Direct enantiomeric analysis of Mentha essential oils

Comprehensive quality assessment of peppermint oils and commercial products: An integrated approach involving conventional and chiral GC/MS coupled with chemometrics

Peppermint essential oil (EO) has a multitude of applications, such as a fragrance in cosmetics, personal care and industrial products, or as a flavoring ingredient in food and beverages. Despite its popularity and economic significance, peppermint EO is often adulterated to reduce production costs and to increase profits. Although the ISO standard for peppermint EO exists, detecting sophisticated forms of adulteration remains challenging.The current study used conventional and chiral GC/MS analysis of volatiles compounds, and chemometric techniques to evaluate an extensive set of authentic peppermint EO (n = 22) and commercial products (n = 36) purported to contain peppermint EO. Specifically, thirty-six terpenoids were examined in each sample and compared with the ISO standard. Fifty-three percent of the selected commercial products did not meet the ISO specifications and the ratio between menthone/isomenthone was proven to be a good indicator for authentication and adulteration detection. Chiral GC/MS was further employed to measure eight terpenoids: α-pinene, β-pinene, limonene, menthol, menthone, isomenthone, pulegone, and menthyl acetate. The enantiomeric compositions of 27 commercial products were above or below the norm measured from authentic peppermint EOs. Of the 27 samples, eight met the ISO standard. A sample class prediction (SCP) model based on partial least squares-discriminant analysis (PLS-DA) of conventional GC/MS data was constructed using authentic peppermint EOs and cornmint EOs. The model can distinguish the most common types of peppermint EOs (US, India, and US/India blend) and cornmint EOs sold in the US market. After construction, the SCP model was then used to analyze commercial samples. One sample, which passed both ISO specification and chiral analysis, was identified as outlier by the SCP model. Overall, the applicability of combining both conventional and chiral GC/MS along with chemometric tools has been successfully demonstrated to address the overall quality of peppermint EOs in commerce and may help combat sophisticated adulteration.

A Study of the Essential Oil Isolated from Ageratina dendroides (Spreng.) R.M. King & H. Rob.: Chemical Composition, Enantiomeric Distribution, and Antimicrobial, Antioxidant, and Anticholinesterase Activities

Ageratina dendroides is an aromatic species native to Ecuador. In this study, the chemical composition, enantiomeric distribution, and antifungal, antibacterial, antioxidant, and anticholinesterase activities of the essential oil isolated from aerial parts of Ageratina dendroides were determined. The quantitative chemical composition was determined using gas chromatography equipped with a flame ionization detector. The qualitative chemical composition was determined using gas chromatography coupled with mass spectrometry. The enantiomeric distribution was determined using an enantioselective chromatographic column. A broth microdilution method was used to determine the antibacterial activity. This antibacterial activity was tested against three Gram-negative bacilli bacteria and three Gram-positive cocci bacteria. The antifungal activity was tested against two fungi, a fungus, and a yeast. The antioxidant activity was determined using the ABTS (2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)) method and DPPH (2,2-diphenyl-1-picrylhydrazyl) method. The anticholinesterase activity was analyzed using the spectrophotometric method. Sixty-eight volatile compounds were identified in the essential oil. These compounds represent 99.49% of the total composition. In terms of the number of compounds and their relative abundance, the most representative group was sesquiterpene hydrocarbons, with thirty-four compounds and an abundance of 49.22%. The main constituents were found to be andro encecalinol (14.41 ± 1.26%), germacrene D (8.86 ± 1.06%), amorpha-4,9-dien-14-al (7.68 ± 0.70%), β-sesquiphellandrene (7.01 ± 1.49%), α-muurolol (5.89 ± 0.93%), and 7-epi-α-selinene (5.68 ± 0.53%). Five pairs of enantiomers were identified in the essential oil of Ageratina dendroides. The essential oil did not report antimicrobial activity at the maximum concentration tested (MIC > 4000 µg/mL) against any of the microorganisms tested. The antioxidant activity of the essential oil was strong in the ABTS method, with an SC50 of 33.2 ± 1.4 µg/mL. Additionally, the Ageratina dendroides essential oil reported moderate anticholinesterase activity, with an IC50 of 297.8 ± 1.03 µg/mL.

Chemical Composition, Enantiomeric Distribution and Biological Activity of Essential Oil from Morella pubescens (Humb. & Bonpl. ex Willd.) Wilbur

The species Morella pubescens, commonly known as wax laurel, is a tree belonging to the Myricaceae family that can be found from Costa Rica to Bolivia. In this study, the chemical composition, enantiomeric distribution, and biological activity of essential oil isolated from the leaves of this species was determined. Hydrodistillation was used to isolate the essential oil (EO). Gas chromatography coupled with mass spectrometry was used to determine the qualitative composition, gas chromatography equipped with a flame ionization detector was used to determine quantitative composition, and gas chromatography on an enantioselective column was used to determine enantiomeric distribution. The broth microdilution method was employed to assess the antibacterial capacity of the essential oil against seven opportunistic microorganisms, including three Gram-positive cocci bacteria, a Gram-positive bacilli bacterium and three Gram-negative bacilli bacteria. 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid radical cation and 2,2-diphenyl-1-picrylhydryl free radical were used as reagents to determine the antioxidant activity of essential oil. The spectrophotometric method was used to analyze the acetylcholinesterase inhibitory effect of the essential oil. The extraction method afforded a low yield of around 0.076 ± 0.008% (v/w). Fifty-eight chemical compounds, which represent 97.9% of the total composition, were identified in the essential oil. Sesquiterpene hydrocarbons were the most representative group with 24 compounds (67.8%). The principal constituents were (E)-caryophyllene (27.5 ± 1.3%), limonene (11.8 ± 0.6%), δ-selinene (9.1 ± 0.2%), β-selinene (8.0 ± 0.2%), selina-3,7(11)-diene (5.3 ± 0.2%) and germacrene B (5.0 ± 0.5%). Three pairs of enantiomers were identified in the essential oil of Morella pubescens. Essential oil presented strong activity against the bacterium Enterococcus faecium (ATCC 27270) with an MIC of 250 μg/mL. The antioxidant activity of essential oil was very strong in the ABTS method with an SC₅₀ of 46.4 ± 1.0 µg/mL and was strong in the DPPH method with an SC₅₀ of 237.1 ± 1.8 µg/mL. Additionally, the essential oil reported strong anticholinesterase activity with an IC₅₀ of 133.5 ± 1.06 µg/mL.

Enantiomeric Composition, Antioxidant Capacity and Anticholinesterase Activity of Essential Oil from Leaves of Chirimoya (Annona cherimola Mill.)

Annona cherimola Mill. is a native species of Ecuador cultivated worldwide for the flavor and properties of its fruit. In this study, hydrodistillation was used to isolate essential oil (EO) of fresh Annona cherimola leaves collected in Ecuadorian Sierra. The EO chemical composition was determined using a non-polar and a polar chromatographic column and enantiomeric distribution with an enantioselective column. The qualitative analysis was carried out by gas chromatography coupled to a mass spectrometer and quantitative analysis using gas chromatography equipped with a flame ionization detector. The antibacterial potency was assessed against seven Gram-negative bacteria and one Gram-positive bacterium. ABTS and DPPH assays were used to evaluate the radical scavenging properties of the EO. Spectrophotometric method was used to measure acetylcholinesterase inhibitory activity. GC-MS analysis allowed us to identify more than 99% of the EO chemical composition. Out of the fifty-three compounds identified, the main were germacrene D (28.77 ± 3.80%), sabinene (3, 9.05 ± 1.69%), β-pinene (4, 7.93 ± 0.685), (E)-caryophyllene (10.52 ± 1.64%) and bicyclogermacrene (11.12 ± 1.39%). Enantioselective analysis showed the existence of four pairs of enantiomers, the (−)-β-Pinene (1S, 5S) was found pure (100%). Chirimoya essential oil exhibited a strong antioxidant activity and a very strong anticholinesterase potential with an IC₅₀ value of 41.51 ± 1.02 µg/mL. Additionally, EO presented a moderate activity against Campylobacter jejuni and Klebsiella pneumoniae with a MIC value of 500 μg/mL.

Chemical, Enantioselective, and Sensory Analysis of a Cholinesterase Inhibitor Essential Oil from Coreopsis triloba S.F. Blake (Asteraceae)

The fresh leaves of Coreopsis triloba S.F. Blake, collected at Cerro Villonaco in Loja, Ecuador, were investigated with respect to their essential oil (EO). The chemical composition was determined qualitatively through gas chromatography coupled with mass spectrometry (GC-MS) and quantitatively by gas chromatography coupled with flame ionization (GC-FID), using relative response factors (RRF) based on the enthalpy of combustion. The essential oil contained between 92.5% and 93.4% of monoterpene hydrocarbons, with (E)-β-ocimene being the main component (35.2–35.9%), followed by β-phellandrene (24.6–25.0%), α-pinene (15.3–15.9%), myrcene (10.9–11.0%), sabinene (2.2–2.4%), (Z)-β-ocimene (1.5%), and germacrene D (1.2–1.3%). The enantiomeric distribution of α-pinene, β-pinene, limonene, and germacrene D was also determined. The main components responsible for the aroma were identified through aroma extract dilution analysis (AEDA), a gas chromatography-olfactometry (GC-O) based technique, being α-pinene, β-pinene (0.6%), terpinolene (0.1%), α-copaene (0.1–0.3%), β-phellandrene, and (E)-4,8-dimethyl-1,3,7-nonatriene (0.1–0.2%) the main olfactory constituents according to the decreasing factor of dilution (FD) order. The biological tests showed IC₅₀ inhibition values of 42.2 and 6.8 µg/mL for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively.

Chromatographic Separation of Vitamin E Enantiomers

Vitamin E is recognized as an essential vitamin since its discovery in 1922. Most vegetable oils contain a mixture of tocopherols and tocotrienols in the vitamin E composition. Structurally, tocopherols and tocotrienols share a similar chromanol ring and a side chain at the C-2 position. Owing to the three chiral centers in tocopherols, they can appear as eight different stereoisomers. Plant sources of tocopherol are naturally occurring in the form of RRR while synthetic tocopherols are usually in the form of all-racemic mixture. Similarly, with only one chiral center, natural tocotrienols occur as the R-isoform. In this review, we aim to discuss a few chromatographic methods that had been used to separate the stereoisomers of tocopherols and tocotrienols. These methods include high performance liquid chromatography, gas chromatography and combination of both. The review will focus on method development including selection of chiral columns, detection method and choice of elution solvent in the context of separation efficiency, resolution and chiral purity. The applications for separation of enantiomers in vitamin E will also be discussed especially in terms of the distinctive biological potency among the stereoisoforms.

In vitro and in vivo toxicological evaluations of methyl ferulate, methyl p-coumarate, and pulegone 1,2-epoxide

CONTEXT

Toxicological screening of natural compounds for medicinal purposes.

OBJECTIVES

The objective of this study is to evaluate the toxicity of methyl ferulate (MF), methyl p-coumarate (MpC), and pulegone 1,2-epoxide (PE) with in vitro and in vivo assays.

MATERIALS AND METHODS

The in vitro toxicity of MF, MpC, and PE was assessed at a concentration of 10 mg/ml with the Ames assay using two strains of Salmonella typhimurium TA98 and TA100. Human red blood cells (RBC) were used to determine the hemolytic activity of these compounds. The cytotoxicity of above compounds was determined with brine shrimp lethality bioassay (BSLB) at the concentrations of 0.1-20 mg/ml. While dermal and ocular irritation studies were conducted on healthy rabbits (n = 8) for 96 and 12 h post-topical application of test compounds, respectively.

RESULTS

PE produced 6-8% hemolysis of RBCs at all the tested concentrations while MF and MpC produced 10-5% hemolysis up to 20 mg/ml, and 50-85% hemolysis at concentrations of 40 and 80 mg/ml, respectively. The Ames assay indicated that MF, MpC, and PE were non-mutagenic as the test values were not significantly higher as compared with background values of the assay. BSLB suggested the lethal concentration (LC50) values of MF, MpC, and PE as 4.38, 6.74, and 25.91 mg/ml, respectively. In vivo ocular and dermal irritation scores of MF, MpC, and PE were comparable with ethanol (control) in rabbits indicating the non-irritant nature of these natural compounds.

CONCLUSION

The present studies suggest that these compounds are non-toxic/non-irritant and might be used for medicinal purposes.