Retronasal Odor Research Articles

Taste enhances the ability to express a preference for a congruent odor in rats.

Foods that make up a typical diet are characterized by a rich set of sensory qualities that are perceived through multiple different modalities. It is well known that multisensory aspects of food are integrated to create our perception of flavor, which in turn affects our behavioral responses to food. However, the principles underlying multisensory integration of flavor-related sensory signals and how they inform perceptual judgments remain poorly understood, partly due to lack of control over flavor experience in human subjects. Here, we used rats as a model to overcome this limitation and tested the hypothesis that taste can enhance discriminability of retronasal odor cues. In a series of two-bottle tests, animals chose between two odorized solutions after learning to associate one of the odors with saccharin. When odors were highly similar, animals showed little preference for the saccharin-associated odor. When adding saccharin to both bottles-rendering one of the solutions' congruent-animals' preference for the saccharin-associated odor was significantly enhanced. No effect of taste was observed when using dissimilar odor pairs or novel taste stimuli. These findings suggest that congruent taste stimuli selectively enhance odor identity representations, aiding in the discriminability of perceptually similar flavors. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A practical test for retronasal odor identification based on aromatized tablets

BackgroundOlfactory perceptions elicited by odors originating from within the body (retronasal olfaction) play a crucial role in well-being and are often disrupted in various medical conditions. However, the assessment of retronasal olfaction in research and the clinical practice is impeded by the lack of commercially available tests and limited standardization of existing testing materials. New MethodThe novel ThreeT retronasal odor identification test employs 20 flavored tablets that deliver a standardized amount of odorous stimuli. The items represent common food- and non-food-related odors. ResultsThe ThreeT test effectively distinguishes patients with olfactory dysfunction from healthy controls, achieving a specificity of 86% and sensitivity of 73%. Its scores remain stable for up to 3 months (r=.79). Comparison with existing methodThreeT test exhibits a strong correlation with “Tasteless powders” measure of retronasal olfaction (r=.78) and classifies people into healthy and patient groups with similar accuracy. Test-retest stability of ThreeT is slightly higher than the stability of “Tasteless powders” (r=.79 vs r=.74). ConclusionsThreeT is suitable for integration into scientific research and clinical practice to monitor retronasal odor identification abilities.

Retronasal sensory characterization of aroma compounds in Baijiu by detection threshold measurement, retronasal OAVs, and time-intensity evaluation.

The retronasal aroma of Baijiu is closely related to its quality and consumer preference. Retronasal detection thresholds (RDTs) of 44 aroma compounds were determined in 46% v/v ethanol using a three-alternative forced-choice procedure, which varied widely and ranged from less than 0.02 to over 1,000,000µg/L. Nineteen aroma compounds, including β-phenylethanol, 2,3,5,6-tetramethylpyrazine, dimethyl trisulfide, and 2-methyl-3-(methyldisulfanyl)furan, had RDTs lower than their orthonasal detection thresholds. Power function curves were used to establish correlations between RDTs and partition coefficients for five esters and four pyrazines (R2 =0.9575, 0.9969, respectively). Twenty-nine aroma compoundshad retronasal odor activity values >1 in a soy sauce aroma type Baijiu. Additionally, time-intensity (TI) results suggested that hexanoic acid, ethyl hexanoate, isoamyl acetate, 3-methyl-butanal, and nonanal contributed to a "burst-aroma" of Baijiu. Conversely, TI results attributed the "after-odor" of Baijiu to dimethyl trisulfide, methional, 2,3,5,6-tetramethylpyrazine, β-phenylethanol, and other compounds. PRACTICAL APPLICATION: This manuscript provides comprehensive information on the retronasal sensory characteristics of aroma compounds in Baijiu. The results obtained may help understand the contribution of aroma compounds to retronasal aroma perception during Baijiu tasting and give helpful information to the Baijiu industry regarding quality control.

Toward the Upgrading Quality of Drinking Water from Flavor Evaluation: Taste, Feeling, and Retronasal Odor Issues

Sensory property (taste and odor, T&O) has become an essential factor in the assessment and selection of drinking water. In addition to odor issues, the taste of drinking water has also drawn consumers’ attentions for causing a lot of misunderstanding and damage to the impression of the public water supply. In fact, the general concept of taste refers to the involved sensations in the tasting process, including taste, feeling, and retronasal odor (jointly called flavor). As an integral part of the drinking water sensory issues, the flavor issues that relate to both volatile and nonvolatile components have received inadequate attention due to the underperformance of a tasting panel and stricter ethical principles for tasting tests; even the flavor threshold for certain substances is lower than the odor threshold. To motivate research that can overcome these challenges, this paper provides an in-depth clarification of relevant concepts and an overview of the predominant and potential substances affecting flavor, as well as a modified wheel for the tasting test. Additionally, considering the current reliance on sensory panels, recent advances in evaluation methodologies have been critically evaluated, with particular emphasis on in vitro approaches. At last, this review proposes future prospects in four major aspects, with upgrading strategies for drinking water quality. It is hoped that this review both illustrates the current state of this field and stimulates further research.

Enhancement of taste by retronasal odors in patients with Wolfram syndrome and decreased olfactory function.

Wolfram syndrome is a rare disease characterized by diabetes, neurodegeneration, loss of vision, and audition. We recently found, in a young sample of participants (mean age 15 years), that Wolfram syndrome was associated with impairment in smell identification with normal smell sensitivity and whole-mouth taste function. However, these senses were assessed separately, and it is unknown whether smell-taste interactions are altered in Wolfram syndrome, which was the focus of this study. Participants with Wolfram syndrome (n = 36; 18.2 ± 6.8 years) and sex-age-equivalent healthy controls (n = 34) were assessed with a battery of sensory tests. Using sip-and-spit methods, participants tasted solutions containing gustatory and olfactory stimuli (sucrose with strawberry extract, citric acid with lemon extract, sodium chloride in vegetable broth, and coffee) with and without nose clips, and rated perceived taste and retronasal smell intensities using the generalized Labeled Magnitude Scale. Participants also completed n-butanol detection thresholds and the University of Pennsylvania Smell Identification Test (UPSIT). Retronasal smell increased taste intensity of sucrose, sodium chloride, and coffee solutions similarly in both groups (P values <0.03). Compared with the control group, participants in the Wolfram group had lower UPSIT scores and reduced smell sensitivity, retronasal intensity, and saltiness (P values <0.03), but rated other taste intensities similarly when wearing the nose clip. Despite impairments in orthonasal smell identification, odor-induced taste enhancement was preserved in participants with Wolfram syndrome who still had some peripheral olfactory function. This finding suggests that odor-induced taste enhancement may be preserved in the presence of reduced olfactory intensity.

A Nasal Aerodynamics Perspective of Retronasal Olfaction: Rodents vs. Humans.

Odor perception can be achieved through ortho or retronasal routes, with the latter being an important component of flavor perception. There are significant olfactory differences that exist between rats and humans and by understanding the role of structural differences, further insight can be gained into the mechanism of odorant perception via ortho or retronasal routes. 3D human and rat (Sprague Dawley) computational models were used to investigate nasal anatomy impact on ortho vs. retronasal odorant transport to the olfactory epithelium. The nasal pharynx region was modified for human and rat models to probe nasal structure impact on ortho vs retro olfaction. 65 odorant absorption rates to the olfactory epithelium were extracted from each model. For human, the retronasal route provided higher peak odorant absorption compared to orthonasal route (left: 90% higher, right: 45% higher), but substantially lowered peak absorption for rat (medial: 97% lower, lateral: 75% lower). For both models, anatomical modification had minimal impact to orthonasal routes, but substantially modulated the retronasal route: decrease (left: -41.4%, right: -44.2%) for human, and increase to the medial (29.5%) but not to lateral (-14.3%) for rat. There exist key differences between humans and rats regarding retro/orthonasal odorant transport routes, which matched well with experimental olfactory bulb activity data in literature. While humans have equivalent odorant delivery between routes, the difference in retro and orthonasal routes in rodents is substantial and changes to the transverse lamina above the nasopharynx can substantially modulate the retronasal route, but not enough to bridge the gap between the two routes.

Olfactory dysfunction in COVID-19: pathology and long-term implications for brain health.

Decreased smell function is related to brain health, future mortality, and quality of life. Most people inflicted with the SARS-CoV-2 virus evidence some measurable smell dysfunction during its acute phase, although many are unaware of the loss. Long-term deficits occur in up to 30% of COVID-19 cases, although total anosmia is relatively rare. This review explores what is presently known about the nature and pathophysiology of olfactory dysfunction due to the SARS-CoV-2 virus, including reversible inflammation within the olfactory cleft, downregulation of olfactory receptor proteins, and long-lasting peripheral and central damage to olfactory structures. It also addresses the question as to whether long-term smell loss might increase the likelihood of future development of cognitive and neurological deficits.

Retronasal olfaction is relatively less affected in older individuals with subjectively normal olfactory function

BackgroundOrthonasal and retronasal olfaction are intimately connected. Still, they exhibit differences. The present study aimed to compare orthonasal and retronasal olfaction at both suprathreshold and threshold levels in a healthy population considering age. Material and methodsA total of 171 participants with subjective normal olfactory function were divided into 2 groups (Young = 98 participants, mean age = 25.8 ± 5.3 vs. Old = 73 participants, mean age = 68.3 ± 10.6) according to their age. Groups were compared in terms of orthonasal odor threshold and identification (Sniffin’ sticks test), retronasal odor threshold (Odor delivery container) and identification (Taste powder). ResultsBoth orthonasal and retronasal olfaction decreased with age, while retronasal odor identification tended to decline to a lesser degree than orthonasal olfaction. In addition, retronasal odor identification ability of those unaware of their olfactory loss (hyposmia and anosmia) was less affected than their orthonasal olfaction. Age correlated negatively with orthonasal and retronasal olfaction. Orthonasal and retronasal olfaction related to each other. ConclusionIn older individuals retronasal odor identification appears to be less affected than orthonasal odor identification. This may be partly due to differential changes at the level of the olfactory mucosa. The maintained retronasal olfactory function probably helps to maintain the pleasures of eating, contributing to the unawareness of the gradual age-related olfactory loss.

Differences in olfactory bulb mitral cell spiking with ortho- and retronasal stimulation revealed by data-driven models.

The majority of olfaction studies focus on orthonasal stimulation where odors enter via the front nasal cavity, while retronasal olfaction, where odors enter the rear of the nasal cavity during feeding, is understudied. The coding of retronasal odors via coordinated spiking of neurons in the olfactory bulb (OB) is largely unknown despite evidence that higher level processing is different than orthonasal. To this end, we use multi-electrode array in vivo recordings of rat OB mitral cells (MC) in response to a food odor with both modes of stimulation, and find significant differences in evoked firing rates and spike count covariances (i.e., noise correlations). Differences in spiking activity often have implications for sensory coding, thus we develop a single-compartment biophysical OB model that is able to reproduce key properties of important OB cell types. Prior experiments in olfactory receptor neurons (ORN) showed retro stimulation yields slower and spatially smaller ORN inputs than with ortho, yet whether this is consequential for OB activity remains unknown. Indeed with these specifications for ORN inputs, our OB model captures the salient trends in our OB data. We also analyze how first and second order ORN input statistics dynamically transfer to MC spiking statistics with a phenomenological linear-nonlinear filter model, and find that retro inputs result in larger linear filters than ortho inputs. Finally, our models show that the temporal profile of ORN is crucial for capturing our data and is thus a distinguishing feature between ortho and retro stimulation, even at the OB. Using data-driven modeling, we detail how ORN inputs result in differences in OB dynamics and MC spiking statistics. These differences may ultimately shape how ortho and retro odors are coded.

Impact of Water on Odor-Active Compounds in Fermented and Dried Cocoa Beans and Chocolates Made thereof.

The impact of water on odor-active compounds in fermented and dried cocoa beans as well as in chocolate either produced by a novel processing (NPC) or a traditional processing (TPC) technology from the same batch of cocoa beans was investigated in this study. Quantitation of selected key odorants revealed significantly higher concentrations of Strecker aldehydes such as 3-(methylsulfanyl)propanal (66-fold) and phenylacetaldehyde (50-fold) after water treatment of the cocoa beans. The comparison of the two chocolates showed that higher amounts of the Strecker aldehydes 2-methylbutanal, 3-methylbutanal, and phenylacetaldehyde are released with water in the NPC (24-fold to 39-fold), compared to the TPC (7.3-fold-11-fold). In addition to Strecker aldehydes, the concentrations of many further characteristic key odorants of cocoa and chocolate increased after water treatment. Based on the results, a more intense retronasal odor perception of the analyzed compounds is expected due to their release during consumption in contact with saliva.

Validation study of a novel approach for assessment of retronasal olfactory function with combination of odor thresholds and identification.

PurposeThe present study aimed to establish a test battery for the clinical assessment of retronasal odor thresholds and retronasal odor identification.Study designProspective case–control series.MethodsSixty participants (36 women, 24 men, mean age 37.6 ± 19.4 years) were enrolled in this study; 36 were healthy controls and 24 were patients with olfactory dysfunction. Orthonasal olfactory function was assessed with the “Sniffin’ Sticks” test battery. Retronasal olfaction was assessed with oral odorant delivery using special containers for threshold function, and with oral tasteless powders for odor identification.ResultsRetronasal and orthonasal olfaction were significantly correlated for threshold scores, identification score, and the sum of threshold and identification score (TI score). Validity analyses showed that the retronasal TI score was able to discriminate between healthy controls and patients with olfactory dysfunction.ConclusionsNormosmic participants can be distinctly differentiated from patients with olfactory dysfunction using a valid test battery comprised of retronasal threshold and identification tests. Based on the current findings, we advocate a TI score of 16 as a cut-off between patients and controls. Therefore, TI scores of 17 and above would indicate retronasal normosmia.

Determination of Retronasal Olfactory Threshold Values.

The aim of this study was to generate normative data of retronasal olfactory threshold values for normosmic and hyposmic individuals and to test the validity of that data by determining the discriminative power for normosmic/hyposmic differentiation. Prospective, descriptive and methodological study. The orthonasal olfactory function of 20 normosmic and 20 hyposmic cases was evaluated using the Sniffin' Sticks Olfactory test. Sniffin' Sticks odor threshold, odor discrimination, and odor identification values and threshold discrimination identification (TDI) scores were recorded. A 13-item test battery previously prepared in our Rhinology Laboratory for retronasal olfactory threshold test that consisted of concentrated solutions prepared from 2:1 diluted 99% phenylethyl alcohol (PEA) and water was used. Each concentration was evaluated with water control, and if not answered correctly, the same process was continued by moving to a higher concentration series. Four consecutive correct answers were determined as the patient's retronasal olfactory threshold. A strong correlation was found between Sniffin' Sticks TDI scores and retronasal odor threshold values in the normosmic group (P < .001, r:0.67). A very strong correlation was found between Sniffin' Sticks TDI scores and retronasal olfactory threshold values in the hyposmic group (P < .001, r:0.81). Furthermore, receiver operating characteristic (ROC) analysis revealed that the sensitivity and the specificity of normosmic/hyposmic differentiation of retronasal olfactory threshold test was 95% and 100%, respectively. The diagnostic cutoff value was 8.5. This study shows that the retronasal olfactory test, a psychophysical odor test performed using an orally presented stimulus, can be used to differentiate normosmic and hyposmic cases. 3 Laryngoscope, 131:1608-1614, 2021.

Duality of Smell: Route-Dependent Effects on Olfactory Perception and Language.

Olfactory research in humans has largely focused on odors perceived via sniffing, orthonasal olfaction, whereas odors perceived from the mouth, retronasal olfaction, are less well understood. Prior work on retronasally presented odors involves animal models and focus mainly on odor sensitivity, but little is known about retronasal olfactory perception and cognition in humans. In this study, we compared orthonasal and retronasal odor presentation routes to investigate differences in odor descriptions and evaluations. Thirty-six individuals participated in a within-subjects study using twelve odors (varying in pleasantness and edibility) in perceptual and semantic tasks. Orthonasal presentation was associated with a better ability to identify odors, and with more concrete (and source-based) language. Exploratory analyses revealed that whereas orthonasal odors were described with words that had visual associations, retronasal odors were described with words that had interoceptive associations. Interestingly, these route-dependent differences in descriptor usage were not explained by differences in sensitivity and intensity, suggesting instead a cognitive and linguistic processing difference between odors presented orthonasally and retronasally. Our results indicate that olfaction is, in fact, a dual sense, in which the routes change the perception of an odor.

Identification of the Volatile Compounds and Sensory Attributes of Long-Term Aging Vin Santo Wine from Malvasia di Candia Aromatic Grapes.

In an effort to offer a contribution to fill the gap of knowledge about the relationship between the sensory properties and aromatic profile of Malvasia grapes, the present work was aimed at evaluating volatile compounds, aroma, and sensory attributes of long-term aging (15 years) Vin Santo wine obtained from Malvasia di Candia aromatica grapes. In this article, the aromatic profile are studied using gas chromatography-mass spectrometry (GC-MS), gas chromatography with flame ionization detection (GC-FID), and sensory analysis by involving a panel of trained assessors to explore the sensory profile resulting after long-term aging (up to 15 years). The GC-MS and GC-FID analyses of wines allowed the identification and semi-quantification of twenty-seven volatiles belonging to 12 conventional groups of compounds. From a sensory perspective, the Vin Santo wines analyzed in this study presented a very complex sensory profile characterized by 19 sensory descriptors of which 14 related to olfactory terms. The relationship between sensory and GC-FID data deduced from three samples representing nearly three years in the past 15 years was investigated by means of Partial Least Square (PLS) modeling, showing that specific volatile compounds could predict a specific orthonasal and/or retronasal odor perceived by the trained panel of assessors, clearly differentiating the Vin Santo vintages. Identifying the main volatiles and aromas of long-term Vin Santo wine may be helpful to winemakers, since wine aging sensory properties are often associated with a prestigious image and contribute to defining wine quality.

Transfer of Odor Perception From the Retronasal to the Orthonasal Pathway.

Although orthonasal odorants are often associated with the external environment, retronasal odorants are accompanied by consummatory behaviors and indicate an internal state of an animal. Our study aimed to examine whether the same odorants may generate a consistent perceptual experience when 2 olfactory routes potentiate variations in concentration in the nasal cavity and orosensory activation. A customized lick spout with vacuum removing odorants around the animal's nares was used to render a pure retronasal exposure experience. We found that pre-exposing rats to odorants retronasally with positive or negative reinforcers (sweet or bitter) lead to a significant learning rate difference between high- and low-vapor-pressure odorants. This effect was not observed for novel odorants, suggesting that odorants may generate similar perceptual quality in a volatility-dependent manner.

Contribution of the retronasal odor of soy sauce to salt reduction.

The characteristic odor of soy sauce has been reported to enhance saltiness. However, soy sauce is used not only as a sauce that is added directly to food, but also as a seasoning. In addition, some of the aromatic compounds that contribute to the soy sauce odor change during cooking or heating. In the present study, the effects of the retronasal odor of uncooked and cooked soy sauce on the enhancement of saltiness and palatability of a low-salt solution were sensory evaluated. A probit analysis indicated that the saltiness-enhancing effect of the odor of 15% uncooked soy sauce was lost by heating. The odors of soy sauce boiled for 10min (cooked SS) and the residue of soy sauce heated at 200°C for 1min improved the palatability of the low-salt solution. Gas chromatography (GC) analyses, namely, GC-olfactometry and GC-mass spectrometry, showed that one active candidate aromatic component of soy sauce contributing to saltiness enhancement was 3-methyl-1-butanol (3-Me-BuOH). The saltiness-enhancing effects of cooked SS could be restored by adding 3-Me-BuOH, as assessed by the sensory evaluation. These data demonstrated that 3-Me-BuOH contributes to saltiness enhancement. PRACTICAL APPLICATION: We found that the odor of cooked soy sauce could improve the palatability of low-salt food. Although the saltiness-enhancing effect provided by the odor of uncooked soy sauce was lost, the saltiness-enhancing effect of the odor of cooked soy sauce can be partially restored by adding 3-methyl butanol. Thus, not only the odor of unheated soy sauce but also the odor of heated soy sauce following addition of 3-methyl butanol may be useful for developing palatable salt-reduced food.

Valorisation of tainted boar meat in patties, frankfurter sausages and cooked ham by means of targeted dilution, cooking and smoking.

Because of the need to abolish the castration of piglets without anaesthesia/analgesia, the pig industry is searching for a mode of action for the valorisation of meat with boar taint, an off-odour in entire male pigs. Carcasses with boar taint were selected by means of sensory and chemical analysis, after which patties with different levels of tainted boar meat were produced, as well as cooked ham and Frankfurter sausages using different smoke condensates and cooking temperatures. For these products orthonasal and retronasal boar taint odour were assessed by a trained expert panel. The results offer guidance regarding dilution of tainted meat (with <400µg/kg androstenone if skatole is low or <200µg/kg androstenone in concurrence with ≥37µg/kg skatole) and the potential application of smoke condensates (e.g., Rudinsmoke C for sausages and Smokez LFBN for ham) as promising boar taint masking strategies.

Orthonasal versus retronasal glomerular activity in rat olfactory bulb by fMRI

Odorants can reach olfactory receptor neurons (ORNs) by two routes: orthonasally, when volatiles enter the nasal cavity during inhalation/sniffing, and retronasally, when food volatiles released in the mouth pass into the nasal cavity during exhalation/eating. Previous work in humans has shown that both delivery routes of the same odorant can evoke distinct perceptions and patterns of neural responses in the brain. Each delivery route is known to influence specific responses across the dorsal region of the glomerular sheet in the olfactory bulb (OB), but spatial distributions across the entire glomerular sheet throughout the whole OB remain largely unexplored. We used functional MRI (fMRI) to measure and compare activations across the entire glomerular sheet in rat OB resulting from both orthonasal and retronasal stimulations of the same odors. We observed reproducible fMRI activation maps of the whole OB during both orthonasal and retronasal stimuli. However, retronasal stimuli required double the orthonasal odor concentration for similar response amplitudes. Regardless, both the magnitude and spatial extent of activity were larger during orthonasal versus retronasal stimuli for the same odor. Orthonasal and retronasal response patterns show overlap as well as some route-specific dominance. Orthonasal maps were dominant in dorsal-medial regions, whereas retronasal maps were dominant in caudal and lateral regions. These different whole OB encodings likely underlie differences in odor perception between these biologically important routes for odorants among mammals. These results establish the relationships between orthonasal and retronasal odor representations in the rat OB.

Factors Contributing to Interindividual Variation in Retronasal Odor Perception from Aroma Glycosides: The Role of Odorant Sensory Detection Threshold, Oral Microbiota, and Hydrolysis in Saliva.

Glycosides are sugar conjugates of aroma compounds that are found in many fruits and vegetables, and while glycosides are non-volatile, they can release flavor during eating, through enzyme hydrolysis from oral microbiota. Recently, a range of sensory phenotypes for glucoside perception have been observed, reflecting interindividual variation in response to precursors of floral and smoky flavors, geranyl glucoside and guaiacyl glucoside. To understand this variation and investigate the role of oral microbiota on in vitro hydrolysis of glucosides in saliva, metagenomic screening was conducted using individuals representing the range of sensory phenotypes for geranyl and guaiacyl glucosides. In parallel, sensory retronasal detection thresholds for geranyl glucoside, guaiacyl glucoside, and the volatile odorants geraniol and guaiacol were determined. Oral microbial communities correlated with hydrolysis of glucosides in saliva, but the relationship did not extend to sensory phenotypes. Overall, the retronasal detection threshold of the volatile odorants studied was the main factor determining sensory phenotype.

Gustation and Olfaction: The Importance of Place and Time

Animals can smell odors from the external environment or from their mouth via two routes: orthonasal and retronasal, respectively. Little is known about how the brain processes orthonasal and retronasal odors associated with taste, but a new study has revealed an important role for the gustatory cortex in such odor processing.