Chemical composition and antibacterial activity of Origanum saccatum P.H. Davis essential oil obtained by solvent-free microwave extraction: comparison with hydrodistillation

The components of the essential oils (EOs) obtained by solvent-free microwave extraction (SFME) and hydrodistillation (HD) from endemic Origanum saccatum P.H. Davis were identified by using GC/MS. The main constituents of both EOs obtained by SFME and HD, respectively, from O. saccatum were p-cymene (72.5 and 70.6%), thymol (9.32 and 8.11%), and carvacrol (7.18 and 6.36%). The EO obtained by SFME contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than did the EO obtained by HD. The antibacterial activities of the EOs obtained by SFME and HD were evaluated with the disc diffusion method by comparison with 10 different bacterial strains. The antibacterial activity of the EO extracted by SFME was found to be more effective than that of the EO extracted by HD against seven of the tested bacteria.     

Antibacterial activities of essential oils extracted from leaves of Murraya koenigii by solvent-free microwave extraction and hydro-distillation

Solvent-free microwave extraction (SFME) for the isolation of essential oil from leaves of Murraya koenigii L. (Rutaceae) has been compared with the conventional hydro-distilled oil (HD) in terms of yield, composition, antioxidant activity, and antibacterial activity against Listeria innocua. The yield of essential oil obtained from 30 min of SFME was similar to that of HD for 180 min. By GC-MS analysis, the major compounds of the essential oil extracted by SFME, which were obtained in somewhat lower amounts than in the essential oil obtained by HD, were alpha-copaene (44.3%), beta-gurjunene (25.5%), isocaryophyllene (12.1%), beta-caryophyllene (8.7%) and germacrene D (2.9%). The content of oxygenated terpenes, slightly higher for the SFME-essential oil (2.3%) than the HD-essential oil (1.4%), were much lower than that of nonoxygenated terpenes in both oils. DPPH radical scavenging activities of both essential oils were relatively low (10%-24%). Complete inhibition of growth of L. innocua was observed with both SFME and HD essential oils, at 400 and 600 microg/mL (minimum inhibitory concentration), respectively. The SFME-essential oil at 300 microg/mL provided 92% inhibition, indicating its potential as a natural antimicrobial agent.     

Evaluation of antileishmanial, cytotoxic and antioxidant activities of essential oils extracted from plants issued from the leishmaniasis-endemic region of Sned (Tunisia)

In this study, we tested 10 essential oils (EOs) extracted from 10 plants issued from Sned region (Tunisia) to evaluate both their leishmanicidal effects against Leishmania major and L. infantum, and their cytotoxicity against murine macrophage cell line RAW 264.7 (ATCC, TIB-71). The antioxidant activity was also monitored by the DDPH method, while the chemical composition of active EO was assessed by GC-MS analysis. The results showed that the EOs obtained from Thymus hirtus sp. algeriensis (rich on monoterpenoids, especially linalool at 17.62% and camphor at 13.82%) is significantly active against both L. major and L. infantum, whereas Ruta chalepensis EO (rich on 2-undecanone at 84.28%) is only active against L. infantum. Both oil extracts showed low cytotoxicity towards murine macrophages. The characteristic ratios (IC?? Raw264.7 cells/IC?? L. infantum and IC?? Raw264.7 cells/IC?? L. major) were, respectively, 2.7 and 1.57 for T. hirtus sp. algeriensis, and 1.34 and 0.19 for R. chalepensis. However, when measuring the antioxidant effects (DDPH method), the two latter EOs presented a moderate 2,2-diphenyl-2-picrylhydrazyl hydrate scavenging effects compared to EOs from Eucaliptus globulus, Pinus halepensis, Pituranthos tortuosus, Rosmarinus officinalis, Tetraclinis articulata or to BHT.     

Effects of solvent-free microwave extraction on the chemical composition of essential oil of Calamintha nepeta (L.) Savi compared with the conventional production method

The essential oil of Calamintha nepeta has been obtained by solvent-free microwave extraction (SFME) and by classical hydrodistillation (HD). A comparative qualitative-quantitative study on the composition of the oils was carried out. A total of 38 compounds, constituting 97.6% of the oil, were identified in the oil obtained by SFME, whereas 46 compounds, representing 95.4% of the oil, were characterized in the HD oil. SFME-distilled oil is richer in lightly oxygenated monoterpenes (LOM) than HD oil. It also has a higher amount of sesquiterpenes and a lower quantity of hydrocarbon monoterpenes. HD oil seems to be affected by chemical changes more than SFME oil.     

Rapid analysis of the essential oils from dried Illicium verum Hook. f. and Zingiber officinale Rosc. by improved solvent-free microwave extraction with three types of microwave-absorption medium

A new method of extracting essential oils from dried plant materials has been studied. By adding a microwave-absorption medium (MAM) to a reactor, solvent-free microwave extraction (SFME) was improved and can be used to extract essential oils from dried plant material without pretreatment. With a microwave irradiation power of 85 W it took only approximately 30 min to extract the essential oils completely. The whole extraction process is simple, rapid, and economical. Three types of MAM, iron carbonyl powder (ICP), graphite powder (GP), and activated carbon powder (ACP), and two types of dried plant material, Illicium verum Hook. f. and Zingiber officinale Rosc., were studied. The results were compared with those obtained by use of conventional SFME, microwave-assisted hydrodistillation (MAHD), and conventional hydrodistillation (HD), and the conclusion drawn was that improved SFME was a feasible means of extracting essential oils from dried plant materials, because there were few differences between the composition of the essential oils extracted by improved SFME and by the other methods.     

Comparative study of the chemical profiling,antioxidant and antimicrobial activities of essential oils of different parts of Thymus willdenowii Boiss & Reut

The analysis of Thymus willdenowii Boiss &; Reut essential oils (TW EOs) shows 33 components accounting for (96.3–97.7%) of all identified. The main constituents of TW EOs were thymol (35.5–47.3%), p-cymene (13.9–23.8%), γ-terpinene (8.9–20.3%). The antioxidant assays revealed that all TW EOs tested showed strong activities, the antimicrobial effect of TW EOs has been tested against isolated clinical strains of Proteus mirabilis (ATCC 35659), Escherichia coli (ATCC 25922), Candida albicans (ATCC 10231), Bacillus cereus (ATCC 10876), and Aspergillus brasilliensis (ATCC 16404). The antimicrobial test indicates that TW EOs show an inhibition effect against all the tested bacteria with a MIC of 6.9 to 27.6 μg/mL^?1. These results proving that the essential oils extracted from Thymus willdenowii Boiss &; Reut may be a new potential source of natural antimicrobial applied in pharmaceutical and food industries.     

Composition of three essential oils, and their mammalian cell toxicity and antimycobacterial activity against drug resistant-tuberculosis and nontuberculous mycobacteria strains

Tuberculosis (TB) is the most ancient epidemic disease in the world and a serious opportunistic disease in HIV/AIDS patients. The increase in multidrug resistant Mycobacterium tuberculosis (MDR-TB, XDR-TB) demands the search for novel antimycobacterial drugs. Essential oils (EOs) have been widely used in medicine and some EOs and their major components have been shown to be active against M. tuberculosis. The aim of this work was to evaluate the antimycobacterial and cell toxicity activities of three EOs derived from Salvia aratocensis, Turnera diffusa and Lippia americana, aromatics plants collected in Colombia. The EOs were isolated by hydrodistillation and analyzed by GC/MS techniques. The EOs were tested against 15 Mycobacterium spp using a colorimetric macrodilution method and against mammalian Vero and THP-1 cells by MTT. The activity was expressed as minimal concentration in microg/mL that inhibits growth, and the concentration that is cytotoxic for 50 or 90% of the cells (CC50 and CC90). The major components were epi-alpha-cadinol (20.1%) and 1,10-di-epi-cubenol (14.2%) for Salvia aratocensis; drima-7,9(11)-diene (22.9%) and viridiflorene (6.6%) for Turnera diffusa; and germacrene D (15.4%) and trans-beta- caryophyllene (11.3%) for Lippia americana. The most active EO was obtained from S. aratocensis, with MIC values below 125 microg mL(-1) for M. tuberculosis Beijing genotype strains, and 200 to 500 microg mL(-1) for nontuberculous mycobacterial strains. The EOs were either partially or non toxic to Vero and THP-1 mammalian cells with CC50 values from 30 to > 100 microg mL(-1), and a CC90 > 100 microg mL(-1). The EOs obtained from the three aromatic Colombian plants are an important source of potential compounds against TB. Future studies using the major EO components are recommended.     

Solvent-free microwave extraction of essential oil from aromatic herbs: comparison with conventional hydro-distillation

Solvent-free microwave extraction (SFME) is a combination of microwave heating and dry distillation, performed at atmospheric pressure without added any solvent or water. Isolation and concentration of volatile compounds are performed by a single stage. SFME has been compared with a conventional technique, hydro-distillation (HD), for the extraction of essential oil from three aromatic herbs: basil (Ocimum basilicum L.), garden mint (Mentha crispa L.), and thyme (Thymus vulgaris L.). The essential oils extracted by SFME for 30min were quantitatively (yield) and qualitatively (aromatic profile) similar to those obtained by conventional hydro-distillation for 4.5 h. The SFME method yields an essential oil with higher amounts of more valuable oxygenated compounds, and allows substantial savings of costs, in terms of time, energy and plant material. SFME is a green technology and appears as a good alternative for the extraction of essential oils from aromatic plants.     

Improved solvent-free microwave extraction of essential oil from dried Cuminum cyminum L. and Zanthoxylum bungeanum Maxim

Solvent-free microwave extraction (SFME) is a recently developed green technique which is performed in atmospheric conditions without adding any solvent or water. SFME has already been applied to extraction of essential oil from fresh plant materials or dried materials prior moistened. The essential oil is evaporated by the in situ water in the plant materials. In this paper, it was observed that an improved SFME, in which a kind of microwave absorption solid medium, such as carbonyl iron powders (CIP), was added and mixed with the sample, can be applied to extraction of essential oil from the dried plant materials without any pretreatment. Because the microwave absorption capacity of CIP is much better than that of water, the extraction time while using the improved SFME is no more than 30 min using a microwave power of 85 W. Compared to the conventional SFME, the advantages of improved SFME were to speed up the extraction rate and need no pretreatment. Improved SFME has been compared with conventional SFME, microwave-assisted hydrodistillation (MAHD) and conventional hydrodistillation (HD) for the extraction of essential oil from dried Cuminum cyminum L. and Zanthoxylum bungeanum Maxim. By using GC-MS system the compositions of essential oil extracted by applying four kinds of extraction methods were identified. There was no obvious difference in the quality of essential oils obtained by the four kinds of extraction methods.     

Sub-inhibitory stress with essential oil affects enterotoxins production and essential oil susceptibility in Staphylococcus aureus

Fourteen wild strains of Staphylococcus aureus positive for gene sea were tested for enterotoxins production and the minimum inhibitory concentration of Leptospermum scoparium, Origanum majorana, Origanum vulgare, Satureja montana and Thymus vulgaris essential oils (EOs) were determined. After this trial, bacteria stressed with sub-inhibitory concentration of each EO were tested for enterotoxins production by an immunoenzymatic assay and resistance to the same EO. Oregano oil exhibited the highest antibacterial activity followed by manuka and thyme oils. After the exposure to a sub-inhibitory concentration of EOs, strains displayed an increased sensitivity in more than 95% of the cases. After treatment with oregano and marjoram EOs, few strains showed a modified enterotoxins production, while 43% of the strains were no longer able to produce enterotoxins after treatment with manuka EO. The results obtained in this study highlight that exposure to sub-inhibitory concentration of EO modifies strains enterotoxins production and EOs susceptibility profile.     

Influence of growth phase on the essential oil composition and antimicrobial activities of Satureja hortensis

The variations in quantity and quality of essential oils (EOs) from the aerial parts of cultivated Satureja hortensis were determined at different stages of harvesting. The EOs of air-dried samples were obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC/MS). The antimicrobial activity of the EOs was investigated by broth microdilution methods. The amount of EOs (w/w, %) were 2.3, 2.5, 2.0, and 1.8% at floral budding, full flowering, immature fruit, and ripened fruit stages, respectively. gamma-Terpinene was the major compound of the EO at all developmental stages, except the ripened fruit stage when it was replaced by carvacrol (46.4%). The EOs exhibited strong antibacterial activities against the tested bacteria. Moreover, the EOs either inhibited or killed the examined yeasts at concentrations ranging from 0.03-8.0 microL/mL. Considering the wide range of antimicrobial activities of the examined EOs, they might have potential to be used in the management of infective agents.     

Antimicrobial activity and phytochemical analysis of crude extracts and essential oils from medicinal plants

We aimed to establish a phytochemical analysis of the crude extracts and performed GC-MS of the essential oils (EOs) of Eugenia uniflora L. (Myrtaceae) and Asteraceae species Baccharis dracunculifolia DC, Matricaria chamomilla L. and Vernonia polyanthes Less, as well as determining their antimicrobial activity. Establishment of the minimal inhibitory concentrations of the crude extracts and EOs against 16 Staphylococcus aureus and 16 Escherichia coli strains from human specimens was carried out using the dilution method in Mueller-Hinton agar. Some phenolic compounds with antimicrobial properties were established, and all EOs had a higher antimicrobial activity than the extracts. Matricaria chamomilla extract and E. uniflora EO were efficient against S. aureus strains, while E. uniflora and V. polyanthes extracts and V. polyanthes EO showed the best antimicrobial activity against E. coli strains. Staphylococcus aureus strains were more susceptible to the tested plant products than E. coli, but all natural products promoted antimicrobial growth inhibition.     

Effects of ascorbic acid on the physiochemical,rheological, and antioxidant properties of citrus essential oil-based emulsion stabilized by pectin

The present study was conducted to enhance the peel of Citrus sinensis (sweet orange) by using their essential oils (EOs) as a potential source of natural bioactive molecules. EOs were obtained by hydrodistillation and their chemical profile was determined through GC-MS analysis. O/W EO emulsions were prepared using pectin as biopolymer emulsifier at different proportions, including different amounts of ascorbic acid (0, 0.5, and 1% w/w). The effect of pectin and ascorbic acid concentrations on the stability and rheological behavior of emulsions was investigated. It was found that adding ascorbic acid to the appropriate concentration of pectin enhances the interfacial membranes surrounding the oil droplets and decreases the droplet sizes. As a result both the viscoelastic modules and the resulting viscosity of emulsions increase leading to an improvement of their stability. Antioxidant activity of orange EO emulsion in combination with ascorbic acid was found significantly higher than that without ascorbic acid, and higher than that of individual components. Overall, this study would be helpful in developing more effectives systems with promising physical and antioxidant characteristics for the preservation of foods.     

Phytochemical Profile,Antimicrobial, Cytotoxic,and Antioxidant Activities of Fresh and Air-Dried Satureja nabateorum Essential Oils

Satureja nabateorum (Danin and Hedge) Bräuchler is a perennial herb in the Lamiaceae family that was discovered and classified in 1998. This green herb is restricted to the mountains overlooking the Dead Sea, specifically in Jordan’s southwest, the Edom mountains, and the Tubas mountains in Palestine. Gas chromatography-mass spectrometry (GC-MS) analysis of essential oil (EO) of air-dried and fresh S. nabateorum resulted in the identification of 30 and 42 phytochemicals accounting for 99.56 and 98.64% of the EO, respectively. Thymol (46.07 ± 1.1 and 40.64 ± 1.21%) was the major compound, followed by its biosynthetic precursors γ-terpinene (21.15 ± 1.05% and 20.65 ± 1.12%), and p-cymene (15.02 ± 1.02% and 11.51 ± 0.97%), respectively. Microdilution assay was used to evaluate the antimicrobial property of EOs against Staphylococcus aureus (ATCC 25923), clinical isolate Methicillin-Resistant Staphylococcus aureus (MRSA), Enterococcus faecium (ATCC 700221) Klebsiella pneumoniae (ATCC 13883), Proteus vulgaris (ATCC 700221), Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853) and Candida albicans (ATCC-90028). With a MIC of 0.135 μg/mL, the EOs has the most potent antibacterial action against K. pneumonia. Both EOs display good antifungal efficacy against C. albicans, with a MIC value of 0.75 μg/mL, which was better than that of Fluconazole’s (positive control, MIC = 1.56 μg/mL). The antioxidant capacity of EOs extracted from air-dried and fresh S. nabateorum was determined using the DPPH assay, with IC₅₀ values of 4.78 ± 0.41 and 5.37 ± 0.40 μg/mL, respectively. The tested EOs showed significant cytotoxicity against Hela, HepG2, and COLO-205 cells, with IC₅₀ values ranging from 82 ± 0.98 to 256 ± 1.95 μg/mL. The current work shows there is a possibility to use the S. nabateorum EOs for various applications.     

Effect of Extraction Methods on Polyphenols,Flavonoids, Mineral Elements,and Biological Activities of Essential Oil and Extracts of Mentha pulegium L.

Our study evaluated the in vitro antioxidant properties, antibacterial and antifungal activities, anti-inflammatory properties, and chemical composition of the essential oils (EOs), total phenol, and total flavonoid of wild Mentha pulegium L. This study also determined the mineral (nutritional and toxic) elements in the plant. The EOs were extracted using three techniques—hydro distillation (HD), steam distillation (SD), and microwave-assisted distillation (MAD)—and were analyzed using chromatography coupled with flame ionization (GC-FID) and gas chromatography attached with mass spectrometry detector (GC-MS). The antioxidant effects of the EOs were tested with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), while the antibacterial and antifungal activities of the EO and methanolic extract were tested using Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. Twenty-six compounds were identified in the essential oil, representing 97.73% of the total oil, with 0.202% yield. The major components were pulegone (74.81%), menthone (13.01%) and piperitone (3.82%). Twenty-one elements, including macro- and micro-elements (Ba, Br, Ca, Cl, Co, Cr, Cs, Eu, Fe, K, Mg, Mn, Mo, Na, Rb, Sb, Sc, Sr, Th, U and Zn), were detected using neutron activation analysis (INAA) and inductively coupled plasma optical emission spectrometry (ICP-OES), with the concentration of mineral element close to the FAO recommendation. The results show that the EOs and extracts from Mentha pulegium L. had significant antimicrobial activities against the microorganisms, including five human pathogenic bacteria, one yeast (Candida albicans), and one phytopathogenic fungi. The in vivo anti-inflammatory activities of the leaf extracts were confirmed. The results indicate that the EOs and extracts from Mentha pulegium L. have promising applications in the pharmaceutical industries, clinical applications, and in medical research.     

Comparative study of chemical composition,antibacterial and antioxidant activity of essential oils isolated from the seeds of Amomum subulatum by using microwave extraction and hydro-distillation methods

Microwave assisted hydro-distillation (MAHD) and conventional hydro-distillation (HD) techniques were compared in the extraction of essential oils from Amomum subulatum seeds. The time required for MAHD method (70 ​min) is lesser than that for HD method (4 ​h). There is a slight increase in the yield of extracted oil in MAHD method (3.35%) compared to HD (3%). Gas chromatography–mass spectrometry GC-MS results show that MAHD extracted essential oil was wealthier in oxygenated compounds. 1, 8-Cineole was found to be a major compound in case of both the essential oil, followed by α-pinene. In MAHD the percentage of the major oxygenated monoterpene (1, 8- cineol) slightly increases from 88% to 89% as compared to hydrodistillation. Contrarily to this, the percentage of monoterpene hydrocarbon was decreased in MAHD than HD extracted oil. MAHD and HD extracted oils show good antibacterial activities against gram-negative and gram-positive bacteria. MAHD extracted oil shows better antibacterial activity than HD extracted against both gram positive and gram-negative bacteria. 2, 2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging antioxidant activities show that MAHD extract has better inhibition percentage than HD extract, and the half-maximal inhibitory concentration IC50 value of MAHD was less than HD extracted oil.     

Nematicidal Activity of Essential Oil from Lavandin (Lavandula × intermedia Emeric ex Loisel.) as Related to Chemical Profile

Essential oils (EOs) from lavandin are known for a large spectrum of biological properties but poorly and contrastingly documented for their activity against phytoparasitic nematodes. This study investigated the toxicity of EOs from three different lavandin cultivars, Abrialis, Rinaldi Cerioni, and Sumiens, either to juveniles (J2) and eggs of the root-knot nematode Meloidogyne incognita and to infective stages of the lesion nematode Pratylenchus vulnus. The suppressive activity of treatments with EOs from the three lavandin cultivars in soil infested by M. incognita was also investigated in a greenhouse experiment on potted tomato. The compositional profiles of tested EOs were also analyzed by GC-FID and GC-MS. Linalool was the major component of all the three EOs, as accounting for about 66%, 48%, and 40% of total EO from cv Rinaldi Cerioni, Sumiens, and Abrialis, respectively. Linalool acetate was the second most abundant compound in the EOs from cv Abrialis (18.3%) and Sumiens (14.9%), while significant amounts of camphor (11.5%) and 1,8-cineole (12.1%) were detected in cv Rinaldi Cerioni and Sumiens EOs, respectively. The mortality of M. incognita J2 peaked 82.0%, 95.8%, and 89.8% after a 24 h treatment with 100 mg·mL⁻¹ solutions of cv Abrialis, Rinaldi Cerioni, and Sumiens EOs, respectively. Infective specimens of P. vulnus were largely more sensitive than M. incognita J2, as there were peak mortality rates of 65.5%, 67.7%, and 75.7% after 4 h of exposure to Abrialis, Rinaldi Cerioni, and Sumiens EO, respectively. All three lavandin EOs significantly affected also M. incognita egg hatchability, which reduced to 43.6% after a 48 h egg mass exposure to a 100 µg·mL⁻¹ solution of cv Rinaldi Cerioni EO. Soil treatments with the three lavandin EOs strongly reduced, according to a dose–effect relationship, density of M. incognita eggs, and J2 both on tomato roots and in soil, as well as significantly reduced gall formation on tomato roots. Finally, almost all soil treatments with the lavandin EOs also resulted in a positive impact on tomato plant growth.     

Chemical Composition and Antioxidant Activity of Essential Oils from Leaves of Two Specimens of Eugenia florida DC.

Eugenia florida DC. belongs to the Myrtaceae family, which is present in almost all of Brazil. This species is popularly known as pitanga-preta or guamirim and is used in folk medicine to treat gastrointestinal problems. In this study, two specimens of Eugenia florida (Efl) were collected in different areas of the same region. Specimen A (EflA) was collected in an area of secondary forest (capoeira), while specimen B (EflB) was collected in a floodplain area. The essential oils (EOs) were extracted from both specimens of Eugenia florida by means of hydrodistillation. Gas chromatography coupled to mass spectrometry (GC/MS) was used to identify the volatile compounds present, and the antioxidant capacity of the EOs was determined by antioxidant capacity (AC-DPPH) and the Trolox equivalent antioxidant (TEAC) assay. For E. florida, limonene (11.98%), spathulenol (10.94%) and α-pinene (5.21%) were identified as the main compounds of the EO extracted from sample A, while sample B comprised selina-3,11-dien-6α-ol (12.03%), eremoligenol (11.0%) and γ-elemene (10.70%). This difference in chemical composition impacted the antioxidant activity of the EOs between the studied samples, especially in sample B of E. florida. This study is the first to report on the antioxidant activity of Eugenia florida DC. essential oils.     

Antibacterial Activity of Thymus vulgaris L. Essential Oil Vapours and Their GC/MS Analysis Using Solid-Phase Microextraction and Syringe Headspace Sampling Techniques

While the inhalation of Thymus vulgaris L. essential oil (EO) is commonly approved for the treatment of mild respiratory infections, there is still a lack of data regarding the antimicrobial activity and chemical composition of its vapours. The antibacterial activity of the three T. vulgaris EOs against respiratory pathogens, including Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pyogenes, was assessed in both liquid and vapour phases using the broth microdilution volatilisation (BMV) method. With the aim of optimising a protocol for the characterisation of EO vapours, their chemical profiles were determined using two headspace sampling techniques coupled with GC/MS: solid-phase microextraction (HS-SPME) and syringe headspace sampling technique (HS-GTS). All EO sample vapours exhibited antibacterial activity with minimum inhibitory concentrations (MIC) ranging from 512 to 1024 μg/mL. According to the sampling technique used, results showed a different distribution of volatile compounds. Notably, thymol was found in lower amounts in the headspace—peak percentage areas below 5.27% (HS-SPME) and 0.60% (HS-GTS)—than in EOs (max. 48.65%), suggesting that its antimicrobial effect is higher in vapour. Furthermore, both headspace sampling techniques were proved to be complementary for the analysis of EO vapours, whereas HS-SPME yielded more accurate qualitative results and HS-GTS proved a better technique for quantitative analysis.     

Cell enumeration and visualisation by transmission electron microscopy of Lactobacillus rhamnosus treated with cinnamon (Cinnamomum zeylanicum B.) essential oil

The use of essential oils (EOs) in functional foods containing probiotic microorganisms must consider the antimicrobial activity of these oils against beneficial bacteria such as Lactobacillus rhamnosus. This study aimed to evaluate the sensitivity of L. rhamnosus cultures treated with cinnamon EO through viable cell counts and visualisation by transmission electron microscopy. Cinnamon EO at a concentration of 0.04% had a bacteriostatic activity after 2?h of incubation. Although slight alterations were detected in the cell structure, this concentration was considered to be bactericidal, since it led to a significant reduction in cell numbers after 24?h. On the other hand, cinnamon EO at a 1.00% concentration decreased cell counts by 3 log units after 2?h incubation and no viable cell count was detected after 24?h. Transmission electron microscopy indicated that cells treated with 1.00% cinnamon EO were severely damaged and presented cell membrane disruption and cytoplasmic leakage.