Odor Threshold Research Articles

Analysis of Free Hydrogen Sulfide in Wines Using Gas Detection Tubes

<h3>Summary</h3> <h3>Goals:</h3> Hydrogen sulfide (H₂S, “rotten egg” aroma) concerns winemakers due to its contribution to sulfur-like off-aromas (SLOs). However, there are a lack of inexpensive, convenient methods for quantitation of H₂S in wines at or below its reported odor threshold. The use of selective, colorimetric gas detection tubes (GDT) for measurement of H₂S during fermentation has been previously described, but this approach has not been adapted and validated for finished wines. We developed and validated protocols for rapid, inexpensive analysis of H₂S using GDTs and Aeration-Oxidation (A-O) glassware commonly available in wineries. Video demonstration of the approaches is also provided (Supplemental Video 1). <h3>Key Findings:</h3> Two approaches were validated for GDT-based quantitation of H₂S in wine. In the first approach, H₂S was sparged from the sample with N₂ gas, analogous to Monier-Williams analyses of SO₂. In the second approach, H₂S was sparged by a vacuum-generated air stream, analogous to A-O analyses of SO₂. Both approaches require &lt;15 min/sample and achieve excellent linearity. The calibration curve for the N₂ Method was identical to the curve predicted from the manufacturer’s markings. The Aspiration Method was less sensitive, likely because of oxidative losses. However, the Aspiration Method was simpler to set up, operate, and adapt to higher concentration samples. The limits of detection were 12-13 ng H₂S for the methods, or ~0.2 μg/L using a 60 mL sample. The mean coefficients of variance (%CV) were &lt;5% for both approaches. Using the new method, we observed that commercially purchased wines stored in aluminum cans have significantly higher H₂S than commercial wines in glass packaging. <h3>Significance:</h3> The novel methods can be used for routine H₂S analysis in wineries without the need for significant investment in new equipment. In addition to cost savings, the ability to test H₂S onsite rather than send samples to an external lab decreases the risk of H₂S losses through oxidation or volatilization. These new analytical tools can be used for benchmarking, diagnosing faulty wines, or evaluating the effects of winemaking parameters, such as yeast selection, remediation treatments, and packaging options on H₂S.

Identification of volatile sulfur odorants emitted from ageing wastewater biosolids

Volatile sulfur compounds (VSCs) are important sources of unpleasant odours in biosolid emissions. However, the study of VSCs may be limited by complications in their gas phase measurements due to reactivity, transformations and varying reported odour detection thresholds. A range of methods were used to quantitatively analyse VSCs in wastewater biosolid emissions. VSCs were identified in aged biosolid emissions by gas chromatography (GC) with a sulfur chemiluminescence detector (SCD) and mass spectrometry coupled with olfactory detection port (MS/O). In total, 10 VSC's were identified with two volatile organic sulfur compounds (VOSCs), allyl methyl sulfide and methyl propyl sulfide being reported for the first time in biosolid emissions. The emission patterns of different VSCs varied as the biosolids aged. Initially, the median concentrations of H2S, dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), methanethiol (MeSH) and ethanethiol (EtSH) were orders of magnitude greater than their reported odour detection threshold, suggesting they would contribute to the odorous impact of the biosolids. The maximum H2S value was equal to 59.9 × 103 μg/m3 and was at least one magnitude higher compared to VOSCs, such as dimethyl disulfide (DMDS) (3.8×103 μg/m3), DMS (4.53 × 103 μg/m3), EtSH (2.83 × 103 μg/m3) and MeSH (3.25 × 103 μg/m3). Among the identified VSCs, H2S was the prominent odorant in terms of the magnitude and the frequency of detection, both initially as well as throughout storage. However, DMTS should be considered as a high priority or key odorant due to its odour activity value (OAV) and frequency of detection (sensorially detected in more than 75% of samples, with an OAVs higher than 1).

Olfactory bulb astrocytes mediate sensory circuit processing through Sox9 in the mouse brain

The role of transcription factors during astrocyte development and their subsequent effects on neuronal development has been well studied. Less is known about astrocytes contributions towards circuits and behavior in the adult brain. Astrocytes play important roles in synaptic development and modulation, however their contributions towards neuronal sensory function and maintenance of neuronal circuit architecture remain unclear. Here, we show that loss of the transcription factor Sox9 results in both anatomical and functional changes in adult mouse olfactory bulb (OB) astrocytes, affecting sensory processing. Indeed, astrocyte-specific deletion of Sox9 in the OB results in decreased odor detection thresholds and discrimination and it is associated with aberrant neuronal sensory response maps. At functional level, loss of astrocytic Sox9 impairs the electrophysiological properties of mitral and tufted neurons. RNA-sequencing analysis reveals widespread changes in the gene expression profiles of OB astrocytes. In particular, we observe reduced GLT-1 expression and consequential alterations in glutamate transport. Our findings reveal that astrocytes are required for physiological sensory processing and we identify astrocytic Sox9 as an essential transcriptional regulator of mature astrocyte function in the mouse OB.

Association Between Anxious Symptom Severity and Olfactory Impairment in Young Adults with Generalized Anxiety Disorder: A Case-Control Study.

ObjectiveThe findings of olfaction are inconsistent in anxiety disorders, and few studies have reported on the olfactory performance in generalized anxiety disorder (GAD). Therefore, we aim to investigate the olfactory function of patients with GAD and the association between olfactory function and anxiety symptoms.MethodsWe conducted a case–control study by selecting 107 patients with GAD and 107 healthy controls matched for sex and age, to investigate olfaction deficits in GAD and the association between anxiety severity and olfaction. All patients were treatment-naïve prior to the inclusion. Anxiety severity and olfaction were assessed by the Hamilton anxiety rating scale (HAM-A) and the Sniffin’ Sticks test (SST), respectively. Partial correlations were used to analyze the relationship between olfaction and anxiety severity. False discovery rate (FDR) correction was used in multi-correlation analyses.ResultsCompared with healthy controls, patients in the GAD group demonstrated odor threshold, discrimination and identification deficits. In the moderate/severe anxiety subgroup, discrimination score was significantly and inversely correlated with the somatic anxiety score (γ=−0.44, q = 0.03), and identification score was significantly and inversely correlated with the HAM-A total score (γ=−0.42, q= 0.04). The TDI score (the sum of threshold, discrimination and identification scores) was significantly and inversely correlated with the somatic (γ=−0.44, q = 0.04) and psychic (γ=−0.45, q = 0.04) anxiety scores in the moderate/severe anxiety subgroup.ConclusionThis study demonstrated the olfactory impairment in patients with GAD and that poorer odor discrimination was correlated with greater severity of somatic anxiety.

Selective dual detection of hydrogen sulfide and methyl mercaptan using CuO/CuFe2O4 nanopattern chemiresistors

Volatile sulfur compounds (VSCs), such as H2S and methyl mercaptan (MM), are malodorous and harmful gases. H2S and MM share analogical origins. However, they should be discriminated because of their different odor thresholds and health impacts. Herein, a nanopattern chemiresistor composed of aligned CuO-loaded CuFe2O4 nanofibers was prepared via direct-write near-field electrospinning. The CuO/CuFe2O4 sensor with the atomic ratio of [Cu]:[Fe] = 3:4 exhibited extremely high responses to ppm-level H2S and MM compared with other nanopattern sensors with different compositions ([Cu]/[Fe] = 2:4, 4:4, and 0:1). This can be attributed to the gas-accessible morphology of the nanopattern sensor, the formation of a nanoscale p(CuO)-n(CuFe2O4) junction, and the intimate reaction between the discretely loaded CuO nanoparticles and the VSCs. Furthermore, the CuO/CuFe2O4 sensor exhibited high selectivities to H2S and MM at 200 ℃ and 400 ℃, respectively. The selective dual detection of H2S and MM using a single CuO/CuFe2O4 sensor via the simple modulation of the sensing temperature opens a new route for indoor air quality monitoring, ventilation control, halitosis diagnosis, and wine quality monitoring.

Characterization of aroma and bacteria profiles of Sichuan industrial paocai by HS-SPME-GC-O-MS and 16S rRNA amplicon sequencing

Sichuan industrial paocai and traditional home-made paocai have different aroma profiles due to different manufacturing techniques, but detailed information about the aroma profiles and aroma-producing microorganism of Sichuan industrial paocai remain largely elusive. For this reason, we established and validated an external standard method of headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC–MS) combined with gas chromatography–olfactometry (GC-O) for identification and accurate quantitation of aroma-active compounds in Sichuan industrial paocai. This method was combined with 16S rRNA amplicon sequencing to comprehensively analyze the aroma and bacteria profiles of Sichuan industrial paocai. A total of 121 volatile compounds were identified, among which 36 odorants were identified as aroma-active compounds with aroma intensities (AIs) ranging from 0.67 to 5.00 by GC-O. The types of aroma-active compounds in Sichuan industrial paocai were variety-specific to some extent, but the aroma-active compounds shared by different varieties of Sichuan industrial paocai (i.e., skeleton aroma-active compounds) were phenylethyl alcohol, acetic acid, butanoic acid, 2-methylbutanoic acid, ethyl hexanoate, 4-ethylphenol and 4-ethylguaiacol. Moreover, 17 key aroma-active compounds of AI > 1 in radish paocai were quantitated by external standard method, and their odor activity values (OAVs) were calculated based on the odor thresholds. Further, 12 aroma-active compounds with OAV ≥ 1 in one of the radish paocai were selected to construct the recombination model, which revealed good agreement with the original sample. Furthermore, Lactobacillus, Pediococcus, Pseudomonas and Sphingomonas were the dominant bacteria in Sichuan industrial paocai. Correlation analysis between 16 dominant bacteria and 36 aroma-active compounds showed that Pediococcus, Arcobacter and Lactobacillus could be the core aroma-producing bacteria of Sichuan industrial paocai.

Screening of Volatile Compounds in Mate (Ilex paraguariensis) Tea—Brazilian Chimarrão Type—By HS-SPDE and Hydrodistillation Coupled to GC-MS

The volatile fraction of mate (Ilex paraguariensis) tea—specifically Brazilian chimarrão type, which has an odor profile comprising distinctive fresh, green, grass, and herbal notes—was investigated. Hydrodistillation in a Clevenger apparatus was employed in order to extract volatiles from the tea matrix. Headspace–solid-phase dynamic extraction (HS-SPDE) was employed to extract the volatiles from two types of infusions of this tea—a simple single infusion and a traditional preparation of consecutive infusions. Volatiles were analyzed by gas chromatography–flame ionization detection/mass spectrometry (GC-FID/MS). In total, 85 compounds were either identified or tentatively identified and semi-quantified. Semi-quantification comprised peak area integration of all the peaks (including the unidentified ones) in the chromatogram. Results obtained by hydrodistillation and by HS-SPDE were distinct, covering mostly different ranges of volatility and showing only 15 compounds in common. The identified compounds had their respective average and minimum odor thresholds and odor characteristics compiled from the literature. Several major compounds considered as key odorants in other mate tea products were not detected or only present at low levels in the samples of this research. Approximately half of the odorants identified in these samples were commonly reported in different mate tea types; the remaining 41 molecules—predominantly terpenoids (isoprenoids)—could be listed as specific to the Brazilian chimarrão type and are suggested to underlie its typical freshness.

In healthy subjects nasal nitric oxide does not correlate with olfactory sensitivity, trigeminal sensitivity, and nasal airflow

The aim of the study was to determine the relationship between nasal nitric oxide (nNO) and olfactory sensitivity, trigeminal sensitivity and nasal airflow in healthy subjects. This is a correlational study. This study was carried out in a tertiary referral centre. Forty healthy participants were recruited. nNO was measured using a chemiluminescence analyser (Niox Vero® , CircassiaAB, Uppsala, Sweden), olfactory sensitivity was determined using phenyl ethyl alcohol odour thresholds using the 'Sniffin' Sticks', trigeminal sensitivity was assessed with carbon dioxide delivered by an automated device, and nasal airflow was measured using the peak nasal inspiratory flow (PNIF). The median nNO was 518ppb (IQR=333) in the right nostril, and it was 567ppb (IQR=314) in the left nostril. The median odour threshold was 7.1 (IQR=4.4), the median CO2 threshold was 919ms (IQR=1297) and the mean PNIF was 108L/min (SEM=4.9). nNO did not correlate significantly with odour threshold, CO2 threshold or PNIF (Spearman's|ρ| <0.15, p>.18). In healthy subjects, nNO does not appear to be associated with olfactory sensitivity, trigeminal sensitivity and PNIF.

Pilot-Scale H2S and Swine Odor Removal System Using Commercially Available Biochar

Although biochars made in laboratory seem to remove H2S and odorous compounds effectively, very few studies are available for commercial biochars. This study evaluated the efficacy of a commercial biochar (CBC) for removing H2S and odorous volatile organic compounds (VOCs). We found that the well-known Ergun equation may not be adequate in predicting pressure drop for properly sizing a ventilation system. The H2S breakthrough adsorption capacity of the CBC was 2.51 mg/g under humid conditions, which was much higher than that for dry conditions. The breakthrough capacity increased with the influent concentration of H2S. The efficacy of a pilot-scale biochar odor removal system (PSBORS) for removing 15 odorous VOCs was evaluated by placing it in a swine gestation stall continually treating the inside air for 21 days. All VOCs in the PSBORS effluent were below detection limit except for acetic acid. However, due to the very high odor threshold of acetic acid, its contribution to the odor would be minimal. It appeared that the CBC could be used to reduce both H2S and odorous VOCs with the potential of recycling the spent CBC for soil health improvement after using it for H2S and odor removal.

Gene therapy rescues olfactory perception in a clinically relevant ciliopathy model of Bardet-Biedl syndrome.

Bardet-Biedl syndrome (BBS) is a hereditary genetic disorder that results in numerous clinical manifestations including olfactory dysfunction. Of at least 21 BBS-related genes that can carry multiple mutations, a pathogenic mutation, BBS1M390R, is the single most common mutation of clinically diagnosed BBS outcomes. While the deletion of BBS-related genes in mice can cause variable penetrance in different organ systems, the impact of the Bbs1M390R mutation in the olfactory system remains unclear. Using a clinically relevant knock-in mouse model homozygous for Bbs1M390R, we investigated the impact of the mutation on the olfactory system and tested the potential of viral-mediated, wildtype gene replacement therapy to rescue smell loss. The cilia of olfactory sensory neurons (OSNs) in Bbs1M390R/M390R mice were significantly shorter and fewer than those of wild-type mice. Also, both peripheral cellular odor detection and synaptic-dependent activity in the olfactory bulb were significantly decreased in the mutant mice. Furthermore, to gain insight into the degree to which perceptual features are impaired in the mutant mice, we used whole-body plethysmography to quantitatively measure odor-evoked sniffing. The Bbs1M390R/M390R mice showed significantly higher odor detection thresholds (reduced odor sensitivity) compared to wild-type mice; however, their odor discrimination acuity was still well maintained. Importantly, adenoviral expression of Bbs1 in OSNs restored cilia length and re-established both peripheral odorant detection and odor perception. Together, our findings further expand our understanding for the development of gene therapeutic treatment for congenital ciliopathies in the olfactory system.

Additivity between Key Odorants in Pig House Air

The verification of odor abatement technologies for livestock production based on chemical odorants requires a method for conversion into an odor value that reflects the significance of the individual odorants. The aim of the present study was to compare the SOAV method (Sum of Odor Activity Values) with the odor detection threshold measured by olfactometry and to investigate the assumption of additivity. Synthetic pig house air with odorants at realistic concentration levels was used in the study (hydrogen sulfide, methanethiol, trimethylamine, butanoic acid, and 4-methylphenol). An olfactometer with only PTFE in contact with sample air was used to estimate odor threshold values (OTVs) and the odor detection threshold for samples with two to five odorants. The results show a good correlation (R2 = 0.88) between SOAV estimated based on the OTVs for panelists in the present study and values found in the literature. For the majority of the samples, the ratio between the odor detection threshold and SOAV was not significantly different from one, which indicates that the OAV for individual odorants in a mixture can be considered additive. In conclusion, the assumption of additivity between odorants measured in pig house air seems reasonable, but the strength of the method is determined by the OTV data used.

Odor-active volatile organic compounds along the seafront of Thessaloniki, Greece. Implications for sources of nuisance odor

Volatile organic compounds (VOCs) have long been associated with odor nuisance at urban sites close to emission sources. Sulfur containing volatile organic compounds (VOSCs) in particular, constitute a major category of malodorous compounds since some of them are characterized by intense odor and low odor thresholds. VOSCs have both, anthropogenic and biogenic sources. The purpose of this study was to assess the concentration levels of a variety of VOCs (mercaptans, sulfides, thiophenes, aromatics and aldehydes) along the seafront of the city of Thessaloniki, northern Greece, a city with frequent citizen complaints for nuisance odor. 1-Hour sampling on adsorption tubes was carried out concurrently at 3 sites along the seafront of the city (EAST, CENTER and WEST) three times during the day in winter and summer 2020. VOCs analysis, performed on a Thermal Desorption - Gas Chromatography/Mass Spectroscopy (TD-GC/MS) system. Diurnal and seasonal variations, and correlations with prevailing meteorological conditions were investigated. Concentrations found along the seafront were compared to previous data from inner-city sites affected by urban and/or industrial activities. Most VOCs were found at lower concentrations at the seafront in comparison to inner-city sites demonstrating better air quality. Typical biogenically-deriving VOSCs such as carbonyl sulfide and dimethyl sulfide were found at the seafront either at higher or at similar levels with inner city thus suggesting negligible contribution from biogenic sources. Odor activity values were further calculated and assessed. Odor nuisance at all seafront sites was significantly higher in winter, being in both seasons maximum at the WEST seafront that is closer to port activities, polluted creek estuaries and industrial facilities. Mercaptans were identified as the major contributors to odor pollution followed by aldehydes. The new findings described in this study might contribute to the better understanding of the odor pollution from VOCs at coastal urban sites.

Olfactory shifts linked to postpartum depression

Postpartum Depression (PPD) is the most common non-obstetric complications associated with childbearing, but currently has poor diagnostic regimes. Sensory symptoms of PPD are understudied, particularly with regard to the sense of olfaction. The present study addresses this research gap by assessing differences in olfactory abilities between 39 depressed mothers, who were within the perinatal period (i.e., during pregnancy and up to 1-year post pregnancy) and assessed with Edinburgh Postnatal Depression Scale, and their case-matched healthy volunteers. The assessments include two olfactory testing sessions conducted 4-weeks apart, each comprising a standard odour detection threshold test (i.e., Snap & Sniff Olfactory Test System), and intensity and valence ratings for 3 “pleasant” and 3 “unpleasant” odorants. The results revealed no difference between patients (M = 5.6; SE = 0.3) and control group (M = 5.7; SE = 0.4) in terms of olfactory detection threshold. However, the patients group perceived the 3 “unpleasant” odours as significantly less pleasant (p < 0.05), and 2 odorants (1 “pleasant” and 1 “unpleasant”) as less intense. Additionally, these results did not appear to be significantly interacted with the individual’s perinatal stage. The present study is the first to evaluate associations between olfactory function and PPD. Findings from the study suggest that, while PPD has little effect on the early stages of olfactory processing, these conditions may have stronger influence on higher-order olfactory perception, including both hedonic and intensity perception. These novel findings add knowledge to sensory symptoms of PPD.

Oral malodor: Epidemiology, Etiology, Physiology, Diagnosis, Counseling aspects and clinical management- An overview

Breath malodor is a social problem, and most patients complained about breath malodor in most countries. The etiological chain of breath malodor originated from the volatile sulfur compounds (VSC), gingival and periodontal diseases. When the threshold concentration, odor power, and volatility of the molecules increase in the expired air, it results in unpleasant breath odor. There are many tests to diagnose oral malodor, and the clinical management includes mechanical reduction of nutrients, clinical reduction of oral microorganisms, conversion, and masking of volatile sulfur compounds. When the dentist's treatment of oral malodor is not successful, then referral to the physician is warranted.

Habitual Exposure to Trigeminal Stimuli and Its Effects on the Processing of Chemosensory Stimuli

Our objective was to compare brain responses to trigeminal and olfactory stimuli in frequent and non-frequent gum chewers in order to explore whether habitual exposure to trigeminal stimuli affects their central-nervous processing. In healthy subjects, fMRI brain scans were obtained for 20 frequent gum chewers (GC) and 20 non-frequent gum chewers (N′GC), in response to four odorous stimuli; 2 ‘trigeminal’ (peppermint and spearmint) and 2 non-trigeminal or ‘olfactory’ (cherry and strawberry). During measurements, subjects reported intensity and pleasantness ratings for all stimuli. In addition, a test for general trigeminal sensitivity test (lateralization test) and an odor threshold test was performed. Brain activations in response to individual odors were investigated for the total study population followed by group wise (GC and N′GC) analysis separately for responses to trigeminal (peppermint + spearmint) and olfactory (cherry + strawberry) odors.(1) The GC group exhibited higher trigeminal sensitivity compared to the N′GC group. (2) Olfactory odors activated bilateral insular cortex and amygdala. Apart from olfactory areas (amygdala, insular cortex), trigeminal odors also produced activations in right thalamus and right substantia nigra. (3) In the GC group, olfactory odors produced higher bilateral insular cortex activation than in N′GC group, but no such differences were observed for trigeminal odors. GC subjects appeared to be more responsive to trigeminal chemosensory stimuli. However, this did not directly translate into differences in central-nervous activations to trigeminal stimuli; instead, the use of chewing gum was associated with stronger brain activation towards olfactory stimuli.

Synthesis of a synthetic analogue for the Sitophilus weevil aggregation pheromone and study on its hygienic and toxicological indexes

The work was initiated to study hygienic and toxicological indices of a synthetic analogue for the Sitophilus weevil aggregation pheromone. The toxicity testing of 5-hydroxy-4-methyl-3-heptanone demonstrated its extremely low toxicity for the warm-blood animals, as compared to the one of the typical pesticides. The average lethal dose of the product per orally administered to the white mice was established to be 4375.0 mg kg-1 LD16 and LD84 being 2225.0 mg kg-1 and 6550.0 mg kg-1, respectively. The average lethal dose for rabbits was 5900.0 mg kg-1 5-hydroxy-4-methyl-3-heptanone proved to have a mild skin and conjunctival irritant action, and equally mild functional cumulation. As to chronic toxicity, the acceptable daily dose of 4.3 mg/person/d was calculated and scientifically substantiated. The odor threshold was determined at the dose ranging from 0.35 to 0.7 mg l-1 with the practical limit ranging from 0.35 to 1.5 mg l-1, taste sensation threshold was found at the dose ranging from 1.0 to 3.0 mg l-1 with the practical limit ranging from 3.0 to 7.0 mg l-1

Cloning and functional characterization of two carotenoid cleavage dioxygenases for ionone biosynthesis in chili pepper (Capsicum annuum L.) fruits

Carotenoids are essential nutrients for the human body and contribute to the coloration and aroma traits of crops. Among plant volatile components, β-ionone has profound effects on scent and aroma due to its very low odor thresholds. In plants, β-ionone is produced from β-carotene (β,β-carotene) by carotenoid cleavage dioxygenases (CCDs), especially members of its CCD1 subfamily. In this study, we isolated two CCD1 genes (CaCCD1A and CaCCD1B) from the chili pepper (Capsicum annuum L.). Both genes have their highest expression levels in fruits among different tissues, and their transcript abundances increase during ripening, along with an increasing accumulation of β-ionone. Both CaCCD1A and CaCCD1B were found to cleave β-carotene specifically at the 9–10/9′–10′ site to produce β-ionone. When these enzymes were expressed in bacterial cells genetically engineered to produce oxygenated derivatives of β-carotene, such as zeaxanthin, antheraxanthin, and violaxanthin, β-ionone was still the only cleavage product, suggesting that β-carotene is preferentially cleaved by CaCCD1s instead of being hydroxylated by the bacterial type carotene hydroxylase CrtZ. In bacterial cells accumulating ε-carotene (ε,ε-carotene), the expression of CaCCD1A or CaCCD1B resulted in the production of α-ionone, indicating that both enzymes have cleavage activities regardless of the β- or ε- ring-type at the end of the substrates.

Synthesis, odour characteristics, and antibacterial activity of optically active cognac lactones

AbstractIn this study, all stereoisomers of cognac lactone (1) were synthesized with over 99% enantiomeric excess via diastereomeric resolution using N‐benzyloxycarbonyl‐l‐proline (N‐Cbz‐l‐proline) as a resolving agent. N‐Cbz‐l‐proline could be applied for the diastereomeric resolution of both syn‐ and anti‐forms and yielded all diastereomers in over 99% diastereomeric excess. The odour properties of racemic and optically active 1 were evaluated for their orthonasal aromas. All the stereoisomers had different odour characteristics and thresholds. In general, the (3S)‐ and (3R)‐forms had fruity and herbal notes, respectively, and (3R,4S)‐1 had the lowest odour threshold at 0.01 ppm. All stereoisomers, except (3R,4S)‐1, showed antibacterial activity against Staphylococcus aureus. Moreover, (3S,4S)‐1 showed high antibacterial activity against both S aureus and Escherichia coli.

A Rapid Gas-Chromatography/Mass-Spectrometry Technique for Determining Odour Activity Values of Volatile Compounds in Plant Proteins: Soy, and Allergen-Free Pea and Brown Rice Protein.

Plant-based protein sources have a characteristic aroma that limits their usage in various meat-alternative formulations. Despite being the most popular plant-based protein, the allergenicity of soy protein severely restricts the potential adoption of soy protein as an animal substitute. Thereby, allergen-free plant-protein sources need to be characterized. Herein, we demonstrate a rapid solid-phase-microextraction gas-chromatography/mass-spectrometry (SPME-GC/MS) technique for comparing the volatile aroma profile concentration of two different allergen-free plant-protein sources (brown rice and pea) and comparing them with soy protein. The extraction procedure consisted of making a 1:7 w/v aqueous plant protein slurry, and then absorbing the volatile compounds on an SPME fibre under agitation for 10 min at 40 °C, which was subsequently injected onto a GC column coupled to an MS system. Observed volatile concentrations were used in conjunction with odour threshold values to generate a Total Volatile Aroma Score for each protein sample. A total of 76 volatile compounds were identified. Aldehydes and furans were determined to be the most dominant volatiles present in the plant proteins. Both brown rice protein and pea protein contained 64% aldehydes and 18% furans, with minor contents of alcohols, ketones and other compounds. On the other hand, soy protein consisted of fewer aldehydes (46%), but a more significant proportion of furans (42%). However, in terms of total concentration, brown rice protein contained the highest intensity and number of volatile compounds. Based on the calculated odour activity values of the detected compounds, our study concludes that pea proteins could be used as a suitable alternative to soy proteins in applications for allergen-free vegan protein products without interfering with the taste or flavour of the product.

Effects of algae proliferation and density current on the vertical distribution of odor compounds in drinking water reservoirs in summer

Reservoirs are an important type of drinking water source for megacities, while lots of reservoirs are threatened by odor problems during certain seasons. The influencing factors of odor compounds in reservoirs are still unclear. During August 2019, a nationwide survey investigating the distribution of odor compounds in reservoirs used as drinking water sources was conducted on seven reservoirs. 2-methylisoborneol (2-MIB) and geosmin were detected in almost every reservoir, and some odor compound concentrations even exceeded the odor threshold concentration. The average concentration of 2-MIB was 2.68 ng/L, and geosmin was 3.63 ng/L. The average chlorophyll a concentration was 8.25 μg/L. The dominant genera of phytoplankton in these reservoirs belonged to cyanobacteria and diatom. Statistical analysis showed that odor compound concentration was significantly related to the chlorophyll a concentration and indicated that the odor compounds mainly came from phytoplankton. The concentration of odor compounds in the euphotic zone was significantly related to phytoplankton species and biomass. Therefore, the odor compound concentrations in the subsurface chlorophyll maxima layer was generally higher than in the surface layer. However, the odor compounds in the hypolimnion layer were related to the density current. This research suggests that both phytoplankton proliferation events and heavy storm events are important risk factors increasing odor compounds in reservoirs. Control of algal bloom, in-situ profile monitoring system and depth-adjustable pumping system will greatly reduce the risk of odor problems in reservoirs using as water supplies for large cities.