on the unique ratio of its compounds. The E. radiata leaf essential oil showed good oil yields, a relatively consistent chemical profile and noteworthy antimicrobial activity that rivals other commercial Eucalypt counterparts.