Sniffing Out the Sustainable Future: The Renewability Revolution in Fragrance Chemistry

In this review, the impact of the transition from today's resource-wasting petrochemical economy towards a 100/100 renewable and biodegradable future is discussed with respect to the fragrance families: "citrus", "green", "fruity", "floral", "floriental", "oriental", "woody", "chypre" and "fougère". After benchmark data on ingredients usage, definitions on biodegradation and sustainability are given. Celebrating the 150th anniversary of synthetic vanillin, its historic synthesis from renewable starting materials serves as introduction. In the grand scheme of things, citrus scents upcycled from the beverages industry, are already an ideal case for 100/100 with new opportunities for artificial essential oils. In the fruity domain, transparent and lactonic ingredients are available in a sustainable manner. However, in the domain of green odorants, there is a lack of green chemistry for important key materials. In the floral family, renewability is more critical than biodegradability, but cost is an issue. Thanks to Ambrox and maltol, florientals and orientals will persist, while woody notes severely lack an Iso E Super replacer. In the chypre genre, patchouli became the new moss, but more musks are increasingly in demand. With their high percentage of linalool and dihydromyrcenol, the construction of fougères could well become a precedent for other families, despite challenges in vetiver and salicylates. Still, the challenges exemplified here create immense opportunities for new perfumery materials.

Application of graphite carbon black assisted-laser desorption ionization-mass spectrometry for soy sauce product discrimination

In a previous study, we developed a novel analytical method to directly and simultaneously detect taste- and odor-active compounds using graphite carbon black (GCB)-assisted laser desorption ionization mass spectrometry (LDI-MS). In this study, we aimed to evaluate food quality using a variety of soy sauces using the method to discriminate each product. GCB-LDI-MS allowed the provision of hundreds of MS peaks derived from soy sauces in both positive and negative modes without any tedious sample pretreatments. Principal component analysis using the obtained MS peaks clearly distinguished three soy sauce products based on the manufacturing countries (Japan, China, and India). Moreover, this method identified distinct MS peaks for discrimination, which significantly correlated with their quantitative amounts in the products. Thus, GCB-LDI-MS analysis was established as a simple and rapid technique for food analysis, illustrating the chemical patterns of food products.

Olfaction: an emerging regulator of longevity and metabolism

Ageing is a malleable process influenced by the environment. Recent research reveals that neurons interact with peripheral organs to regulate metabolism and longevity by responding to olfactory cues through specific pathways, such as the unfolded protein response (UPR) and microRNAs. Here, we examine the significance of these findings.

The subapical labial sensory organ of spotted lanternfly Lycorma delicatula

Deciphering how spotted lanternfly (SLF), an invasive polyphagous planthopper in North America, engages with its environment is a pressing issue with fundamental biological significance and economic importance. This interaction primarily depends on olfaction. However, the cellular basis of olfaction in SLF remains elusive. Here we investigate the neuronal and functional organization of the subapical labial sensory organ using scanning electron microscopy and electrophysiological recordings. This organ is believed to supply planthoppers with crucial sensory information that influences their subsequent feeding behaviour. We find in SLF that this organ comprises two identical placoid sensilla, each housing two distinct neurons. The A neuron displays a remarkable sensitivity to changes in airflow speed. Importantly, the same neuron also exhibits robust excitatory responses exclusively to three aldehydes out of a diverse pool of 85 tested odorants and inhibitory responses to 62 other odorants. By contrast, the B neuron solely serves as an olfactory detector, showing strong excitatory responses to 17 odorants and inhibitory responses to only three. The results provide a potential cellular basis for the behavioural responses of SLF to its ecologically relevant stimuli. Our study also identifies new odorants that may be useful for managing this serious pest.

Chemosensory Characteristics of Brandies from Chinese Core Production Area and First Insights into Their Differences from Cognac

This work aimed to compare the aroma characteristics of representative brandies with different grades from Yantai (one of the Chinese core production areas) and Cognac and to establish relationships between sensory descriptors and chemical composition. Descriptive analysis was performed with a trained panel to obtain the sensory profiles. Forty-three aroma-active compounds were quantified by four different methodologies. A prediction model on the basis of partial least squares analysis was performed to identify candidate compounds that were unique to a certain group of brandies. The result showed that brandies from Yantai could be distinguished from Cognac brandies on the basis of spicy, dried fruit, floral, and fruity-like aromas, which were associated with an aromatic balance between concentrations of a set of compounds such as 5-methylfurfural, γ-nonalactone, and γ-dodecalactone. Meanwhile, brandy with different grades could be distinguished on the basis of compounds derived mostly during the aging process.

Olfactory Stimulation as Environmental Enrichment for Domestic Horses-A Review

Horses constantly face several challenges inherent to the domestic environment, and it is common for the expression of their natural behavior to be drastically limited. Environmental enrichment has been suggested as an alternative to improve the captive situation of domestic horses. Among the recently proposed enrichment strategies, olfactory stimulation has emerged as a method for improving several aspects related to animal behavior. Olfaction is a sensory modality that plays a significant role in the expression of equine behavior, and in recent years, studies have shown that olfactory stimulation can influence the physiological and behavioral parameters of horses. This review provides current information on the anatomical particularities of the equine olfactory system, presents the physiological mechanisms involved in the odor detection process, and demonstrates how stress can interfere with this process. Finally, the use of olfactory stimulation as an environmental enrichment for domestic horses (Equus ferus caballus) is explored. The need for new studies that answer pertinent questions related to this topic is discussed throughout the manuscript.

Developing human olfactory network and exploring olfactory receptor-odorant interaction

The Olfactory receptor (OR)-odorant interactions are perplexed. ORs can bind to structurally diverse odorants associated with one or more odor percepts. Various attempts have been made to understand the intricacies of OR-odorant interaction. In this study, experimentally documented OR-odorant interactions are investigated comprehensively to; (a) suggest potential odor percepts for ORs based on the OR-OR network; (b) determine how odorants interacting with specific ORs differ in terms of inherent pharmacophoric features and molecular properties, (c) identify molecular interactions that explained OR-odorant interactions of selective ORs; and (d) predict the probable role of ORs other than olfaction. Human olfactory receptor network (hORnet) is developed to study possible odor percepts for ORs. We identified six molecular properties which showed variation and significant patterns to differentiate odorants binding with five ORs. The pharmacophore analysis revealed that odorants subset of five ORs follow similar pharmacophore hypothesis, (one hydrogen acceptor and two hydrophobic regions) but differ in terms of distance and orientation of pharmacophoric features. To ascertain the binding site residues and key interactions between the selected ORs and their interacting odorants, 3D-structure modelling, docking and molecular dynamics studies were carried out. Lastly, the potential role of ORs beyond olfaction is explored. A human OR-OR network was developed to suggest possible odor percepts for ORs using empirically proven OR-odorant interactions. We sought to find out significant characteristics, molecular properties, and molecular interactions that could explain OR-odorant interactions and add to the understanding of the complex issue of odor perception.Communicated by Ramaswamy H. Sarma.

Natural gas odorants: A scoping review of health effects

PURPOSE OF REVIEW

Organosulfur compounds are intentionally added to natural gas as malodorants with the intent of short-term nasal inhalation to aid in leak detection. Regulatory exposure limits have not been established for all commonly used natural gas odorants, and recent community-level exposure events and growing evidence of indoor natural gas leakage have raised concerns associated with natural gas odorant exposures. We conducted a scoping review of peer-reviewed scientific publications on human exposures and animal toxicological studies of natural gas odorants to assess toxicological profiles, exposure potential, health effects and regulatory guidelines associated with commonly used natural gas odorants.

RECENT FINDINGS

We identified only 22 studies which met inclusion criteria for full review. Overall, there is limited evidence of both transient nonspecific health symptoms and clinically diagnosed causative neurotoxic effects associated with prolonged odorant exposures. Across seven community-level exposure events and two occupational case reports, consistent symptom patterns included: headache, ocular irritation, nose and throat irritation, respiratory complaints such as shortness of breath and asthma attacks, and skin irritation and rash. Of these, respiratory inflammation and asthma exacerbations are the most debilitating, whereas the high prevalence of ocular and dermatologic symptoms suggest a non-inhalation route of exposure. The limited evidence available raises the possibility that organosulfur odorants may pose health risks at exposures much lower than presently understood, though additional dose-response studies are needed to disentangle specific toxicologic effects from nonspecific responses to noxious organosulfur odors. Numerous recommendations are provided including more transparent and prescriptive natural gas odorant use practices.

Behavioral evidence of olfactory imprinting during embryonic and larval stages in lake sturgeon

Many migratory fishes are thought to navigate to natal streams using olfactory cues learned during early life stages. However, direct evidence for early-life olfactory imprinting is largely limited to Pacific salmon, and other species suspected to imprint show life history traits and reproductive strategies that raise uncertainty about the generality of the salmonid-based conceptual model of olfactory imprinting in fishes. Here, we studied early-life olfactory imprinting in lake sturgeon (Acipenser fulvescens), which have a life cycle notably different from Pacific salmon, but are nonetheless hypothesized to home via similar mechanisms. We tested one critical prediction of the hypothesis that early-life olfactory imprinting guides natal homing in lake sturgeon: that exposure to odorants during early-life stages results in increased activity when exposed to those odorants later in life. Lake sturgeon were exposed to artificial odorants (phenethyl alcohol and morpholine) during specific developmental windows and durations (limited to the egg, free-embryo, exogenous feeding larvae and juvenile stages), and later tested as juveniles for behavioral responses to the odorants that were demonstrative of olfactory memory. Experiments revealed that lake sturgeon reared in stream water mixed with artificial odorants for as little as 7 days responded to the odorants in behavioral assays over 50 days after the initial exposure, specifically implicating the free-embryo and larval stages as critical imprinting periods. Our study provides evidence for olfactory imprinting in a non-salmonid fish species, and supports further consideration of conservation tactics such as stream-side rearing facilities that are designed to encourage olfactory imprinting to targeted streams during early life stages. Continued research on lake sturgeon can contribute to a model of olfactory imprinting that is more generalizable across diverse fish species and will inform conservation actions for one of the world's most imperiled fish taxonomic groups.

Biocatalytic Production of Odor-Active Fatty Aldehydes from Fungal Lipids

Odor-active fatty aldehydes are important compounds for the flavor and fragrance industry. By a coupled enzymatic reaction using an α-dioxygenase (α-DOX) and an aldehyde dehydrogenase (FALDH), scarcely available aldehydes from the biotransformation of margaroleic acid [17:1(9Z)] were characterized and have shown highly interesting odor profiles, including citrus-like, soapy, herbaceous, and savory notes. In particular, (Z)-8-hexadecenal and (Z)-7-pentadecenal exhibited notable meaty odor characteristics. Submerged cultivation of Mortierella hyalina revealed the accumulation of the above-mentioned, naturally uncommon fatty acid 17:1(9Z). Its production was significantly increased by the modulation of culture conditions, whereas the highest accumulation was observed after 4 days at 24 °C and l-isoleucine supplementation. The lipase-, α-DOX-, and FALDH-mediated biotransformation of M. hyalina lipid extract resulted in a complex aldehyde mixture with a high aldehyde yield of ∼50%. The odor qualities of the formed aldehydes were assessed by means of gas chromatography-olfactometry, and several of the obtained fatty aldehydes have been sensorially described for the first time. To assess the aldehyde mixture's potential as a flavor ingredient, a sensory evaluation was conducted. The obtained product exhibited intense citrus-like, green, and soapy odor impressions.

Combining the Classification and Pharmacophore Approaches to Understand Homogeneous Olfactory Perceptions at Peripheral Level: Focus on Two Aroma Mixtures

The mechanisms involved in the homogeneous perception of odorant mixtures remain largely unknown. With the aim of enhancing knowledge about blending and masking mixture perceptions, we focused on structure-odor relationships by combining the classification and pharmacophore approaches. We built a dataset of about 5000 molecules and their related odors and reduced the multidimensional space defined by 1014 fingerprints representing the structures to a tridimensional 3D space using uniform manifold approximation and projection (UMAP). The self-organizing map (SOM) classification was then performed using the 3D coordinates in the UMAP space that defined specific clusters. We explored the allocating in these clusters of the components of two aroma mixtures: a blended mixture (red cordial (RC) mixture, 6 molecules) and a masking binary mixture (isoamyl acetate/whiskey-lactone [IA/WL]). Focusing on clusters containing the components of the mixtures, we looked at the odor notes carried by the molecules belonging to these clusters and also at their structural features by pharmacophore modeling (PHASE). The obtained pharmacophore models suggest that WL and IA could have a common binding site(s) at the peripheral level, but that would be excluded for the components of RC. In vitro experiments will soon be carried out to assess these hypotheses.

Screening and Validation of Odorants against Influenza A Virus Using Interpretable Regression Models

Influenza is a respiratory infection caused by the influenza virus that is prevalent worldwide. One of the most contagious variants of influenza is influenza A virus (IAV), which usually spreads in closed spaces through aerosols. Preventive measures such as novel compounds are needed that can act on viral membranes and provide a safe environment against IAV infection. In this study, we screened compounds with common fragrances that are generally used to mask unpleasant odors but can also exhibit antiviral activity against a strain of IAV. Initially, a set of 188 structurally diverse odorants were collected, and their antiviral activity was measured in vapor phase against the IAV solution. Regression models were built for the prediction of antiviral activity using this set of odorants by taking into account their structural features along with vapor pressure and partition coefficient (n-octanol/water). The models were interpreted using a feature weighting approach and Shapley Additive exPlanations to rationalize the predictions as an additional validation for virtual screening. This model was used to screen odorants from an in-house odorant data set consisting of 2020 odorants, which were later evaluated using in vitro experiments. Out of 11 odorants proposed using the final model, 8 odorants were found to exhibit antiviral activity. The feature interpretation of screened odorants suggested that they contained hydrophilic substructures, such as hydroxyl group, which might contribute to denaturation of proteins on the surface of the virus. These odorants should be explored as a preventive measure in closed spaces to decrease the risk of infections of IAV.

Characterization of Key Odorants in Lingtou Dancong Oolong Tea and Their Differences Induced by Environmental Conditions from Different Altitudes

Lingtou Dancong oolong tea is a famous Chinese oolong tea due to its special honey-like aroma. However, little is known about its specific aroma profile and key contributors. Furthermore, whether the aroma characteristics of Lingtou Dancong oolong tea are affected by the environmental conditions at different altitudes is unknown. In this study, the aromas in Lingtou Dancong oolong tea were extracted and analyzed by stir-bar sorptive extraction (SBSE) combined with gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (GC-MS), and the aroma profiles of tea plants grown at different altitudes were compared. We detected 59 odor compounds in Lingtou Dancong oolong tea. Eight compounds with honey and floral odors were identified as key components on the basis of GC-O, GC-MS, odor activity value, and flavor dilution analyses. Differences in the contents of precursor geranyl diphosphate and transcript levels of structural genes were found to be responsible for the differential accumulation of linalool and hotrienol among plants grown at different altitudes. This is the first report on the aroma characteristics and key contributors of Lingtou Dancong oolong tea and their differences, as affected by altitude. These results provide details of the chemical basis of the aroma quality of Lingtou Dancong oolong tea.

Spirocyclic Compounds in Fragrance Chemistry: Synthesis and Olfactory Properties

In this Review, both the scientific literature and patents have been analysed to gather, examine and classify synthetic strategies developed to access spirocyclic molecules having olfactory properties of interest for the perfume industry. New structures have been reported at a steady state since 1961 with a particularly intense activity in the 80's. In the diversity of olfactory properties observed, spirocyclic molecules were found to be quite frequently woody, as well as fruity and ambery, among other tonalities. More recent data reflect the evolution of modern synthetic organic chemistry towards bioinspiration, enantioselective reactions, green and sustainable chemistry and biotechnology.

Synthesis of odorants in flow and their applications in perfumery

Continuous flow technology is a key technology for sustainable manufacturing with numerous applications for the synthesis of fine chemicals. In recent years, the preparation of odorants utilizing the advantages of flow reactors received growing attention. In this review, we give an overview of selected methods for the synthesis of odorants in flow, including heterogeneously catalyzed reactions, gas reactions, and photochemical C–H functionalization processes. After a brief introduction on types of odorants, the presented odorant syntheses are ordered according to the main odor families “fruity”, “green”, “marine”, “floral”, “spicy”, “woody”, “ambery”, and “musky” and their use and importance for perfumery is briefly discussed.

Home is Where the Pipeline Ends: Characterization of Volatile Organic Compounds Present in Natural Gas at the Point of the Residential End User

The presence of volatile organic compounds (VOCs) in unprocessed natural gas (NG) is well documented; however, the degree to which VOCs are present in NG at the point of end use is largely uncharacterized. We collected 234 whole NG samples across 69 unique residential locations across the Greater Boston metropolitan area, Massachusetts. NG samples were measured for methane (CH₄), ethane (C₂H₆), and nonmethane VOC (NMVOC) content (including tentatively identified compounds) using commercially available USEPA analytical methods. Results revealed 296 unique NMVOC constituents in end use NG, of which 21 (or approximately 7%) were designated as hazardous air pollutants. Benzene (bootstrapped mean = 164 ppbv; SD = 16; 95% CI: 134-196) was detected in 95% of samples along with hexane (98% detection), toluene (94%), heptane (94%), and cyclohexane (89%), contributing to a mean total concentration of NMVOCs in distribution-grade NG of 6.0 ppmv (95% CI: 5.5-6.6). While total VOCs exhibited significant spatial variability, over twice as much temporal variability was observed, with a wintertime NG benzene concentration nearly eight-fold greater than summertime. By using previous NG leakage data, we estimated that 120-356 kg/yr of annual NG benzene emissions throughout Greater Boston are not currently accounted for in emissions inventories, along with an unaccounted-for indoor portion. NG-odorant content (tert-butyl mercaptan and isopropyl mercaptan) was used to estimate that a mean NG-CH₄ concentration of 21.3 ppmv (95% CI: 16.7-25.9) could persist undetected in ambient air given known odor detection thresholds. This implies that indoor NG leakage may be an underappreciated source of both CH₄ and associated VOCs.

Nasal Odorant Competitive Metabolism Is Involved in the Human Olfactory Process

Within the peripheral olfactory process, odorant metabolizing enzymes are involved in the active biotransformation of odorants, thus influencing the intensity and quality of the signal, but little evidence exists in humans. Here, we characterized the fast nasal metabolism of the food aroma pentane-2,3-dione in vivo and identified two resulting metabolites in the nasal-exhaled air, supporting the metabolizing role of the dicarbonyl/l-xylulose reductase. We showed in vitro, using the recombinant enzyme, that pentane-2,3-dione metabolism was inhibited by a second odorant (e.g., butanoic acid) according to an odorant-odorant competitive metabolic mechanism. Hypothesizing that such mechanism exists in vivo, pentane-2,3-dione, presented with a competitive odorant, both at subthreshold concentrations, was actually significantly perceived, suggesting an increase in its nasal availability. Our results, suggesting that odorant metabolizing enzymes can balance the relative detection of odorants in a mixture, in turn influencing the intensity of the signal, should be considered to better manage flavor perception in food.

Data Analytics Determines Co-occurrence of Odorants in Raw Water and Evaluates Drinking Water Treatment Removal Strategies

A complex dataset with 140 sampling events was generated using triple quadrupole gas chromatography-mass spectrometer to track the occurrence of 95 odorants in raw and finished water from 98 drinking water treatment plants in 31 cities across China. Data analysis identified more than 70 odorants with concentrations ranging from not detected to thousands of ng/L. In raw water, Pearson correlation analysis determined that thioethers, non-oxygen benzene-containing compounds, and pyrazines were classes of chemicals that co-occurred, and geosmin and p(m)-cresol, as well as cyclohexanone and benzaldehyde, also co-occurred, indicating similar natural or industrial sources. Based on classification and regression tree analysis, total dissolved organic carbon and geographical location were identified as major factors affecting the occurrence of thioethers. Indoles, phenols, and thioethers were well-removed through conventional and advanced treatment processes, while some aldehydes could be generated. For other odorants, higher removal was achieved by ozonation-biological activated carbon (39.3%) compared to the conventional treatment process (14.5%). To our knowledge, this is the first study to systematically identify the major odorants in raw water and determine suitable treatment strategies to control their occurrence by applying data analytics and statistical methods to the complex dataset. These provide informative reference for odor control and water quality management in drinking water industry.

Olfactory stimulation Inhibits Nociceptive Signal Processing at the Input Stage of the Central Trigeminal System

The spinal trigeminal nucleus caudalis (SpVc) in the mammalian brainstem serves a pivotal function in pain processing. As the main relay center for nociceptive signals, SpVc conducts pain-related signals from various regions of the head toward higher levels of central processing such as the thalamus. SpVc also receives modulatory signals from other brain areas, which can alleviate the perception of headache. We studied the impact of olfactory co-stimulation on pain-related behavior and SpVc neural activity in mice. Using the TRPA1 agonist allyl isothiocyanate (AITC) as noxious stimulus, we quantified the aversive response and the perceived pain intensity by evaluating explorative running and the mouse grimace scale, respectively. We found that the floral odorants phenylethyl alcohol (PEA) and lavender oil mitigated the aversive response to AITC. Consistent with this finding, a newly developed, automated quantification of c-Fos expression in SpVc revealed that co-stimulation with PEA or lavender profoundly reduced network activity in the presence of AITC. These results demonstrated a substantial analgesic potential of odor stimulation in the trigeminal system and provide an explanation for the palliative effect of odors in the treatment of headache.

[Research Progress in the Odorants and Their Emissions from Indoor Building Decoration Materials]

The emission of pollutants from building decoration and furbishing materials associated with unpleasant odors is the main reason for complaints relating to poor quality indoor air. Currently, few studies have focused on the identification of odorants and the quantification of emissions from these building materials. Here, we summarize the analytical methods available for the study of indoor odorants and evaluate existing understanding of odorants from nine kinds of building materials, namely plaster board, wood-based materials, linoleum, carpets, plastics, rubber, artificial leather, paints, and adhesives. The possible odor-causing compounds emitted by these different materials and their odor threshold values are identified. Finally, suggestions are proposed for future research and control measures to minimize indoor odor pollution. Overall, olfactometry is the most important tool for odor analysis desite the non-standardized application of the technique when used in the assessment of odor emissions from building materials. In addition, there are large differences in the reported patterns of odorant emissions from building materials, although oxidized substances such as aldehydes, ketones, and acids are frequently identified in association with the aging of the materials via processes such as oxidation and ozone degradation over time.

Strategies for the identification and sensory evaluation of volatile constituents in wine

Wine aroma, which stems from complex perceptual and cognitive processes, is initially driven by a multitude of naturally occurring volatile constituents. Its interpretation depends on the characterization of relevant volatile constituents. With large numbers of volatile constituents already identified, the search for unknown volatiles in wine has become increasingly challenging. However, the opportunities to discover unknown volatile compounds contributing to the wine volatilome are still of great interest, as demonstrated by the recent identification of highly odorous trace (µg/L) to ultra-trace (ng/L) volatile compounds in wine. This review provides an overview of both existing strategies and future directions on identifying unknown volatile constituents in wine. Chemical identification, including sample extraction, fractionation, gas chromatography, olfactometry, and mass spectrometry, is comprehensively covered. In addition, this review also focuses on aspects related to sensory-guided wine selection, authentic reference standards, artifacts and interferences, and the evaluation of the sensory significance of discovered wine volatiles. Powerful key volatile odorants present at ultra-trace levels, for which these analytical approaches have been successfully applied, are discussed. Research areas where novel wine volatiles are likely to be identified are pointed out. The importance of perceptual interaction phenomena is emphasized. Finally, future avenues for the exploration of yet unknown wine volatiles by coupling analytical approaches and sensory evaluation are suggested.

An Overview of Artificial Olfaction Systems with a Focus on Surface Plasmon Resonance for the Analysis of Volatile Organic Compounds

The last three decades have witnessed an increasing demand for novel analytical tools for the analysis of gases including odorants and volatile organic compounds (VOCs) in various domains. Traditional techniques such as gas chromatography coupled with mass spectrometry, although very efficient, present several drawbacks. Such a context has incited the research and industrial communities to work on the development of alternative technologies such as artificial olfaction systems, including gas sensors, olfactory biosensors and electronic noses (eNs). A wide variety of these systems have been designed using chemiresistive, electrochemical, acoustic or optical transducers. Among optical transduction systems, surface plasmon resonance (SPR) has been extensively studied thanks to its attractive features (high sensitivity, label free, real-time measurements). In this paper, we present an overview of the advances in the development of artificial olfaction systems with a focus on their development based on propagating SPR with different coupling configurations, including prism coupler, wave guide, and grating.

Application to Model Wine Aroma

Although perceptual interactions are usually mentioned and blamed for the difficulties in understanding the relationship between odorant composition and aromatic sensory properties, they are poorly defined and categorised. Furthermore, old classifications refer mainly to effects on the odour intensity of the mixture of dissimilar non-blending odours and do not consider odour blending, which is one of the most relevant and influential perceptual interactions. Beginning with the results from classical studies about odour interaction, a new and simple systematic is proposed in which odour interactions are classified into four categories: competitive, cooperative, destructive and creative. The first categories are most frequent and display a mild level of interaction, being characterised mostly by analytical processing. The last two are less frequent and activate (or deactivate) configurational processes of object recognition with deep effects on the quality and intensity of the perception. These interactions can be systematically applied to interpret the formation of sensory descriptors from the odorant composition, suggesting that qualitatively the system works. However, there is a lack of quantitative data to work with odour intensities reliably, and a pressing need to systematise the effects of creative interactions.

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

Methyl-Cyclohexane Methanol (MCHM) Isomer-Dependent Binding on Amorphous Carbon Surfaces

In January 2014, over 10,000 gallons of methyl-cyclohexane methanol (MCHM) leaked into the Elk River in West Virginia, in a chemical spill incident that contaminated a large portion of the state’s water supply and left over 300,000 residents without clean water for many days and weeks. Initial efforts to remove MCHM at the treatment plant centered on the use of granulated activated carbon (GAC), which removed some of the chemical from the water, but MCHM levels were not lowered to a “non-detect” status until well after the chemical plume had moved downstream of the intake. Months later, MCHM was again detected at the outflow (but not the inflow) at the water treatment facility, necessitating the full and costly replacement of all GAC in the facility. The purpose of this study is to investigate the hypothesis that preferential absorbance of one of the two MCHM isomers, coupled with seasonal variations in water temperature, explain this contrary observation. Calculated intermolecular potentials between ovalene (a large planar polycyclic aromatic hydrocarbon) and the MCHM isomers were compared to physisorption potentials of MCHM onto an amorphous carbon model. While a molecular mechanics (MM) force field predicts no difference in the average interaction potentials between the cis- and trans-MCHM with the planar ovalene structure, MM predicts that the trans isomer binds stronger than the cis isomer to the amorphous carbon surface. Semi-empirical and density functional theory also predict stronger binding of trans-MCHM on both the planar and amorphous surfaces. The differences in the isomer binding strengths on amorphous carbon imply preferential absorbance of the trans isomer onto activated charcoal filter media. Considering seasonal water temperatures, simple Arrhenius kinetics arguments based on these predicted binding energies help explain the environmental observations of MCHM leeching from the GAC filters months after the spill. Overall, this work shows the important implications that can arise from detailed interfacial chemistry investigations.

Odour reduction interventions for simple pit latrines in rural Ethiopia: a randomized study

Pit latrines are promoted in resource-limited settings, but unpleasant odours may deter their use. In this study, latrines in rural Ethiopia were randomized to the addition of cooking ash, the addition of boiling water or neither. Study staff ranked odour on a 6-point scale before and approximately 24 h after intervention. Following intervention, odour grades were on average 0.2 points lower (95% confidence interval [CI] 0.7 lower to 0.3 higher) in ash-treated latrines and 0.4 points lower (95% CI 0.9 lower to 0.1 higher) in boiled water-treated latrines, although the difference between the three groups was not statistically significant (p = 0.21). Larger studies might detect a smaller difference.

Smell-Based Memory Training: Evidence of Olfactory Learning and Transfer to the Visual Domain

Human and non-human animal research converge to suggest that the sense of smell, olfaction, has a high level of plasticity and is intimately associated with visual-spatial orientation and memory encoding networks. We investigated whether olfactory memory (OM) training would lead to transfer to an untrained visual memory (VM) task, as well as untrained olfactory tasks. We devised a memory intervention to compare transfer effects generated by olfactory and non-olfactory (visual) memory training. Adult participants were randomly assigned to daily memory training for about 40 days with either olfactory or visual tasks that had a similar difficulty level. Results showed that while visual training did not produce transfer to the OM task, olfactory training produced transfer to the untrained VM task. Olfactory training also improved participants' performance on odor discrimination and naming tasks, such that they reached the same performance level as a high-performing group of wine professionals. Our results indicate that the olfactory system is highly responsive to training, and we speculate that the sense of smell may facilitate transfer of learning to other sensory domains. Further research is however needed in order to replicate and extend our findings.

Pleasantness of Binary Odor Mixtures: Rules and Prediction

Pleasantness is a major dimension of odor percepts. While naturally encountered odors rely on mixtures of odorants, few studies have investigated the rules underlying the perceived pleasantness of odor mixtures. To address this issue, a set of 222 binary mixtures based on a set of 72 odorants were rated by a panel of 30 participants for odor intensity and pleasantness. In most cases, the pleasantness of the binary mixtures was driven by the pleasantness and intensity of its components. Nevertheless, a significant pleasantness partial addition was observed in 6 binary mixtures consisting of 2 components with similar pleasantness ratings. A mathematical model, involving the pleasantness of the components as well as τ-values reflecting components' odor intensity, was applied to predict mixture pleasantness. Using this model, the pleasantness of mixtures including 2 components with contrasted intensity and pleasantness could be efficiently predicted at the panel level (R2 > 0.80, Root Mean Squared Error < 0.67).

Important Odorants of Four Brassicaceae Species, and Discrepancies between Glucosinolate Profiles and Observed Hydrolysis Products

It is widely accepted that the distinctive aroma and flavour traits of Brassicaceae crops are produced by glucosinolate (GSL) hydrolysis products (GHPs) with other non-GSL derived compounds also reported to contribute significantly to their aromas. This study investigated the flavour profile and glucosinolate content of four Brassicaceae species (salad rocket, horseradish, wasabi, and watercress). Solid-phase microextraction followed by gas chromatography-mass spectrometry and gas chromatography-olfactometry were used to determine the volatile compounds and odorants present in the four species. Liquid chromatography-mass spectrometry was used to determine the glucosinolate composition, respectively. A total of 113 compounds and 107 odour-active components were identified in the headspace of the four species. Of the compounds identified, 19 are newly reported for ‘salad’ rocket, 26 for watercress, 30 for wasabi, and 38 for horseradish, marking a significant step forward in understanding and characterising aroma generation in these species. There were several non-glucosinolate derived compounds contributing to the ‘pungent’ aroma profile of the species, indicating that the glucosinolate-derived compounds are not the only source of these sensations in Brassicaceae species. Several discrepancies between observed glucosinolates and hydrolysis products were observed, and we discuss the implications of this for future studies.

An Insight by Molecular Sensory Science Approaches to Contributions and Variations of the Key Odorants in Shiitake Mushrooms

An insight using molecular sensory science approaches to the contributions and variations of the key odorants in shiitake mushrooms is revealed in this study. Odorants were extracted by headspace solid phase microextraction (HS-SPME) and direct solvent extraction combined with solvent-assisted flavor evaporation (DSE-SAFE) in fresh and hot-air-dried shiitake mushrooms. Among them, 18 and 22 predominant odorants were determined by detection frequency analysis (DFA) and aroma extract dilution analysis (AEDA) combined with gas chromatography-olfactometry (GC-O) in the fresh and dried samples, respectively. The contributions of these predominant odorants in the food matrix were determined by quantification and odor activity values (OAVs) with aroma recombination verification. There were 13 and 14 odorants identified as key contributing odorants to overall aroma, respectively. 1-Octen-3-ol and 1-octen-3-one were the most key contributing odorants in the fresh samples in contributing mushroom-like odor. After hot-air-drying, the OAV and concentrations on dry basis of the key contributing odorants changed, due to oxidation, degradation, caramelization and Maillard reactions of fatty acids, polysaccharides and amino acids. 1-Octen-3-ol was reduced most significantly and degraded to 1-hydroxy-3-octanone, while phenylethyl alcohol increased the most and was formed by phenylalanine. In hot-air-dried samples, lenthionine became the most important contributor and samples were characterized by a sulfury odor. Overall contributions and variations of odorants to the aroma of shiitake mushrooms were revealed at the molecular level.

Human ectopic olfactory receptors and their food originated ligands: a review

Ectopic olfactory receptors (EORs) are expressed in non-nasal tissues of human body. They belong to the G-protein coupled receptor (GPCR) superfamily. EORs may not be capable of differentiating odorants as nasal olfactory receptors (ORs), but still can be triggered by odorants and are involved in different biological processes such as anti-inflammation, energy metabolism, apoptosis etc. Consumption of strong flavored foods like celery, oranges, onions, and spices, is a good aid to attenuate inflammation and boost our immune system. During the digestion of these foods in human digestive system and the metabolization by gut microbiota, the odorants closely interacting with EORs, may play important roles in various bio-functions like serotonin release, appetite regulation etc., and ultimately impact health and diseases. Thus, EORs could be a potential target linking the ligands from food and their bioactivities. There have been related studies in different research fields of medicine and physiology, but still no systematic food oriented review. Our review portrays that EORs could be a potential target for functional food development. In this review, we summarized the EORs found in human tissues, their impacts on health and disease, ligands interacting with EORs exerting specific biological effects, and the mechanisms involved.

Investigation of Normative Value of Commercialized Taiwan Smell Identification Test

Background

The Taiwan Smell Identification Test (TWSIT) was developed and successfully administered in Taiwanese population since 2015. However, for sanitation reason, the original liquid-jar form of this test is not appropriate. The commercialized TWSIT was then re-designed as “scratch-and-sniff” version: the TIBSIT (Top International Biotech, Taipei, Taiwan). This project aims to investigate the normative value of TIBSIT in different age groups and genders.

Methods

Volunteers aged 20 to 80 with no subjective smell loss were recruited in a rhinology clinic. The participants were given full instructions on using the TIBSIT.

Results

Two hundred and nine healthy subjects (female: male =107: 102) were enrolled into this study. The median TIBSIT score in female and male subjects is 47 and 46, respectively. Subjects were further divided into three age groups: (A) 20∼34 years (n = 77), (B) 35∼54 years (n = 77), and (C) 55∼80 years (n = 55). The TIBSIT scores at the tenth percentile value at each age group of male patients are 43, 42 and 37; while the scores at the tenth percentile value at each age group of female patients are 42, 42 and 41. TIBSIT score was significantly and inversely correlated with age (Spearman rho = − 0.20, p = 0.004.).

Conclusion

We established the normative values of the new TIBSIT in different age groups in Taiwan. Future nation-wide screening is needed for more sophisticated norms establishment.

The Structural Properties of Odorants Modulate Their Association to Human Odorant Binding Protein

The binding of known odorant molecules to the human odorant-binding protein (hOBP) was evaluated in silico. Docking experiments elucidate the preferable binding site and binding affinity of odorant molecules to hOBP. The physicochemical properties molecular weight (MW), vapor pressure (Vp), hydrophobicity level (logP), number of double bonds (NºDB), degree of unsaturation (DoU) and the chemical classification, were selected for the study of odorant modulation. Here, these properties were analyzed concerning 30 pleasant and 30 unpleasant odorants, chosen to represent a wide variety of compounds and to determine their influence on the binding energy to hOBP. Our findings indicate that MW, logP and Vp are the most important odorant variables, directly correlated to odorant-binding energies (ΔG_binding) towards hOBP. Understanding how the odorants behave when complexed with the OBP in human olfaction opens new possibilities for the development of future biotechnological applications, including sensory devices, medical diagnosis, among others.

Gas Chromatography Olfactometry (GC-O) for the (Semi)Quantitative Screening of Wine Aroma

This review discusses the different approaches developed by researchers in the last 40 years for the qualitative and semi-quantitative screening of odorants, with special emphasis in wine aroma profiling. In the first part, the aims and possibilities of Gas chromatography-olfactometry (GC-O) as odour-screening and aroma profiling technique are discussed. The critical difference between approaches is whether the ranking of odorants is carried out on an extract containing all the odorants present in the product, or on an extract representative of the odorants contained in the vapour phases that cause the odour and flavour. While the second alternative is more direct and can be more efficient, it requires a good understanding of the factors affecting orthonasal olfaction, handling volatiles (purging, trapping, eluting, and separating) and about the sensory assessment of GC effluents. The review also includes an updated list compiling all the odorants detected in wine by GC-O, including retention indexes and odour descriptions with a general guideline for the identification of odorants.

The Trained Sniffer Dog Could Accurately Detect the Urine Samples from the Patients with Cervical Cancer, and Even Cervical Intraepithelial Neoplasia Grade 3: A Pilot Study

Simple Summary

Tumor detection by dog sniffing is a possible new method in cancer diagnosis. The aim of this study is to assess whether a trained dog can distinguish urine samples from cervical cancer patients. Urine samples were collected from 34 with cervical cancer, 49 patients with CIN3, 49 with benign uterine diseases, and 63 healthy volunteers. In all 83 test runs, one positive sample among five samples were presented to the dog. The trained dog accurately distinguished the urine sample of a cancer patient from those of the controls. This study showed that cancer detection by dog sniffing can be a non-invasive, cost-effective screening technique for cervical cancer.

Abstract

(1) Background: Previous reports have indicated that cancers of the stomach, lung, and pancreas can be detected by dog sniffing, but results have been varied. Here, a highly trained dog was used to determine whether urine from patients with cervical premalignant lesions and malignant tumors have a cancer-specific scent. (2) Methods: A total of 195 urine samples were collected from patients with cervical cancer, cervical intraepithelial neoplasia grade 3 (CIN3), benign uterine diseases, and healthy volunteers. Each test was performed using one urine sample from a cancer patient and four samples from different controls. Each of the five urine samples was placed in a separate box. When the cancer sniffing dog stopped and sat in front of the box with a sample from a cancer patient, the test was considered as positive. (3) Results: 83 patients with cervical cancer (34 cases of cervical cancer and 49 cases of cervical intraepithelial neoplasia grade 3), 49 patients with uterine benign diseases, and 63 healthy volunteers were enrolled, and their urine samples were collected. In 83 times out of 83 runs in a double-blind test, the trained dog could correctly identify urine samples of cervical cancer patients. (4) Conclusion: A trained dog could accurately distinguish the urine of all patients with cervical cancer or CIN3, regardless of the degree of cancer progression.

Binding Site Switch by Dispersion Interactions: Rotational Signatures of Fenchone-Phenol and Fenchone-Benzene Complexes

Non-covalent interactions between molecules determine molecular recognition and the outcome of chemical and biological processes. Characterising how non-covalent interactions influence binding preferences is of crucial importance in advancing our understanding of these events. Here, we analyse the interactions involved in smell and specifically the effect of changing the balance between hydrogen-bonding and dispersion interactions by examining the complexes of the common odorant fenchone with phenol and benzene, mimics of tyrosine and phenylalanine residues, respectively. Using rotational spectroscopy and quantum chemistry, two isomers of each complex have been identified. Our results show that the increased weight of dispersion interactions in these complexes changes the preferred binding site in fenchone and sets the basis for a better understanding of the effect of different residues in molecular recognition and binding events.

Exploring the Characteristics of an Aroma-Blending Mixture by Investigating the Network of Shared Odors and the Molecular Features of Their Related Odorants

The perception of aroma mixtures is based on interactions beginning at the peripheral olfactory system, but the process remains poorly understood. The perception of a mixture of ethyl isobutyrate (Et-iB, strawberry-like odor) and ethyl maltol (Et-M, caramel-like odor) was investigated previously in both human and animal studies. In those studies, the binary mixture of Et-iB and Et-M was found to be configurally processed. In humans, the mixture was judged as more typical of a pineapple odor, similar to allyl hexanoate (Al-H, pineapple-like odor), than the odors of the individual components. To explore the key features of this aroma blend, we developed an in silico approach based on molecules having at least one of the odors—strawberry, caramel or pineapple. A dataset of 293 molecules and their related odors was built. We applied the notion of a “social network” to describe the network of the odors. Additionally, we explored the structural properties of the molecules in this dataset. The network of the odors revealed peculiar links between odors, while the structural study emphasized key characteristics of the molecules. The association between “strawberry” and “caramel” notes, as well as the structural diversity of the “strawberry” molecules, were notable. Such elements would be key to identifying potential odors/odorants to form aroma blends.

Reversal of Olfactory Disturbance in Allergic Rhinitis Related to OMP Suppression by Intranasal Budesonide Treatment

PURPOSE

We evaluated the severity of olfactory disturbance (OD) in the murine model of allergic rhinitis (AR) and local allergic rhinitis (LAR) in mice. We also investigated the therapeutic effect of an intranasal steroid on OD.

METHODS

Forty BALB/c mice were divided into 5 groups (n = 8 for each). The control group was sensitized intraperitoneally (i.p.) and challenged intranasally (i.n.) with saline. Mice in the AR group got i.p. and i.n. ovalbumin (OVA) administration for AR induction. The LAR group was challenged i.n. with 1% OVA for inducing local nasal allergic inflammation, without inducing the systemic allergy. The OD group got an i.p. methimazole administration (75 mg/kg) to induce total destruction of olfactory mucosa. Mice in the intranasal budesonide group received i.n. budesonide (12.8 μ per time, 30 minutes after the i.n. OVA challenge) while using OVA to cause systemic allergies. We conducted a buried-food pellet test to functionally assess the degree of OD in each group by measuring the time taken until finding hidden food. We evaluated the damage to olfactory epithelium using histopathologic evaluation and compared the degree of olfactory marker protein (OMP) expression in olfactory epithelium using immunofluorescent staining.

RESULTS

Mice of the AR (81.3 ± 19.8 seconds) and LAR groups (66.2 ± 12.7 seconds) spent significantly more time to detect the pellets than the control group (35.6 ± 12.2 seconds, P < 0.01). After treatment, the intranasal budesonide group exhibited significantly better results (35.8 ± 11.9 seconds) compared with the AR and LAR groups (P < 0.01). The AR and LAR groups showed considerable olfactory epithelial damage and suppression of OMP expression compared with the control group. In the intranasal budesonide group, the olfactory lesions and OMP expression had improved substantially.

CONCLUSIONS

OD may be caused by olfactory epithelial damage and suppression of OMP expression in nasal allergic inflammation and could be reversed using an intranasal steroid.

Egg yolk phospholipids: a functional food material to generate deep-fat frying odorants

BACKGROUND

Phospholipids are an important precursor for the generation of carbonyl compounds that play a significant role in the characteristic aroma of deep-fat fried foods.

RESULTS

Phospholipids extracted from hen egg yolks were added into sunflower oil (2.0 g kg^-1 ) and heated with or without chicken meat at 160 °C for 10 min, and then dynamic headspace extraction and gas chromatography-mass spectrometry were used to extract and analyse the volatiles. The results showed that the characteristic deep-fat frying odorants, such as (E,E)-2,4-decadienal and (E,Z)-2,4-decadienal, as well as 1-octen-3-one, (E)-2-nonenal, octanal, methional, dimethyl disulfide and alkylpyrazines, had increased by 3-65 times in the sunflower oil with added phospholipids, and increased up to six times in chicken meat that had been treated with phospholipids prior to heating.

CONCLUSION

There is potential for the food industry to use low levels of phospholipids, particularly egg yolk phospholipids, to increase deep-fat frying odorants in a wide range of deep-fried products. © 2019 Society of Chemical Industry.

Synthetic terpenoids in the world of fragrances: Iso E Super® is the showcase

The history of fragrances is closely associated with the chemistry of terpenes and terpenoids. For thousands of years mankind mainly used plant extracts to collect ingredients for the creation of perfumes. Many of these extracts contain complex mixtures of terpenes, that show distinct olfactoric properties as pure compounds. When organic synthesis appeared on the scene, the portfolio of new scents increased either in order to substitute natural fragrances without change of olfactoric properties or to broaden the scope of scents. This short review describes the story of the most successful synthetic fragrance ever which is called Iso E Super^® as it is an ingredient in a large number of perfumes with varying percentages and is the first example being used as a pure fragrance. Structurally, it is related to natural terpenes like many other synthetic fragrances. And indeed, the story began with a classic in the field of fragrances, the natural product ionone.

Unified Flavor Quantitation: Toward High-Throughput Analysis of Key Food Odorants and Tastants by Means of Ultra-High-Performance Liquid Chromatography Tandem Mass Spectrometry

Because foods are perceived through combined inputs from taste and odor, which are determined by the concentration of the individual odor and taste molecules, the unified high-throughput quantitation of volatile odorants and non-volatile tastants with the very same instrumental setup has been a long-standing but yet unmet dream. The research presented here for the first time demonstrates, after only minimal sample workup, the highly accurate, rapid, and sensitive unified quantitation of odorants and tastants of key flavor molecules in apple juice on a single ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) platform over a large dynamic range of up to 6 orders of magnitude. While flavor-active aldehydes, ketones, and organic acids were analyzed after derivatization with 3-nitrophenylhydrazine, taste-active polyphenols and odor-active esters were directly analyzed by means of UHPLC-MS/MS with and without target analyte enrichment through stir-bar sorptive extraction. This "unified flavor quantitation" approach holds promise to accelerate the transition of today's labor and time-consuming, low-throughput analysis of odorants and tastants into a new era of high-performance quantitation of key flavor molecules.

Molecular Basis of Mammalian Odor Discrimination: A Status Report

Humans have 396 unique, intact olfactory receptors (ORs), G-protein coupled receptors (GPCRs) containing receptor-specific binding sites; other mammals have more. Activation of these transmembrane proteins by an odorant initiates a signaling cascade, evoking an action potential leading to perception of a smell. Because the number of distinguishable odorants vastly exceeds the number of ORs, research has focused on mechanisms of recognition and signaling processes for classes of odorants. In this review, selected recent examples will be presented of "deorphaned" mammalian receptors, where the OR ligands (odorants) as well as key aspects of receptor-odorant interactions were identified using odorant-mediated receptor activation data together with site-directed mutagenesis and molecular modeling. Based on cumulative evidence from OR deorphaning and olfactory receptor neuron activation studies, a receptor-ligand docking model rather than an alternative bond vibration model is suggested to best explain the molecular basis of the exquisitely sensitive odor discrimination in mammals.

Could the Olfactory System Be a Target for Homeopathic Remedies as Nanomedicines?

Homeopathic remedies (HRs) contain odorant molecules such as flavonoids or terpenes and can lose their efficiency in presence of some competitive odors. Such similarities, along with extreme sensitivity of the olfactory system, widespread presence of olfactory receptors over all organic tissues (where they have metabolic roles besides perception of odors), and potential direct access to the brain through olfactory nerves (ONs) and trigeminal nerves, may suggest the olfactory system as target for HRs. Recent works highlighted that HRs exist in a dual form, that is, a still molecular form at low dilution and a nanoparticulate form at high dilution, and that remnants of source remedy persist in extremely high dilutions. From the literature, both odorants and nanoparticles (NPs) can enter the body through inhalation, digestive absorption, or through the skin, especially, NPs or viruses can directly reach the brain through axons of nerves. Assuming that HRs are recognized by olfactory receptors, their information could be transmitted to numerous tissues through receptor-ligand interaction, or to the brain by either activating the axon potential of ONs and trigeminal nerves or, in their nanoparticulate form, by translocating through axons of these nerves. Moreover, the nanoparticulate form may activate the immune system at multiple levels, induce systemic various biological responses through the pituitary axis and inflammation factors, or modulate gene expression at the cellular level. As immunity, inflammation, pituitary axis, and olfactory system are closely linked together, their permanent interaction triggered by olfactory receptors may thus ensure homeostasis.

Combining In Vivo and In Vitro Approaches To Identify Human Odorant Receptors Responsive to Food Odorants

Olfactory perception plays an important role in food flavor. Humans have around 400 odorant receptors (ORs), which can be activated by an enormous number of odorants in a combinatorial fashion. To date, only a few odorant receptors have been linked to their respective odorants, due to the difficulties in expressing these receptor proteins in heterologous cell systems. In vivo approaches allow for the analysis of odorant-receptor interactions in their native environment and have the advantage that the complete OR repertoire is simultaneously tested. Once mouse odorant-receptor pairs are defined, one can search for the corresponding human orthologues, which can be validated against the odorants in heterologous cells. Thus, the combination of in vivo and in vitro methods should contribute to the identification of human ORs that recognize odorants of interest, such as key food odorants.

Key Odorants from Pig Production Based on Improved Measurements of Odor Threshold Values Combining Olfactometry and Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Analytical measurements of odorants in combination with odor threshold values is an alternative to sensory measurements that can be used to evaluate abatement technologies for pig production facilities. The purpose of the present study was to estimate odor threshold values for key odorants found in pig house air. A new method was applied where an olfactometer was used to dilute the sample air and the concentrations of odorants presented to the panelists at the dilutions steps were measured by proton-transfer-reaction mass spectrometry (PTR-MS). The results demonstrate that the odor threshold values of acetic acid, butanoic acid, and 4-methylphenol are considerably lower than reported previously, whereas the values of hydrogen sulfide, methanethiol and dimethylsulfide were comparable. Consequently, acetic acid, butanoic acid, and 4-methyl-phenol will have a larger influence on odor from pig production facilities than previously assumed. The results highlight the necessity for directly measuring exposure concentrations when determining odor threshold values.

Different Ways to Apply a Measurement Instrument of E-Nose Type to Evaluate Ambient Air Quality with Respect to Odour Nuisance in a Vicinity of Municipal Processing Plants

This review paper presents different ways to apply a measurement instrument of e-nose type to evaluate ambient air with respect to detection of the odorants characterized by unpleasant odour in a vicinity of municipal processing plants. An emphasis was put on the following applications of the electronic nose instruments: monitoring networks, remote controlled robots and drones as well as portable devices. Moreover, this paper presents commercially available sensors utilized in the electronic noses and characterized by the limit of quantification below 1 ppm v/v, which is close to the odour threshold of some odorants. Additionally, information about bioelectronic noses being a possible alternative to electronic noses and their principle of operation and application potential in the field of air evaluation with respect to detection of the odorants characterized by unpleasant odour was provided.

Task-Related Phasing of Circadian Rhythms in Antennal Responsiveness to Odorants and Pheromones in Honeybees

The insect antennae receive olfactory information from the environment. In some insects, it has been shown that antennal responsiveness is dynamically regulated by circadian clocks. However, it is unknown how general this phenomenon is and what functions it serves. Circadian regulation in honeybee workers is particularly interesting in this regard because they show natural task-related chronobiological plasticity. Forager bees show strong circadian rhythms in behavior and brain gene expression, whereas nurse bees tend brood around-the-clock and have attenuated circadian rhythms in activity and whole-brain gene expression. Here, we tested the hypothesis that there is task-related plasticity in circadian rhythms of antennal responsiveness to odorants in worker honeybees. We used electroantennogram (EAG) to measure the antennal responsiveness of nurses and foragers to general odorants and pheromones around the day. The capacity to track 10-Hz odorant pulses varied with time of day for both task groups but with different phases. The antennal pulse-tracking capacity was higher during the subjective day for the day-active foragers, whereas it was better during the night for around-the-clock active nurses. The task-related phases of pulse-tracking rhythms were similar for all the tested stimuli. We also found evidence for circadian rhythms in the EAG response magnitude of foragers but not of nurses. To the best of our knowledge, these results provide the first evidence for circadian regulation of antennal olfactory responsiveness and odorant pulse-tracking capacity in bees or any other hymenopteran insect. Importantly, our study shows for the first time that the circadian phase of olfactory responsiveness may be socially regulated.

Neurotransmitter Switching Regulated by miRNAs Controls Changes in Social Preference

Changes in social preference of amphibian larvae result from sustained exposure to kinship odorants. To understand the molecular and cellular mechanisms of this neuroplasticity, we investigated the effects of olfactory system activation on neurotransmitter (NT) expression in accessory olfactory bulb (AOB) interneurons during development. We show that protracted exposure to kin or non-kin odorants changes the number of dopamine (DA)- or gamma aminobutyric acid (GABA)-expressing neurons, with corresponding changes in attraction/aversion behavior. Changing the relative number of dopaminergic and GABAergic AOB interneurons or locally introducing DA or GABA receptor antagonists alters kinship preference. We then isolate AOB microRNAs (miRs) differentially regulated across these conditions. Inhibition of miR-375 and miR-200b reveals that they target Pax6 and Bcl11b to regulate the dopaminergic and GABAergic phenotypes. The results illuminate the role of NT switching governing experience-dependent social preference. VIDEO ABSTRACT.

Organization and function of Drosophila odorant binding proteins

Odorant binding proteins (Obps) are remarkable in their number, diversity, and abundance, yet their role in olfactory coding remains unclear. They are widely believed to be required for transporting hydrophobic odorants through an aqueous lymph to odorant receptors. We construct a map of the Drosophila antenna, in which the abundant Obps are mapped to olfactory sensilla with defined functions. The results lay a foundation for an incisive analysis of Obp function. The map identifies a sensillum type that contains a single abundant Obp, Obp28a. Surprisingly, deletion of the sole abundant Obp in these sensilla does not reduce the magnitude of their olfactory responses. The results suggest that this Obp is not required for odorant transport and that this sensillum does not require an abundant Obp. The results further suggest a novel role for this Obp in buffering changes in the odor environment, perhaps providing a molecular form of gain control.

DOI:http://dx.doi.org/10.7554/eLife.20242.001

Insects use their sense of smell to find mates, to find food and – in the case of insects that transmit diseases such as malaria and Zika – to find us. If we can understand how insect scent detection works at the molecular and cellular level, we may be able to devise new ways of manipulating the insects’ sense of smell and prevent them from finding us.

Insects contain a family of proteins called odorant binding proteins that are intriguing in several ways. They are numerous (there are 52 kinds in the fruit fly Drosophila), they are diverse and some are made in remarkably large amounts in the antennae. Fine hair-like structures known as olfactory sensilla protrude from the surface of the antennae. Odorant binding proteins are widely believed to carry odorant molecules through the fluid inside the sensilla to olfactory neurons, which then send signals that trigger the insect’s response to the scent.

Larter et al. have now mapped the most abundant odorant binding proteins to the various olfactory sensilla of Drosophila. This revealed that a type of sensillum known as ab8 contained only one abundant odorant binding protein, called Obp28a. Unexpectedly, Larter et al. found that ab8 sensilla that are deprived of this protein respond strongly to odorant molecules. This result suggests that Obp28a is not required to transport odorants to the neurons in ab8; indeed, it appears that these neurons do not require an abundant odorant binding protein in order to respond to a scent. Instead, Obp28a helps to moderate the effects of sudden changes in the level of an odorant in the environment, so that concentrated odors do not trigger too large a response from the olfactory neurons.

The details of the role that Obp28a plays in olfactory sensilla remain to be investigated in future studies, and the map created by Larter et al. also lays a foundation for studying the roles of other odorant binding proteins. The discovery that Obp28a is not needed to transport odorant molecules also raises questions about how insects are able to detect smells. Many odorant molecules repel water, so how do these molecules travel through the fluid in the sensilla if odorant binding proteins are not needed to transport them?

DOI:http://dx.doi.org/10.7554/eLife.20242.002

[Odorants Removal and Microbial Characteristics in Treatment of Micro-polluted Source Water with Biological Powdered Activated Carbon-Ultrafiltration Combined Process]

The odorants in simulated micro-polluted source water were removed by the Biological Powdered Activated Carbon-Ultrafiltration (BPAC-UF) combined process, and variations of microorganisms in the combined process were discussed. Compared with the conventional process of coagulation and sedimentation, BPAC-UF combined process had better performance in controlling odorants in micro-polluted source water. The average removal rates of dimethyl trisulfide, 2-methylisoborneol and β-ionone reached up to 77.51%, 65.86% and 98.43%, respectively. The process was more adaptable to raw water shock load. The carbon tank which had much more microbial biomass than other areas was determined to be the main unit for removing odorants. The biomass changed smoothly in the carbon tank, while the removal of odorants in raw water was stable in the process.