Odor Threshold Research Articles

Considerations in managing wastewater odor at pulp and paper operations

Many pulp and paper mills are, at least periodically, faced with the release of odors that can migrate offsite and be considered a nuisance by nearby residents. At chemical pulp mills, perceptible odors associated with reduced sulfur compounds (RSCs) are common, many of which are highly perceptible owing to their low odor thresholds. As releases of RSCs and other odorous substances from production processes are progressively controlled, the proportional contribution from wastewater treatment systems to areal odors can increase. This review paper summarizes important fundamentals of odor generation, source identification, and control. Common odorous substances are identified, and mechanisms for their generation are summarized. Approaches for measuring odorous substances are detailed to enable more effective management, and various odor control strategies are discussed.

Molecular characterisation of an atypical coconut-like odour in cocoa

Parallel application of an aroma extract dilution analysis (AEDA) to the volatiles isolated from a sample of fermented cocoa with an atypically pronounced coconut note and to the volatiles isolated from a reference cocoa sample revealed coconut-like smelling compounds δ-octalactone, δ-2-octenolactone, γ-nonalactone, γ-decalactone, δ-decalactone, and δ-2-decenolactone as potential causative odorants. Quantitation of these six compounds and calculation of odour activity values as ratios of the concentrations to the odour threshold values suggested δ-2-decenolactone as the crucial compound. Chiral analysis showed the presence of pure (R)-δ-2-decenolactone, commonly referred to as massoia lactone. Its key role for the coconut note was finally demonstrated in a spiking experiment: the addition of (R)-δ-2-decenolactone to the reference cocoa in an amount corresponding to the concentration difference between the two samples was able to provoke a coconut note in an intensity comparable to the one in the atypically smelling cocoa. To avoid an undesired coconut note caused by (R)-δ-2-decenolactone in the final products, the chocolate industry may consider its odour threshold value, that is 100 µg/kg, as a potential limit for the acceptance of fermented cocoa in the incoming goods inspection.

Ultrathin δ-MnO2 nanoribbons for highly efficient removal of a human-related low threshold odorant - acetic acid

Efficient removal of human-emitted gaseous pollutants in indoor air may greatly reduce ventilation-related energy consumption, however few efforts have been made. Here we reported the room and low-temperature catalytic removal of a human-emitted odorant - acetic acid with odor threshold of 5.6 ppb. Ultrathin δ-MnO2 nanoribbons (δ-MnO2 UTNRs) with the thickness of 1–1.5 nm and aspect ratio of 200–600 was synthesized, which produced abundant active oxygen species such as hydroxyl radicals and superoxide at room temperature without light irradiation. Accordingly, as-prepared δ-MnO2 UTNRs could transform acetic acid into CO2 even at room temperature. The 100% one-through removal capacity for ~1 ppm acetic acid was about 20 mg/g, and it could be completely regenerated at 140 °C. This study opens a new research direction and demonstrates that it is possible to catalytically remove human-emitted gaseous pollutant at low and even at room temperature.

Determining the Optimal Cooking Time for Cooking Loss, Shear Force, and Off-Odor Reduction of Pork Large Intestines

The objective of this study was to determine the optimal cooking time by considering the cooking loss, shear force, and off-odor reduction of pork large intestines. Commercial pork large intestines were purchased, quartered perpendicularly, and cooked in boiling water for 40, 120, 180, and 240 min. Cooking loss of the samples increased after 240 min of cooking (10.92, p<0.05) while shear force value was lower at 240 min (4.45) compared to that at other cooking times (p<0.001). The amount of major volatile organic compounds showed a decreasing trend with increasing cooking time. In particular, the amount of methyl pentanoate (17,528.71) and methyl isobutyrate (812.51), compounds with a relatively low odor threshold, decreased significantly after 120 min of cooking and no change was observed thereafter (p<0.05). In addition, the amount of 2-pentanol (3,785.65) and 1-propanol (622.26), possibly produced by lipid oxidation, significantly decreased at the same cooking time (p<0.001). In the principal component analysis, only the 40 min cooking time was significantly different from other cooking time by high amounts of 1-propanol, 2-pentanol, and methyl isobutyrate. In conclusion, in the present study, the optimal cooking time for pork large intestines was 120 min in terms of off-odor reduction, cooking loss, and shear force.

Chemical and organoleptic properties of bread enriched with Rosmarinus officinalis L.: The potential of natural extracts obtained through green extraction methodologies as food ingredients

The potential of R. officinalis L. (RO) extracts as a source of aromas was accessed by hydrodistillation (HD) and supercritical fluid extraction using carbon dioxide (SFE-CO2), followed by a series of analysis: quantification by GC-MS, sensory perception and description, and cytotoxicity against Vero cells. The extracts shown abundancy of α-pinene, eucalyptol, S-verbenone and camphor, contributing for the green, fresh, citric, and woody as main sensory notes. The odour threshold (ODT) value (less than 3.0 × 10−3 µg·mL−1) and the cytotoxic potential (ca. 220 µg∙mL−1) defined the concentration range for food application. The most promising extract was added to bread doughs and the final volatile profile was characterised by GC-MS through HS-SPME over time. Among the 34 compounds found, furfural showed an evident contribution in the bread crust aroma, which persisted over four hours of storage, contributing to a pleasant bread fragrance according to the evaluators. This study aims to represent a stepping stone for the use of natural aromas as ingredients for the development of innovative food products.

Nasal polyp load determines the recovery of olfaction after surgery for chronic rhinosinusitis.

Chronic rhinosinusitis (CRS) is typically accompanied by impairment of olfaction. Despite of this, until today the efficacy of endonasal sinus surgery (ESS) in terms of olfactory function is still unclear. So far it is known that patients with nasal polyps are most likely to experience post-operative recovery. Within the present study we investigated the sense of smell and other parameters of impairment in CRS before and after ESS in relation to the degree of nasal polyposis, determined with the nasal endoscopic Lildholdt-score. Patients with different degrees of severity of nasal polyposis were included. Olfactory function was assessed for odor thresholds [T], odor discrimination [D] and odor identification [I] and the changes of these parameters were investigated postoperatively. For 72 patients baseline measures were available and in 47 patients, postoperative changes were described. There was a correlation between olfactory scores and nasal anatomy/polyposis scores (Lildholdt scores, Lund-Mackay CT score), rated nasal health, and nasal quality of life (sinonasal outcome test). Three months after surgery the average TDI-Score improved by 3.1 points with 30% of patients showing significant clinical improvement. Patients with severe polyposis (Lildholdt score of 5 or 6) benefited most in terms of olfaction. Other significant prognostic indicators of a postoperative increase of olfactory scores included younger age, low pre-operative TDI-scores and high CT-scores. This study shows that not only the presence of polyps in CRS, but also the degree of nasal polyposis - measured by a grading system - predicts the results in olfactory test results. Additionally, the degree of recovery of olfaction after ESS seems to be most relevant in patients with high polyp scores.

Characterization of aroma compounds of Pu-erh ripen tea using solvent assisted flavor evaporation coupled with gas chromatography-mass spectrometry and gas chromatography-olfactometry

Pu-erh ripen tea becomes popular worldwide owing to its unique taste and aroma. In the present study, volatile compounds from Pu-erh ripen tea were extracted using a solvent assisted flavor evaporation (SAFE) and analyzed with a gas chromatography-mass spectrometry (GC-MS) and a gas chromatography olfactometry (GC-O). Results demonstrated that 58 major volatile compounds and 24 aroma active substances of Pu-erh ripen tea were identified by GC-MS and GC-O analysis. Among volatile compounds identified, methoxyphenyl compounds were considered as the dominate compounds in the aroma of Pu-erh ripen tea. Further investigation showed that 6 methoxybenzenes were responsible for the aging aroma in Pu-erh ripen tea; α-ionone, 3,4-dimethoxytoluene, 1,3-dimethoxybenzene, etc. were responsible for the wood-like aroma. Linalool, α-terpineol, α-ionone, β-ionone, and benzeneacetaldehyde were responsible for the floral odor. Compared the odor detection threshold (ODT) among the 8 methoxyphenyl compounds in water, 1,2,3-trimethoxybenzene showed the highest ODT, followed by 3,4-dimethoxyphenol. 1,3-Dimethoxybenzene (105 μg/L) and 1,2,3-trimethoxy-5-methylbenzene (100 μg/L) were present at relatively low odor threshold values. The result indicated that methoxyphenyl compounds play a vital role in the unique flavor of Pu-erh ripen tea.

Omega-3 supplementation in postviral olfactory dysfunction: a pilot study.

This study aimed to examine whether omega-3 supplementation would support olfactory recovery among postviral olfactory dysfunction patients. Patients with postviral olfactory dysfunction were included in this non-blinded, prospective pilot study. Structured medical history was taken from the patients, including the following: age, sex, history of COVID-19 infection, and duration of symptoms. Patients were randomly assigned to receive olfactory training only (control group) versus olfactory training with omega-3 supplementation (treatment group). All patients exposed themselves twice a day to four odours (phenyl ethyl alcohol [rose], eucalyptol [eucalyptus], citronellal [lemon], and eugenol [cloves]). Olfactory function was measured before and after training using 'Sniffin' Sticks', comprised of tests for odour threshold, discrimination, and identification. The average interval between olfactory tests was 3 months. Fifty-eight patients were included in the study, 25 men and 33 women. Generally, an improvement in olfactory scores was observed. Compared to the control group, the improvement in odour thresholds was more pronounced in the omega-3 group. Age, sex, and duration of symptoms had no effect on olfactory scores among both control and treatment groups. Overall, the present results indicate that omega-3 supplementation may be an option for adjunct therapy with olfactory training in patients with postviral olfactory dysfunction.

Photoinduced release of odorous volatile organic compounds from aqueous pollutants: The role of reactive oxygen species in increasing risk during cross-media transformation

Photoinduced volatile organic compounds (VOCs) release from fatty alcohols at the air-water interface, has attracted considerable attention. This paper comprehensively explores the release of odorous VOCs from aqueous micropollutants under photoirradiation, especially in terms of the important role of the reactive oxygen species (ROS) in increased risk by cross-media transformation. The formation and distribution of photoinduced VOCs produced by aqueous benzyl alcohol (BzOH), a common ingredient in personal care products, were monitored in situ by online gas chromatography equipped with mass spectrometry and flame ionization detector (GC–MS/FID). The photoreaction of BzOH followed first-order kinetics with a rate constant of 0.0158/min under air. After 180 min of ultraviolet irradiation, the accumulated output of the gas-phase products benzene and benzaldehyde (BA) reached 3.8 μmol and 2.6 μmol respectively, being approximately 10 times that under nitrogen. According to electron paramagnetic resonance measurements, singlet oxygen mainly promoted the oxidation of BzOH to BA, which was an important intermediate producing benzene via photocleavage. Odorous alicyclic hydrocarbons were also generated through photorearrangement under nitrogen. On the other hand, the Henry's law constants of the main products were much lower than those of BzOH, indicating that the photoproducts would volatilize from the aqueous phase into the gas phase. The odor threshold of gas-phase products decreased to varying degrees after photoirradiation. Especially for BA, one of the main products, its odor threshold decreased 130 times compared with BzOH. This study shows that the risk of cross-media pollution could significantly increase due to the transformation of aqueous pollutants into odorous VOCs under photoirradiation and provides new insight into its risk prevention.

Should Panelists Refrain from Wearing a Personal Fragrance Prior to Sensory Evaluation? The Effect of Using Perfume on Olfactory Performance.

It is typically recommended that panelists should refrain from wearing personal fragrances, such as perfume or cologne, prior to sensory evaluation. Interestingly, no study has been reported as to whether panelists’ perceptions of test samples could be affected by personal fragrances worn by themselves. The objective of this study was, therefore, to determine the effect of such a personal fragrance on olfactory performance. Nineteen untrained participants were screened, recruited for, and underwent the Sniffin’ Sticks test designed for measuring olfactory performances that included the odor threshold, discrimination, and identification (TDI). The olfactory performance tasks were conducted under three fragrance level conditions: (1) control (no fragrance), (2) just-about-right (JAR), and (3) excessive, with a preliminary study used to identify both the JAR and excessive fragrance levels. The results showed that the odor discrimination, odor threshold, and combined TDI performances were significantly lowered in the two conditions with the perfume fragrance, while the odor identification performance exhibited no significant differences across all three conditions. These findings provide empirical evidence that even low to moderate levels of personal fragrance can significantly reduce individuals’ olfactory capabilities, possibly subsequently altering the perception of test samples during sensory evaluation.

Olfactory Impairment in Parkinson's Disease Patients with Tremor Dominant Subtype Compared to Those with Akinetic Rigid Dominant Subtype: A Pilot Study.

Background: Parkinson’s disease (PD) may present different motor subtypes depending on the predominant symptoms (tremor or rigidity/bradykinesia). Slower disease progression and cognitive decline were observed in tremor-dominant (TD) patients compared to those with the akinetic-rigid dominant (ARD) subtype. Although olfactory dysfunctions are well-known disturbances in PD patients, correlations among PD different subtypes and olfactory impairment were not clearly studied. Thus, we investigated the possible olfactory impairment in PD patients with TD and ARD subtypes as compared to healthy controls. Methods: A sample of 132 participants were enrolled: 62 PD patients divided into ARD (n = 42) and TD (n = 20) subgroups using tremor/rigidity ratio, and 70 healthy controls. Olfactory function was assessed with the Sniffin’ Sticks Test. Results: Odor threshold was significantly lower in the ARD than in the TD subtype, while odor identification, discrimination scores, and their sum (TDI score) were not significantly different. On multivariate linear regression analysis, the tremor/rigidity ratio was a significant predictor of odor threshold. Conclusions: Our pilot study showed a significant olfactory dysfunction in PD patients with the ARD subtype. This evidence confirms the biological relevance of clinical subgroups in PD patients, suggesting the existence of a different pathophysiological mechanism between the ARD and TD clinical subtypes.

Neuroimmunoendocrine Link Between Chronic Kidney Disease and Olfactory Deficits.

Chronic kidney disease (CKD) is a multifactorial pathology that progressively leads to the deterioration of metabolic functions and results from deficient glomerular filtration and electrolyte imbalance. Its economic impact on public health is challenging. Mexico has a high prevalence of CKD that is strongly associated with some of the most common metabolic disorders like diabetes and hypertension. The gradual loss of kidney functions provokes an inflammatory state and endocrine alterations affecting several systems. High serum levels of prolactin have been associated with CKD progression, inflammation, and olfactory function. Also, the nutritional status is altered due to impaired renal function. The decrease in calorie and protein intake is often accompanied by malnutrition, which can be severe at advanced stages of the disease. Nutrition and olfactory functioning are closely interconnected, and CKD patients often complain of olfactory deficits, which ultimately can lead to deficient food intake. CKD patients present a wide range of deficits in olfaction like odor discrimination, identification, and detection threshold. The chronic inflammatory status in CKD damages the olfactory epithelium leading to deficiencies in the chemical detection of odor molecules. Additionally, the decline in cognitive functioning impairs the capacity of odor differentiation. It is not clear whether peritoneal dialysis and hemodialysis improve the olfactory deficits, but renal transplants have a strong positive effect. In the present review, we discuss whether the olfactory deficiencies caused by CKD are the result of the induced inflammatory state, the hyperprolactinemia, or a combination of both.

Screening Wild Yeast Isolated from Cocoa Bean Fermentation Using Volatile Compounds Profile.

Yeasts are one of the main ingredients responsible for flavor precursors production associated with sensorial characteristics in chocolate. Using wild yeast isolated from cocoa beans fermentation is emerging as a strategy for developing starter cultures. However, the volatile compounds (VCs) produced by yeasts are not yet known. This study aimed to select wild yeasts with the potential to produce volatile compounds associated with desirable flavor attributes. A total of 150 wild yeasts strains were isolated from the spontaneous cocoa beans fermentation, of which 40 were identified by morphology and physiological features. VCs produced were identified and quantified using SPME-GC-MS and GC-FID and profiles were evaluated statistically by PCA and cluster analysis for the compounds that had a high odor threshold value. Thirty-six VCs produced by these yeasts were identified into six main families, namely esters, alcohols, acids, aldehydes, ketones, and pyrazines. PCA showed the separation of the yeasts into two main clusters. Strains, Y195 and Y246, belong to the first cluster and are the highest producers of alcohols related to floral perceptions. In the second cluster, thirty-three yeasts were grouped by their ability to produce esters. Of all of them, Y110MRS stood out for producing 2-phenyl ethyl acetate and isoamyl acetate associated with fruity perceptions. This screening allowed us to identify yeasts that produced VCs of technological interest and which could be used to develop a starter culture.

Obtaining Aromatic Extracts from Portuguese Thymus mastichina L. by Hydrodistillation and Supercritical Fluid Extraction with CO2 as Potential Flavouring Additives for Food Applications.

Humans often respond to sensory impulses provided by aromas, and current trends have generated interest in natural sources of fragrances rather than the commonly used synthetic additives. For the first time, the resulting aroma of a selected culture of Thymus mastichina L. was studied as a potential food ingredient. In this context, dried (DR) and fresh (FR) samples were submitted to carbon dioxide (CO2) supercritical extraction (SFE) and hydrodistillation (HD) methods. The extracts were characterised according to their volatile composition by GC-MS, cytotoxicity against a non-tumour cell culture, and sensory attributes (odour threshold and olfactive descriptors). The most abundant aromas were quantified, and the analysis performed by GC-MS revealed an abundance of terpenoids such as thymol chemotype, followed by the precursors α-terpinene and p-cymene. DR and FR extracts (EX) obtained from SFE-CO2 show the highest content of thymol, achieving 52.7% and 72.5% of the isolated volatile fraction. The DR essential oil (EO) contained the highest amount of terpenoids, but it was also the most cytotoxic extract. In contrast, SFE-CO2 products showed the lowest cytotoxic potential. Regarding FR-OE, it had the lowest extraction yield and composition in aroma volatiles. Additionally, all samples were described as having green, fresh and floral sensory notes, with no significant statistical differences regarding the odour detection threshold (ODT) values. Finally, FR-EX of T. mastichina obtained by SFE-CO2 presented the most promising results regarding food application.

Production of an Anise- and Woodruff-like Aroma by Monokaryotic Strains of Pleurotus sapidus Grown on Citrus Side Streams.

The production of natural flavors by means of microorganisms is of great interest for the food and flavor industry, and by-products of the agro-industry are particularly suitable as substrates. In the present study, Citrus side streams were fermented using monokaryotic strains of the fungus Pleurotus sapidus. Some of the cultures exhibited a pleasant smell, reminiscent of woodruff and anise, as well as herbaceous notes. To evaluate the composition of the overall aroma, liquid/liquid extracts of submerged cultures of a selected monokaryon were prepared, and the volatiles were isolated via solvent-assisted flavor evaporation. Aroma extract dilution analyses revealed p-anisaldehyde (sweetish, anisic- and woodruff-like) with a flavor dilution factor of 218 as a character impact compound. The coconut-like, herbaceous, and sweetish smelling acyloin identified as (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone also contributed to the overall aroma and was described as an aroma-active substance with an odor threshold in air of 0.2 ng L−1 to 2.4 ng L−1 for the first time. Supplementation of the culture medium with isotopically substituted l-tyrosine elucidated this phenolic amino acid as precursor of p-anisaldehyde as well as of (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone. Chiral analysis via HPLC revealed an enantiomeric excess of 97% for the isolated product produced by P. sapidus.

Olfactory dysfunction is associated with cognitive impairment in patients with obstructive sleep apnea: a cross-sectional study.

Obstructive sleep apnea (OSA) increases the risk for olfactory dysfunction. However, the relationship between olfactory function and cognition in OSA patients is unclear. The present study aimed to investigate the relationship between cognition and olfactory dysfunction (OD) in patients with OSA. This was a cross-sectional study in which 74 patients with OSA and 22 controls were recruited. All subjects completed polysomnography, Sniffin' Sticks, and -neurocognitive assessments. According to results of Sniffin' Sticks, OSA patients were divided into two groups: OSA with OD (53 cases) and OSA without OD (21 cases). Neurocognitive function was assessed by Montreal Cognitive Assessment (MoCA), Memory and Executive Screening (MES), and Shape Trail Test (STT). Cognition was compared between OSA with and without OD. Correlation between olfactory parameters and respiratory sleep parameters and neurocognitive assessments was analyzed. Compared with OSA without OD, OSA with OD showed significantly decreased neurocognitive scores of MoCA (29-27 vs 27-23, p < 0.01), MES-5R (45-40.1 vs 43-33.5, p < 0.01) and increased consuming time of STT-B (91.66 vs 121.63, p < 0.01). A positive correlation was found between the scores of MoCA and MES-5R and all olfactory parameters. In addition, a negative correlation was present between the time consumed for STT-B and odor thresholds (r = - 0.344, p < 0.01), odor identification (r = - 0.335, p < 0.01), and threshold-discrimination-identification scores (r = - 0.448, p < 0.01). Olfactory function is associated cognitive function in patients with OSA and may provide a new direction for early treatment interventions in OSA patients at risk for cognitive impairment.

Identification of volatile compounds correlated with consumer acceptability of strawberry preserves: Untargeted GC–MS analysis

Volatile compounds that impact the acceptability of strawberry preserves were investigated by untargeted GC–MS flavoromics analysis. Chemical profiles for fifteen strawberry preserves were modeled against consumer liking scores by orthogonal partial least squares (OPLS) with good fit (R2Y = 0.998) and predictive ability (Q2 = 0.853). Ten highly predictive compounds were selected, nine of which were identified, and eight of which were quantified using tandem mass spectrometry. Sensory recombination difference testing revealed that the addition of predictive compounds to an average-liked preserve at levels found in the most-liked preserve induced a perceptible difference to frequent consumers of strawberry jams. One of the highly predictive compounds was identified (MS and synthesis) as a novel linalool oxide product 2-methyl-2-vinyl-tetrahydrofuran with a fruity, herbal-minty, piney aroma and a low odor threshold value.

Efficacy of olfactory training program in conjunction with nasal steroid irrigation in treating persistent smell loss in COVID-19 patients

Background: Smell loss is a challenging clinical problem. There is still no evidence-based medical intervention to treat patients with persistent smell loss as a result of Coronavirus Disease 2019 (COVID-19). The aim is to analyze the efficacy of treating patients with persistent smell loss due to COVID-19 using olfactory training (OT) combined with nasal steroid irrigation. Methods: A cross-sectional study enrolled 196 COVID-19 patients with persistent smell loss were recruited. All patients underwent two testing sessions. At the first session, patients were examined by a history taking followed by an Otorhinolaryngological examination including, a thorough nasal endoscopy. In addition, an olfactory performance assessment was performed to assess the severity of smell loss. All patients were then treated with OT and nasal steroid irrigation with budesonide for 12 weeks. The second session includes an olfactory performance assessment to assess if there is an improvement in olfactory function. Results: Patients after treatment showed improvement in overall Threshold-Detection-Identification (TDI) score, odor detection threshold score, odor discrimination score, and odor identification score, which were higher than before treatment. Statistically significant differences before and after treatment results were very pronounced for the overall TDI score (p = 0.014) and odor detection threshold score (p = 0.003). There was no significant difference in odor discrimination (p = 0.08) or odor identification (p = 0.126) scores before and after treatment. Conclusion: The results of this study support the efficacy of the combination of budesonide nasal irrigation and OT in treating persistent smell loss due to COVID-19 infection.

The Adaptive Olfactory Measure of Threshold (ArOMa-T): a rapid test of olfactory function.

Many widely used psychophysical olfactory tests have limitations that can create barriers to adoption. For example, tests that measure the ability to identify odors may confound sensory performance with memory recall, verbal ability, and prior experience with the odor. Conversely, classic threshold-based tests avoid these issues, but are labor intensive. Additionally, many commercially available tests are slow and may require a trained administrator, making them impractical for use in situations where time is at a premium or self-administration is required. We tested the performance of the Adaptive Olfactory Measure of Threshold (ArOMa-T)-a novel odor detection threshold test that employs an adaptive Bayesian algorithm paired with a disposable odorant delivery card-in a non-clinical sample of individuals (n = 534) at the 2021 Twins Day Festival in Twinsburg, OH. Participants successfully completed the test in under 3 min with a false alarm rate of 7.5% and a test-retest reliability of 0.61. Odor detection thresholds differed by sex (~3.2-fold lower for females) and age (~8.7-fold lower for the youngest versus the oldest age group), consistent with prior studies. In an exploratory analysis, we failed to observe evidence of detection threshold differences between participants who reported a history of COVID-19 and matched controls who did not. We also found evidence for broad-sense heritability of odor detection thresholds. Together, this study suggests the ArOMa-T can determine odor detection thresholds. Additional validation studies are needed to confirm the value of ArOMa-T in clinical or field settings where rapid and portable assessment of olfactory function is needed.

Olfaction in pregnancy: systematic review and meta-analysis.

Little attention has been paid to olfactory changes during pregnancy with contemporary studies limited in number and sample size. We examined whether pregnancy is associated with differences in olfactory performance and if there were any specific gestational ages at which these differences occur through a comprehensive systematic review and meta-analysis of the current literature. An initial electronic database search identified 234 citations, which were screened at the abstract level. Twenty-three citations were germane for full-text review, and 13 met criteria for inclusion. Our review assessed 5 olfactory measures of interest: odor identification (n = 11 articles), threshold (n = 8), discrimination (n = 5), hedonics (n = 6), and intensity (n = 5). Nine of these 13 studies contained sufficient data for meta-analysis, and these studies included a total of 523 pregnant women and 365 non-pregnant controls. Despite previous subjective and objective reports of odor intolerances and odor hypersensitivity, we did not find any significant differences between pregnant and non-pregnant women in odor discrimination, thresholds, or hedonics. However, meta-analysis of 506 cases and 333 controls showed worse odor identification in pregnant women compared to controls in a random-effects model. Thus, we demonstrate worse performance at odor identification during pregnancy. In this review, we discuss the current evidence (and lack thereof) regarding olfaction in pregnancy as well as highlight current knowledge gaps in this field.