Odor Concentration Research Articles

Characterization of diffuse odorous emissions from lignocellulosic biomass storage

The use of lignocellulosic biomass for green energy production is increasing, but the wood storage may lead to ambient odor related issues. This study aims to assess the odor potential and to investigate the mechanisms that promote odorous emissions from wood chip heaps. To achieve this goal, four experimental campaigns were conducted in an Italian thermal power plant. During these campaigns, odor concentration and chemical-physical parameters, that should theoretically affect the odor potential of biomass heaps, were investigated. The first important outcome revealed a strong heterogeneity on the heaps surface, classified as dry or smoking according to the superficial humidity and smoke. Smoking areas proved to be much more emissive and at self-ignition risk than dry regions. Indeed, odor concentration on smoking regions reached values in the order of 105 ouE/m3, significantly higher than dry region ones (102 ouE/m3). In addition, the highest values of odor concentration have been detected in the first days of storage, when fatty acids are oxidized and terpenes are released. Again, after 30 ÷ 80 days, i.e. about 20 days after the temperature peak caused by biological activity, odor concentration increases, suggesting a possible cause-effect mechanism between biological processes and odor release. Unexpectedly, odor emissions decreased during summer, reasonably due to the high ambient temperature which reduces the moisture content limiting biological activity. However, after about 100 days of storage, smoking regions extent and odor emissions can be considered negligible.

A versatile odor detection system based on automatically trained rats for chemical sensing

We report a versatile odor detection system that employs rats trained through automated operant conditioning paradigms. While detection animals possess remarkable olfactory capabilities, their practical use has been limited by non-automated training methods, which involve lengthy training periods, high costs, handler dependency, and low reliability. Our primary research goal was to develop detection animals using a fully automated system. To achieve this, we employed four distinct operant conditioning approaches to train four rats (Numbers 3, 7, 10, and 12) in an automated apparatus for detecting 2,4-dinitrotoluene (DNT). Our system performed exceptionally well, with DNT-trained rats achieving a 95 % accuracy rate, 99 % sensitivity, 91 % specificity, 92 % positive predictive value (PPV), and 99 % negative predictive value (NPV) across 380 tests. Additionally, we observed a linear decrease in response time as DNT concentration increased from 20 parts per billion (ppb) to 1000 ppb, indicating the system's potential for quantitative odor concentration measurement. Impressively, the rats retained their odor discrimination skills for up to four months after their last training session, underscoring the durability of their olfactory memory. Our study introduces a novel, highly effective system for specific odorant component detection, offering a faster, more reliable, and accurate method for distinguishing between various odors.

A perspective of randomness in a clinical test of olfactory performance

Random walks describe stochastic processes characterized by a sequence of unpredictable changes in a random variable with no correlation to past changes. This report describes the random walk component of a clinical sensory test of olfactory performance. The precise definition of this stochastic process allows the establishment of precise diagnostic cut-offs for the identification of olfactory loss. Within the Sniffin`Sticks olfactory test battery, odor discrimination (D) and odor identification (I) are assessed by four- and three-alternative forced-choice designs, respectively. Meanwhile, the odor threshold (T) test integrates a three-alternative forced-choice paradigm within a staircase paradigm with seven turning points. We explored this paradigm through computer simulations and provided a formal description. The odor threshold assessment test consists of two sequential components, the first of which sets the starting point for the second. Both parts can be characterized as biased random walks with significantly different probabilities of moving to higher (11%) or lower (89%) values. The initial odor concentration step for the first phase of the test and the length of the subsequent random walk in the second phase significantly affect the probability of randomly achieving high test scores. Changing the odor concentration from where the starting point determination for the second test part begins has raised the current cut-off for anosmia, represented as T + D + I < 16, from the 87th quantile of random test scores to the 97th quantile. Analogous findings are likely applicable to other sensory tests that use the staircase paradigm characterized as random walk.

Association of the AspP298Asn polymorphism in the MC4R gene with fattening productivity of immunologically castrated and uncastrated gilts

The study was aimed at establishing the presence of MC4R (c.1426 A&gt;G) gene polymorphism among the population of immunologically castrated and native gilts (Large White × Landrace) × Maxgro. Asp298Asn polymorphism affects the economic rate of growth and fattening productivity of commercial lines of pigs. Since the polymorphism of the MC4R gene correlates with the concentration of androstenone, skatole, and indole, the possible use of polymorphism as a molecular DNA marker MC4R for genetic selection in order to reduce the level of boar odor in gilts meat and fat. This will establish which alleles and genotypes in general will be determined as desirable in the marker dilution of hybrid pigs. With this in mind, the purpose of the study was to determine the effect of the MC4R genotype on fattening performance indicators and correlation with boar odor in hybrid gilts based on population-genetic variability. Genomic DNA was isolated from the ear hair follicle of native gilts (n=42) and epithelial tissue from the ear of immunologically castrated ones (n=52). Genotyping was performed using polymorphism of the lengths of restrictive fragments (RFLP). Genetic-correlation parameters for native and immunologically castrated gilts were evaluated by ADG/AGE30 and ADG/AGE100. However, the polymorphism of the c.1426 A&gt;G gene did not significantly affect the ADG/AGE100 performance of hybrid gilts. The predominance of the frequency of allele A (0.55) is established above the frequency of the allele G (0.45). Analysis of the frequency distribution of genotypes showed the saturation of micropopulation with heterozygotes AG (0.51) with a small proportion of GG carriers (0.19). Immunologically castrated and uncastrated gilts with an MC4RA allele are characterized by a sufficiently high ADG/AGE100 and are probably characterized by a high level of boar-specific odor compared to gilts with lower ADG/AGE100 with an MC4RG allele. According to the data obtained, the desired genotype for an equilibrium of the concentration of boar odor without compromising physiological development, growth rate, and productivity formation is heterozygous offspring with the MC4RAG genotype.

Effect of peat moss as a feed additive on odorous compound concentration and odor contribution in stored pig slurry

Effect of peat moss as a feed additive on odorous compound concentration and odor contribution in stored pig slurry

SENSORIAL TECHNIQUES OF ODOUR MEASUREMENTS – A RELATIONSHIP BETWEEN ODOUR CONCENTRATION AND ODOUR INTENSITY FOR A SELECTED WASTE MANAGEMENT FACILITY

Sensory analyses are one of the most frequently used odour research methods that allowestablishing the most important odour characteristics, i.e. odour concentration and odourintensity, characterised by a high degree of interrelationship. During an11-month study odourconcentration and intensity were measured at selected mechanical-biological solid municipalwaste treatment plant at 35 measuring locations to assess the degree of correlation between thosetwo parameters. Commonly used Weber-Fechner law was applied to assess the correlation. Resultsindicate a high degree of correlation between odour concentration and intensity, for example, R2valued for two different approaches at 0.87, and 0.95, while Pearson’s r valued at 0.93, and 0.97.Following the results this proves that odour concentration and odour intensity could potentially beused interchangeably for odour assessment. However, applying Weber-Fechner law for predictionof odour concentration based on odour intensity measurements gives imprecise results. Suchapproach could be potentially applied when limited measurements of odour concentration areavailable as determination of odour intensity that could be performed even by Facility employees.

Implementation of an electronic nose for real -time identification of odour emission peaks at a wastewater treatment plant

This paper proposes a novel approach for the real-time monitoring of odour emissions from a WasteWater Treatment Plant (WWTP) using an Instrumental Odour Monitoring System (IOMS). The plant is characterized by unpredictable odour peaks at its arrival tank (AT), generating nuisance and complaints in the population living nearby the plant. Odour peaks are most likely due to the conferment of non-identified and malodorous wastewaters coming from various industrial activities. Due to the high variability of sources collecting their wastewaters to the WWTP, a new methodology to train the IOMS, based on the use of a one-class classifier (OCC), has been exploited. The OCC enables to detect deviations from a “Normal Operating Region” (NOR), defined as to include odour concentrations levels unlikely to cause nuisance in the citizenship. Such deviations from the NOR thus should be representative of the odour peaks. The results obtained prove that the IOMS is able to detect real-time alterations of odour emissions from the AT with an accuracy on independent validation data of about 90% (CI95% 55–100%). This ability of detecting anomalous conditions at the AT of the WWTP allowed the targeted withdrawal of liquid and gas samples in correspondence of the odour peaks, then subjected to further analyses that in turn enabled to investigate their origin and take proper counteractions to mitigate the WWTP odour impact.

QPCR-Based Monitoring of 2-Methylisoborneol/Geosmin-Producing Cyanobacteria in Drinking Water Reservoirs in South Korea.

Cyanobacteria can exist in water resources and produce odorants. 2-Methylisoborneol (2-MIB) and geosmin are the main odorant compounds affecting the drinking water quality in reservoirs. In this study, encoding genes 2-MIB (mic, monoterpene cyclase) and geosmin (geo, putative geosmin synthase) were investigated using newly developed primers for quantitative PCR (qPCR). Gene copy numbers were compared to 2-MIB/geosmin concentrations and cyanobacterial cell abundance. Samples were collected between July and October 2020, from four drinking water sites in South Korea. The results showed similar trends in three parameters, although the changes in the 2-MIB/geosmin concentrations followed the changes in the mic/geo copy numbers more closely than the cyanobacterial cell abundances. The number of odorant gene copies decreased from upstream to downstream. Regression analysis revealed a strong positive linear correlation between gene copy number and odorant concentration for mic (R2 = 0.8478) and geo (R2 = 0.601). In the analysis of several environmental parameters, only water temperature was positively correlated with both mic and geo. Our results demonstrated the feasibility of monitoring 2-MIB/geosmin occurrence using qPCR of their respective synthase genes. Odorant-producing, gene-based qPCR monitoring studies may contribute to improving drinking water quality management.

Relationship between human behavior and indoor air quality of private room in a care facility for the elderly in Japan

In Japan, the number of elderly people in need of nursing care is increasing while the population of young people is decreasing, and the potential for labor shortages in the field of elder care is of great concern. This study aimed to estimate the behavior of the elderly by using sensors to monitor indoor air quality (IAQ), without placing undue burden on the elderly or their caregivers. Odor and carbon dioxide (CO2) concentrations were monitored in a private room of a nursing home in the Kanto Region of Japan, the behaviors of the resident and staff members were recorded, and the relationship between the two was analyzed. Both odor and CO2 concentrations were higher when the resident was present than when absent, indicating that the resident was one of the main sources of indoor odor and CO2. In addition, after the resident entered the room, the CO2 concentration increased and remained stable, whereas the odor concentration tended to vary after the resident entered the room, first increasing and later decreasing. This suggested that the increase or decrease in odor could be used to monitor the behavior of the resident and staff members. The relationship between the slopes of odor and CO2 in typical behavioral events suggest that if only odor increases and CO2 does not change, the likelihood of the event in which feces were observed during diaper changes is high. In addition, based on the behavior near the sensor, the rate of CO2 and odor emissions differed between the elderly resident and the younger staff members, suggesting that the ratio of odor slope to CO2 slope may be greater in the elderly than in younger people. Furthermore, the repeated number of increases and decreases in odor and CO2 suggested that multiple events could be distinguished. These results suggest that IAQ can be utilized to estimate the behavior of residents and staff in nursing care facilities for the elderly.

Modeling of olfactory transduction in AWCON neuron via coupled electrical-calcium dynamics.

Amphid wing "C" (AWC) neurons are among the most important and studied neurons of the nematode Caenorhabditis elegans. In this work, we unify the existing electrical and intracellular calcium dynamics descriptions to obtain a biophysically accurate model of olfactory transduction in AWCON neurons. We study the membrane voltage and the intracellular calcium dynamics at different exposure times and odorant concentrations to grasp a complete picture of AWCON functioning. Moreover, we investigate the complex cascade of biochemical processes that allow AWC activation upon odor removal. We analyze the behavior of the different components of the models and, by suppressing them selectively, we extrapolate their contribution to the overall neuron response and study the resilience of the dynamical system. Our results are all in agreement with the available experimental data. Therefore, we provide an accurate mathematical and biophysical model for studying olfactory signal processing in C. elegans.

ODOUR EMISSIONS FROM A MUNICIPAL SOLID WASTE DUMPING AREA THAT ARE AT THE MODERATE STAGE OF DISINTEGRATION

&lt;p&gt;Odour is a major concern as they are termed hazardous to the surroundings as well as life forms when they are exposed to the environment. Odour emission is also one of the indicators of environmental changes that impact the environment. Among the different sources of odour emission, in the dumping yard itself, different types and ages of waste are dumped in the municipal solid waste (MSW) dumping yards. This study aims to relate odour emission and concentration changes caused by different weather patterns. Different periods of waste (fresh waste, moderate waste, and ripened waste) and weather seasons (summer and winter) affect the odour concentrations. Mixtures of gases and intolerable odours are major components of the MSW dumping yard. The odour concentration was monitored in the different periods of waste (moderate wastes) at different locations in the MSW dumping yard. In this study, it was found that meteorological conditions are also one of the main influences on odour concentrations in the environment. In this study, a comprehensive investigation of odour pollution from a local MSW dumping yard has been performed. The odour concentration indicates that the maximum range of aromatic hydrocarbon chemical compounds (volatile organic compounds) reported was T-butylbenzene at 1.41µg/m3 and the minimum range was Sec-butylbenzene at 0.07µg/m3. This study will provide information on odour emissions in urban areas and how VOC (Volatile Organic Compounds) components are present and affect the dumping yards surrounding those areas&lt;/p&gt;&#x0D;

Odour Perception Using a Sniffing Team at a Municipal Solid Waste Treatment Plant: A Case Study

The monitoring of odour intensity, generated by a landfill area, is a difficult activity since it is a multi-source problem with discontinuous odour emissions. A modified sniffing team method is described here and applied to determine the main odour sources in a landfill located in Pomerania, Poland. Four consecutive test sessions were performed during the following months: August, December, April, and June. It was found that the main odour sources are as follows: a closed-chamber composting facility for leach storage; the site wherein technological operations associated with compost turn-over during open-air aeration processes are performed; and the landfill site. The results of the sniffing team method present the indicative values of sensory testing. The application of the presented method was limited by disturbances due to changing atmospheric conditions. The calculated odour intensities and concentrations correspond with real sensitive perceptions of the tested environment.

Continuous odor profile monitoring to study olfactory navigation in small animals.

Olfactory navigation is observed across species and plays a crucial role in locating resources for survival. In the laboratory, understanding the behavioral strategies and neural circuits underlying odor-taxis requires a detailed understanding of the animal's sensory environment. For small model organisms like Caenorhabditis elegans and larval Drosophila melanogaster, controlling and measuring the odor environment experienced by the animal can be challenging, especially for airborne odors, which are subject to subtle effects from airflow, temperature variation, and from the odor's adhesion, adsorption, or reemission. Here, we present a method to control and measure airborne odor concentration in an arena compatible with an agar substrate. Our method allows continuous controlling and monitoring of the odor profile while imaging animal behavior. We construct stationary chemical landscapes in an odor flow chamber through spatially patterned odorized air. The odor concentration is measured with a spatially distributed array of digital gas sensors. Careful placement of the sensors allows the odor concentration across the arena to be continuously inferred in space and monitored through time. We use this approach to measure the odor concentration that each animal experiences as it undergoes chemotaxis behavior and report chemotaxis strategies for C. elegans and D. melanogaster larvae populations as they navigate spatial odor landscapes.

Comparison of Flavor Profile Relationship of Soy Sauce under Different Storage Conditions.

To elucidate the relation of flavor in soy sauce (SS) kept at room temperature (SSAT) and SS kept under accelerated aging condition (SSAA), four analytical instruments, including electronic nose (E-nose), electronic tongue (E-tongue), gas chromatography-mass spectrometry-olfactory combined with solvent assisted flavor evaporation, and amino acid analyzer, were applied for analyzing the overall flavor profiles and flavor constituents in SSAT and SSAA. The results of E-nose and E-tongue showed overall flavor profile in SSAT for 3 weeks was similar to that of SSAA for 1 week, and 6 weeks (SSAT) was similar to 2 weeks (SSAA). In SS, a total of 35 odor-active compounds were identified and quantitated, and 22 compounds with odor activity value ≥1 were determined as key odorants. The compounds with the highest concentration were 4-hydroxy-2,5-dimethyl-3(2H)-furanone (28,756 μg/mL), followed by acetic acid (8838 μg/mL) and maltol (7984 μg/mL). The heatmap and hierarchical cluster analysis indicated that the concentrations of key odorants and amino acids in SSAT for 3 weeks was close to those of SSAA for 1 week, and 6 weeks (SSAT) was similar to 2 weeks (SSAA). Based on the results obtained above, it was concluded that the flavor changes in SSAA for 1 week were equivalent to those in SSAT for 3 weeks.

Gain control in olfactory receptor neurons and the detection of temporal fluctuations in odor concentration.

The ability of the cockroach to locate an odor source in still air suggests that the temporal dynamic of odor concentration in the slowly expanding stationary plume alone is used to infer odor source distance and location. This contradicts with the well-established view that insects use the wind direction as the principle directional cue. This contribution highlights the evidence for, and likely functional relevance of, the capacity of the cockroach's olfactory receptor neurons to detect and process-from one moment to the next-not only a succession of odor concentrations but also the rates at which concentration changes. This presents a challenge for the olfactory system because it must detect and encode the temporal concentration dynamic in a manner that simultaneously allows invariant odor recognition. The challenge is met by a parallel representation of odor identity and concentration changes in a dual pathway that starts from olfactory receptor neurons located in two morphologically distinct types of olfactory sensilla. Parallel processing uses two types of gain control that simultaneously allocate different weight to the instantaneous odor concentration and its rate of change. Robust gain control provides a stable sensitivity for the instantaneous concentration by filtering the information on fluctuations in the rate of change. Variable gain control, in turn, enhances sensitivity for the concentration rate according to variations in the duration of the fluctuation period. This efficiently represents the fluctuation of concentration changes in the environmental context in which such changes occur.

Gain modulation and odor concentration invariance in early olfactory networks.

The broad receptive field of the olfactory receptors constitutes the basis of a combinatorial code that allows animals to detect and discriminate many more odorants than the actual number of receptor types that they express. One drawback is that high odor concentrations recruit lower affinity receptors which can lead to the perception of qualitatively different odors. Here we addressed the contribution that signal-processing in the antennal lobe makes to reduce concentration dependence in odor representation. By means of calcium imaging and pharmacological approach we describe the contribution that GABA receptors play in terms of the amplitude and temporal profiles of the signals that convey odor information from the antennal lobes to higher brain centers. We found that GABA reduces the amplitude of odor elicited signals and the number of glomeruli that are recruited in an odor-concentration-dependent manner. Blocking GABA receptors decreases the correlation among glomerular activity patterns elicited by different concentrations of the same odor. In addition, we built a realistic mathematical model of the antennal lobe that was used to test the viability of the proposed mechanisms and to evaluate the processing properties of the AL network under conditions that cannot be achieved in physiology experiments. Interestingly, even though based on a rather simple topology and cell interactions solely mediated by GABAergic lateral inhibitions, the AL model reproduced key features of the AL response upon different odor concentrations and provides plausible solutions for concentration invariant recognition of odors by artificial sensors.

Portable chemical detection platform for on-site monitoring of odorant levels in natural gas

The adequate odorization of natural gas is critical to identify gas leaks and to reduce accidents. To ensure odorization, natural gas utility companies collect samples to be processed at core facilities or a trained human technician smells a diluted natural gas sample. In this work, we report a detection platform that addresses the lack of mobile solutions capable of providing quantitative analysis of mercaptans, a class of compounds used to odorize natural gas. Detailed description of the platform hardware and software components is provided. Designed to be portable, the platform hardware facilitates extraction of mercaptans from natural gas, separation of individual mercaptan species, and quantification of odorant concentration, with results reported at point-of-sampling. The software was developed to accommodate skilled users as well as minimally trained operators. Detection and quantification of six commonly used mercaptan compounds (ethyl mercaptan, dimethyl sulfide, n-propylmercaptan, isopropyl mercaptan, tert‑butyl mercaptan, and tetrahydrothiophene) at typical odorizing concentrations of 0.1–5 ppm was performed using the device. We demonstrate the potential of this technology to ensure natural gas odorizing concentrations throughout distribution systems.

Chronic exposure to odors at naturally occurring concentrations triggers limited plasticity in early stages of Drosophila olfactory processing.

In insects and mammals, olfactory experience in early life alters olfactory behavior and function in later life. In the vinegar fly Drosophila, flies chronically exposed to a high concentration of a monomolecular odor exhibit reduced behavioral aversion to the familiar odor when it is reencountered. This change in olfactory behavior has been attributed to selective decreases in the sensitivity of second-order olfactory projection neurons (PNs) in the antennal lobe that respond to the overrepresented odor. However, since odorant compounds do not occur at similarly high concentrations in natural sources, the role of odor experience-dependent plasticity in natural environments is unclear. Here, we investigated olfactory plasticity in the antennal lobe of flies chronically exposed to odors at concentrations that are typically encountered in natural odor sources. These stimuli were chosen to each strongly and selectively excite a single class of primary olfactory receptor neuron (ORN), thus facilitating a rigorous assessment of the selectivity of olfactory plasticity for PNs directly excited by overrepresented stimuli. Unexpectedly, we found that chronic exposure to three such odors did not result in decreased PN sensitivity but rather mildly increased responses to weak stimuli in most PN types. Odor-evoked PN activity in response to stronger stimuli was mostly unaffected by odor experience. When present, plasticity was observed broadly in multiple PN types and thus was not selective for PNs receiving direct input from the chronically active ORNs. We further investigated the DL5 olfactory coding channel and found that chronic odor-mediated excitation of its input ORNs did not affect PN intrinsic properties, local inhibitory innervation, ORN responses or ORN-PN synaptic strength; however, broad-acting lateral excitation evoked by some odors was increased. These results show that PN odor coding is only mildly affected by strong persistent activation of a single olfactory input, highlighting the stability of early stages of insect olfactory processing to significant perturbations in the sensory environment.

Mushroom body output neurons MBON-a1/a2 define an odor intensity channel that regulates behavioral odor discrimination learning in larval Drosophila.

The sensitivity of animals to sensory input must be regulated to ensure that signals are detected and also discriminable. However, how circuits regulate the dynamic range of sensitivity to sensory stimuli is not well understood. A given odor is represented in the insect mushroom bodies (MBs) by sparse combinatorial coding by Kenyon cells (KCs), forming an odor quality representation. To address how intensity of sensory stimuli is processed at the level of the MB input region, the calyx, we characterized a set of novel mushroom body output neurons that respond preferentially to high odor concentrations. We show that a pair of MB calyx output neurons, MBON-a1/2, are postsynaptic in the MB calyx, where they receive extensive synaptic inputs from KC dendrites, the inhibitory feedback neuron APL, and octopaminergic sVUM1 neurons, but relatively few inputs from projection neurons. This pattern is broadly consistent in the third-instar larva as well as in the first instar connectome. MBON-a1/a2 presynaptic terminals innervate a region immediately surrounding the MB medial lobe output region in the ipsilateral and contralateral brain hemispheres. By monitoring calcium activity using jRCamP1b, we find that MBON-a1/a2 responses are odor-concentration dependent, responding only to ethyl acetate (EA) concentrations higher than a 200-fold dilution, in contrast to MB neurons which are more concentration-invariant and respond to EA dilutions as low as 10-4. Optogenetic activation of the calyx-innervating sVUM1 modulatory neurons originating in the SEZ (Subesophageal zone), did not show a detectable effect on MBON-a1/a2 odor responses. Optogenetic activation of MBON-a1/a2 using CsChrimson impaired odor discrimination learning compared to controls. We propose that MBON-a1/a2 form an output channel of the calyx, summing convergent sensory and modulatory input, firing preferentially to high odor concentration, and might affect the activity of downstream MB targets.

Soft, miniaturized, wireless olfactory interface for virtual reality

Recent advances in virtual reality (VR) technologies accelerate the creation of a flawless 3D virtual world to provide frontier social platform for human. Equally important to traditional visual, auditory and tactile sensations, olfaction exerts both physiological and psychological influences on humans. Here, we report a concept of skin-interfaced olfactory feedback systems with wirelessly, programmable capabilities based on arrays of flexible and miniaturized odor generators (OGs) for olfactory VR applications. By optimizing the materials selection, design layout, and power management, the OGs exhibit outstanding device performance in various aspects, from response rate, to odor concentration control, to long-term continuous operation, to high mechanical/electrical stability and to low power consumption. Representative demonstrations in 4D movie watching, smell message delivery, medical treatment, human emotion control and VR/AR based online teaching prove the great potential of the soft olfaction interface in various practical applications, including entertainment, education, human machine interfaces and so on.