Retronasal Perception Research Articles

Saliva bubbles: How saliva foam impacts aroma release and retronasal perception during oral processing

Saliva foam can be easily formed upon different oral movement, but the impact of saliva foam on aroma release and perception is less investigated. Recruited subjects were asked to chew mint-flavor gums to mimic saliva foam generation. During gum-chewing, i.) subjects' retronasal release and dynamic perception of menthol and ii) their salivary bubble number and size, were continuously monitored. In the ‘normal series’ of experiments, bubbles were generated by the oral behavior of mastication; and in the ‘defoamed series’ of experiments, a defoaming agent was simultaneously added to eliminate the bubble effect during mastication. A continuous formation and collapse of saliva bubbles in the normal group led to a stable higher release of menthol in subjects' exhalation and significantly higher mint flavor perception (p < 0.05). In the defoamed series, saliva bubble numbers were reduced drastically (1–2 orders of magnitude) and more menthol was retained in saliva, which further affected subjects' intensity perception. Multiple physiological factors including salivary protein concentration, viscosity and surface tension contributed to the individual sensory perception variations, and no single parameter could explain the exact relationship between aroma release and retronasal perception. This study provided insights on the aroma delivery in food matrix design and development.

Impact of tannins on intraoral aroma release and retronasal perception, including detection thresholds and temporal perception by taste, in model wines

Tannins, as an important wine nonvolatile matrix component, can cause astringency, which may affect aroma perception through cross-modal interactions during wine consumption. An aromatic model wine with tannin extracts was evaluated by intraoral aroma release and sensory analysis after wine spitting. Overall, tannin extracts could significantly decrease all initial aroma release, while they could not reduce most aroma release at 150 s after wine spitting. Regarding the sensory evaluation results, the retronasal detection threshold of most aromas increased. The temporal aroma intensity showed a significant decrease at early time points and was almost unaffected at later time points. In addition, temporal dominance of sensation (TDS) curves revealed that the presence of astringency could reduce the dominant time of most aromas. Therefore, although there was good consistency between instrumental analysis and sensory evaluation, the effect of astringency induced by tannins on retronasal perception cannot be ignored.

Elucidation of retro‐ and orthonasal aroma differences in biscuits ( panis biscoctus ) using artificial masticator

The present study aimed to define the interest in using a mastication simulator to understand the release of aroma compounds of biscuits in the mouth. The development of aroma compounds during artificial, human mastication and without masticated samples of veritable biscuits was determined. Then, the evaluations of aroma compounds in different types of biscuits were studied. A total of 32 compounds were identified in the veritable sample while 36 were identified in both sugar-free and organic samples. The aldehydes and pyrazines were the main chemical groups in the samples. The number of aroma compounds in the biscuit samples revealed essential changes during mastication and increased about 2.5 times. Additionally, the presence of artificial and human saliva showed a similar effect. They increased the number of volatiles while influencing some volatile groups either by increasing the quantity of ketones or decreasing acids, alcohols, and aldehydes. Novelty impact statement The aroma of biscuits overwhelmingly effects consumer behavior. Hence, the improvements ingredients and manipulation in biscuits have become increasingly important. The artificial mouth would be particularly useful to study whether there is a difference between orthonasal and retronasal perception of dry and starch-rich foods.

Influence of tannins, human saliva, and the interaction between them on volatility of aroma compounds in a model wine.

During wine drinking, aroma release is mainly impacted by wine matrix compositions and oral physiological parameters. Notably, tannins in wine could interact with saliva protein to form aggregates which might also affect the volatility of volatiles. To explore tannins, saliva, and the interaction between them on the volatility of volatiles, the volatility of 16 aroma compounds in the model wine mixed with the commercial tannin extracts, human saliva, or both respectively, was evaluated in vitro static condition by using HS-SPME-GC/MS. The volatility of aroma compounds with high hydrophobicity or benzene ring appeared to decrease more when increasing the tannin levels. Specifically, the volatility of ethyl octanoate, β-ionone, and guaiacol was decreased more than 20% by adding 2 g/L tannin extract. The addition of human saliva could significantly inhibit volatility of most aroma compounds in the model wine. Furthermore, the volatility of most aroma compounds in the mixture of tannins and human saliva was significantly lower than the control or the sample which were added with tannins or human saliva individually. The volatility of some aroma compounds in the mixture of the tannin and saliva was only around 50% or less, relative to the control. Two-way ANOVA analysis showed that there was a synergistic effect between tannin and saliva on decreasing the volatility of most aroma compounds (p < 0.05). Overall, understanding the effect of key factors such as tannins and saliva on volatility of volatiles could help to understand the sophisticated retronasal perceptions during wine tasting. PRACTICAL APPLICATION: The outputs of this research will be helpful in understanding the impact of tannins on retronasal aroma release during wine tasting. It might promote the control of tannins in the viticulture and brewing process to improve the retronasal perception of wine aroma.

Evaluation of the Effect of a Grape Seed Tannin Extract on Wine Ester Release and Perception Using In Vitro and In Vivo Instrumental and Sensory Approaches.

This study aimed to systematically evaluate the effect of a commercial grape seed tannin extract (GSE) fully characterized (53% monomers, 47% procyanidins) on wine ester release and perception using a global approach. The behavior of two esters (ethyl hexanoate, ethyl decanoate) was studied in a control wine or in the same wine supplemented with the GSE in preconsumption (in vitro headspace-stir bar sorptive extraction-gas chromatography mass spectrometry (HS-SBSE-GC/MS) and orthonasal perception) and consumption (intraoral-HS-SBSE-GC/MS and dynamic retronasal perception) conditions. For the compound ethyl hexanoate, no significant differences (p > 0.05) among wines were observed in the in vitro analyses while they were observed in the three in vivo experiments (p < 0.05). Thus, the wine supplemented with the GSE showed lower (35%) in vivo release and ortho (36%) and retronasal (16%) perception scores than the control wine. Overall, this suggests that components of the GSE could interact with this compound, directly and/or through complexes with oral components, affecting its release and conditioning its perception. However, perceptual interactions and effects of polyphenols on oral esterases cannot be discarded. On the contrary, the compound ethyl decanoate was not significantly affected by the addition of GSE. In conclusion, the addition of tannin extracts to wines can modulate aroma perception in a compound-dependent manner.

Impact of bitter tastant sub-qualities on retronasal coffee aroma perception.

The impact of different bitter taste compounds on the retronasal perception of coffee aroma was investigated. A sorted napping experiment was carried out on thirteen compounds at iso-intense bitter concentrations. Differences in perceptual bitter sub-qualities among the compounds were reported by Multidimensional Scaling (MDS) and Multiple Factor Analysis (MFA) analyses. Seven exemplar compounds were further selected to investigate the impact of taste sub-qualities on cross-modal flavor interactions. In general, the different bitter compounds, when paired with a coffee aroma isolate, significantly modified the perception of the retronasal coffee aroma profile. Interestingly, the three bitter compounds endogenous to coffee had the most similar impact on the coffee aroma profile. Further sensory analysis of these sample sets indicated no significant effect of the bitter compounds on the orthonasal perception. Gas Chromatography/Mass Spectrometry (GC/MS) analysis of the volatile composition of the samples headspace also indicated negligible impact of the bitter compounds on aroma release. Altogether evidence of cross-modal interactions occurring at a higher cognitive level were demonstrated in a complex food sample, supporting the importance of multi-modal sensory integration on flavor perception.

Association between the rs2590498 polymorphism of Odorant Binding Protein (OBPIIa) gene and olfactory performance in healthy subjects

Olfactory function varies by several orders of magnitude among healthy individuals, who may exhibit a reduced sensitivity (hyposmia), a high sensitivity (hyperosmia), or an olfactory blindness (anosmia). Environmental and genetic factors seem to account for this variability. Most of odorant molecules are hydrophobic and it has been suggested that odorants are transported to the olfactory receptors by means of odorant binding proteins (OBPs). Aim of this study was to evaluate the presence of a relationship between the olfactory performance of healthy subjects and the polymorphism in the odor binding-protein (OBPIIa) gene, the only OBP found in the olfactory epithelium of humans. Using the “Sniffin’ Sticks” Extended Test we assessed the olfactory performance in 69 subjects, who were genotyped for the rs2590498 polymorphism of the OBPIIa gene, whose major allele A has been associated with a higher retronasal perception as compared to the minor allele G. We found that subjects homozygous for the A-allele exhibited threshold scores higher than subjects homozous for the G-allele or heterozygous. In addition, subjects classified as normosmic and hyposmic differed on the basis of genotype distribution and allelic frequencies. In fact, a normosmic condition was associated with genotype AA and allele A and a hyposmic condition was associated with genotype GG and allele G. In conclusion, our results show that a relationship exists between the physiological variations of olfactory performance and the OBPIIa gene polymorphism.

Odor Identification Performance in Idiopathic Parkinson's Disease Is Associated With Gender and the Genetic Variability of the Olfactory Binding Protein.

Deficits in olfaction are among the most frequent non-motor symptoms in Parkinson's disease (PD) and can be detected early compared with motor symptoms. The reason for the early onset, as well as the mechanism involved remains unknown. We aimed to characterize the olfactory performance of patients with PD and age-matched healthy control (HC) participants in association with gender and a specific polymorphism in the odorant-binding protein IIa (OBPIIa) gene, which plays a crucial role in the perception of odors. The olfactory performance was assessed using the odor identification part of the Sniffin' Sticks test in 249 participants (patients with PD: n = 131 and HC participants: n = 118). All participants were genotyped for the rs2590498 polymorphism of the OBPIIa gene, whose major allele A is associated with a higher retronasal perception than the minor allele G. A higher number of men with PD than women with PD exhibited hyposmia. Importantly, OBPIIa gene polymorphism showed an effect on PD-related olfactory deficits only in women. Women with PD carrying two sensitive alleles (AA) showed a better olfactory performance than women with PD with at least one insensitive allele (G); the olfactory scores of the AA genotype women with PD were not different from those of HC participants. In conclusion, our results confirmed a sex effect on the reduced olfactory performance of patients with PD and identified the OBPIIa locus, which may provide a mechanism to determine the risk factor for olfactory deficits in women with PD at the molecular level.

UDP-glucosyltransferase PpUGT85A2 controls volatile glycosylation in peach.

The monoterpene linalool is a major contributor to aroma and flavor in peach (Prunus persica) fruit. It accumulates during fruit ripening, where up to ~40% of the compound is present in a non-volatile glycosylated form, which affects flavor quality and consumer perception by retronasal perception during tasting. Despite the importance of this sequestration to flavor, the UDP-glycosyltransferase (UGT) responsible for linalool glycosylation has not been identified in peach. UGT gene expression during peach fruit ripening and among different peach cultivars was analyzed using RNA sequencing, and transcripts correlated with linalyl-β-d-glucoside were selected as candidates for functional analysis. Kinetic resolution of a racemic mixture of R,S-linalool was shown for PpUGT85A2, with a slight preference for S-(+)-linalool. PpUGT85A2 was shown to catalyze synthesis of linalyl-β-d-glucoside in vitro, although it did not exhibit the highest enzyme activity between tested substrates. Subcellular localization of PpUGT85A2 in the cytoplasm and nucleus was detected. Application of linalool to peach leaf disks promoted PpUGT85A2 expression and linalyl-β-d-glucoside generation. Transient expression in peach fruit and stable overexpression in tobacco and Arabidopsis resulted in significant accumulation of linalyl-β-d-glucoside in vivo. Taken together, the results indicate that PpUGT85A2 expression is a major control point predicting linalyl-β-d-glucoside content.

Investigating the oronasal contributions to metallic perception

AbstractMetallic taints elicited when consuming food can be unpleasant for the consumer and are therefore problematic to food manufacturers. Although metallic has been proposed as a taste in the past, evidence remains inconclusive. This study investigates the oral and nasal contributions to metallic perception using sensory evaluation and headspace analysis using gas chromatography–mass spectrometry (GC‐MS). When sniffing the headspace over divalent salt solutions, some were discriminated from water. GC‐MS did not detect volatiles in the sample headspace, one hypothesis being that sample volatiles react with phospholipids in the nasal cavity and it is lipid oxidation products which are perceived. Copper sulphate was reported as metallic when tasted with the nose occluded to eliminate retronasal perception, suggesting a gustatory or trigeminal mechanism may be involved. This work indicates orthonasal stimulation is involved in metallic perception, and contributes to the ongoing debate over metallic being a taste, trigeminal or flavour response.

The contribution of wine-derived monoterpene glycosides to retronasal odour during tasting

This study investigated the sensory significance of monoterpene glycosides during tasting, by retronasal perception of odorant aglycones released in-mouth. Monoterpene glycosides were isolated from Gewürztraminer and Riesling juices and wines, chemically characterised and studied using sensory time-intensity methodology, together with a synthesised monoterpene glucoside. When assessed in model wine at five times wine-like concentration, Gewürztraminer glycosides and geranyl glucoside gave significant fruity flavour, although at wine-like concentrations, or in the presence of wine volatiles, the effect was not significant. Gewürztraminer glycosides, geranyl glucoside and guaiacyl glucoside were investigated using a sensory panel (n=39), revealing large inter-individual variability, with 77% of panellists responding to at least one glycoside. The study showed for the first time that grape-derived glycosides can contribute perceptible fruity flavour, providing a means of enhancing flavour in wines, and confirms the results of previous studies that the effect is highly variable across individuals.

Comparing the relative sensitivity of ortho‐ and retronasal perception of a strawberry flavour model using omission testing

AbstractSensory omission experiments are used to identify the key volatiles contributing to a flavour but a review of the literature suggests that some omission studies are underpowered, with only five to 19 assessors. Here a more sensitive and powerful approach is described that combines a same‐different test with the Thurstonian measure d′ which enabled evaluation of the relative contributions of each volatile to the overall perceived flavour. A sensory panel evaluated the relative contributions of volatiles in a nine‐component, commercial strawberry flavour both ortho‐ and retro‐nasally. In addition, Odour Activity Values (OAVs) reported in the literature were compared to d′ values established in this study to determine if OAVs were representative of the individual contribution of volatiles to the perceived strawberry flavour. Compared to retronasal perception, orthonasal perception was more sensitive to the removal of all individual volatiles, except for two compounds, 2,3‐butandione and methyl dihydrojasmonate. OAVs did not always reflect the relative importance of individual volatiles in flavour represented by d′. This study highlights that the same‐different approach coupled with d′ measures represents an improved opportunity for the evaluation of the key components of flavour and that orthonasal omission tests may not best represent how flavours perform during consumption.Key findings – Same‐different testing and the use of the Thurstonian d′ value, was successfully applied to measure the relative contributions of the individual volatiles in a simple strawberry flavour to the overall flavour perception when delivered ortho‐ or retronasally. Results showed that orthonasal perception was more sensitive but does not necessarily represent retronasal perception. Comparison between d′ values and Odour Activity Values (OAV) showed that OAVs do not always reflect the relative importance of individual volatiles in flavour: the removal of ethyl butanoate was not perceived orthonasally, despite its relatively high OAV. On the contrary, the higher d′ measured for 2,3‐butandione (0.40) compared to other volatiles in the strawberry flavour could be due to synergistic interactions in this flavour. Although all orthonasal OAVs were above 1, the removal of seven out of nine individual volatiles was not perceived orthonasally (p &gt; 0.05). Copyright © 2016 John Wiley &amp; Sons, Ltd.

The Feasibility of Gelatin-Based Retronasal Stimuli to Assess Olfactory Perception

Links between some psychological disorders and olfactory deficits are well documented, and screening tests have been developed to exploit these associations. Odors can take one of two routes to the olfactory receptors in the nasal epithelium, the orthonasal or retronasal route. This article discusses the potential use of the retronasal route to assess olfaction using gelatin-based stimuli delivered orally. Using a relatively new psychophysical method, the Single-Interval Adjustment Matrix task, we estimated vanillin thresholds for five healthy participants sampling small vanillin flavored gels. Our data demonstrate the feasibility of using solid-state gustatory stimuli to assess retronasal perception.

Retronasal perception and flavour thresholds of iron and copper in drinking water

Drinking water flavour has a strong role in water quality perception, service satisfaction, willingness to pay and selection of water sources. Metallic flavours are often caused by the dissolved iron and copper, commonly found in groundwater or introduced to tap water by corroding infrastructure. Taste thresholds of iron and copper have been investigated by several studies; however, reported results and test methods vary considerably. This study determined the taste thresholds of ferrous and cuprous ions in room temperature reagent water by using the one-of-five test with multi-nation panellists in the United States. For ferrous and cuprous ions, individual thresholds ranged from 0.003 to &amp;gt;5 mg l−1 and 0.035 to &amp;gt;5 mg l−1, respectively. Population thresholds were determined by logistic regression and geometric mean methods as 0.031 and 0.05 mg l−1 for ferrous ion, and 0.61 mg l−1 for cuprous ion by both methods. The components of metallic sensation were investigated by use of nose-clips while panellists ingested iron and copper solutions. Results showed that metallic sensation has a significant odour component and should be treated as a flavour instead of a taste. Ferrous, cuprous and cupric ions also produced weak bitter and salty tastes as well as astringent mouthfeel. In comparison, ferric ion produced no sensation.

The sense of smell: contributions of orthonasal and retronasal perception applied to metallic flavor of drinking water

The human senses are important assessment tools that assist water industry with effective water quality and water security monitoring. Flavor perception is combination of taste and odor; odor perception is a combination of orthonasal and retronasal perception. Orthonasal perception is associated with the sniff and describes entry of odor molecules though nostrils to nasal cavity followed by interaction with odor receptor neurons. Retronasal perception describes mechanism in which odor molecules present in mouth are transported to back of nasopharynx and then to odor receptor neurons. Although both pathways bring odor molecules to olfactory epithelium where they are perceived and processed by brain, retronasal route is more important for humans in terms of detecting ingested odors. For copper (II), metallic flavour is a combination of a weak bitter taste and a strong metallic odor that is produced as a biochemical reaction in mouth. Copper (II) in presence of oxygen causes lipid oxidation of arachidonic, linoleic, and oleic acids in mouth. A more thorough understanding of sense of smell will greatly aid water industry in its quest to produce a palatable product.

Investigation of the retronasal perception of palm wine (&lt;i&gt;Elaeis Guineensis&lt;/i&gt;) aroma by application of sensory analysis and exhaled odorant measurement (exom).

The headspace profile of palm wine was evaluated by time-resolved sensory analysis showing significant changes of the diverse odour attributes with time after swallowing. Fruity and citrusy were the most intense aroma qualities perceived upon sample introduction into the mouth, while swallowing of the palm wine elicited a more acidic impression followed by citrusy and fruity nuances respectively. After swallowing, panelists described an increase in the nutty and popcorn-like aroma impressions. Based on these sensory observations, the retronasal aroma perception of palm wine was investigated by application of the modified Exhaled Odorant Measurement (EXOM)-approach. In EXOM analysis, odorants that are exhaled through the nose during food consumption and swallowing are collected and analysed by high resolution gas chromatography-olfactometry and mass spectrometry, respectively. EXOM results revealed an initial 24 odor-active compounds in the \'swallow\' breath with 23 of these odorants being identified on the basis of their odor qualities and intensities, as well as chromatographic and mass spectral data. Only 14 compounds were detectable in the exhaled breath 20 s after swallowing the palm wine and 11 of these were subsequently identified. Generally, the identified odorants belonged to very diverse odorant substance classes such as heteroaromatic compounds, esters, alcohols, carbonyl and thio compounds and many more. Among these, higher persistence intervals in the exhalation breath were obtained for the buttery smelling compounds butan-2,3-dione and 3-hydroxy-butan-2-one (acetoine), 3-isobutyl 2- methoxypyrazine with bell pepper-like aroma impression, the malty smelling 2- and 3-methylbutanols, and the coconut-like smelling &#947;-dodecalactone. The popcorn-like smelling 2-acetyl 1-pyrroline, the fresh flowery linalool and two unknown compounds with citrusy and buttery aroma impressions were only detectable at 20 s after swallowing. Dynamic changes were also observed in retronasal sensory evaluations that were attributed to specific palm wine odorants. Accordingly, both sensory and analytical data on retronasal aroma perception of palm wine monitored the dynamic flavour changes during palm wine consumption. Keywords: Retronasal, EXOM, swallow breath, 2-acetyl 1-pyrroline African Journal of Food, Agriculture, Nutrition and Development Vol. 9 (2) 2009: pp. 793-813

Temporal processing of olfactory stimuli during retronasal perception

Odorants can be perceived via the nose during an inhalation or sniff (orthonasal perception) and via the mouth, nasopharynx and nasal cavity during mastication or drinking (retronasal perception). Previous data suggest that orthonasal perception provides a more efficient route with greater difficulty being reported when detecting [Halpern BP. Retronasal and orthonasal smelling. Chemosense 2004;6:1–7; Voirol E, Daget N. Comparative study of nasal and retronasal olfactory perception. Lebensmittel-Wissenschaft Technol 1986;19:316–9] and identifying [Heilmann S, Hummel T. A new method for comparing orthonasal and retronasal olfaction. Behav Neurosci 2004;118:412–9; Sun BC, Halpern BP. Identification of air-phase retronasal and orthonasal odorant pairs. Chem Senses 2005;30:1–14] single odorants retronasally. Whether the poorer sensitivity obtained via the retronasal route is largely due to the greater adsorption of odorants by the nasopharyngeal mucus compared to the nasal mucus thereby reducing their peak concentration and/or slowing their passage, has not been resolved. Importantly, the question of whether solubility of odorants in mucus or water predicts the outcomes for perception of stimuli presented via the retronasal route has not been resolved. Accordingly, the present study investigates this question by determining whether the solubility of an odorant in mucus predicts which component of a binary odour mixture is perceived first during retronasal perception. The results indicate that solubility in mucus rather than solubility in water is a better predictor of which odour will be perceived first and identified more readily during the retronasal perception of a binary mixture. In addition, lower intensity levels of single odorants occurred via the retronasal route suggesting that adsorption was greater via this route. Whether this was due to nasopharyngeal mucus having a greater adsorptive area or different composition compared to the orthonasal pathway is not known.

Separate signals for orthonasal vs. retronasal perception of food but not nonfood odors.

There is a controversy concerning whether smelling via the nose (ortho-nasally) or the mouth (retro-nasally) represent two routes to the same modality or two distinct submodalities. Since olfactory coding is dependent upon experience, and since food odors are experienced retro-nasally, the authors tested the hypothesis that whether an odor represents a food may influence whether sensation via the two routes leads to separable responses. The authors demonstrate that salivary response to food odors decrease with repeated presentation and show that this response rebounds upon presentation of a novel food odor via the same route and upon presentation of the same food odor via a novel route. This finding indicates that the novel odor and the novel route represent distinct sensory signals. This effect is specific, in that it does not depend on differences in odor intensity or pleasantness and is selective, in that it occurs for food odors but not for equally pleasant and intense nonfood odors. These results demonstrate that separable signals are generated for the same food odor depending upon route and support the existence of category-specific processing.

Retronasal Perception of Odors

Odors often produce different sensations when presented in front of the nose or intraorally, when eaten. It is a long-standing question whether these differences in sensations are due, for example, to the additional mechanical sensations elicited by the food in the mouth or additional odor release during mastication. To study this phenomenon in detail, a stimulation technique has been developed that allows controlled ortho- or retronasal presentation of odorous stimuli. Results from psychophysical, electrophysiological, and imaging studies suggest that there are clear differences in the perception of ortho- and retronasal stimuli. This 'duality of the sense of smell' is also observed in a clinical context where some patients exhibit good retronasal olfactory function with little or no orthonasal function left, and vice versa. The differences between ortho- and retronasal perception of odors are thought to be, at least partly, due to absorption of odors to the olfactory epithelium, which appears to differ in relation to the direction of the airflow across the olfactory epithelium.

Orthonasal and Retronasal Perception of Some Green Leaf Volatiles Used in Beverage Flavors

Orthonasal perception of six green leaf volatiles (GLVs) classified only hexanal, (E)-2-hexenal, and (Z)-3-hexen-1-yl formate as green. (Z)-3-Hexen-1-yl hexanoate and (Z)-3-hexen-1-yl 3-methylbutyrate were more floral, and (Z)-3-hexen-1-yl acetate fell between the two groups. For retronasal perception, classification along a bipolar green-fruity scale is proposed for describing these GLVs. Data from grouping and dissimilarity tests as well as from sensory profiling show green character for these compounds in standard beverage bases having low Brix or high acidity. As the Brix value increases (or acidity decreases) within the limits encountered in commercial beverages, the character becomes fruity. Several tastant-dependent changes in intensity scores for retronasal descriptors were shown to occur for mixtures of GLVs. The GLVs did not affect intensity scores for gustatory descriptors.