Biosynthesis of essential oils in aromatic plants: A review

In aromatic plants species, biosynthesis of essential oils occurs through two complex natural biochemical pathways involving different enzymatic reactions. Isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP) are the universal precursors of essential oil biosynthesis and are produced by the cytosolic enzymatic MVA (mevalonic acid) pathway or by plastidic and enzymatic 1-deoxy-d-xylolose-5-phosphate (DXP) pathway, also called the 2-C-methylerythritol-4-phosphate (MEP) pathway. In the particular plant cell part, prenyl diphosphate synthases condense isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) further to form prenyl diphosphates, which are used as substrates for geranyl diphosphate (GPP; C₁₀) or for fernesyl diphosphate (FPP; C₁₅). Essential oils are final terpenoid products and are formed by a huge group of enzymes known as terpene synthases (TPS). Essential oils are important secondary metabolites of plants and have been used not only in different industries but also in ethnobotanical medicines for centuries. Hence, considerable research has been undertaken to understand the essential oil biosynthetic pathways. This review will be a valuable source of information in the field of natural products, as we give detailed insights about biosynthesis of essential oils in plants and thus indicate also new unexplored horizons for further research.     

Composition and biological activities of essential oils from four Heracleum species

The composition of essential oils from aerial parts of Heracleum persicum, a widely used medicinal plant, and three other Heracleum species growing wild in Iran were analysed by GC and GC–MS. Myristicin (53.6%), (E)-anethole (25.0%), hexyl butanoate (29.7%) and elemicin (41.1%) were the major compounds of Heracleum pastinacifolium, H. persicum, Heracleum rechingeri and Heracleum transcaucasicum, respectively. Cytotoxic activity assessed on three human cancer cell lines (HeLa, LS180 and Raji), showed that essential oils from H. transcaucasicum (IC₅₀ values; 0.362–0.594 mg/ml) followed by H. pastinacifolium (0.497–1.398 mg/ml) had moderate antitumoral activities. In the DPPH radical scavenging assay, H. pastinacifolium and H. persicum oils showed the highest activities with IC₅₀ values of 7.3 and 7.4 mg/ml, respectively. Antioxidant activity correlated well with the total phenolic content of the oils. None of the essential oils showed significant antimicrobial activities.     

In vitro antimicrobial activity of essential oils from aromatic plants against selected foodborne pathogens

The purpose of this study was to examine the effectiveness of selected essential oils for the control of growth and survival of pathogenic microorganisms of significant importance in food hygiene and to determine whether the antimicrobial effect was due to the major compounds of the oils. MIC and MBC were determined by the tube dilution method. Essential oils from Thymus vulgaris from Spain and France, Salvia sclarea, Salvia officinalis, Salvia lavandulifolia, Lavandula latifolia, Lavandula angustifolia, three hybrids of Lavandula latifolia x Lavandula angustifolia (Lavandin 'Super', Lavandin 'Abrialis', and Lavandin 'Grosso'), Rosmarinus officinalis, Hissopus officinalis, and Satureja montana were evaluated. Inhibition ranged from the strong activity of Satureja montana and Thymus vulgaris (France) to no inhibition with Salvia sclarea and Hissopus officinalis for each of the test strains: Salmonella Enteritidis, Salmonella Typhimurium, Escherichia coli O157:H7, Yersinia enterocolitica, Shigella flexneri, Listeria monocytogenes serovar 4b, and Staphylococcus aureus. Because some of the essential oils were highly inhibitory in small quantities to selected pathogenic microorganisms, they may provide alternatives to conventional antimicrobial additives in foods.     

Evaluation of five essential oils from aromatic plants of Cameroon for controlling food spoilage and mycotoxin producing fungi

Five essential oils (EO) extracted from Cymbopogon citratus, Monodora myristica, Ocimum gratissimum, Thymus vulgaris and Zingiber officinale were investigated for their inhibitory effect against three food spoilage and mycotoxin producing fungi, Fusarium moniliforme, Aspergillus flavus and Aspergillus fumigatus. Five strains of each fungus were tested. The agar dilution technique was used to determine the inhibitory effect of each EO on the radial growth of the fungus, and a dose response was recorded. The EO from O. gratissimum, T. vulgaris and C. citratus were the most effective and prevented conidial germination and the growth of all three fungi on corn meal agar at 800, 1000 and 1200 ppm, respectively. Moderate activity was observed for the EO from Z. officinale between 800 and 2500 ppm, while the EO from M. myristica was less inhibitory. These effects against food spoilage and mycotoxin producing fungi indicated the possible ability of each essential oil as a food preservative. A comparative test on the preservative ability of the EO from O. gratissimum and potassium sorbate against A. flavus at pH 3.0 and 4.5 showed that the EO remained stable at both pH, whereas the efficacy of potassium sorbate was reduced at higher pH. We concluded that the EO from O. gratissimum is a potential food preservative with a pH dependent superiority against potassium sorbate, and these are novel scientific information.     

Unusual essential oils with aromatic properties

Summary The essential oil obtained by steam distillation of cinchona bark (Cinchona spp.,Rubiaceae family) — a plant well known for its pharmacological properties, also employed in the food industry, especially in making liqueurs - was investigated. The oil, of completely unknown chemical composition, was analyzed by GLC and GLC/MS after separation on a silica gel column, and one hundred components were identified. The presence of 2-hexyl-3-methylmaleic anhydride is rather unusual.

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Ungewöhnliche ätherische Öle mit aromatischen Eigenschaften. Die flüchtigen Aromastoffe der China-Rinde

Zusammenfassung Es wurde ätherisches Öl analysiert, das durch Wasserdampfdestillation von Chinarinde (Cinchona spp. derRubiaceae-Familie) gewonnen wurde. Diese Pflanze ist aufgrund ihrer pharmakologischen Eigenschaften bekannt und wird auch in der Lebensmittelindustrie verwendet, ganz besonders für die Likör- und Magenbitterherstellung. Die chemische Zusammensetzung dieses Öls war unbekannt. Nach Abtrennung auf einer Kieselgelsäule wurden im Öl mit GLC und GLC/MS etwa 100 Verbindungen identifiziert. Das Vorhandensein von 2-Hexyl-3-methyl-maleinsäureanhydrid ist ziemlich ungewöhnlich.

     

Comparative study on volatile compounds from Tunisian and Sicilian monovarietal virgin olive oils

The effects of ripening degree of olives on volatile profile of monovarietal virgin olive oils (VOO) from Tunisian and Sicilian cultivars were investigated. Fruits obtained from Tunisia (Chétoui and Chemlali) and Italy (Nocellara del Belice, Biancolilla and Cerasuola) were picked at three different stages of ripeness and then immediately processed. Moreover, the changes in volatile composition were evaluated in Chétoui variety as a function of the irrigation regime versus the rain-fed control. Using headspace–solid-phase microextraction (HS–SPME) technique coupled to GC–MS and GC–FID, the volatile compounds of the monovarietal virgin olive oils were identified and quantitatively analyzed. The proportions of different classes of volatiles of oils showed significant differences throughout the maturity process. The results suggest that adding to the genetic factor; agronomic conditions affect the volatile formation and therefore the organoleptic properties of VOO.     

Comparative study of the essential oils of three Beilschmiedia species and their biological activities

This study was designed to examine the chemical compositions of the essential oils from three Beilschmiedia species and antioxidant, antimicrobial, antityrosinase, acetylcholinesterase and anti‐inflammatory activities. The essential oils of B. kunstleri, B. maingayi, B. penangiana gave β‐caryophyllene (10.6–12.1%), β‐eudesmol (17.5–24.1%) and δ‐cadinene (17.5–28.7%) as the most abundant components respectively. The bark oil of B. maingayi showed the highest activity in β‐carotene/linoleic acid (125.9%) and phenolic content (288.2 mg GA g^?1), while B. penangiana bark oil was found to have strong activity in DPPH (IC₅₀ 84.7 μg mL^?1) and ABTS (IC₅₀ 108.3 μg mL^?1). The essential oils of B. penangiana showed the best activity against Candida glabrata with MIC value 31.3 μg mL^?1. The bark oil of B. penangiana gave 82.5% tyrosinase inhibiton. The leaf oil of B. maingayi gave the highest inhibition in AChE (66.6%) and lipoxygenase (77.0%) assay. Our findings demonstrate that the essential oils have great potential for applications in pharmaceutical and food industries.     

Chemical composition,antioxidant and antibacterial activities of the essential oils isolated from Tunisian Thymus capitatus Hoff. et Link.

The chemical composition, antioxidant and antibacterial activities of essential oils isolated by hydrodistillation from the aerial parts of Tunisian Thymus capitatus Hoff. et Link. during the different phases of the plant development, and from different locations, were evaluated. The chemical composition was analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The main components of the essential oils were carvacrol (62–83%), p-cymene (5–17%), γ-terpinene (2–14%) and β-caryophyllene (1–4%). The antioxidant activity of the oils (100–1000 mg l⁻¹) was assessed by measurement of metal chelating activity, the reductive potential, the free radical scavenging (DPPH) and by the TBARS assay. The antioxidant activity was compared with that of synthetic antioxidants: butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Both the essential oils and BHA and BHT showed no metal chelating activity. Although with the other methodologies, there was a general increase in the antioxidant activity, with increasing oil concentration, maxima being obtained in the range of 500 and 1000 mg l⁻¹ for flowering and post-flowering phase oils. Major differences were obtained according to the methodology of antioxidant capacity evaluation. Antibacterial ability of Th. capitatus essential oils was tested by disc agar diffusion against Bacillus cereus, Salmonella sp., Listeria innocua, four different strains of Staphylococus aureus (C15, ATCC25923, CFSA-2) and a multi-resistant form of S. aureus (MRSA-2). Antibacterial properties were compared to synthetic antibiotics. Higher antibacterial activity was observed with the flowering and the post-flowering phase essential oils.     

Chemical composition and insecticidal properties of some aromatic herbs essential oils from Algeria

The biological effects on Sitophilus granarius were evaluated for three aromatic herbs essential oils: Foeniculum vulgare, Rosmarius officinalis and Lippia citriodora. Stored grain pests were currently controlled by chemical pesticides. This control method leads to pollution of the environment and intoxication of consumers. Essential oils of aromatic plants are more considered as good control alternative tools. Filter papers treated with 5, 50 and 500 μl of test oil were placed in the bottom cover of 1 l plastic bottle. The insects, 50 adults per bottle, were exposed for 1–5 days. Cumulative mortalities were determined 24 and 120 h after treatment. All treatments were replicated five times. The components of the essential oils were identified through GC and GC–MS. The identity of the constituents was confirmed and their relative proportions determined. The results indicate that these natural products may find potential application as useful, environmentally safe insect control and crop protectant agents.     

香橼精油体外抗氧化及其抑菌活性研究

为了研究香橼精油的抗氧化性及对细菌、酵母和霉菌的抑菌活性,本文采用体外抗氧化法和琼脂平板扩散法,研究香橼精油总还原力,清除DPPH自由基、·OH自由基和H2O2能力,以及对大肠杆菌、金黄色葡萄球菌、枯草芽孢杆菌、酿酒酵母、黑曲霉的抑制作用。结果表明:香橼精油的抗氧化能力与质量浓度呈正相关,对DPPH自由基、·OH自由基(IC50值为0.32 mg/m L)和H2O2(IC50值为148μg/m L)均有一定的清除能力。香橼精油对霉菌的抑制作用明显强于酵母与细菌,其中对黑曲霉的抑制效果最显著(25.39±1.12)mm,对金黄色葡萄球菌抑制最弱(14.04±1.35)mm。最小抑菌浓度在0.31~1.25 mg/m L,且在p H5~7范围内、温度80、115、121℃及一定时间紫外线照射(20、40 min)影响下,对大肠杆菌和酿酒酵母仍保持较强的抑制作用。      

Repellent activity of essential oils from seven aromatic plants grown in Colombia against Sitophilus zeamais Motschulsky (Coleoptera)

Essential oils isolated from seven aromatic plants grown in Colombia were analyzed by gas chromatography–mass spectrometry (GC–MS) and evaluated for repellent activity against Sitophilus zeamais (Coleoptera: Curculionidae) using the area preference method. Most oil components were oxygenated monoterpenoids or phenolic compounds. Six oils were repellent, with Lippia origanoides the most active. Eucalyptus citriodora and Tagetes lucida were also repellant at doses between 0.063 and 0.503 μL/cm².     

Insecticidal activities of aromatic plant extracts and essential oils against Sitophilus oryzae and Callosobruchus chinensis

Methanol extracts from 30 aromatic medicinal plant species and five essential oils were tested for their insecticidal activities against adults of Sitophilus oryzae (L.) and Callosobruchus chinensis (L.), using direct contact application and fumigation methods. Responses varied with plant material, insect species, and exposure time. In a test with a filter paper diffusion method at 3.5 mg/cm², potent insecticidal activity against both species was produced by an extract from Cinnamomum cassia bark, cinnamon (C. cassia) oil, horseradish (Cocholeria aroracia) oil, and mustard (Brassica juncea) oil within 1 day after treatment. Over 90% mortality at 3 or 4 days after treatment was achieved using extracts of Acorus calamus var. angustatus rhizome, Acorus gramineus rhizome, Illicium verum fruit, and Foeniculum vulgare fruit. An extract from Cinnamomum sieboldii root bark gave 100% mortality at 2 days after treatment. At 0.7 mg/cm², extracts from C. cassia, C. sieboldii, and F. vulgare as well as cinnamon oil, horseradish oil and mustard oil were highly effective against both species. In a fumigation test with S. oryzae adults, the oils described were much more effective in closed containers than in open ones, indicating that the insecticidal activity of the oils was attributable to fumigant action. The plant extracts and essential oils described could be useful for managing field populations of S. oryzae and C. chinensis.     

Fatty acid composition and biological activities of volatiles from fruits of two Tunisian olive cultivars

This study investigates volatile compounds, fatty acid composition and antioxidant, antibacterial and antifungal activities of fruits from two olive cultivars (Chemlali and Neb Jmel). Fatty acid profiles varied significantly between cultivars (cvs) where Neb Jmel seem to have higher contents of palmitic and oleic acids (16.4% and 66.4%, respectively) and lower of linoleic acid (9.4%). The volatile profile indicated the apparent difference between cvs. In fact, the main components detected in Chemlali cv. were (E,E)‐2,4‐decadienal (23.0%), (E,Z)‐2,4‐decadienal (14.9%) and nonanal (6.7%), while 3‐ethenylpyridine (15.5%), (E)‐2‐decenal (14.4%) and (E)‐2‐undecenal (7.0%) were the major components in Neb Jmel cv. Furthermore, these volatiles were subjected to screening for their possible antioxidant activities where volatiles from Neb Jmel fruits were found to be better. Results presented here may suggest that the volatiles fraction of two cultivars possess antimicrobial and antifungal activities.     

笃斯越橘果酱特征香气成分分析

以笃斯越橘果酱为研究对象,采用2种萃取方法结合气相色谱质谱联用技术同时辅以气相色谱嗅闻联用技术分离鉴定其香气成分。结果:液液萃取法鉴定出32种化合物,固相微萃取法鉴定出61种化合物,2种萃取方法检测出的香气化合物组分含量和种类存在差异,固相微萃取法更适合作为笃斯越橘果酱香气分析的萃取技术。根据固相微萃取果酱香气组分含量计算出各组分香气值,其中紫罗兰酮、(E,E)-2,4-壬二烯醛、正己醛、反-2-癸烯醛、苯乙醛等19种物质对笃斯越橘果酱香气有贡献,赋予产品花香、木香、脂肪味、水果香、坚果香、青草香、焦糖味等特征香气。结果表明,来源于果实的香气组分是构成笃斯越橘果酱典型风味的重要物质基础,应采用适度的热加工工艺以降低生产过程中该类组分的损失。     

Volatile compounds characterising Tunisian virgin olive oils: the influence of cultivar

In this work, the volatile profiles of four Tunisian virgin olive oils were established by headspace‐solid phase microextraction and gas chromatography, using flame ionisation and mass spectrometer detectors. More than eighty compounds were isolated and characterised, representing 97–99% of the total GC area. The main volatile compounds present in the oil samples were determined quantitatively, the major constituents were often aldehydes, particularly (E)‐2‐hexenal (48–90%). Significant differences in the content of volatile constituents were observed. These quantitative differences were used to distinguish between virgin olive oils from different varieties.     

Antimicrobial activity of essential oils from plants against selected pathogenic and saprophytic microorganisms.

The beneficial health effects of extracts from many types of plants that are used as seasoning agents in foods and beverages have been claimed for centuries. The purpose of this study was to examine the effectiveness of selected herb and spice essential oils for control of growth and survival of microorganisms. Inhibition of growth was tested by the paper disc agar diffusion method. Antibiotic susceptibility discs were used as control. Minimum lethal concentration (MLC) was determined by the tube dilution method. Essential oils from anise, angelica, basil, carrot, celery, cardamom, coriander, dill weed, fennel, oregano, parsley, and rosemary were evaluated. Inhibition ranged from complete with oregano to no inhibition with carrot oil for each of the test strains that included: Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O:157:H7, Yersinia enterocolitica, Pseudomonas aeruginosa, Lactobacillus plantarum, Aspergillus niger, Geotrichum, and Rhodotorula. Oregano essential oil showed the greatest inhibition (zone, > or = 70 to 80 mm) (MLC, approximately 8 ppm). Coriander and basil were also highly inhibitory (MLC, approximately 25 to 50 ppm) to E. coli O:157:H7 and to the other bacteria and fungi tested. Anise oil was not particularly inhibitory to bacteria (inhibition zone, approximately 25 mm); however, anise oil was highly inhibitory to molds. Because some of the herbal and spice essential oils are highly inhibitory to selected pathogenic and spoilage microorganisms, they may provide alternatives and supplements to conventional antimicrobial additives in foods.     

Profiles of volatile compounds from some monovarietal Tunisian virgin olive oils. Comparison with French PDO

The volatile profiles of seven Tunisian and four French virgin olive oils were established by solid phase micro-extraction (SPME) and gas chromatography (GC), using flame ionisation and mass spectrometer detectors. Eighty-six compounds were identified and characterized, representing 97.4–99.9% of the total GC area. (E)-2-hexenal, the main compound extracted by SPME, characterized the olive oil headspace for approximately 90% of the oils examined. Significant differences in the proportions of volatile constituents from oils of different varieties were detected. The results demonstrated that the accumulation of the different metabolites in the oils obtained from the various cultivars was strictly connected with the varietal parameters on the basis of the enzyme differences genetically determined. This feature made possible the differentiation of the examined cultivars on the basis of the percent of each metabolite.     

植物挥发油抗氧化活性的研究

采用脂质过氧化方法和1,1-diphenyl-2-picry1hydrazy1(DPPH)方法检测了桂丁、花椒2种挥发油的抗氧化活性.目前检测物质抗氧化活性的方法很多,但大多数是在水相体系,而脂质过氧化方法和DPPH方法中的脂质体系和乙醇体系比较适合于检测挥发油的抗氧化活性,且研究发现2种挥发油的抗自由基活性强于抗氧化活性.     

Composition and antioxidant activity of essential oils from Oregano plants grown wild in Greece

In this study, four samples of essential oils obtained from plant species with a wide distribution in Greece and economic importance for the world-wide spice market and also carvacrol and thymol were tested for their possible antioxidant activity. The four plant species wereOriganum vulgare subsp.hirtum, O. onites, Coridothymus capitatus andSatureja thymbra. The essential oils were chemically characterised by gas chromatography-ion trap detection. All the essential oils examined and also carvacrol and thymol were found to have antioxidant activity when tested on TLC plates and by measuring peroxide values of lard stored at 35° C. The results indicate that the antioxidant effect may be related to the presence of carvacrol and thymol in essential oils.     

Correlative metabolite profiling approach to understand antioxidant and antimicrobial activities from citrus essential oils

The objective of this study was to investigate the chemical composition of the essential oils from citrus species, as well as their antioxidant and antimicrobial activities. By gas chromatography-mass spectrometry, we identified thirty-seven metabolites and a range of unique compounds, contributing to the discrimination of the species. Different biological potentialities were detected depending on the species supported the significant effect of the genetic factor. C. aurantium and C. limon exhibited the highest antioxidant activities which make them a potential source of natural preservative. C. limon exhibited the highest antibacterial activities and C. reticulata the highest antifungal activities. Essential oils extracted from these agro-wastes could serve as natural food preservatives to prevent food pathogens and then extending the shelf life. A set of potential metabolites could be implicated in the observed biological activity, underlying that the antimicrobial activity is a complex trait.