Biosynthesis of essential oils in aromatic plants: A review

Ginger essential oil-based microencapsulation as an efficient delivery system for the improvement of Jujube (Ziziphus jujuba Mill.) fruit quality

Microencapsulation of Zingiber officinale essential oil (EO) in polysaccharide, chitosan (CH) and sodium carboxymethyl cellulose (CMC) based on the electrostatic interaction between charged polysaccharides at pH 3.0 in dual delivery system. Ratio variations of CH and CMC in microencapsulation were studied at 1:2, 2:1 and 1:1. This study aimed to evaluate the influence of the encapsulating materials combination on freeze-dried EO powders and to present the mechanisms for loading and releasing EO involved in the preparation of CH/CMC microcapsules. The spectroscopy analysis, physical properties, microstructural, encapsulation efficiency and EO release behavior in obtained EO microparticles were evaluated by using the analysis of fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas chromatography mass spectrometry (GC-MS), respectively. Afterwards, the above prepared microcapsules were applied on winter jujube fruit (Ziziphus jujuba Mill.) preservation. Results demonstrated that both the microstructure and stability of microencapsulation were improved in delivery system loading with CH and CMC (1:1) with the encapsulation efficiency of 88.50%, compared to other ratios of CH and CMC (1:2 and 2:1). Furthermore, the microencapsulation had a capacity to control and reduce the EO release, therefore the morphological and sensory quality of jujube fruits in EO delivery system during storage was enhanced significantly (P < 0.05), in comparison to control. Results revealed that the microparticles produced with CH and CMC (1:1) was considered to present better characteristics of microstructure, encapsulation efficiency, as well as to maintain higher nutritional quality for jujube fruit. Thus, EO microencapsulation loaded in CH/CMC-based dual delivery system has potential application and developmental value prospects in food industries.

Quorum sensing system: Target to control the spread of bacterial infections

Quorum Sensing (QS) systems regulate the gene expression of different types of virulence factors in accordance with the cell population density. A literature search was performed, including electronic databases such as MEDLINE/PubMed, SciELO, and LILACS, as well as other databases not indexed, such as Google Scholar. The search was conducted between July 2018 and April 2019, through online research. Antimicrobial resistance is one of the biggest threats to global health and the dissemination of resistant microbes in the environment is a major public health problem. Therefore, it is important to develop new therapies to control the spread of resistant bacteria to humans. Thus, interference in the chemical signal (autoinducers) of the QS system has been postulated as a good alternative, technically known as "Quorum Quenching" or QS inhibitors. Inhibition of QS signaling is not intended to kill the microorganism, but to block the expression of the target genes, making the cells less virulent and more vulnerable to host immune response. Anti-virulence therapy by agents that interfere with this system in pathogenic bacteria is a well-studied strategy, including medicinal plants and their bioactive constituents, and presents good prospects. This review aims to provide an overview of the QS system in bacteria and describe the main inhibitors of the system.

The essential oil composition of selected Hemerocallis cultivars and their biological activity

The horticultural cultivars of Hemerocallis (daylily) have been used to treat diseases such as insomnia, inflammation and depression, and also as a vegetable in eastern Asia. Taking into consideration the fact, that the volatile compounds in Hemerocallis cultivars have not been investigated to date, we decided to study the composition of the essential oils (EOs) from the aerial parts of ten varieties collecting in Poland. EOs, obtained by hydrodistillation, were analyzed by GC/MS method that resulted in identification of 23-36 volatile compounds comprising 89.5%–96.3% of the total amount. The essential oils differed in their composition and they can be classified into three groups. The antibacterial and antioxidant activities of EOs were also evaluated. Gram-negative strains were most strongly inhibited by all tested oils. Two model systems have been used for the antioxidant efficacy, 2,2-diphenyl-1-picryl-hydrazyl (DPPH•) andβ-carotene bleaching assays. The essential oils with the high presence of oxygenated monoterpenes and monoterpene hydrocarbons showed higher antioxidant activity. The chemical composition of EOs of Hemerocallis cultivars and their biological activity is reported for the first time. Thus, the findings presented here suggest that the aerial parts of Hemerocallis cultivars may be candidates for the development of new phytomedicine.

Chemical Composition of Essential Oil from Flower Heads of Arnica Chamissonis Less. under a Nitrogen Impact

Chamisso arnica (Arnica chamissonis Less.) is a valuable plant species used in the pharmaceutical industry due to the content of many pharmacologically active substances and the similarity of its chemical composition to that of Arnica montana—a medicinal plant commonly used in pharmacy and cosmetics. The similarity of the two plant species implies that chamisso arnica can be a pharmaceutical substitute for the mountain arnica, i.e., an endangered and endemic plant species in Europe. Chamisso arnica extracts exhibit anti-inflammatory and antiradical activity and possesses high antioxidant properties that might be helpful in preventing or delaying the progress of free radical dependent diseases. The attributes of A. chamissonis are mainly related to the content and chemical composition of essential oil. Therefore, the objective of this study was to characterize the chemical composition of essential oil derived from A. chamissonis flower heads under a nitrogen impact. The experiment was performed on experimental fields in mid-eastern Poland on two soil types (sandy and loamy soils). The nitrogen fertilizer was applied as ammonium sulfate (control, 30, 60, 90, and 120 kg N ha⁻¹). Collection of flower heads was carried out in the full flowering phase, which was characterized by the highest content of essential oil. The chemical composition of essential oil was examined using GC-MS. Among the 75 ingredients of the volatile oil of chamisso arnica flower heads, alpha-pinene, cumene, p-cymene, germacrene D, spathulenol, decanal, caryophyllene oxide, beta-pinene, and benzene acetaldehyde were present at relatively high levels. Both the nitrogen application and the soil type had an effect on the oil concentration and the yield of the main constituents (alpha-pinene and germacrene D) with pharmacological value. Different levels of nitrogen application could be considered as a relevant way to modify the chemical composition and to increase the essential oil production.

Characterisation and screening of antimicrobial essential oil components against clinically important antibiotic-resistant bacteria using thin layer chromatography-direct bioautography hyphenated with GC-MS, LC-MS and NMR

INTRODUCTION

The antimicrobial activity of many essential oils (EOs) is well established, indicating that EOs may be a source of compounds for antimicrobial drug development. Thin layer chromatography-direct bioautography (TLC-DB) can quickly identify antimicrobial components in complex mixtures and can be applied to the screening of EOs for lead compounds.

OBJECTIVES

This study aimed to identify antimicrobial components of oregano, rosewood and cumin EOs against antibiotic-sensitive and -resistant bacteria using TLC-DB and a multi-faceted approach of GC-MS, LC-MS and NMR techniques to characterise bioactive compounds. The study also aimed to quantify the antimicrobial activity of bioactive compounds in order to evaluate their potential for the development of therapies against antibiotic-resistant bacteria.

MATERIALS AND METHODS

EOs were eluted on TLC plates and sprayed with a suspension of Staphylococcus aureus, Enterococcus faecium, Escherichia coli or Pseudomonas aeruginosa (antibiotic-sensitive and -resistant isolates). Zones of inhibition, visualised with iodonitrotetrazolium chloride, were subject to GC-MS, LC-MS and NMR to characterise the bioactive compounds.

RESULTS

Seven compounds were identified from the three EOs using GC-MS, while LC-MS and NMR failed to detect the presence of any further non-volatile or heat labile compounds. Carvacrol was most antimicrobial compound identified, with minimum inhibitory concentrations ranging 0.99-31.62 mM.

CONCLUSION

The identified antimicrobial compounds present in oregano, rosewood and cumin EOs including carvacrol may be candidates for the development of novel antimicrobial therapies against antibiotic-resistant bacteria.

RNA-Seq in the discovery of a sparsely expressed scent-determining monoterpene synthase in lavender (Lavandula)

Using RNA-Seq, we cloned and characterized a unique monoterpene synthase responsible for the formation of a scent-determining S-linalool constituent of lavender oils from Lavandula × intermedia. Several species of Lavandula produce essential oils (EOs) consisting mainly of monoterpenes including linalool, one of the most abundant and scent-determining oil constituents. Although R-linalool dominates the EOs of lavenders, varying amounts (depending on the species) of the S-linalool enantiomer can also be found in these plants. Despite its relatively low abundance, S-linalool contributes a sweet, pleasant scent and is an important constituent of lavender EOs. While several terpene synthase genes including R-linalool synthase have been cloned from lavenders many important terpene synthases including S-linalool synthase have not been described from these plants. In this study, we employed RNA-Seq and other complementary sequencing data to clone and functionally characterize the sparsely expressed S-linalool synthase cDNA (LiS-LINS) from Lavandula × intermedia. Recombinant LiS-LINS catalyzed the conversion of the universal monoterpene precursor geranyl diphosphate to S-linalool as the sole product. Intriguingly, LiS-LINS exhibited very low (~ 30%) sequence similarity to other Lavandula terpene synthases, including R-linalool synthase. However, the predicted 3D structure of this protein, including the composition and arrangement of amino acids at the active site, is highly homologous to known terpene synthase proteins. LiS-LINS transcripts were detected in flowers, but were much less abundant than those corresponding to LiR-LINS, paralleling enantiomeric composition of linalool in L. × intermedia oils. These data indicate that production of S-linalool is at least partially controlled at the level of transcription from LiS-LINS. The cloned LiS-LINS cDNA may be used to enhance oil composition in lavenders and other plants through metabolic engineering.

Volatile composition and classification of Lilium flower aroma types and identification, polymorphisms, and alternative splicing of their monoterpene synthase genes

Lily is a well-known ornamental plant with a diversity of fragrant types. Basic information on lily floral scent compounds has been obtained for only a few accessions, and little is known about Lilium aroma types, the terpene synthase genes that may play roles in the production of key volatiles, or the range of monoterpenes that these genes produce. In this study, 41 cultivars were analyzed for volatile emissions, and a total of 46 individual volatile compounds were identified, 16 for the first time in lilies. Lily accessions were classified into six groups according to the composition of major scent components: faint-scented, cool, fruity, musky, fruity-honey, and lily. Monoterpenes were one of the main groups of volatiles identified, and attention was focused on terpene synthase (TPS) genes, which encode enzymes that catalyze the last steps in monoterpene synthesis. Thirty-two candidate monoterpene synthase cDNAs were obtained from 66 lily cultivars, and 64 SNPs were identified. Two InDels were also shown to result from variable splicing, and sequence analysis suggested that different transcripts arose from the same gene. All identified nucleotide substitution sites were highly correlated with the amounts of myrcene emitted, and InDel site 230 was highly correlated with the emission of all major monoterpenoid components, especially (E)-β-ocimene. Heterologous expression of five cDNAs cloned from faint-scented and strong-scented lilies showed that their corresponding enzymes could convert geranyl diphosphate to (E)-β-ocimene, α-pinene, and limonene. The findings from this study provide a major resource for the assessment of lily scent volatiles and will be helpful in breeding of improved volatile components.

Synchronous application of antibiotics and essential oils: dual mechanisms of action as a potential solution to antibiotic resistance

Antibiotic resistance has increased dramatically in recent years, yet the antibiotic pipeline has stalled. New therapies are therefore needed to continue treating antibiotic resistant infections. One potential strategy currently being explored is the use of non-antibiotic compounds to potentiate the activity of currently employed antibiotics. Many natural products including Essential Oils (EOs) possess broad spectrum antibacterial activity and so have been investigated for this purpose. This article aims to review recent literature concerning the antibacterial activity of EOs and their interactions with antibiotics, with consideration of dual mechanisms of action of EOs and antibiotics as a potential solution to antibiotic resistance. Synergistic interactions between EOs and their components with antibiotics have been reported, including several instances of antibiotic resensitization in resistant isolates, in support of this strategy to control antibiotic resistance. However, a lack of consistency in methods and interpretation criteria makes drawing conclusions of efficacy of studied combinations difficult. Synergistic effects are often not explored beyond preliminary identification of antibacterial interactions and mechanism of action is rarely defined, despite many hypotheses and recommendations for future study. Much work is needed to fully understand EO-antibiotic associations before they can be further developed into novel antibacterial formulations.

Antidiabetic Potential of Monoterpenes: A Case of Small Molecules Punching above Their Weight

Monoterpenes belong to the terpenoids class of natural products and are bio-synthesized through the mevalonic acid pathway. Their small molecular weight coupled with high non-polar nature make them the most abundant components of essential oils which are often considered to have some general antioxidant and antimicrobial effects at fairly high concentrations. These compounds are however reported to have antidiabetic effects in recent years. Thanks to the ingenious biosynthetic machinery of nature, they also display a fair degree of structural complexity/diversity for further consideration in structure-activity studies. In the present communication, the merit of monoterpenes as antidiabetic agents is scrutinized by assessing recent in vitro and in vivo studies reported in the scientific literature. Both the aglycones and glycosides of these compounds of rather small structural size appear to display antidiabetic along with antiobesity and lipid lowering effects. The diversity of these effects vis-à-vis their structures and mechanisms of actions are discussed. Some key pharmacological targets include the insulin signaling pathways and/or the associated PI3K-AKT (protein kinase B), peroxisome proliferator activated receptor-γ (PPARγ), glucose transporter-4 (GLUT4) and adenosine monophosphate-activated protein kinase (AMPK) pathways; proinflammatory cytokines and the NF-κB pathway; glycogenolysis and gluconeogenesis in the liver; glucagon-like-1 receptor (GLP-1R); among others.

Structure-activity modelling of essential oils, their components, and key molecular parameters and descriptors

Many essential oil components are known to possess broad spectrum antimicrobial activity, including against antibiotic resistant bacteria. These compounds may be a useful source of new and novel antimicrobials. However, there is limited research on the structure-activity relationship (SAR) of essential oil compounds, which is important for target identification and lead optimization. This study aimed to elucidate SARs of essential oil components from experimental and literature sources. Minimum Inhibitory Concentrations (MICs) of essential oil components were determined against Escherichia coli and Staphylococcus aureus using a microdilution method and then compared to those in published in literature. Of 12 essential oil components tested, carvacrol and cuminaldehyde were most potent with MICs of 1.98 and 2.10 mM, respectively. The activity of 21 compounds obtained from the literature, MICs ranged from 0.004 mM for limonene to 36.18 mM for α-terpineol. A 3D qualitative SAR model was generated from MICs using FORGE software by consideration of electrostatic and steric parameters. An r² value of 0.807 for training and cross-validation sets was achieved with the model developed. Ligand efficiency was found to correlate well to the observed activity (r² = 0.792), while strongly negative electrostatic regions were present in potent molecules. These descriptors may be useful for target identification of essential oils or their major components in antimicrobial/drug development.