Myrcene

Variations of volatile flavour compounds in finger citron (Citrus medica L. var. sarcodactylis) pickling process revealed by E-nose, HS-SPME-GC-MS and HS-GC-IMS.[Pubmed:33292962]

Food Res Int. 2020 Dec;138(Pt A):109717.

The pickled products of finger citron are famous in southern China for their unique taste and flavor. Although pickling process involves complex treatments including salting, desalting, sugaring, cooking and drying, extended shelf-life up to ten years after pickling can be achieved. In this study, the variations of volatile flavour components in the pickling process of finger citron were investigated by electronic nose (E-nose), headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). HS-SPME-GC-MS identified 85 substances, and HS-GC-IMS identified 81 substances, including terpenoids (21), aromatic hydrocarbons (11), alcohols (11), aldehydes (10), esters (7), phenols (6), acids (5), ethers (2), ketones (2), and other species (10). Linalool, limonene, (E)-3,7-dimethyl-1,3,6-octatriene, Myrcene, 3-carene, beta-pinene, alpha-pinene, terpinolene, 1-methyl-4-(1-methylethyl)-1,4-cyclohexadiene, alpha-terpinene, (S)-beta-bisabolene, 1-isopropyl-2-methylbenzene and 1-methyl-4-(1-methylethenyl)-benzene were the stable substances at relatively high contents in finger citron at different pickling process. Salting and drying steps in the pickling process exerted greatest influence on the volatile components of finger citron. Salting promoted the generation of aldehydes, esters and acids, but led to the disappearance of alcohols, while drying promoted the generation of alcohols, phenols, aldehydes and acids at the expense of reduction in terpenoids. Our study revealed that the characteristic volatile compounds of finger citron pickled products was mainly formed by the biological reactions in the salting stage and thermal chemical transformations in the drying stage. This study also validated the suitability of E-nose combined with HS-SPME-GC-MS and HS-GC-IMS in tracking the changes of volatile components in finger citron during the pickling process.

Differentiation of aromatic, bittering and dual-purpose commercial hops from their terpenic profiles: An approach involving batch extraction, GC-MS and multivariate analysis.[Pubmed:33292948]

Food Res Int. 2020 Dec;138(Pt A):109768.

Terpenes are one of the main classes of compounds in hops (Humulus lupulus, L). They play an important role in brewing due to their central function, which is related to beer aroma. A screening of terpenes in several commercial hop varieties was carried out by gas chromatography coupled to mass spectrometry after employing a simple, straightforward and high throughput extraction method. A single batch extraction, using hexane as solvent, was employed to obtain the terpenic fraction of the hop samples. Nineteen terpenes were identified in analyzed samples with beta-Myrcene (2.22-45.30%), alpha-humulene (20.20-67.64%), and beta-caryophyllene (9.97-24.62%) being the major terpenes in all samples. The studied system was multivariate modeled by principal component analysis. Based on the proposed approach, it was possible to correlate the terpenic hop profiles to their specific purpose in the brewing industry and to distinguish aromatic hops (high alpha-humulene content), bittering hops (high beta-Myrcene content), and dual-purpose hops (more complex and intermediate terpenic profile) among the samples.

Comparison of headspace solid-phase microextraction high capacity fiber coatings based on dual mass spectrometric and broadband vacuum ultraviolet absorption detection for untargeted analysis of beer volatiles using gas chromatography.[Pubmed:33248666]

Anal Chim Acta. 2021 Jan 2;1141:91-99.

Despite the same basic ingredients used in brewing, there is a significant variation in beer styles. With the rapid increase in craft brewing, beer styles have become even more numerous and complex in the recent past. A GC-MS/VUV (post-column split for dual detection) instrument with headspace high capacity SPME was used to investigate 21 different beers which represent three beer styles - India pale ales, blondes, and hefeweizens. Since results from untargeted studies can be affected by the sorbent material used, the extraction performances of three high capacity SPME fibers, i.e., polydimethylsiloxane, polydimethylsiloxane/carbon wide range, and polydimethylsiloxane/carbon wide range/divinylbenzene, were evaluated. Good reproducibility (<10% RSD) was obtained for each high capacity fiber using both detectors. The tandem MS/VUV detection coupled with GC separation proved to be particularly valuable for compound identification, especially for isomers and compounds with similar structures. The evaluation of VUV detection for untargeted analysis led to similar performances as MS detection. Both the VUV and the MS were able to effectively differentiate between beer styles using principal component analysis. In addition, the use of 3 different statistical approaches, one-way ANOVA (p-value < 0.05), partial least square discriminant analysis, and random forest, universally identified 12 of the components most influential in distinguishing the three beer styles (e.g., beta-Myrcene, linalool, isopentyl acetate, 2,4-di-tert-butylphenol). This is the first reported evaluation of VUV detection and the first comparison of simultaneous VUV and MS detection for untargeted classification of complex mixtures using GC.

Essential Oil Variation within Warburgia salutaris-A Coveted Ethnomedicinal Aromatic Tree.[Pubmed:33231346]

Chem Biodivers. 2020 Nov;17(11):e2000542.

Warburgia salutaris, known as 'Pepper bark', is an ethnomedicinally important tree found in the southern regions of Africa. A total of 75 fresh leaf specimens of W. salutaris (n=40 wild and 35 cultivated) were collected from the Limpopo (wild) and KwaZulu-Natal provinces (cultivated), two distinct locations in South Africa. In this study, the leaf essential oils obtained by hydrodistillation were characterized using gas chromatography coupled to mass spectrometry/flame ionization detection (GC/MS/FID). More than 15 compounds, accounting for 90-99 % of the total oil composition were identified. The analysis revealed that Myrcene (0.6-65.3 %), (E)-beta-ocimene (nd-56.9 %), (Z)-beta-ocimene (nd-19.1 %), alpha-pinene (nd-19.1 %) and limonene (nd-11.7 %) are major constituents of W. salutaris essential oils. Chemometric analysis revealed two major chemotypes within the essential oils with a modeled variation of approximately 60 %. Linalool and germacrene D were revealed as markers associated with the wild-harvested oils, while cultivated oils were distinguished by higher levels of limonene and alpha-humulene. The intra-population variation indicated two chemically distinct chemotypes from three different populations, however, the season of harvest did not have a direct influence on the chemical profiles of the essential oils.

Biobased Epoxies Derived from Myrcene and Plant Oil: Design and Properties of Their Cured Products.[Pubmed:33225122]

ACS Omega. 2020 Nov 6;5(45):28918-28928.

Two biobased epoxy resin monomers derived from Myrcene and plant oil are synthesized without using petroleum-based bisphenol A. To obtain material with balanced strength and toughness, the two epoxy monomers are cured together in different weight proportions. Properties of cured epoxy resin are tested by different techniques. Tensile and impact tests indicate that when the content of Myrcene-based epoxy is 50-75 wt %, the cured sample has a high strain of 32.30-161.47%, and a moderate tensile strength of 9.57-15.96 MPa. Dynamic mechanical analysis suggests that the glass transition temperature (T g) of cured samples increases from 17 to 71 degrees C with the increasing content of Myrcene-based epoxy. Morphology of fracture surface indicates that the cured sample containing plant oil-based epoxy resin shows obvious plastic deformation. The curing kinetics of the two epoxies resin is studied by differential scanning calorimetry. Also, the calculated activation energy is 70.49 kJ/mol for Myrcene-based epoxy and 64.02 kJ/mol for poly-fatty acid-derived epoxy resin. The thermogravimetric analysis indicates that the main degradation temperature of all cured samples is above 300 degrees C. The sustainable biobased epoxy has some potential in preparing flexible epoxy materials and can be used to toughen conventional petroleum-based epoxy.

Investigation of sugars, organic acids, phenolic compounds, antioxidant activity and the aroma fingerprint of small white apricots grown in Xinjiang.[Pubmed:33190235]

J Food Sci. 2020 Nov 14.

Small white apricot is well known as a famous fresh fruit and even a folk medicine in Xinjiang. To investigate nutritive value, antioxidant activity, and flavor of small white apricot, sugars, organic acids, total flavonoids, phenolic compounds, antioxidant activities, and volatile compounds in five apricot cultivars were examined by high-performance liquid chromatography (HPLC) and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that sucrose (32.94% to 42.49%), malic acid (69.21% to 76.75%), and quercetin-3-rutinoside (72.84% to 74.05%) were the dominant sugar, organic acid, and phenolic compounds in small white apricot, respectively. The antioxidant activity reached up to 61.72 to 135.52 mg TEs 100 g(-1) . Furthermore, the aroma fingerprint of the small white apricot consisted of 1-octen-3-ol, 1-dodecanol, pentanal, hexanal, (E)-2-hexenal, (E)-2-heptenal, 6-methyl-5-hepten-2-one, (E)-2-nonenal, 1-octen-3-one, beta-Myrcene, and linalool, providing clear green, grassy, and fatty notes. Apricots from different cultivars possessed a similar flavor, while linalool and (E)-2-hexenal had been identified as the characteristic aroma compounds in small white apricot. The results provide a complete chemical characterization of the taste, functional ingredients and aroma of the small white apricot. PRACTICAL APPLICATION: The nutritive value, antioxidant activity and flavor of small white apricot were investigated in this study. The results will provide a theoretical basis for developing characteristic variety aroma, nutritive value, and medicinal value of small white apricot.

Enhancing the Extraction of Phenolic Compounds from Juniper Berries Using the Box-Behnken Design.[Pubmed:33163782]

ACS Omega. 2020 Oct 21;5(43):27990-28000.

Juniper berry is an important medicinal plant used in pharmaceutical and petrochemical industries thanks to its strong antioxidant potential, which is attributed to the presence of phenolic compounds. In this study, four different solvents, namely, aqueous acetone, aqueous ethanol, aqueous NaOH, and water, were used in the extraction process with a view to optimize and determine the polyphenolic contents in the juniper berry using ultraviolet (UV) spectrophotometry. Many experiments were performed at different solvent concentrations, time, temperature, and liquid-solid ratio. The models to evaluate the effects and the optimum of these variables on the polyphenols extraction using the response surface methodology (RSM) were developed. The predicted values of the polyphenol content of juniper berry were thus highly correlated with costly measured values (SECV = 0.14 and R (2) = 0.97), and the optimal conditions of extraction were determined for the different solvents. Following the numerical optimization, the maximum predicted polyphenol contents obtained under the optimum extraction conditions are as follows: 17.57% for 58 degrees C extraction temperature, 78.5 min extraction time, 60% acetone concentration, and 29.8 liquid-solid ratio for the aqueous ethanol extraction; 20.68% for 71.46 degrees C extraction temperature, 79.2 min extraction time, 21.9% ethanol concentration, and 26.4:1 liquid-solid ratio for the aqueous acetone extraction; 34.51% for 96.4 degrees C extraction temperature, 37.7 min extraction time, 1.48% NaOH concentration, and 15.2:1 liquid-solid ratio for the aqueous NaOH extraction; and 9.8% was obtained under the optimum extraction conditions of 69 degrees C extraction temperature, 126 min extraction time, and 23:1 liquid-solid ratio for the water extraction. The GC-MS analysis of the chemical composition of juniper Berry revealed 60 identified components that represent 97.43% of the sample. The predominant fraction was monoterpene representing 80.87% especially for alpha-pinene (39.12%), beta-pinene (12. 68%), and Myrcene (12.92%). In the other fraction of sesquiterpene representing 16.54%, the predominant components were beta-caryophyllene (4.41%) and germacrene D (4.23%).

Piper capitarianum essential oil: a promising insecticidal agent for the management of Aedes aegypti and Aedes albopictus.[Pubmed:33159226]

Environ Sci Pollut Res Int. 2020 Nov 6. pii: 10.1007/s11356-020-11148-6.

Mosquitoes are responsible for serious public health problems worldwide, and as such, Aedes aegypti and Aedes albopictus are important vectors in the transmission of dengue, chikungunya, and Zika in Brazil and other countries of the world. Due to growing resistance to chemical insecticides among populations of vectors, environmentally friendly strategies for vector management are receiving ever more attention. Essential oils (EOs) extracted from plants have activities against insects with multiple mechanisms of action. These mechanisms hinder the development of resistance, and have the advantages of being less toxicity and biodegradable. Thus, the present study aimed to evaluate the chemical composition of the EOs obtained from Piper capitarianum Yunck, as well as evaluating their insecticidal potential against Aedes aegypti and A. albopictus, and their toxicity in relation to Artemia salina. The yields of the EOs extracted from the leaves, stems, and inflorescences of P. capitarianum were 1.2%, 0.9%, and 0.6%, respectively, and their main constituents were trans-caryophyllene (20.0%), alpha-humulene (10.2%), beta-Myrcene (10.5%), alpha-selinene (7.2%), and linalool (6.0%). The EO from the inflorescences was the most active against A. aegypti and A. albopictus, and exhibited the respective larvicidal (LC50 = 87.6 mug/mL and 76.1 mug/mL) and adulticide activities (LC50 = 126.2 mug/mL and 124.5 mug/mL). This EO was also the most active in the inhibition of AChE, since it presented an IC50 value of 14.2 mug/mL. Its larvicidal effect was observed under optical and scanning electron microscopy. Additionally, non-toxic effects against A. salina were observed. Docking modeling of trans-caryophyllene and alpha-humulene on sterol carrier protein-2 (SCP-2) suggests that both molecules have affinity with the active site of the enzyme, which indicates a possible mechanism of action. Therefore, the essential oil of P. capitarianum may be used in the development of new insecticide targets for the control of A. aegypti and A. albopictus in the Amazonian environment.

The santalene synthase from Cinnamomum camphora: Reconstruction of a sesquiterpene synthase from a monoterpene synthase.[Pubmed:33121934]

Arch Biochem Biophys. 2020 Nov 30;695:108647.

Plant terpene synthases (TPSs) can mediate formation of a large variety of terpenes, and their diversification contributes to the specific chemical profiles of different plant species and chemotypes. Plant genomes often encode a number of related terpene synthases, which can produce very different terpenes. The relationship between TPS sequence and resulting terpene product is not completely understood. In this work we describe two TPSs from the Camphor tree Cinnamomum camphora (L.) Presl. One of these, CiCaMS, acts as a monoterpene synthase (monoTPS), and mediates the production of Myrcene, while the other, CiCaSSy, acts as a sesquiterpene synthase (sesquiTPS), and catalyses the production of alpha-santalene, beta-santalene and trans-alpha-bergamotene. Interestingly, these enzymes share 97% DNA sequence identity and differ only in 22 amino acid residues out of 553. To understand which residues are essential for the catalysis of monoterpenes resp. sesquiterpenes, a number of hybrid synthases were prepared, and supplemented by a set of single-residue variants. These were tested for their ability to produce monoterpenes and sesquiterpenes by in vivo production of sesquiterpenes in E. coli, and by in vitro enzyme assays. This analysis pinpointed three residues in the sequence which could mediate the change in product specificity from a monoterpene synthase to a sesquiterpene synthase. Another set of three residues defined the sesquiterpene product profile, including the ratios between sesquiterpene products.

Essential Oils from Monarda fistulosa: Chemical Composition and Activation of Transient Receptor Potential A1 (TRPA1) Channels.[Pubmed:33105614]

Molecules. 2020 Oct 22;25(21). pii: molecules25214873.

Little is known about the pharmacological activity of Monarda fistulosa L. essential oils. To address this issue, we isolated essential oils from the flowers and leaves of M. fistulosa and analyzed their chemical composition. We also analyzed the pharmacological effects of M. fistulosa essential oils on transient receptor potential (TRP) channel activity, as these channels are known targets of various essential oil constituents. Flower (MEOFl) and leaf (MEOLv) essential oils were comprised mainly of monoterpenes (43.1% and 21.1%) and oxygenated monoterpenes (54.8% and 77.7%), respectively, with a high abundance of monoterpene hydrocarbons, including p-cymene, gamma-terpinene, alpha-terpinene, and alpha-thujene. Major oxygenated monoterpenes of MEOFl and MEOLv included carvacrol and thymol. Both MEOFl and MEOLv stimulated a transient increase in intracellular free Ca(2+) concentration ([Ca(2+)]i) in TRPA1 but not in TRPV1 or TRPV4-transfected cells, with MEOLv being much more effective than MEOFl. Furthermore, the pure monoterpenes carvacrol, thymol, and beta-Myrcene activated TRPA1 but not the TRPV1 or TRPV4 channels, suggesting that these compounds represented the TRPA1-activating components of M. fistulosa essential oils. The transient increase in [Ca(2+)]i induced by MEOFl/MEOLv, carvacrol, beta-Myrcene, and thymol in TRPA1-transfected cells was blocked by a selective TRPA1 antagonist, HC-030031. Although carvacrol and thymol have been reported previously to activate the TRPA1 channels, this is the first report to show that beta-Myrcene is also a TRPA1 channel agonist. Finally, molecular modeling studies showed a substantial similarity between the docking poses of carvacrol, thymol, and beta-Myrcene in the binding site of human TRPA1. Thus, our results provide a cellular and molecular basis to explain at least part of the therapeutic properties of these essential oils, laying the foundation for prospective pharmacological studies involving TRP ion channels.

The Flower Essential Oil of Dalea mutisii Kunth (Fabaceae) from Ecuador: Chemical, Enantioselective, and Olfactometric Analyses.[Pubmed:33096831]

Plants (Basel). 2020 Oct 21;9(10). pii: plants9101403.

An essential oil was distilled with 0.25% yield from fresh flowers of Dalea mutisii Kunth, a native species mainly growing in the Andean region of Ecuador. A total of 50 compounds were identified, and most of them were quantified. The chemical composition was characterized by the prevalence of monoterpene hydrocarbons (>90%). Major components were alpha-pinene (42.9%), beta-pinene (15.1%), beta-phellandrene (12.6%), Myrcene (6.7%), and (Z)-beta-ocimene (5.4%). The essential oil was then submitted to enantioselective analysis, with a 2,3-diethyl-6-tert-butyldimethylsilyl-beta-cyclodextrin-based capillary column. An enantiomeric excess was measured for (1R,5R)-(+)-alpha-pinene (91.6%), (1R,5R)-(+)-beta-pinene (15.2%), (R)-(-)-alpha-phellandrene (4.8%), and (R)-(-)-beta-phellandrene (88.8%), whereas (R)-(+)-limonene was enantiomerically pure. A gas chromatography-olfactometry (GC-O) analysis was additionally carried out on this pleasantly fragrant essential oil, following an aroma extract dilution analysis (AEDA) approach. Main odorants were alpha-pinene, beta-pinene, alpha-phellandrene, and (Z)-beta-ocimene, with dilution factors (FD) of 8, 4, 2, and 2, respectively.

Tangerines Cultivated on Madeira Island-A High Throughput Natural Source of Bioactive Compounds.[Pubmed:33076393]

Foods. 2020 Oct 15;9(10). pii: foods9101470.

Tangerines (Citrus reticulata) are popular fruits worldwide, being rich in many bioactive metabolites. The setubalense variety cultivated on Madeira Island has an intense aroma easily distinguishable from other tangerines, being traditionally used to enrich several foods and beverages. Nonetheless, setubalense volatile composition has never been characterized, and we aimed to unveil the bioactive potential of peels and juices of setubalense tangerines and compare them with the murcott variety grown in Portugal mainland. Using headspace solid-phase microextraction coupled to gas chromatography mass spectrometry (HS-SPME/GC-MS), we identified a total of 128 volatile organic metabolites (VOMs) in the juice and peels, with d-limonene, gamma-terpinene, beta-Myrcene, alpha- and beta-pinene, o-cymene, and terpinolene, the most dominant in both cultivars. In contrast, setubalense juices are richer in terpenes, many of them associated with health protection. Discriminant analysis revealed a pool of VOMs, including beta-caryophyllene and E-ocimene, with bioactive properties able to differentiate among tangerines according to variety and sample type (peel vs. juice). This is the first report on the volatile composition of setubalense tangerines grown on Madeira Island revealing that its pungent aroma is constituted by secondary metabolites with specific aroma notes and health properties. This is strong evidence of the higher nutraceutical value of such fruit for the human diet.

Temperature Variation Enables the Design of Biobased Block Copolymers via One-Step Anionic Copolymerization.[Pubmed:33047426]

Macromol Rapid Commun. 2020 Oct 12:e2000513.

A one-pot approach for the preparation of diblock copolymers consisting of polystyrene and polyMyrcene blocks is described via a temperature-induced block copolymer (BCP) formation strategy. A monomer mixture of styrene and Myrcene is employed. The unreactive nature of Myrcene in a polar solvent (tetrahydrofuran) at -78 degrees C enables the sole formation of active polystyrene macroinitiators, while an increase of the temperature (-38 degrees C to room temperature) leads to poly(styrene-block-Myrcene) formation due to polymerization of Myrcene. Well-defined BCPs featuring molar masses in the range of 44-117.2 kg mol(-1) with dispersities, Eth, of 1.09-1.21, and polyMyrcene volume fractions of 30-64% are accessible. Matrix assisted laser desorption ionization-time of flight mass spectrometry measurements reveal the temperature-controlled polyMyrcene block formation, while both transmission electron microscopy and small-angle X-ray scattering measurements prove the presence of clearly microphase-separated, long range-ordered domains in the block copolymers. The temperature-controlled one-pot anionic block copolymerization approach may be general for other terpene-diene monomers.

Pimenta Oil as A Potential Treatment for Acinetobacter Baumannii Wound Infection: In Vitro and In Vivo Bioassays in Relation to Its Chemical Composition.[Pubmed:33036456]

Antibiotics (Basel). 2020 Oct 7;9(10). pii: antibiotics9100679.

Bacterial biofilm contributes to antibiotic resistance. Developing antibiofilm agents, more favored from natural origin, is a potential method for treatment of highly virulent multidrug resistant (MDR) bacterial strains; The potential of Pimenta dioica and Pimenta racemosa essential oils (E.Os) antibacterial and antibiofilm activities in relation to their chemical composition, in addition to their ability to treat Acinetobacter baumannii wound infection in mice model were investigated; P. dioica leaf E.O at 0.05 microg.mL(-1) efficiently inhibited and eradicated biofilm formed by A. baumannii by 85% and 34%, respectively. Both P. diocia and P. racemosa leaf E.Os showed a bactericidal action against A. baumanii within 6h at 2.08 microg.mL(-1). In addition, a significant reduction of A. baumannii microbial load in mice wound infection model was found. Furthermore, gas chromatography mass spectrometry analysis revealed qualitative and quantitative differences among P. racemosa and P. dioica leaf and berry E.Os. Monoterpene hydrocarbons, oxygenated monoterpenes, and phenolics were the major detected classes. beta-Myrcene, limonene, 1,8-cineole, and eugenol were the most abundant volatiles. While, sesquiterpenes were found as minor components in Pimenta berries E.O; Our finding suggests the potential antimicrobial activity of Pimenta leaf E.O against MDR A. baumannii wound infections and their underlying mechanism and to be further tested clinically as treatment for MDR A. baumannii infections.

Influence of pre-drying storage time on essential oil components in dried hops (Humulus lupulus L.).[Pubmed:33009828]

J Sci Food Agric. 2020 Oct 3.

BACKGROUND: It is well known that duration of pre-drying storage impacts on hop quality. However, little knowledge exists regarding its actual effects on valuable hop components. To investigate these effects, fresh hop cones were stored for 5 or 24 h and dried for 210 min at 65 degrees C thereafter. Furthermore, to understand the effect of freezing hop cones on the essential oil content, both fresh and stored samples were frozen before and after drying. RESULTS: The results from gas chromatography analysis show an increase in linalool, beta-caryophyllene, humulene, geraniol content and decrease in Myrcene content dependent on the period of storage. Total colour difference DeltaE values of 4.61 and 5.27 were obtained for fresh and stored hops respectively, indicating discoloration of hops during storage. Modelling of moisture curves revealed the Wang and Singh model to be suitable, with R adj 2 values of 0.978 and 0.989 and root-mean-square error values of 0.037 and 0.019 for fresh and stored hops respectively. CONCLUSION: The results from this study provide an in-depth understanding on the changes occurring within the hop cones both during storage and drying and will further help hop processors optimize their storage times.