Thymol and Thyme Essential Oil-New Insights into Selected Therapeutic Applications

Thymol (2-isopropyl-5-methylphenol) belongs to the phenolic monoterpenes and mostly occurs in thyme species. It is one of the main compounds of thyme essential oil. Both thymol and thyme essential oil have long been used in traditional medicine as expectorant, anti-inflammatory, antiviral, antibacterial, and antiseptic agents, mainly in the treatment of the upper respiratory system. The current search for new directions of biological or therapeutic activities of natural plant substances with known structures includes thyme essential oil and thymol. Novel studies have demonstrated their antibiofilm, antifungal, antileishmanial, antiviral, and anticancer properties. Also, their new therapeutic formulations, such as nanocapsules containing these constituents, can be beneficial in medicinal practice and create opportunities for their extensive use. Extensive application of thymol and thyme essential oil in the healthcare sector is very promising but requires further research and analysis.

Development of antibacterial nanoemulsions incorporating thyme oil: Layer-by-layer self-assembly of whey protein isolate and chitosan hydrochloride

The aim of this study was to develop a thyme oil emulsion with good physicochemical properties and antibacterial activity. Initially, oil-in-water emulsions containing whey protein-coated essential oil droplets were prepared by high-pressure homogenization. The double-layer emulsions were formed around the oil droplets by electrostatic deposition of cationic chitosan hydrochloride onto the anionic protein-coated droplets. Then, the structure, physicochemical properties, and storage stability of the emulsions were determined. Emulsions formulated using 1% v/v thyme oil, 0.7 wt% whey protein, and 0.25 wt% of chitosan hydrochloride contained relatively small cationic droplets. Moreover, the emulsions containing double-layer coatings were shear-thinning fluids. Storage tests indicated that double-layer emulsions had better stability than the single-layer. Antibacterial tests indicated that the double-layer emulsions exhibited prolonged antibacterial activity against two model food pathogens: E. coli and S. aureus. These results provide a scientific basis for the rational design of antimicrobial delivery systems for use in foods.

Synergistic antibacterial effects of ultrasound and thyme essential oils nanoemulsion against Escherichia coli O157:H7

Essential oil nanoemulsions have been proven to have stronger antimicrobial effects compared to the essential oil alone or coarse emulsion. Sonoporation could be the promising candidate to trigger a synergistic effect with thyme essential oil nanoemulsion (TEON) and produce a more effective antibacterial efficacy. Therefore, in this study, the bactericidal effects of ultrasound (US) in combination with TEON treatments against Escherichia coli (E. coli) O157:H7 were investigated. The remarkable synergistic effects of US (20 kHz, 255 W/cm², 9 min) and TEON (0.375 mg/mL) treatments at 22 °C reduced E. coli O157:H7 populations by 7.42 ± 0.27 log CFU/mL. The morphological changes of cells exposed to different treatments were observed by scanning electron microscopy and transmission electron microscopy. The results showed that the synergistic effects of the ultrasound and TEON treatments altered the morphology and interior microstructure of organism cells. Laser scanning confocal microscopy (LSCM) images revealed that the combination treatments of ultrasound and TEON altered the permeability of cell membranes, and this affected the integrity of E. coli O157:H7 cells. This was further indicated by the high amounts of nucleic acids and proteins released from these cells following treatment. The results from this study illustrated the mechanisms of the synergistic effects of sonoporation and TEON treatments and provided valuable information for their potential in food pasteurization.

Electrospun potato starch nanofibers for thyme essential oil encapsulation: antioxidant activity and thermal resistance

BACKGROUND

Thyme essential oil (TEO) is an excellent natural substitute for synthetic compounds to maintain the quality and safety of food products. It acts as an antioxidant agent. We aimed to nanoencapsulate TEO at concentrations of 1%, 3%, and 5% (v/w, dry basis) in electrospun nanofibers made of starch (50% w/v) and formic acid (75% v/v). The rheological parameters of the fiber-forming solutions were measured, and various physical and chemical properties of the nanofibers were analyzed.

RESULTS

The starch/TEO nanofibers presented homogeneous morphology. The starch nanofibers showed high encapsulation efficiency (EE, 99.1% to 99.8%), which, along with the Fourier transform infra-red (FTIR) spectrum and thermogravimetric analysis (TGA) analysis, indicate strong protection of the phenolic compounds of TEO. Nanofibers with 5% TEO retained up to 50% of the phenolic compounds after exposure to thermal treatment. The antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals of the starch/TEO nanofibers varied from 11.1% to 14.2% and the inhibition values (29.8%, P ≤ 0.05) against hydroxyl radicals were the same for free TEO and the nanofibers.

CONCLUSION

Owing to these properties, electrospun starch/TEO nanofibers can be applied in food products or food packaging.

Syzygium aromaticum (clove) and Thymus zygis (thyme) essential oils increase susceptibility to colistin in the nosocomial pathogens Acinetobacter baumannii and Klebsiella pneumoniae

The discovery of new antibiotics that are effective against Acinetobacter baumannii and Enterobacteralesis a research priority. Several essential oils (EOs) have displayed some antimicrobial activity and could potentially act as antibiotic adjuvants. Research in this area aims to develop new therapeutic alternatives to treat infections caused by these pathogens. MICs of different EOs were determined against A. baumannii and Klebsiella pneumoniae. Combined disk diffusion tests and checkerboard assays were used to study the synergy between the EOs and antibiotics. The fractional inhibitory concentration index (FIC_index) was calculated in order to categorize the interaction. Time-kill assays were also performed. The EOs that displayed the highest levels of antimicrobial activity were clove (Syzygium aromaticum L.) and thyme (Thymus zygis L.). Combined disk diffusion tests and checkerboard assays revealed synergy between these EOs and colistin. Addition of either clove or thyme EO decreased the MIC of colistin by 8- to 64-fold and 8- to 128-fold in the colistin-resistant A. baumannii and K. pneumoniae strains, respectively (FIC_index ≤ 0.5, synergy). MICs were also reduced in the colistin-susceptible strains. Time-kill assays also indicated the strong activity of the combined therapy. In summary, the use of clove or thyme EO in combination with colistin could improve the efficacy of the antibiotic and significantly reduce the concentrations needed to inhibit growth of A. baumannii and K. pneumoniae.

Effects of Thymus vulgaris L., Cinnamomum verum J.Presl and Cymbopogon nardus (L.) Rendle Essential Oils in the Endotoxin-induced Acute Airway Inflammation Mouse Model

Thyme (TO), cinnamon (CO), and Ceylon type lemongrass (LO) essential oils (EOs) are commonly used for inhalation. However, their effects and mechanisms on inflammatory processes are not well-documented, and the number of in vivo data that would be important to determine their potential benefits or risks is low. Therefore, we analyzed the chemical composition and investigated the activity of TO, CO, and LO on airway functions and inflammatory parameters in an acute pneumonitis mouse model. The components of commercially available EOs were measured by gas chromatography-mass spectrometry. Airway inflammation was induced by intratracheal endotoxin administration in mice. EOs were inhaled during the experiments. Airway function and hyperresponsiveness were determined by unrestrained whole-body plethysmography on conscious animals. Myeloperoxidase (MPO) activity was measured by spectrophotometry from lung tissue homogenates, from which semiquantitative histopathological scores were assessed. The main components of TO, CO, and LO were thymol, cinnamaldehyde, and citronellal, respectively. We provide here the first evidence that TO and CO reduce inflammatory airway hyperresponsiveness and certain cellular inflammatory parameters, so they can potentially be considered as adjuvant treatments in respiratory inflammatory conditions. In contrast, Ceylon type LO inhalation might have an irritant effect (e.g., increased airway hyperresponsiveness and MPO activity) on the inflamed airways, and therefore should be avoided.

Antibacterial and antibiofilm activities of thyme oil against foodborne multiple antibiotics-resistant Enterococcus faecalis

The inhibitory and bactericidal activities of thyme oil against the foodborne multiple antibiotics-resistant Enterococcus faecalis biofilm were evaluated in this study. Gas chromatography-mass spectrometry revealed that more than 70% of the composition of thyme oil is thymol. Crystal violet staining assay showed that 128 and 256 μg/mL thyme oil significantly inhibited the biofilm formation of E. faecalis. The cell adherence of E. faecalis, as shown by its swimming and swarming motilities, was reduced by thyme oil. The exopolysaccharide (EPS) quantification assay showed that thyme oil inhibited the EPS synthesis in E. faecalis biofilms. The 3D-view observations through confocal laser scanning and scanning electron microscopy suggested that cell adherence and biofilm thickness were decreased in thyme oil–treated biofilms. Quantitative real-time analyses showed that the transcription of ebp and epa gene clusters, which were related to cell mobility and EPS production, was inhibited by thyme oil. Thus, thyme oil effectively inhibited the biofilm formation of E. faecalis by affecting cell adherence and EPS synthesis. Furthermore, 2,048 and 4,096 μg/mL thyme oil can effectively inactivate E. faecalis population in the mature E. faecalis biofilms by 5.75 and 7.20 log CFU/mL, respectively, after 30 min of treatment. Thus, thyme oil at different concentrations can be used as an effective antibiofilm or germicidal agent to control E. faecalis biofilms.

Bioactive Natural Compounds and Antioxidant Activity of Essential Oils from Spice Plants: New Findings and Potential Applications

Spice plants have a great influence on world history. For centuries, different civilizations have used them to condiment the foods of kings and nobles and applied them as embalming preservatives, perfumes, cosmetics, and medicines in different regions of the world. In general, these plants have formed the basis of traditional medicine and some of their derived substances have been utilized to treat different human diseases. Essential oils (EOs) obtained from these plants have been also used as therapeutic agents and have shown supportive uses in remedial practices. The discovery and development of bioactive compounds from these natural products, based on their traditional uses, play an important role in developing the scientific evidence of their potential pharmaceutical, cosmetic, and food applications. In the present review, using recent studies, we exhibit a general overview of the main aspects related to the importance of spice plants widely used in traditional medicine: Cinnamomum zeylanicum (true cinnamon), Mentha piperita (peppermint), Ocimum basilicum (basil), Origanum vulgare (oregano), Piper nigrum (black pepper), Rosmarinus officinalis (rosemary), and Thymus vulgaris (thyme); and we discuss new findings of the bioactive compounds obtained from their EOs, their potential applications, as well as their molecular mechanisms of action, focusing on their antioxidant activity. We also exhibit the main in vitro methods applied to determine the antioxidant activities of these natural products.

Synergistic antimicrobial action and effect of active chitosan-gelatin biopolymeric films containing Thymus vulgaris, Ocimum basilicum and Origanum majorana essential oils against Escherichia coli and Staphylococcus aureus

To replace synthetic preservatives and expand green consumption, several essential oils have been tested in foods and food packaging due to their antimicrobial properties. This study aimed to analyze the synergistic antimicrobial action of a chitosan-gelatin based active biopolymers with the addition of essential oils (EOs). The antimicrobial agents were tested against foodborne microorganisms Staphylococcus aureus and Escherichia coli strains. The antibacterial activity of Thymus vulgaris, Ocimum basilicum, Origanum majorana, and the synergistic interactions among them were assessed according to the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using the microdilution method. Chitosan-gelatin based active biopolymers were developed, and 23% (w/w) of each essential oil and combined oils were added. The antimicrobial effect of active films was measured using the disk diffusion method. Active films with the addition of essential oils have potential applications as active packaging agents, especially those that demonstrated inhibition zones. Combined EOs can be used to enhance the antimicrobial activity, ensuring reduced doses used in active packaging and decreasing the association with adverse sensory characteristics.

Curcuma longa L. (turmeric), Rosmarinus officinalis L. (rosemary), and Thymus vulgaris L. (thyme) extracts aid murine macrophages (RAW 264.7) to fight Streptococcus mutans during in vitro infection

Finding an effective alternative way to aid defense cells to fight Streptococcus mutans was the main goal of this study. The effect of plant extracts from Curcuma longa L. (turmeric), Rosmarinus officinalis L. (rosemary), and Thymus vulgaris L. (thyme) was evaluated on murine macrophages (RAW 264.7) infected by S. mutans. Minimum inhibitory concentration (MIC) of the extracts was determined. Macrophages were infected by S. mutans and treated with each extract. From the supernatants, it was measured nitric oxide (NO) level. Posteriorly, RAW 264.7 were lysed to expose living and phagocytosed bacteria. Cytotoxicity was checked by lysosomal activity analysis, using neutral red assay. Each extract helped RAW 264.7 to eliminate S. mutans during infection, as observed by a significant bacterial reduction. Significant cell viability was also found. Besides, an increased production of NO was verified using R. officinalis L. and T. vulgaris L. extracts. The evaluated extracts demonstrated an effective action to assist RAW 264.7 to fight S. mutans during infection.

Thymus vulgaris L. Essential Oil Solid Formulation: Chemical Profile and Spasmolytic and Antimicrobial Effects

A new Thymus vulgaris L. solid essential oil (SEO) formulation composed of liquid EO linked to solid excipients has been chemically analysed and evaluated for its intestinal spasmolytic and antispastic effects in ex vivo ileum and colon of guinea pig and compared with liquid EO and excipients. Liquid EO and solid linked EO were analysed by original capillary electrochromatography coupled to diode array detection (CEC-DAD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodologies. The main bioactive constituents are thymol and carvacrol, with minor constituents for a total of 12 selected analysed compounds. Liquid EO was the most effective in decreasing basal contractility in ileum and colon; excipients addiction permitted normal contractility pattern in solid linked EO SEO. In ileum and colon, the Thymus vulgaris L. solid formulation exerted the relaxant activity on K⁺-depolarized intestinal smooth muscle as well as liquid EO. The solid essential oil exhibits antimicrobial activity against different strains (Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, Escherichia coli, Salmonella Thyphimurium, Candida albicans) similarly to liquid oil, with activity against pathogen, but not commensal strains (Bifidobacterium Breve, Lactobacillus Fermentum) in intestinal homeostasis. Therefore, Thymus vulgaris L. solid essential oil formulation can be proposed as a possible spasmolytic and antispastic tool in medicine.

Thymus algeriensis and Thymus fontanesii: Chemical Composition, In Vivo Antiinflammatory, Pain Killing and Antipyretic Activities: A Comprehensive Comparison

This study aimed to investigate the chemical composition, and evaluate the antioxidant, anti-inflammatory, anti-pyretic, and the analgesic properties of methanol extracts from the leaves of Thymus algeriensis and Thymus fontanesii (Lamiaceae). Thirty-five secondary metabolites were characterized in both extracts using HPLC-PDA-ESI-MS/MS. Phenolic acids, mainly rosmarinic acid and its derivatives, dominated the T. algeriensis extract, while the phenolic diterpene carnosol and the methylated flavonoid salvigenin, prevailed in T. fontanesii extract. Molecular docking study was carried out to estimate the anti-inflammatory potential and the binding affinities of some individual secondary metabolites from both extracts to the main enzymes involved in the inflammation pathway. In vitro enzyme inhibitory assays and in vivo assays were used to investigate the antioxidant and anti-inflammatory activities of the extracts. Results revealed that both studied Thymus species exhibited antioxidant, anti-inflammatory, analgesic, and antipyretic effects. They showed to be a more potent antioxidant than ascorbic acid and more selective against cyclooxygenase (COX-2) than diclofenac and indomethacin. Relatively, the T. fontanesii extract was more potent as COX-2 inhibitor than T. algeriensis. In conclusion, Thymus algeriensis and Thymus fontanesii may be interesting candidates for the treatment of inflammation and oxidative stress-related disorders.

Contribution of surface application of chitosan-thyme and chitosan-rosemary essential oils to the volatile composition, microbial profile, and physicochemical and sensory quality of dry-fermented sausages during storage

The effect of chitosan (C), chitosan enriched with thyme (CT) or rosemary (CR) essential oils, and potassium sorbate (PS) against superficial fungal growth was investigated in fermented sausages during 3 months of storage at 4 °C. For control groups, distilled water (DW) and acetic acid (AA) were used. PS, C, CT and CR treatments inhibited fungal growth on casings while they resulted in lower Gram(+) catalase(+) cocci, Enterobacteriaceae, mold and yeast counts in sausages. Lower TBARS values were determined for CT and CR (p < .05). A total of 44 and 64 volatile compounds were identified in sausages and casings, respectively. Sausages coated with C, CT or CR had acceptable sensory attributes at the end of storage; however, DW and AA groups were rejected in the second and third month (p < .05), respectively, due to intense fungal growth which resulted in sensory defects.

Strategies for reducing Ostwald ripening phenomenon in nanoemulsions based on thyme essential oil

BACKGROUND

White thyme essential oil, which can be incorporated in clean-label and food emulsion-based products, is a natural antimicrobial agent. However, emulsions containing essential oils commonly undergo Ostwald ripening as the main destabilization process. The main objective of this work was to evaluate various strategies for the inhibition of Ostwald ripening so as to develop stable nanoemulsions containing white thyme essential oil as food preservative and Kolliphor EL as surfactant.

RESULTS

In a first approach, the influence of the surfactant/dispersed phase ratio and the number of cycles through a microfluidizer on droplet size distribution was evaluated. Unfortunately, these emulsions underwent Ostwald ripening, which was demonstrated by the application of the Lifshitz-Slyozov-Wagner theory. In order to reduce this destabilization mechanism, two different techniques based on the modification of the formulation (addition of rosin gum or Aerosil COK84) were analysed using laser diffraction and multiple light scattering techniques. The addition of rosin gum inhibited the Ostwald ripening mechanism, but only partially. Conversely, the incorporation of Aerosil COK84 to the continuous phase led to a gel-like rheological behaviour which seemed to practically avoid Ostwald ripening.

CONCLUSIONS

Aerosil particles cover the droplets and form a three-dimensional network suggesting a Pickering stabilization, which was confirmed using transmission electronic microscopy. The results confirmed the role of Aerosil COK84, not only as a thickener or gelling agent, but also as an Ostwald ripening inhibitor. © 2019 Society of Chemical Industry.

Composition, Antifungal, Phytotoxic, and Insecticidal Activities of Thymus kotschyanus Essential Oil

Essential oils (EOs) are some of the outstanding compounds found in Thymus that can exert antifungal, phytotoxic, and insecticidal activities, which encourage their exploration and potential use for agricultural and food purposes. The essential oils (EO) obtained from Thymus kotschyanus collected in the East Azerbaijan Province (Iran) were characterized using a gas chromatography-mass spectrometry (GC-MS) analysis. Thymol was the most important compound (60.48%), although 35 other active compounds were identified in the EO. Significant amounts of carvacrol (3.08%), p-cymene (5.56%), and γ-terpinene (6.67%) were found in the EO. The T. kotschyanus EO was tested against important phytopathogenic fungi (Botrytis cinerea, Aspergillus niger, and Penicillium expansum). The antifungal assay showed that the use of ≥500 ppm of EO resulted in a fungicidal effect against all funguses tested. In a similar way, the use of ≥500 ppm of EO inhibited the germination of all crop weed seeds (Amaranthus retroflexus L. and Panicum miliaceum L.) and their subsequent growth, which demonstrated its herbicidal effect. Finally, the insecticidal capacity of T. kotschyanus EO was also observed against selected insects (Oryzaephilus surinamensis and Sitophilus oryzae). O. surinamensis was more susceptible to the effect of EO (LC50 = 4.78 µL/L air) than S. oryzae (LC50 = 13.20 µL/L air). The obtained results of the present study can provide new safe resources to the development of new products for the food, agriculture, and pharmaceutical industries.

Exploring essential oils of Slovak medicinal plants for insecticidal activity: The case of Thymus alternans and Teucrium montanum subsp. jailae

Thymus alternans and Teucrium montanum subsp. jailae are medicinal and aromatic plants, typical of Slovakian flora, producing bioactive essential oils. In the present study, we evaluated the insecticidal potential of the essential oils, obtained by hydrodistillation from the plant aerial parts and analysed by GC-MS, as insecticidal agents. For the purpose, they were assayed against three insect species acting as agricultural pests or vectors of medical relevance, such as the common housefly, Musca domestica L., the lymphatic filariasis vector, Culex quinquefasciatus and the Egyptian cotton leafworm Spodoptera littoralis; α-cypermethrin was tested as positive control. The two essential oils exhibited a different chemical profile, with monoterpenes and sesquiterpenes being the main fractions in the essential oils from Th. alternans and T. montanum subsp. jailae, respectively. Insecticidal tests showed that the T. montanum essential oil was effective against S. littoralis (LD₅₀₍₉₀₎ = 56.7 (170.0) μg larva^-1) and Cx. quinquefasciatus larvae (LC₅₀₍₉₀₎ = 180.5 (268.7) mg L^-1), whereas T. alternans essential oil displayed good toxicity against M. domestica adults (LD₅₀₍₉₀₎ = 103.7 (223.9) μg adult^-1). Overall, our results add useful knowledge about the potential of Slovakian flora as a source of botanicals for the eco-friendly management of insect pests and vectors.

Effects of active edible coating based on thyme and garlic essential oils on lamb meat shelf life after long-term frozen storage

BACKGROUND

The frozen preservation of lamb meat could be crucial for successful international trade. The shelf life of thawed meat is shorter than that of fresh meat, so techniques or procedures are required to improve post-thawing meat quality attributes. This study investigated the effect of alginate-based edible coatings after the incorporation of essential oils of thyme (Thymus vulgaris L.) and garlic (Allium sativum L.) on thawed lamb meat (longissimus thoracis et lumborum muscle) quality after long-term frozen storage. Meat samples came from ten light lambs and the evolution of attributes related to shelf life, such as water-holding capacity, color stability, and lipid oxidation, was monitored during display (1, 4 and 7 days). Four meat treatments were evaluated: control (CON, uncoated meat), edible coat of alginate meat (ECA), and ECA with thyme or garlic essential oils (0.05%) (THY and GAR).

RESULTS

The alginate-based edible coatings decreased exudative losses (P < 0.001) and modified color characteristics, especially increasing yellowness (P < 0.001) and chrome (P < 0.001). GAR decreased redness (P < 0.001) and the oxy/met ratio [R (630/580) wavelength light reflectance] or discoloration [R (630-580)]. THY was the treatment that best retained color during display and also showed a significantly lower lipid oxidation (P < 0.05) than CON and ECA, whereas GAR presented intermediate values.

CONCLUSION

The addition of bioactive essential oils to alginate-based edible coatings improved preservation and shelf life of lamb meat after thawing. © 2019 Society of Chemical Industry.

A New Method for Determination of Thymol and Carvacrol in Thymi herba by Ultraperformance Convergence Chromatography (UPC2)

Ultraperformance convergence chromatography is an environmentally friendly analytical technique for dramatically reducing the use of organic solvents compared to conventional chromatographic methods. In this study, a rapid and sensitive ultraperformance convergence chromatography method was firstly established for quantification of thymol and carvacrol, two positional isomers of a major bioactive in the volatile oil of Thymi herba, the dried leaves and flowers of Thymus mongolicus or Thymus przewalskii, known in China as "Dijiao." Using a TrefoilTM CEL1 column, thymol and carvacrol were separated in less than 2.5 min and resolution was enhanced. The method was validated with respect to precision, accuracy, and linearity according to the National Medical Products Administration guidelines. The optimized method exhibited good linear correlation (r = 0.9998-0.9999), excellent precision (relative standard deviations (RSDs) < 1.50%), and acceptable recoveries (87.29-102.89%). The limits of detection for thymol and carvacrol were 1.31 and 1.57 ng/L, respectively, while their corresponding limits of quantification were 2.63 and 3.14 ng/L. Finally, the quantities of the two compounds present in 16 T. mongolicus and four T. przewalskii samples were successfully evaluated by employing the developed method. It is hoped that the results of this study will serve as a guideline for the quality control of Thymi herba.

Thyme and suico essential oils: promising natural tools for potato common scab control

Potato common scab is a worldwide disease mainly caused by Streptomyces scabiei. It seriously affects potato crops by decreasing tuber quality. Essential oils (EO) are natural products with recognised antimicrobial properties. In this research, the antibacterial activities of thyme, oregano, suico and mint EO against S. scabiei were analysed. Infected tubers and soil samples were used for bacterial isolation; the obtained isolates were genetically identified. The chemical composition of the EO was determined by GC-MS. The broth microdilution method was used to analyse antibacterial properties of EO. Thirty-one bacterial isolates were obtained. The isolate chosen for antibacterial assays was morpho-physiologically and genetically identified as S. scabiei. Thyme EO was mainly composed of thymol and o-cymene; suico EO of dihydrotagetone, trans-tagetone and verbenone; oregano EO of trans-sabinene hydrate, thymol and ɣ-terpinene; and mint EO of menthone and menthol. All the EO tested were effective against S. scabiei, but thyme and suico EO were the most successful, with a minimum inhibitory concentration of 0.068 g·l^-1 and 0.147 g·l^-1 , respectively, and a minimum bactericidal concentration of 0.137 g·l^-1 and 0.147 g·l^-1 , respectively. Scanning electron microscopy showed similar damage caused by both thyme and suico EO to the bacterial envelope. Total phenolic content of EO was not related to their antibacterial activity. Thyme and suico EO are effective antibacterial agents against S. scabiei, impeding bacterial viability and disturbing the bacterial cell envelope. These EO are promising tools for control of potato common scab.

FTICR mass spectrometry-based multivariate analysis to explore distinctive metabolites and metabolic pathways: A comprehensive bioanalytical strategy toward time-course metabolic profiling of Thymus vulgaris plants responding to drought stress

In this research, metabolic profiling/pathways of Thymus vulgaris (thyme) plant were assessed during a water deficit stress using an FTICR mass spectrometry-based metabolomics strategy incorporating multivariate data analysis and bioinformatics techniques. Herein, differences of MS signals in specific time courses after water deficit stress and control cases without any timing period were distinguished significantly by common pattern recognition techniques, i.e., PCA, HCA-Heatmap, and PLS-DA. Subsequently, the results were compared with supervised Kohonen neural network (SKN) ones as a non-linear data visualization and capable mapping tool. The classification models showed excellent performance to predict the level of drought stress. By assessing variances contribution on the PCA-loadings of the MS data, the discriminant variables related to the most critical metabolites were identified and then confirmed by ANOVA. Indeed, FTICR MS-based multivariate analysis strategy could explore distinctive metabolites and metabolic pathways/profiles, grouped into three metabolism categories including amino acids, carbohydrates (i.e., galactose, glucose, fructose, sucrose, and mannose), and other metabolites (rosmarinic acid and citrate), to indicate biological mechanisms in response to drought stress for thyme. It was achieved and approved through the MS signals, genomics databases, and transcriptomics factors to interpret and predict the plant metabolic behavior. Eventually, a comprehensive pathway analysis was used to provide a pathway enrichment analysis and explore topological pathway characteristics dealing with the remarkable metabolites to demonstrate that galactose metabolism is the most significant pathway in the biological system of thyme.

Sequencing and variation of terpene synthase gene (TPS2) as the major gene in biosynthesis of thymol in different Thymus species

Thyme (Thymus spp.) is a valuable genus of Lamiaceae family with different pharmaceutical and food properties. Thymol has also been considered as the major essential oil compound in most of the studied Thymus species. In this research, the gene encoding γ-terpinene synthase (Ttps2) was sequenced in T. vulgaris and in eight Iranian thymes including T. carmanicus, T. daenensis, T. fedtschenkoi, T. kotschyanus, T. migricus, T. pubescens, T. serpyllum, and T. trautvetteri. Genetic relationships based on terpene synthase genes were also determined among the studied species. Rapid Amplification of cDNA Ends (RACE) PCR was done to complete the sequence of all species. The cDNA of the studied species possessed an open reading frame ranging from 1788 to 1794 bp that encode for a protein of 596-598 amino acids, presenting all the conserved motifs characteristics of monoterpene synthases. The taxonomic status of Thymus species was determined based on eight reported sections. The species were classified in three major groups. The first and second group comprised species of Micantes and Mastichina sections. The third cluster included the species belonging to Serpyllum and Pseudothymbra sections. Overall, phylogenetic analysis according to whole sequence of Ttps2 gene can help providing insights in respect to its evolutionary process. Finally, clustering based on the amount of main essential oils components (thymol and carvacrol) was compared with that based on Ttps2 gene classification in the studied Thymus species, showing that clustering is not always in accordance.

Fumigant effect of essential oils on mortality and fertility of thrips Frankliniella occidentalis Perg

The western flower thrips (Frankliniella occidentalis Perg.) is one of the most economically important insect pests of greenhouse plants. Plant protection against this pest is based predominantly on synthetic insecticides; however, this form of protection poses problems in terms of thrip resistance to the active substances, along with health risks associated with insecticide residues on the treated plants. Therefore, new active substances need to be sought. Essential oils could be a new, appropriate, and safe alternative for greenhouse culture protection. As greenhouses are enclosed areas, fumigation application of EOs is possible. This paper presents acute toxicity results for 15 commercial EOs applied by fumigation, as well as the effect of sublethal concentrations on fertility of F. occidentalis females. The most efficient EOs were obtained from Mentha pulegium and Thymus mastichina, with LC₅₀₍₉₀₎ estimated as 3.1(3.8) and 3.6 (4.6) mg L^-1 air, respectively. As found for the very first time, sublethal concentrations of EOs could result in a significant reduction in the fertility of surviving T. occidentalis females. Among the tested EOs, the EO from Nepeta cataria provided the highest inhibition of fertility, with EC₅₀₍₉₀₎ estimated as 0.18 (0.36) mg L^-1 air. Chemical composition of the most efficient EOs and possible applications of the results in practice are discussed. In conclusion, in light of the newly determined facts, EOs can be recommended as active substances for botanical insecticides to be applied against Thysanopteran pests by fumigation.

Essential oils as tick repellents on clothing

Essential oils show promise as natural alternatives to synthetic tick repellents, but few studies have investigated their repellent efficacy in vivo or under field conditions. Here, blanket-drags and standardised walks were employed to evaluate tick acquisition by 1 m² cotton blankets or cotton trousers, respectively, in woodland edge habitats of known high tick abundance. Blankets and trousers had been treated with one of 5% oregano, rosemary, spearmint or thyme oils, 20% DEET (N,N-diethyl-3-methylbenzamide) (positive control) or ethanol excipient-only (negative control). The number of ticks present on the blankets or trousers differed significantly between treatments: spearmint oil treatments resulted in significantly fewer ticks than the negative controls for both blankets and trousers and significantly fewer ticks were present on the oregano oil treated blankets. For ticks that did attach to the trousers, the rate of drop off within 3 min was significantly higher for trousers treated with spearmint oil or thyme oil than ethanol, oregano oil and rosemary oil. No reduction in repellence was detected over a 24 h period between treatment and testing. The results suggest that 5% oregano and spearmint oils exhibit potential as natural clothing repellents, with an effective equivalence to 20% DEET.

Phytochemical Profile and Antimicrobial Potential of Extracts Obtained from Thymus marschallianus Willd

Thymus marschallianus Willd. is a Lamiaceae species spread in a large variety of habitats worldwide. The aim of the present research was to analyse two different samples belonging to this species, one obtained from the spontaneous flora and one from culture. The total polyphenols, flavonoids, and phenolic acid contents were spectrophotometrically determined. Qualitative and quantitative analysis of polyphenols was performed by an HPLC-DAD-ESI (+)-MS method. For the antibacterial assay, the well-diffusion and the broth microdilution methods were used. Analysis of polyphenols revealed for both samples the presence of flavonoids like luteolin, quercetin, apigenin and their derivatives, but also of rosmarinic acid and methyl-rosmarinate. Differences regarding the amount of these compounds were emphasized. Significantly larger amounts of flavonoids were found for the sample harvested in the spontaneous flora, while for the rosmarinic acid, larger amounts were found for the cultured sample. Both samples displayed promising antibacterial activity, particularly towards Gram positive organisms. T. marschallianus represents, therefore, a rich source of polyphenolic compounds that prove its promising potential as a medicinal species.

LC-MS- and NMR-Guided Isolation of Monoterpene Dimers from Cultivated Thymus vulgaris Varico 3 Hybrid and Their Antityrosinase Activity

Targeted isolation based on a combination of NMR and HPLC-PDA-MS of a dichloromethane extract of Thymus vulgaris Varico 3 aerial parts afforded one new p-cymene dimer, 6,3',4'-trihydroxy-5,5'-diisopropyl-2,2'-dimethylbiphenyl (1: ), together with two known p-cymene derivatives (2: and 3: ), as well as five known compounds, namely, thymol (4: ), oleanolic acid (5: ), ursolic acid (6: ), cirsimaritin (7: ), and xanthomicrol (8: ). The structural elucidation of all compounds was performed by spectroscopic analyses, including 1D and 2D NMR, and HRESIMS experiments. The biphenyls were assayed for their inhibitory activity on tyrosinase. Compounds 2: and 3: showed negligible activity on tyrosinase, while compound 1: effectively inhibited the enzyme with 35% (± 0.3) inhibitory activity, higher than the inhibition of the reference compound kojic acid (18.6 ± 0.02).