Structure-Odor Relationship Study on Geraniol, Nerol, and Their Synthesized Oxygenated Derivatives

Dietary monoterpenoids and human health: Unlocking the potential for therapeutic use

Natural products are widely used in different aspects of our lives - from household cleaners and food production, via cosmetics and aromatherapy, to both alternative and traditional medicine. In our research group, we have recently described several monoterpenoids with potential in the antiviral and anticancer therapy by allosteric targeting of aryl hydrocarbon receptor (AhR). Prior to any practical application, biological effects on human organism must be taken in concern. This review article is focused on the biological effects of 5 monoterpenoids on the human health previously identified as AhR antagonists with a therapeutic potential as antiviral and anticancer agents. We have thoroughly described cytotoxic, anti-inflammatory, anti-proliferative, and anticancer effects, as well as known interactions with nuclear receptors. As clearly demonstrated, monoterpenoids in general represent almost an inexhaustible reservoir of natural compounds possessing the ability to influence, modulate and improve human health.

Combination of Chromatographic Analysis and Chemometric Methods with Bioactivity Evaluation of the Antibacterial Properties of Helichrysum italicum Essential Oil

Helichrysum italicum (immortelle) essential oil is one of the most popular essential oils worldwide and it has many beneficial properties, including antimicrobial. However, in this plant, the chemical diversity of the essential oil is very pronounced. The aim of this work was to process the GC-MS results of four samples of H. italicum essential oil of Serbian origin by chemometric tools, and evaluate the antimicrobial activity in vitro and in silico. Overall, 47 compounds were identified, the most abundant were γ-curcumene, α-pinene, and ar-curcumene, followed by α-ylangene, neryl acetate, trans-caryophyllene, italicene, α-selinene, limonene, and italidiones. Although the four samples of H. italicum essential oil used in this study were obtained from different producers in Serbia, they belong to the type of essential oil rich in sesquiterpenes (γ-curcumene and ar-curcumene chemotype). In vitro antimicrobial potential showed that five were sensitive among ten strains of tested microorganisms: Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Saccharomyces cerevisiae, and Candida albicans. Therefore, these microorganism models were used further for in silico molecular docking through the mechanism of ATP-ase inhibitory activity. Results showed that among all compounds from H. italicum essential oil, neryl acetate has the highest predicted binding energy. Artificial neural network modeling (ANN) showed that two major compounds γ-curcumene and α-pinene, as well as minor compounds such as trans-β-ocimene, terpinolene, terpinene-4-ol, isoitalicene, italicene, cis-α-bergamotene, trans-α-bergamotene, italidiones, trans-β-farnesene, γ-selinene, β-selinene, α-selinene, and guaiol are responsible for the antimicrobial activity of H. italicum essential oil. The results of this study indicate that H. italicum essential oil samples rich in γ-curcumene, α-pinene, and ar-curcumene cultivated in Serbia (Balkan) have antimicrobial potential both in vitro and in silico. In addition, according to ANN modeling, the proportion of neryl acetate and other compounds detected in these samples has the potential to exhibit antimicrobial activity.

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Separation techniques for manufacturing fruit spirits: From traditional distillation to advanced pervaporation process

Separation process is one of the key processes in the production of fruit spirits, including the traditional distillation method and the new pervaporation membrane method. The separation process significantly determines the constituents and proportions of compounds in the fruit spirit, which has a significant impact on the spirit quality and consumer acceptance. Therefore, it is important and complex to reveal the changing rules of chemical substances and the principles behind them during the separation process of fruit spirits. This review summarized the traditional separation methods commonly used in fruit spirits, covering the types, principles, and corresponding equipment of distillation methods, focused on the enrichment or removal of aroma compounds and harmful factors in fruit spirits by distillation methods, and tried to explain the mechanism behind it. It also proposed a new separation technology for the production of fruit spirits, pervaporation membrane technology, summarized its working principle, operation, working parameters, and application in the production of fruit spirits, and outlined the impact of the separation method on the production of fruit spirits based on existing research, focusing on the separation of flavor compounds, sensory qualities, and hazard factors in fruit spirits, along with a preliminary comparison with distillation. Finally, according to the current researches of the separation methods and the development requirement of the separation process of fruit spirits, the prospect of corresponding research is put forward, in order to propose new ideas and development directions for the research in this field.

Combining Feature-Based Molecular Networking and Contextual Mass Spectral Libraries to Decipher Nutrimetabolomics Profiles

Untargeted metabolomics approaches deal with complex data hindering structural information for the comprehensive analysis of unknown metabolite features. We investigated the metabolite discovery capacity and the possible extension of the annotation coverage of the Feature-Based Molecular Networking (FBMN) approach by adding two novel nutritionally-relevant (contextual) mass spectral libraries to the existing public ones, as compared to widely-used open-source annotation protocols. Two contextual mass spectral libraries in positive and negative ionization mode of ~300 reference molecules relevant for plant-based nutrikinetic studies were created and made publicly available through the GNPS platform. The postprandial urinary metabolome analysis within the intervention of Vaccinium supplements was selected as a case study. Following the FBMN approach in combination with the added contextual mass spectral libraries, 67 berry-related and human endogenous metabolites were annotated, achieving a structural annotation coverage comparable to or higher than existing non-commercial annotation workflows. To further exploit the quantitative data obtained within the FBMN environment, the postprandial behavior of the annotated metabolites was analyzed with Pearson product-moment correlation. This simple chemometric tool linked several molecular families with phase II and phase I metabolism. The proposed approach is a powerful strategy to employ in longitudinal studies since it reduces the unknown chemical space by boosting the annotation power to characterize biochemically relevant metabolites in human biofluids.

Influence of elongation and desaturation on chemosensory properties in acrylates and their corresponding 1-alken-3-ones

Acrylates as well as 1-alken-3-ones are both known to be odour active substances but are generally identified in different materials. Nonetheless, butyl acrylate and 1-octen-3-one were both found to elicit a similar mushroom-like odour in previous studies. This led to the question of whether acrylates and enones with the same overall chain length generally elicited similar odours and whether they had similar odour thresholds. Overall, most of the investigated substances showed a mushroom-like, geranium-like or fruity odour. In contrast, short chained substances elicited garlic-like, lighter gas-like or glue-like, odour qualities, suggesting a correlation between the odour quality and the overall chain length. The results showed that only between the analogue structures butyl acrylate and 1-octen-3-one as well as hexyl acrylate and 1-decen-3-one could similar odour qualities be observed. All investigated substances showed low odour threshold values in air between 0.0032 ng/l_air (1-hexen-3-one) and 55 ng/l_air (1-dodecen-3-one). Overall, 1-alken-3-ones revealed a higher dependency on the chain length when compared to their respective acrylates. The introduction of a second terminal double bond led to a decrease of OT values in case of the acrylates and to an increase in case of the ketones that neither contained a second terminal double bond nor a double bond located close to the carbonyl group. Despite their structural similarities, the results suggest that both substance classes are perceived in a different manner and are therefore likely to be recognized by different types of receptors or are related to different activation patterns in multi-receptor stimulation processes.

Rapid-killing efficacy substantiates the antiseptic property of the synergistic combination of carvacrol and nerol against nosocomial pathogens

Globally, new classes of synthetic and natural antibiotics and antivirulents have continuously been validated for their potential broad-spectrum antagonistic activity with the aim of identifying an effective active molecule to prevent the spread of infectious agents in both food industry and medical field. In view of this, present study is aimed at evaluating the rapid killing efficacy of bioactive molecules Carvacrol (C) and Nerol (N) through British Standard European Norm 1276: phase2/step1 (EN1276) protocol. Active molecules C and N showed broad-spectrum antimicrobial activity against the test strains Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus hirae at concentration range of 78.125, 625, 156.25 and 312.5 μg/mL, respectively, for C, and 625 μg/mL for N. Whereas, combinatorial approach showed efficient activity with four times reduced concentration of C and N at 78.125 and 156.25 µg/mL, respectively, against test strains. Further, EN1276 results proved the rapid killing efficacy of test strains in 1 min of contact time with significant (> 5 log) growth reduction at 100X concentration of actives. SEM analysis and reduced concentration of protease, lipids and carbohydrate contents of treated group biofilm components ascertained preformed biofilm disruption potential of C + N on polystyrene and nail surfaces. C + N at synergistic concentration exhibited no adverse effect on HaCaT cells at 78.125 µg/mL (C) + 156.25 µg/mL (N). Taken together, based on the observed experimental results, present study evidence the antiseptic/disinfectant ability of C + N and suggest that the combination can preferentially be used in foam-based hand wash formulations.

Generation of Flavor-Active Compounds by Electrochemical Oxidation of (R)-Limonene

Terpenes may be converted by electrochemical oxidation to various oxidized products with appealing aroma properties. In this study, (R)-limonene was anodically oxidized in the presence of ethanol, and the resulting mixture exhibited a pleasing fruity, herbal, citrus-like, and resinous odor. The aroma-active compounds were purified by means of preparative high-performance liquid chromatography, and their structures were elucidated by means of gas chromatography (GC)-mass spectrometry and nuclear magnetic resonance spectroscopy. In addition, the odor of the isolated compounds was determined by means of GC-olfactometry. Seventeen compounds were isolated, and for only four of them, analytical data had been reported previously in the literature. Furthermore, only for two of the compounds, an odor description had been available in the literature.

Odor Characteristics of Novel Non-Canonical Terpenes

Several non-canonical, methylated terpenes have been described as products of genetically modified Escherichia coli recently, and the aroma properties of 28 odor-active methylated derivatives of prenol, isoprenol, bornane, camphene, carene, citronellol, fenchol, geraniol, limonene, linalool, terpineol, and farnesol were characterized for the first time in the current study. Twelve methylated monoterpenes exhibited a particularly intense and pleasant odor and were therefore chosen for the determination of their respective odor thresholds (OTs) in comparison to their non-methylated equivalents. In addition to the determination of OTs based on the literature value for the internal standard, (2E)-decenal, the threshold values of the compounds with individually determined OTs of the participants were calculated. This enabled a more precise identification of the OTs. Among the non-canonical terpenes, the lowest OTs in the air were found for 2-methyllinalool (flowery, 1.8 ng L⁻¹), 2-methyl-α-fenchol (moldy, 3.6 ng L⁻¹), 2-methylgeraniol (flowery, 5.4 ng L⁻¹), 2-methylcitronellol (citrus-like, 7.2 ng L⁻¹), and 4-methylgeraniol (citrus-like, 16 ng L⁻¹). The derivatives of geraniol, linalool, and citronellol showed very pleasant odor impressions, which could make them interesting for use as flavoring agents in the flavor and fragrance industry.

Comparison of Aroma Trait of the White-Fleshed Peach ‘Hu Jing Mi Lu’ and the Yellow-Fleshed Peach ‘Jin Yuan’ Based on Odor Activity Value and Odor Characteristics

Peach flesh colors and aromas impact greatly on consumer behaviors and these two traits are closely associated in white- and yellow-fleshed peaches. However, current understanding of their aromas is rather limited and confined to the concentration differences of some volatiles. Therefore, this study aims to compare the overall aromas of the white-fleshed peach ‘Hu Jing Mi Lu’ (HJML) and yellow-fleshed peach ‘Jin Yuan’ (JY), two fresh cultivars with intense aromas and industrial influence by applications such as HS-SPME/GC-MS analysis, odor activity value evaluations, and odor note analysis. The significant contributions of 26 odor-active compounds to their aromas were revealed. Among which, 15 compounds showed no concentration differences and contributed to the fruity, floral, sweet, etc., odors in both HJML and JY; (E)-2-nonenal, 1-pentanol, and styrene showed significantly higher concentrations in HJML and conveyed much stronger fusel-like and balsamic odors; likewise, (Z)-3-hexenyl acetate, octanal, nonanal, and 3,5-octadien-2-one showed significantly higher concentrations in JY and conveyed much stronger banana, citrus-like, and honey odors; besides, benzyl alcohol, 1-heptanol, 1-octen-3-ol, and 3-octanone with woody, earthy, mushroom, and lavender odors were exclusively detected in HJML. Overall, apart from the common and stronger specific odors in either the white- or yellow-fleshed peach cultivar, the white-fleshed peach was endowed with a unique aroma.

Determination of Droplet-Bound and Free Gas-Phase Fragrances Using a Filter-Incorporated Needle-Trap Device and Solid-Phase Microextraction Technologies

Some of the fragrance compounds in aerosols tend to remain trapped inside the droplets. The ability to capture these droplets would make it possible to desorb and transfer the analytes dissolved within for determination. In this study, we design a novel filter-incorporated needle-trap device and use it to capture fragrance compounds in droplets as well as the gas phase of seven aerosol spray samples. For comparison, thin-film and solid-phase microextraction were also employed to extract gas-phase-borne fragrances from the same sprays. The results revealed that the filter-incorporated needle-trap device enables the extraction of total concentrations due to its ability to trap fragrance-containing droplets, whereas thin-film and solid-phase microextraction are only able to extract unbound compounds present in the gas phase. In addition, the developed needle-trap device provided acceptable results, proving its applicability for the analysis of aroma in other samples, such as beer and soda.

Diagnosing complex odor problems occurring in micro-polluted source water: Primary approach and application

The odor problems in river-type micro-polluted water matrixes are complicated compared to those in lakes and reservoirs. For example, the TY River in Jiangsu Province has been associated with complex odors, whereas the specific odor compounds were not clear. In this paper, a comprehensive study on characterizing the odors and odorants in source water from the TY River was conducted. Six odor types, including earthy, marshy, fishy, woody, medicinal, and chemical odors, were detected for the first time; correspondingly, thirty-three odor-causing compounds were identified. By means of evaluating odor activity values and reconstituting the identified odorants, 95, 93, 92, 90, 89 and 88% of the earthy, marshy, fishy, woody, medicinal and chemical odors in the source waters could be clarified. Geosmin and 2-methylisoborneol were associated with earthy odor, while amyl sulfide, dibutyl sulfide, propyl sulfide, dimethyl disulfide, dimethyl trisulfide and indole were related to marshy odor. The major woody and fishy odor compounds were vanillin, geraniol, β-cyclocitral and 2,4-decadienal, 2-octenal, respectively. Medicinal and chemical odors were mainly caused by 2-chlorophenol, 4-bromophenol, 2,6-dichlorophenol and naphthalene, and 1,4-dichlorobenzene, respectively. This is the first study in which six odor types and thirty-three odorants were identified simultaneously in a river-type micro-polluted water source, which can offer a reference for odor management in drinking water treatment plants.

Monoterpenoids from the Fruits of Amomum tsao-ko Have Inhibitory Effects on Nitric Oxide Production

In our search for novel plant-derived inhibitors of nitric oxide (NO) with potential for treating inflammatory diseases, the phytochemicals of Amomum tsao-ko fruits were investigated, leading to the isolation of one bicyclic nonane (1), three menthene skeleton monoterpenoids (2-4), and two acyclic monoterpenoids (5 and 6). Their structures were identified using one- and two-dimensional nuclear magnetic resonance spectroscopy, and mass spectrometry. To the best of our knowledge, compounds 2-5 were obtained from the genus Amomum for the first time. All isolates were tested for their ability to inhibit lipopolysaccharide-stimulated NO overproduction in RAW264.7 cells. Compound 4 was found to inhibit NO production. Western blotting analysis indicated that active compound 4 can regulate inducible NO synthase expression. In addition, lipopolysaccharide-induced interleukin 1 beta and interleukin-6 overproduction was reduced in a concentration-dependent manner.

Hepatoprotective Impact of Geraniol Against CCl₄-Induced Liver Fibrosis in Rats

BACKGROUND AND OBJECTIVE

Numerous experimental studies have shown various pharmacological activities including geraniol's cancer prevention agent and antioxidant capacity. The goal of this investigation is to mark the prospective defensive role of geraniol in rat's carbon tetrachloride (CCl4) instigated in liver fibrosis.

MATERIALS AND METHODS

Liver fibrosis was prompted by subcutaneous injections of CCl4, twice week by week and for about a month. Simultaneously, geraniol (200 mg kg-1) was orally regulated every day. Post-Hoc-Test were carried out where p<0.05 has been established as a significant value.

RESULTS

The biochemical results showed that geraniol reduced liver damage just as manifestations of liver fibrosis. The administration of geraniol diminished the CCl4-initiated the elevation in serum aminotransferase activities and alkaline phosphatase activity. Geraniol diminished the levels of TNF-α, NO and myeloperoxidase activity which were prompted by the CCl4 treatment. The rise of serum hyaluronidase activity and hepatic hydroxyproline content was also curtailed by geraniol treatment. Besides, geraniol fundamentally declined hepatic malondialdehyde (MDA) formation and increased reduced glutathione (GSH) in CCl4-treated rats. Geraniol has also increased the activity of hepatic antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione-S-transferase (GST) and glutathione peroxidase (GPx) in the rats treated with CCl4. Finally, the histological analysis of the liver bolstered the biochemical results.

CONCLUSION

Our study has demonstrated that geraniol has a hepatoprotective upshot on liver fibrosis caused by CCl4, supposedly due to its free radical scavenging, antioxidant and anti-inflammatory characteristics.

Structure-Odor Activity Studies on Derivatives of Aromatic and Oxygenated Monoterpenoids Synthesized by Modifying p-Cymene

Thymoquinone was recently reported as having a unique pencil-like odor and being the impact compound for the cedar-like and cedar wood-based product smell such as pencils. The compounds thymol and carvacrol are structurally related odorants commonly found in plants and foods such as thyme and oregano, also having a significant contribution to their overall aroma. However, a systematic elucidation of the sensory properties in this class of oxygenated, aromatic monoterpenoids has not been carried out. To close this gap and gain new insights into structure-odor relationships leading to pencil-like and woody odors, 19 structurally related derivatives of p-cymene starting from thymol and carvacrol were synthesized and characterized. The compounds had odor thresholds ranging from 2.0 ng/L air to 388.8 ng/L air, being lowest for thymol and carvacrol and highest for thymohydroquinone. The compounds smelled mostly thyme-like, oregano-like, and pencil-like with phenolic, earthy, and medicinal variations in their odor character, which could be successfully linked to structural motifs.

Volatilomic Analysis of Four Edible Flowers from Agastache Genus

Volatilomes emitted from edible flowers of two species of Agastache (A. aurantiaca (A.Gray) Lint & Epling, and A. mexicana (Kunth) Lint & Epling) and from two hybrids (Agastache ‘Arcado Pink’ and Agastache ‘Blue Boa’) were investigated using a solid-phase microextraction technique as well as the extraction of its essential oils. Oxygenated monoterpenes were almost always the predominant class (>85%) of volatile organic compounds (VOCs) in each sample of A. aurantiaca, A. ‘Blue Boa’ and A. mexicana, with the exception of A. ‘Arcado Pink’ (38.6%). Pulegone was the main compound in A. aurantiaca (76.7%) and A. ‘Blue Boa’ (82.4%), while geranyl acetate (37.5%) followed by geraniol (16%) and geranial (17%) were the principal ones in A. mexicana. The essential oil composition showed the same behavior as the VOCs both for the main class as well as the major constituent (pulegone) with the same exception for A. mexicana. Total soluble sugars, secondary metabolites (polyphenols, flavonoids and anthocyanins) and antioxidant activity were also investigated to emphasize the nutraceutical properties of these edible flowers.

Chiral donor-acceptor azetines as powerful reactants for synthesis of amino acid derivatives

Coupling reactions of amines and alcohols are of central importance for applications in chemistry and biology. These transformations typically involve the use of a reagent, activated as an electrophile, onto which nucleophile coupling results in the formation of a carbon-nitrogen or a carbon–oxygen bond. Several promising reagents and procedures have been developed to achieve these bond forming processes in high yields with excellent stereocontrol, but few offer direct coupling without the intervention of a catalyst. Herein, we report the synthesis of chiral donor–acceptor azetines by highly enantioselective [3 + 1]-cycloaddition of enoldiazoacetates with aza-ylides and their selective coupling with nitrogen and oxygen nucleophiles via 3-azetidinones to form amino acid derivatives, including those of peptides and natural products. The overall process is general for a broad spectrum of nucleophiles, has a high degree of electronic and steric selectivity, and retains the enantiopurity of the original azetine.

Chiral 3-azetidinones are structural analogues of medicinally relevant β-lactams, however their synthesis and reactivity are underexplored. Here, the authors show a highly enantioselective copper-catalyzed [3 + 1]-cycloaddition generating 2-azetidines, which react with nucleophiles yielding amino acids via 3-azetidinones.

Metabolic Products of Linalool and Modulation of GABAA Receptors

Terpenoids are major subcomponents in aroma substances which harbor sedative physiological potential. We have demonstrated that various monoterpenoids such as the acyclic linalool enhance GABAergic currents in an allosteric manner in vitro upon overexpression of inhibitory α1β2 GABA_A receptors in various expression systems. However, in plants or humans, i.e., following intake via inhalation or ingestion, linalool undergoes metabolic modifications including oxygenation and acetylation, which may affect the modulatory efficacy of the generated linalool derivatives. Here, we analyzed the modulatory potential of linalool derivatives at α1β2γ2 GABA_A receptors upon transient overexpression. Following receptor expression control, electrophysiological recordings in a whole cell configuration were used to determine the chloride influx upon co-application of GABA EC₁₀₋₃₀ together with the modulatory substance. Our results show that only oxygenated linalool metabolites at carbon 8 positively affect GABAergic currents whereas derivatives hydroxylated or carboxylated at carbon 8 were rather ineffective. Acetylated linalool derivatives resulted in non-significant changes of GABAergic currents. We can conclude that metabolism of linalool reduces its positive allosteric potential at GABA_A receptors compared to the significant potentiation effects of the parent molecule linalool itself.

Characterization of odorous contaminants in post-consumer plastic packaging waste using multidimensional gas chromatographic separation coupled with olfactometric resolution

The increasing world population with their growing consumption of goods escalates the issue of sustainability concepts with increasing demands in recycling technologies. Recovery of post-consumer packaging waste is a major topic in this respect. However, contamination with odorous constituents currently curtails the production of recycling products that meet the high expectations of both consumers and industry. To guarantee odor-free recyclates, the main prerequisite is to characterize the molecular composition of the causative odorants in post-consumer plastic packaging waste. However, targeted characterization of odorous trace contaminants among an abundance of volatiles is a major challenge and requires specialized and high-resolution analytical approaches. For this aim, post-consumer packaging waste was characterized by sensory analysis and two-dimensional high resolution gas chromatography coupled with mass spectrometry and olfactometry. The 33 identified odorants represent various structural classes as well as a great diversity of smell impressions with some of the compounds being identified in plastics for the first time. Substances unraveled within this study provide insights into sources of odorous contamination that will require specific attention in the future in terms of screening and prevention in recycling products.