Volatile Organic Compounds Profiles Research Articles

Flavor Variations in Precious Tricholoma matsutake under Different Drying Processes as Detected with HS-SPME-GC-MS.

By employing headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), this study displayed the compositional changes in volatile organic compounds (VOCs) in Tricholoma matsutake samples subjected to hot-air drying (HAD) and vacuum freeze-drying (VFD) processes from their fresh samples. A total of 99 VOCs were detected, including 2 acids, 10 aldehydes, 10 alcohols, 13 esters, 12 ketones, 24 alkanes, 14 olefins, 7 aromatic hydrocarbons, and 7 heterocyclic compounds. Notably, the drying process led to a decrease in most alcohols and aldehydes, but an increase in esters, ketones, acids, alkanes, olefins, aromatic, and heterocyclic compounds. Venn diagram (Venn), principal component analysis (PCA), and partial least squares-discriminant analysis (PLS-DA) analyses enabled an easy and rapid distinction between the VOC profiles of T. matsutake subjected to different drying methods. Among the identified VOCs, 30 were designated as marker VOCs indicative of the employed drying process. And the VFD method was more capable of preserving the VOCs of fresh T. matsutake samples than the HAD method. Benzaldehyde, 1-Octen-3-ol, 3-Octanol, and (E)-2-Octen-1-ol were identified as markers for FRESH T. matsutake. Conversely, (E)-3-Hexene, lavender lactone, and α-Pinene were associated with VFD T. matsutake. For HAD T. matsutake, olefins, pyrazine, and esters, particularly ocimene, 2,5-Dimethyl-pyrazine, and methyl cinnamate, significantly contributed to its particularities. The results from this present study can provide a practical guidance for the quality and flavor control of volatile organic compounds in preciously fungal fruiting bodies by using drying processes.

Volatile organic compounds produced by thermophilic and non-thermophilic ampylobacter spp.: Influence of growth phase and nutrient composition

Bacteria produce a plethora of volatile organic compounds (VOCs) into the atmosphere as a means of interacting with their habitats, as well as for intra- and interkingdom communication, and to survive and thrive in nature and inside their hosts. Campylobacter, which is commonly found in poultry and ruminants, has demonstrated remarkable endurance in aquatic settings, making it one of the world's most hazardous foodborne pathogens that kill thousands of humans every year. In the present work, the VOCs released by both thermophilic (C. jejuni, C. coli, and C. lari) and non-thermophilic (C. fetus) Campylobacter of clinical significance, which were influenced by nutrient composition (media) and growth phase, were profiled using an active sampling approach, with active charcoal adsorbent and gas chromatography-mass spectrometry. Alcohols and ketones were detected only in the thermophilic Campylobacter strains, C. jejuni subsp. jejuni (1-heptadecanol; 1,8-nonadien-3-ol; 3,7,11-trimethyl-3-dodecanol; 1s,4R,7R,11R-1,3,4,7-tetramethyltricyclo [5.3.1.0(4,11)] undec-2-en-8-one; and isophorone), C. coli (isophorone and 3,5-bis(1,1-dimethylethyl)-phenol), and C. lari (3,7,11-trimethyl-3-dodecanol and 1s,4R,7R,11R-1,3,4,7-tetramethyltricyclo [5.3.1.0(4,11)] undec-2-en-8-one) between early stationary and stationary growth phases. The non-thermophilic C. fetus produced only a range of unidentified compounds that need to be investigated further in the future. The results from the principal component analysis showed distinctive clustering of VOC markers between the four bacteria taxa and within the strains of C. jejuni, including distinguishable groupings of VOCs throughout the growth phase of each bacterium and between different culture media. This demonstrates the influence of bacterial growth and media composition on the volatilome of the studied Campylobacter spp. Overall, the VOC profiling of these foodborne pathogens, under influencing factors of growth phase and media, paves the way for future rapid identification of Campylobacter spp. in food matrices.

Influence of wheat content and origin on the volatilome of craft wheat beer: An investigation by combined multivariate statistical approaches

A deeper knowledge of the effect of wheat origin on the volatile organic compounds (VOCs) profile of craft wheat beer is crucial for its quality improvement and local product valorisation.The VOCs profile of 17 craft wheat beers obtained by common and durum, heritage and modern, wheat varieties grown in different fields sited at different altitudes was analysed.Data were processed by multivariate analysis using different approaches. Partial least square (PLS) analysis evidenced that wheat concentration was the highest source of VOCs variance, followed by, wheat species, wheat ancientness, and altitude of cultivation. An insight into the effect of wheat concentration was given by sparse PLS analysis (sPLS). The effect of wheat variety was explored by linear discriminant analysis (LDA), which permitted to correctly classify craft beers made with wheat of different origin (species and variety) on the basis of their VOCs profile. sPLS regression analysis permitted to find a combination of VOCs able to predict the altitude of wheat cultivation as well as to correctly classify wheat beers made with wheat cultivated at different altitudes. A further ‘one versus all’ approach by Soft Independent Modelling of Class Analogies (SIMCA) permitted to correctly authenticate beers made with different cereal species. Finally, shape analysis by generalized Procrustes analysis (GPA) revealed that the differences among samples were conserved and reflected from wheat kernels to wheat beers. This study suggests a promising use of volatiles fingerprinting with a combination of different statistical approaches to authenticate beer made with wheat of different origin and cultivated at different altitudes, thus stressing out the importance of territory in craft beer production, which, until now, was a neglected topic.

Examination of internal metabolome and VOCs profile of brewery yeast and their mutants producing beer with improved aroma

Volatile organic compounds (VOCs) are metabolites pivotal in determining the aroma of various products. A well-known VOC producer of industrial importance is Saccharomyces cerevisiae, partially responsible for flavor of beers and wines. We identified VOCs in beers produced by yeast strains characterized by improved aroma obtained in UV-induced mutagenesis. We observed significant increase in concentration of compounds in strains: 1214uv16 (2-phenylethyl acetate, 2- phenylethanol), 1214uv31 (2-ethyl henxan-1-ol), 1214uv33 (ethyl decanoate, caryophyllene). We observed decrease in production of 2-phenyethyl acetate in strain 1214uv33. Analysis of intracellular metabolites based on 1H NMR revealed that intracellular phenylalanine concentration was not changed in strains producing more phenylalanine related VOCs (1214uv16 and 1214uv33), so regulation of this pathway seems to be more sophisticated than is currently assumed. Metabolome analysis surprisingly showed the presence of 3-hydroxyisobutyrate, a product of valine degradation, which is considered to be absent in S. cerevisiae. Our results show that our knowledge of yeast metabolism including VOC production has gaps regarding synthesis pathways for individual metabolites and regulation mechanisms. Detailed analysis of 1214uv16 and 1214uv33 may enhance our knowledge of the regulatory mechanisms of VOC synthesis in yeast, and analysis of strain 1214uv31 may reveal the pathway of 2-ethyl henxan-1-ol biosynthesis.

Volatile organic compounds: A promising new frontier for cancer screening

The late onset of cancer symptoms can cause a significant delay in diagnosis, impacting patients’ prognosis and quality of life, thus prompting a need for alternative screening and detection methods. Neoplastic processes cause distinct and immediate changes to the body’s metabolism, creating unique patterns in the volatile organic compounds (VOCs) produced and released through exhaled breath. For this reason, VOC profiles have emerged as diagnostic indicators for several types of malignancies, facilitating early cancer detection. Both non-invasive and accessible, the analysis of breath VOCs for cancer screening and detection has gained recognition as a new frontier in cancer diagnostics. Using exhaled breath instead of gold-standard cancer detection and screening tools that are traditionally invasive and uncomfortable for the patient could be revolutionary in improving patient compliance. Further, compared to the gold-standard tools, breath testing is relatively inexpensive, and the method of analysis, storage, and transporting the samples is simplified. Several studies have demonstrated the accuracy of VOC analysis in detecting various types of cancer, including breast cancer, colon cancer, prostate cancer, gastric cancer, and melanoma. This article summarizes the evidence supporting VOC analysis for cancer screening and detection. It reviews the clinical utility, current limitations, and necessity for standardization across all VOC screening tools to ensure the standardization and reliability of measurements. The evidence supporting breath tests to detect cancer accurately is strong, demonstrating that VOC sampling improves patient outcomes and decreases the global burden of malignant conditions by detecting cancer earlier.

The effect of extraction conditions on the chemical profile of obtained raw poplar propolis extract

Various conditions of extraction were applied to obtain active extracts of raw poplar-type propolis. The extraction efficiency of traditional maceration was evaluated in terms of used solvent: ethanol (70 and 96% v/v), acetone (pure and 70%), propylene glycol, glycerol (50%), water and water with extraction modifiers: PEG 400 and lecithin. For obtained extracts, the total amounts of extracted phenolics and flavonoids as well as antioxidant activity were compared. For the most active extracts, the profile of volatile organic compounds with the use of GC × GC–MS and selected polyphenols content by HPLC–DAD was compared. To increase the activity of water propolis, extract ultrasound and microwave-assisted extraction were applied and obtained water extracts were compared regarding the main polyphenolic compounds content quantified by HPLC method. The recovery of 70% ethanolic extraction and the effect of the extension of extraction time were also examined by the HPTLC method. Based on conducted analyses, 70% ethanolic extract was found as the most aromatic and bioactive, followed by pure acetone and polypropylene glycol extracts. Compared to the classic maceration, water extraction assisted by microwaves and ultrasounds did not provide a higher extraction yield. In the case of 70% ethanolic extraction, the 5-day duration is recommended which allows to recovery of close to 80% of bioactive components of raw propolis.

Seasonal and height dynamics of volatile organic compounds in rubber plantation: Impacts on ozone and secondary organic aerosol formation

Rubber trees emit a range of volatile organic compounds (VOCs), including isoprene, monoterpenes, and sesquiterpenes, as part of their natural metabolism. These VOCs can significantly influence air quality through photochemical reactions that produce ozone and secondary organic aerosols (SOAs). This study examines the impact of VOCs detected in a rubber tree plantation in Northeastern Thailand on air quality, highlighting their role in atmospheric reactions that lead to the formation of ozone and SOAs. VOCs were collected at varying heights and seasons using Tenax-TA tubes paired with an atmospheric sampler pump and identified by gas chromatography–mass spectrometry. In total, 100 VOCs were identified, including alkanes, alkenes, terpenes, aromatics, and oxygenated VOCs. Principal Coordinate Analysis (PCoA) revealed distinct seasonal VOC profiles, with hydrocarbons, peaking in summer and terpenes in the rainy season. The Linear Mixed-Effects (LME) model indicates that VOC concentrations are more influenced by seasonal changes than by sampling heights. Secondary organic aerosol potential (SOAP) and ozone formation potential (OFP) of selected VOC species were also determined. The total SOAP ranged from 67.24 μg/m3 in summer to 17.87 μg/m3 in winter, while the total OFP ranged from 377.87 μg/m3 in summer to 139.39 μg/m3 in winter. Additionally, positive matrix factorization (PMF) analysis identified four main VOC sources: gasoline combustion (18.3 %), microbial activity (38.6 %), monoterpene emissions during latex production (15.0 %), and industrial sources (28.1 %). These findings provide essential information for managing air pollution in rubber tree plantations. By adopting focused air quality management strategies, plantation operators can mitigate the adverse effects of VOCs, promoting a healthier and more sustainable future.

Molecular Regulatory Mechanisms Affecting Fruit Aroma.

Aroma, an important quality characteristic of plant fruits, is produced by volatile organic compounds (VOCs), mainly terpenes, aldehydes, alcohols, esters, ketones, and other secondary metabolites, in plant cells. There are significant differences in the VOC profile of various fruits. The main pathways involved in the synthesis of VOCs are the terpenoid, phenylalanine, and fatty acid biosynthesis pathways, which involve several key enzyme-encoding genes, transcription factors (TFs), and epigenetic factors. This paper reviews the main synthetic pathways of the main volatile components in fruit, summarizes studies on the regulation of aroma formation by key genes and TFs, summarizes the factors affecting the fruit aroma formation, describes relevant studies on the improvement of fruit flavor quality, and finally proposes potential challenges and prospects for future research directions. This study provides a theoretical basis for the further precise control of fruit aroma quality and variety improvement.

Diagnosis of chondrosarcoma in a noninvasive way using volatile organic compounds in exhaled breath: a pilot study.

Aim: Aim of this explorative pilot study was to evaluate the capability of an electronic nose (aeoNose, the eNose Company) to classify healthy individuals and patients with chondrosarcoma, based on their volatile organic compound profiles in exhaled breath.Materials &methods: Fifty-seven patients (25 healthy controls, 24 chondrosarcoma and 8 different benign lesions) were included in the study from 2018 to2023. An artificial neural network was used as classifier.Results: The developed model had a sensitivity of 75%, and a specificity of 65% with an AUC of 0.66.Conclusion: Results show that there is not enough evidence to include the aeoNose as diagnostic biomarker for chondrosarcoma in daily practice. However, the aeoNose might play an additional role alongside MRI, in questionable chondrosarcoma cases.

An improved genome assembly of Chrysanthemum nankingense reveals expansion and functional diversification of terpene synthase gene family

BackgroundTerpenes are important components of plant aromas, and terpene synthases (TPSs) are the key enzymes driving terpene diversification. In this study, we characterized the volatile terpenes in five different Chrysanthemum nankingense tissues. In addition, genome-wide identification and expression analysis of TPS genes was conducted utilizing an improved chromosome-scale genome assembly and tissue-specific transcriptomes. The biochemical functions of three representative TPSs were also investigated.ResultsWe identified tissue-specific volatile organic compound (VOC) and volatile terpene profiles. The improved Chrysanthemum nankingense genome assembly was high-quality, including a larger assembled size (3.26 Gb) and a better contig N50 length (3.18 Mb) compared to the old version. A total of 140 CnTPS genes were identified, with the majority representing the TPS-a and TPS-b subfamilies. The chromosomal distribution of these TPS genes was uneven, and 26 genes were included in biosynthetic gene clusters. Closely-related Chrysanthemum taxa were also found to contain diverse TPS genes, and the expression profiles of most CnTPSs were tissue-specific. The three investigated CnTPS enzymes exhibited versatile activities, suggesting multifunctionality.ConclusionsWe systematically characterized the structure and diversity of TPS genes across the Chrysanthemum nankingense genome, as well as the potential biochemical functions of representative genes. Our results provide a basis for future studies of terpene biosynthesis in chrysanthemums, as well as for the breeding of improved chrysanthemum varieties.

AI Applied to Volatile Organic Compound (VOC) Profiles from Exhaled Breath Air for Early Detection of Lung Cancer.

Volatile organic compounds (VOCs) are an increasingly meaningful method for the early detection of various types of cancers, including lung cancer, through non-invasive methods. Traditional cancer detection techniques such as biopsies, imaging, and blood tests, though effective, often involve invasive procedures or are costly, time consuming, and painful. Recent advancements in technology have led to the exploration of VOC detection as a promising non-invasive and comfortable alternative. VOCs are organic chemicals that have a high vapor pressure at room temperature, making them readily detectable in breath, urine, and skin. The present study leverages artificial intelligence (AI) and machine learning algorithms to enhance classification accuracy and efficiency in detecting lung cancer through VOC analysis collected from exhaled breath air. Unlike other studies that primarily focus on identifying specific compounds, this study takes an agnostic approach, maximizing detection efficiency over the identification of specific compounds focusing on the overall compositional profiles and their differences across groups of patients. The results reported hereby uphold the potential of AI-driven techniques in revolutionizing early cancer detection methodologies towards their implementation in a clinical setting.

Comparative study of volatile organic compound profiles in aromatic and non-aromatic rice cultivars using HS-GC–IMS and their correlation with sensory evaluation

Analyzing of volatile organic compounds (VOCs) is important in rice quality control and breeding aromatic cultivars. This study utilized HS-GC–IMS, known for its simplicity, high sensitivity, and low cost, to analyze VOCs in 59 aromatic and 6 non-aromatic rice cultivars. The aromatic intensity of each rice cultivar was determined by artificial sensory evaluation, thus the correlation between sensory evaluation scores and VOC peak volumes was explored. A total of 77 VOCs were identified, with aromatic cultivars exhibiting prevalent short-chain aliphatic aldehydes, alcohols, and ketones, while non-aromatic samples contained higher concentrations of esters, furans, terpenes, and benzene derivatives. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) based on VOC data effectively distinguished the two rice types, and 35 VOCs were regarded as the marker VOCs contributing to the volatile variations. Furthermore, the correlation analysis between sensory evaluation and VOC markers revealed that most of these VOCs had a positive correlation with the sensory evaluation scores, with 1-pentanol, 2-acetyl-1-pyrroline (D), and 1-hexanol (M) exhibiting the highest correlation coefficients. Meanwhile, most VOC markers also exhibited positive correlations with other volatiles. The results confirm the suitability of HS-GC–IMS for VOC detection and rice category discrimination.

Influence of Drying and Storage Conditions on the Volatile Organic Compounds Profile of Spirulina Platensis

Spirulina platensis (SP) has gained popularity over the last few years, owing to its remarkable nutritional properties and high potential across various industrial sectors. In this study, we analyzed the volatile profile of eight SP samples from the same strain subjected to different drying (oven-drying, air-drying, and spray-drying) and storing conditions (“freshly prepared” and after 12 months of storage) using HS-SPME-GC-MS. Principal component analysis (PCA) was used as a multivariate technique to discern similarities and differences among the samples. The main aim was to assess the impact of the drying technique on the aroma profile and storage life of SP samples. Air-drying leads to the less pronounced formation of by-products related to heat treatment, such as Maillard and Strecker degradation compounds, but promotes oxidative and fermentative phenomena, with the formation of organic acids and esters, especially during storage. Thermal treatment, essential for limiting degradation and fermentation during storage and extending shelf life, alters the aroma profile through the formation of volatile compounds, such as Strecker aldehydes and linear aldehydes, from amino acid and lipid degradation. High temperatures in spray-drying favor the formation of pyrazines. The findings underscore the trade-offs inherent in choosing an appropriate drying method, thereby informing decision-making processes in industrial settings aimed at optimizing both product quality and efficiency.

Gas-chromatographic analyses of volatile organic compounds in essential oils extracted from Slovak juniper berries and needles (Juniperus communis L.)

Juniper essential oils (EOs) are mainly extracted from berries; however, nowadays studies point to needles as a viable source of EOs. Total qualitative-quantitative profiles of individual volatile organic compounds (VOCs) of EOs extracted from berries, old and young needles, gathered from the same locality, were obtained by GC–MS and GC–FID analyses. Moreover, qualitative-quantitative differences were determined among particular EOs within two subsequent years. Generally, VOC profiles of EOs were mainly represented by monoterpenes, sesquiterpenes and their oxygenated derivatives. Depending on the harvest year, α-pinene (27.70–35.42 %) was the most abundant VOC in juniper berry EOs, followed by germacrene D, sabinene, myrcene, germacrene B and β-pinene. Overall, needle EOs were primarily characterised by sabinene, α-pinene, γ-terpinene and terpinen-4-ol, but with an intense dependence on the needle age and harvest year. β-Ylangene and α-cubebene were specific to berry EOs, whereas trans-2-hexenal was specific to needle EOs. Discriminant analysis achieved 100 % accuracy of correctly classified EOs according to the raw material and harvest year. α-Cubebene, germacrene B, γ-muurolene, one unknown compound and trans-2-hexenal were identified as the most significant for discrimination according to the source, while juniper camphort, cis-2-p-menthen-1-ol, terpinen-4-ol and β-elemene played dominant roles in discrimination according to the harvest year.

Profile of Volatile Organic Compounds from Cuscuta Campestris Yunck

Profile of Volatile Organic Compounds from Cuscuta Campestris Yunck

Using ethically sourced training aids for human remains detection dog training

Human remains detection dogs (HRDDs) play vital roles in forensic investigations and search and rescue missions by detecting decomposing human remains. However, there is a lack of standardized training protocols globally. This study evaluates various ethically sourced HRDD training aids, including amputated limbs, blood, and teeth used by the Ontario Provincial Police (OPP). Expanding on prior research, this study assesses amputated limbs stored outdoors, bone, tissue, blood, and teeth. The volatile organic compound (VOC) profiles of these aids are compared to cadavers decomposing at the Research in Experimental and Social Thanatology (REST) facility. The results highlighted that the combined VOC profile from all HRDD training aid types demonstrates a 68% similarity to REST cadavers, emphasizing the potential benefit of exposing HRDDs to a diverse range of training aids. This is because the similarities in VOC profiles of individual training aid types (amputated limbs stored indoors, bone, blood, tissue, amputated limbs stored outdoors, teeth) with REST cadavers were lower than 68%. Teeth (without organic matter) were identified as the least ideal training aid for enabling dogs to detect cadavers based on VOC profiles and HRDD responses. However, training on teeth may be required for operational needs, particularly when HRDDs need to locate teeth during field searches. This study also highlights the effectiveness of using amputated limbs and blood together as they comprise a majority of the 68% VOCs found similar to the REST cadavers and elicit desirable HRDD responses to decomposition odor.

Stereoscopic imaging of volatile organic compounds distribution in the region and tracing emission sources of volatile organic compounds using a novel movable single-photon ionization time-of-flight mass spectrometer.

This paper presents a newly developed high-performance mobile single-photon ionization time-of-flight mass spectrometry (M-SPI-TOFMS) system for on-line analysis and stereoscopic monitoring of complex gas mixtures. The system is designed for stereoscopic imaging to map the distribution of volatile organic compounds (VOCs) and trace their emission sources in urban areas and industrial parks. It mainly consists of a SPI-TOFMS instrument, a customized commercial vehicle, a meteorological five-parameter monitor with GPS, a high-power generator, and an uninterruptible power supply. The SPI technique, using a 118 nm VUV lamp, can ionize compounds with an ionization potential below 10.78 eV. Mass spectra obtained using this technique show the profiles of various VOCs and some inorganic compounds. The VOCs composition information and mobile location data are simultaneously sent to the GIS software. In GIS software, this data is used for real-time stereoscopic imaging of VOC distribution and precise tracking of VOC movement. The system can achieve a spatial data resolution of 0.69 mm at 25 km/h due to the microsecond detection speed of the M-SPI-TOFMS instrument. The laboratory test provides a rapid overview characterization of benzene, toluene, and xylene. The M-SPI-TOFMS has limits of detection and mass resolution of 33.7 pptv and 1060, respectively. Several field applications were carried out using M-SPI-TOFMS at various locations to identify VOC sources near different factories. The M-SPI-TOFMS system has a navigation monitoring speed of 25 km/h with a time resolution of 1 s. The widespread use of this system will provide accurate data to support environmental management departments in formulating VOCs pollution control policies and improving control efficiency.

Characterization of the volatile organic compounds and sensory properties of fermented soymilks as affected by carbohydrates and starter cultures

Soymilks were fermented by two starter cultures and with different levels of added glucose or lactose respectively. GC-MS, HS-GC-IMS and GC × GC-TOFMS were compared and the latter reported much more volatile organic compounds (VOCs). The VOCs profiles of the fermented soymilks were divided into four groups using principal component analysis and hierarchical clustering analysis. Based on the variable importance in the projection value greater than 1.0 and one way ANOVA (P < 0.05), 22 VOCs were respectively identified as the critical differential VOCs in starter culture A and B fermented soymilk, and the concentrations of the critical differential VOCs changed in different patterns in response to the addition of carbohydrates. Four significant metabolic pathways were involved via the metabolite set enrichment analysis, including the glycolysis/gluconeogenesis, pyruvate metabolism. Among critical differential VOCs, there were 11 and 13 aroma-active compounds with odor activity values greater than 1.0, for starter culture A and B fermented soymilks respectively. The deductive sensory properties of the fermented soymilks as affected by carbohydrate addition were evaluated. This study provides experimental and theoretical bases for improving flavor quality of fermented soymilks.

Leaf volatile organic compounds profiles from two citrus genotypes differing in susceptibility to Phytophthora citrophthora infection

The leaves of two citrus genotypes, citrange ‘Carrizo’ and sweet orange ‘Washington Navel’ were artificially infected by the oomycete Phytophthora citrophthora, the causal agent of trunk gummosis and fruit brown rot of citrus, to study the profile of leaf stored terpenoids in the response to the pathogen infection. On ‘Washington Navel’ leaves the symptoms were more severe and manifested earlier than on ‘Carrizo’ leaves.Overall, 35 volatile organic compounds (VOCs) were identified by GC-MS analysis in the not-infected (control) and infected leaf extracts from the two citrus genotypes. Interesting the two volatile profiles differed not in the quality, but in the quantity of each compound. After infection, the amount of 15 out of the 35 identified VOCs varied significantly. The level of five metabolites changed in both species, while two of the compounds changed exclusively in ‘Citrange’ and eight exclusively in ‘Washington Navel’. To understand the potential role of differentially expressed stored volatiles in the citrus response mechanisms to the infection, the inhibitory activity of ten of them volatiles was tested in vitro on P. citrophthora. Citral, linalool and trans-2-hexenal completely inhibited the mycelium growth suggesting the possible involvement of these compounds in the defence mechanisms of citrus against P. citrophthora. This study provides new insights into a potential role of stored VOCs in the response mechanisms against the oomycete pathogen P. citrophthora in citrus species. Furthermore, it paves the way for future investigations aimed at assessing the potential utilization of VOCs for priming purposes.

Floral structure, histochemistry, and volatile compounds in Bulbophyllum species of the ‘Cirrhopetalum alliance’ (Orchidaceae)

Abstract Bulbophyllum is the most species-rich orchid genus. Recent molecular data groups certain of its species into a monophyletic ‘Cirrhopetalum alliance’. Within this alliance are a monophyletic section Cirrhopetaloides and a non-monophyletic section Cirrhopetalum. Floral morphology and scent are partially conserved phylogenetically compared to the molecular data. Here, floral morphology, histochemistry, anatomy, and floral volatile organic compounds (VOCs) of selected Bulbophyllum species are analysed to assess whether there are structural or chemical differences that support separation into the two sections, to update available VOC data from this genus, and to consider evolutionary adaptations in the ‘Cirrhopetalum alliance’. We found that ‘Cirrhopetalum alliance’ flowers differ from some sections of Bulbophyllum in the structure of cells lining the longitudinal groove on the labellum or lip and report, for the first time in Bulbophyllum, a type of atypical oleiferous trichome probably involved in VOC production. We show a clear difference in floral VOC profiles between B. bicolor (sect. Cirrhopetaloides) and four other Bulbophyllum species, three previously assigned to sect. Cirrhopetalum, but VOC profiles do not support separation into the two sections. The lack of congruence between already established molecular phylogeny, floral anatomy, and VOC data suggests that VOC differences are due to recently and independently evolved pollinator specificity. We therefore show that there is no clear separation of these sections based on floral anatomy, histochemistry, or VOC profiles.