Enhancement of retronasal odors by taste

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).

The effect of mango aroma in low-sugar beverage: A sensory study on odor induced sweetness enhancement

Excessive intake of sugar has become a public concern. However, it is challenging for food industries to decrease sugar level without sacrificing safety and sensory profile. Odor-induced sweetness enhancement (OISE) is believed to be a novel and promising strategy for sugar reduction. In order to investigate the OISE effect of mango aroma and evaluate its degree of sugar reduction in low-sugar beverages, a mathematical model was constructed through sensory evaluation in this study. The results showed that the maximum liking of low-sugar model beverages was 4.28 % sucrose and 0.57 % mango flavor. The most synergistic of OISE was at the concentration level of 2.24 % sucrose + 0.25 % mango flavor, which was equivalent to 2.96 % pure sucrose solution. With 32.14 % sugar reduction, the mango aroma was suggested to generate the OISE effect. However, the same level of garlic aroma was not able to enhance sweetness perception, suggesting that the congruency of aroma and taste is a prerequisite for the OISE effect to occur. This study demonstrated that the cross-modal interaction of mango aroma on sweetness enhancement in low-sugar model beverages could provide practical guidance for developing sugar-reduced beverages without applying sweeteners.

Multisensory Integration Underlies the Distinct Representation of Odor-Taste Mixtures in the Gustatory Cortex of Behaving Rats

The perception of food relies on the integration of olfactory and gustatory signals originating from the mouth. This multisensory process generates robust associations between odors and tastes, significantly influencing the perceptual judgment of flavors. However, the specific neural substrates underlying this integrative process remain unclear. Previous electrophysiological studies identified the gustatory cortex as a site of convergent olfactory and gustatory signals, but whether neurons represent multimodal odor-taste mixtures as distinct from their unimodal odor and taste components is unknown. To investigate this, we recorded single-unit activity in the gustatory cortex of behaving female rats during the intraoral delivery of individual odors, individual tastes, and odor-taste mixtures. Our results demonstrate that chemoselective neurons in the gustatory cortex are broadly responsive to intraoral chemosensory stimuli, exhibiting time-varying multiphasic changes in activity. In a subset of these chemoselective neurons, odor-taste mixtures elicit nonlinear cross-modal responses that distinguish them from their olfactory and gustatory components. These findings provide novel insights into multimodal chemosensory processing by the gustatory cortex, highlighting the distinct representation of unimodal and multimodal intraoral chemosensory signals. Overall, our findings suggest that olfactory and gustatory signals interact nonlinearly in the gustatory cortex to enhance the identity coding of both unimodal and multimodal chemosensory stimuli.

Inducing Novel Sound-Taste Correspondences via an Associative Learning Task

The interest in crossmodal correspondences, including those involving sounds and involving tastes, has experienced rapid growth in recent years. However, the mechanisms underlying these correspondences are not well understood. In the present study (N = 302), we used an associative learning paradigm, based on previous literature using simple sounds with no consensual taste associations (i.e., square and triangle wave sounds at 200 Hz) and taste words (i.e., sweet and bitter), to test the influence of two potential mechanisms in establishing sound-taste correspondences and investigate whether either learning mechanism could give rise to new and long-lasting associations. Specifically, we examined an emotional mediation account (i.e., using sad and happy emoji facial expressions) and a transitive path (i.e., sound-taste correspondence being mediated by color, using red and black colored squares). The results revealed that the associative learning paradigm mapping the triangle wave tone with a happy emoji facial expression induced a novel crossmodal correspondence between this sound and the word sweet. Importantly, we found that this novel association was still present two months after the experimental learning paradigm. None of the other mappings, emotional or transitive, gave rise to any significant associations between sound and taste. These findings provide evidence that new crossmodal correspondences between sounds and tastes can be created by leveraging the affective connection between both dimensions, helping elucidate the mechanisms underlying these associations. Moreover, these findings reveal that these associations can last for several weeks after the experimental session through which they were induced.

The role of the mediodorsal thalamus in chemosensory preference and consummatory behavior in rats

Experience plays a pivotal role in determining our food preferences. Consuming food generates odor-taste associations that shape our perceptual judgements of chemosensory stimuli, such as their intensity, familiarity, and pleasantness. The process of making consummatory choices relies on a network of brain regions to integrate and process chemosensory information. The mediodorsal thalamus is a higher-order thalamic nucleus involved in many experience-dependent chemosensory behaviors, including olfactory attention, odor discrimination, and the hedonic perception of flavors. Recent research has shown that neurons in the mediodorsal thalamus represent the sensory and affective properties of experienced odors, tastes, and odor-taste mixtures. However, its role in guiding consummatory choices remains unclear. To investigate the influence of the mediodorsal thalamus in the consummatory choice for experienced odors, tastes, and odor-taste mixtures, we pharmacologically inactivated the mediodorsal thalamus during 2-bottle brief-access tasks. We found that inactivation altered the preference for specific odor-taste mixtures, significantly reduced consumption of the preferred taste and increased within-trial sampling of both chemosensory stimulus options. Our results show that the mediodorsal thalamus plays a crucial role in consummatory decisions related to chemosensory preference and attention.

Taste and odor interactions after metabolic surgery

Most patients report "taste" changes after undergoing metabolic surgeries. Yet, most studies that used validated sensory evaluation techniques, including ours, found no changes in perceived taste intensity from before to after surgery. However, we assessed participants with pure gustatory stimuli and after an overnight fast, which raises questions about whether patients' self-reported "taste" changes are due to conflating changes in retronasal smell/"flavor" with taste changes or whether they only manifest during the fed state. To investigate this, we conducted a cross-sectional study comparing sensory responses in women who underwent metabolic surgery 2 to 6 yr ago (n = 15) with 2 nonoperated control groups: one with a body mass index (BMI) equivalent (n = 15) and one with a healthy BMI (n = 15). Participants attended 2 sessions, one fed and one fasted. Using a sip-and-spit method, women tasted liquid samples containing gustatory and olfactory stimuli and puddings with varying fat content with and without nose clips. They used separate general labeled magnitude scales to rate their perceived intensity of taste, smell, flavor, and liking. Mixed ANOVAs indicated that the surgery and BMI equivalent groups rated retronasal smell intensity of coffee stronger than the healthy BMI group (P ≤ 0.015). However, there were no differences in taste/flavor intensity or liking ratings among groups. Additionally, feeding conditions did not significantly affect perceived intensity ratings. Our findings suggest that changes in the sensory-discriminatory component of taste or taste-odor interactions are not significant contributors to dietary modifications following metabolic surgery.

Enhancement effect of odor and multi-sensory superposition on sweetness

The impact of sugary foods on public health has contributed to the development of low-sugar and sugar-substituted products, and sugar reduction has become a major challenge for the food industry. There is growing empirical evidence that odor can enhance the perception of sweetness without increasing the caloric load. This current review summarizes the researches on odor-induced sweetness enhancement published in recent years and discusses the mechanisms and influencing factors of odor-sweetness interactions. In addition, by combing existing studies, this paper also summarizes the research methods and strategies to investigate odor-induced sweetness enhancement. Finally, the feasibility of synergistic enhancement of sweetness through the superposition of odor with other senses (texture, visual, etc.) is also discussed and analyzed. In conclusion, odor-induced sweetness enhancement may present an alternative or complementary approach for developing foods with less sugar.

Analysis of Non-Volatile Compounds in Jasmine Tea and Jasmine Based on Metabolomics and Sensory Evaluation

Scenting tea with Jasminum sambac is beneficial to forming a unique taste of jasmine tea, which is regulated by numerous compounds. To investigate the relationship between metabolites in jasmine and jasmine tea, as well as the impact of metabolites on the characteristic taste of jasmine tea, the liquid chromatography-mass spectrometry, sensory evaluation, and multivariate analysis were applied in this study. A total of 585 and 589 compounds were identified in jasmine tea and jasmine, respectively. After scented, jasmine tea added 70 compounds, which were believed to come from jasmine flowers. Furthermore, seventy-four compounds were identified as key characteristic compounds of jasmine tea, and twenty-two key differential metabolite compounds were believed to be used to distinguish jasmine tea scented differently and contribute to the taste of jasmine tea. Additionally, the relationship between taste compounds and aroma quality was also explored, and it was found that five compounds were positively correlated with the aroma properties of jasmine tea and seven compounds were negatively correlated with the aroma properties of jasmine tea. Overall, these findings provided insights into the future study of the mechanism of taste formation in jasmine tea and provided the theoretical basis for the production of jasmine tea.

Dynamic Instrumental and Sensory Methods Used to Link Aroma Release and Aroma Perception: A Review

Perception of flavor is a dynamic process during which the concentration of aroma molecules at the olfactory epithelium varies with time as they are released progressively from the food in the mouth during consumption. The release kinetics depends on the food matrix itself but also on food oral processing, such as mastication behavior and food bolus formation with saliva, for which huge inter-individual variations exist due to physiological differences. Sensory methods such as time intensity (TI) or the more-recent methods temporal dominance of sensations (TDS) and temporal check-all-that-apply (TCATA) are used to account for the dynamic and time-related aspects of flavor perception. Direct injection mass spectrometry (DIMS) techniques that measure in real time aroma compounds directly in the nose (nosespace), aimed at obtaining data that reflect the pattern of aroma release in real time during food consumption and supposed to be representative of perception, have been developed over the last 25 years. Examples obtained with MS operated in chemical ionization mode at atmospheric or sub-atmospheric pressure (atmospheric pressure chemical ionization APCI or proton-transfer reaction PTR) are given, with emphases on studies conducted with simultaneous dynamic sensory evaluation. Inter-individual variations in terms of aroma release and their relevance for understanding flavor perception are discussed as well as the evidenced cross-modal interactions.

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.

Multisensory integration of orally-sourced gustatory and olfactory inputs to the posterior piriform cortex in awake rats

Flavour refers to the sensory experience of food, which is a combination of sensory inputs sourced from multiple modalities during consumption, including taste and odour. Previous work has demonstrated that orally-sourced taste and odour cues interact to determine perceptual judgements of flavour stimuli, although the underlying cellular- and circuit-level neural mechanisms remain unknown. We recently identified a region of the piriform olfactory cortex in rats that responds to both taste and odour stimuli. Here, we investigated how converging taste and odour inputs to this area interact to affect single neuron responsiveness ensemble coding of flavour identity. To accomplish this, we recorded spiking activity from ensembles of single neurons in the posterior piriform cortex (pPC) in awake, tasting rats while delivering taste solutions, odour solutions and taste + odour mixtures directly into the oral cavity. Our results show that taste and odour inputs evoke highly selective, temporally-overlapping responses in multisensory pPC neurons. Comparing responses to mixtures and their unisensory components revealed that taste and odour inputs interact in a non-linear manner to produce unique response patterns. Taste input enhances trial-by-trial decoding of odour identity from small ensembles of simultaneously recorded neurons. Together, these results demonstrate that taste and odour inputs to pPC interact in complex, non-linear ways to form amodal flavour representations that enhance identity coding. KEY POINTS: Experience of food involves taste and smell, although how information from these different senses is combined by the brain to create our sense of flavour remains unknown. We recorded from small groups of neurons in the olfactory cortex of awake rats while they consumed taste solutions, odour solutions and taste + odour mixtures. Taste and smell solutions evoke highly selective responses. When presented in a mixture, taste and smell inputs interacted to alter responses, resulting in activation of unique sets of neurons that could not be predicted by the component responses. Synergistic interactions increase discriminability of odour representations. The olfactory cortex uses taste and smell to create new information representing multisensory flavour identity.

Olfactory-gustatory simultaneity judgments: A preliminary study on the congruency-dependent temporal window of multisensory binding

BACKGROUND

A greater congruency of audio and video expands the temporal binding window (TBW). A similar phenomenon may occur with a combination of odor and taste, which are the main components of flavor.

OBJECTIVE

TBW is defined as the temporal resolution of synchrony perception. The larger the TBW, the lower the resolution. We hypothesized that the more congruent the odor and taste, the lower the temporal resolution of synchrony perception.

METHODS

To examine this hypothesis, 10 female participants performed simultaneity judgment (SJ) tasks under congruent (soy sauce odor with saline) and incongruent (cherry tree leaf odor with saline) conditions and evaluated the congruency with saltiness for the two odors. In the SJ tasks, participants reported whether odor and taste were presented simultaneously or successively. We assumed a Gaussian distribution for the temporal distributions of the simultaneous response rates and calculated the approximations. In addition, we computed the half width at half height (HWHH) as an index of TBW based on the coefficient of approximation for the temporal distribution of the simultaneous response rates.

RESULTS

HWHH was significantly larger under congruent condition than under incongruent condition. In addition, congruency with saltiness had a significant moderate positive correlation with HWHH.

CONCLUSION

The larger the HWHH, the lower the temporal resolution of synchrony perception, supporting the hypothesis. This study suggests that the width of TBW depends on the cross-modal congruency similar to the case for audio-visual SJs. However, methodological improvements, including a larger sample size and gender-independent recruitment of participants, are essential to enhance the reliability of the findings because some of the results did not provide sufficient ESs or power.

Neural Representation of Intraoral Olfactory and Gustatory Signals by the Mediodorsal Thalamus in Alert Rats

The mediodorsal thalamus is a multimodal region involved in a variety of cognitive behaviors, including olfactory attention, odor discrimination, and the hedonic perception of flavors. Although the mediodorsal thalamus forms connections with principal regions of the olfactory and gustatory networks, its role in processing olfactory and gustatory signals originating from the mouth remains unclear. Here, we recorded single-unit activity in the mediodorsal thalamus of behaving female rats during the intraoral delivery of individual odors, individual tastes, and odor-taste mixtures. Our results are the first to demonstrate that neurons in the mediodorsal thalamus dynamically encode chemosensory signals originating from the mouth. This chemoselective population is broadly tuned, exhibits excited and suppressed responses, and responds to odor-taste mixtures differently than an odor or taste alone. Furthermore, a subset of chemoselective neurons encodes the palatability-related features of tastes and may represent associations between previously experienced odor-taste pairs. Our results further demonstrate the multidimensionality of the mediodorsal thalamus and provide additional evidence of its involvement in processing chemosensory information important for ingestive behaviors.SIGNIFICANCE STATEMENT The perception of food relies on the concurrent processing of olfactory and gustatory signals originating from the mouth. The mediodorsal thalamus is a higher-order thalamic nucleus involved in a variety of chemosensory-dependent behaviors and connects the olfactory and gustatory cortices with the prefrontal cortex. However, it is unknown how neurons in the mediodorsal thalamus process intraoral chemosensory signals. Using tetrode recordings in alert rats, our results are the first to show that neurons in the mediodorsal thalamus dynamically represent olfactory and gustatory signals from the mouth. Our findings are consistent with the mediodorsal thalamus being a key node between sensory and prefrontal cortical areas for processing chemosensory information underlying ingestive behavior.

Odor-Induced Taste Enhancement Is Specific to Naturally Occurring Temporal Order and the Respiration Phase

Interaction between odor and taste information creates flavor perception. There are many possible determinants of the interaction between odor and taste, one of which may be the somatic sensations associated with breathing. We assumed that a smell stimulus accompanied by inhaling or exhaling enhances taste intensity if the order is congruent with natural drinking. To present an olfactory stimulus from the identical location during inhalation and exhalation, we blocked the gap between the tube presenting the olfactory stimulus and the nostril. Participants breathed and ingested the solution according to the instructions on the screen and evaluated the solution's taste intensity. Vanilla odor enhanced the sweet taste in both retronasal and orthonasal conditions when the order of stimuli was congruent with natural drinking, but it did not do so in either condition when they were incongruent. The results suggest that breathing is a determinant of odor-taste interaction. The methods of presenting olfactory stimuli used in this study were compared and discussed in relation to those used in previous studies. Odor-induced taste enhancement depends on the time order of smell with breathing and taste congruency in natural drinking. Taste enhancement was induced by odor in both conditions by minimizing differences in odor presentation between them.

Gustatory dysfunction in patients with olfactory dysfunction and the associated factors

BACKGROUND

Little is known about the occurrence of gustatory dysfunction (GD) in relation to different aetiologies of olfactory dysfunction (OD) as assessed by psychophysical chemosensory tests. The aim of this study was to analyse gustatory function in patients with OD and to investigate clinical factors associated with GD.

METHODS

A total of 742 individuals who underwent both olfactory and gustatory function tests at a tertiary medical centre from November 2019 to March 2021 were retrospectively enrolled. Olfactory and gustatory function were assessed by the YSK olfactory and gustatory function tests, respectively. Patients with OD were classified into four groups according to the aetiology: sinonasal disease, post-infection OD (PIOD), post-traumatic OD (PTOD), and others. Secondary outcomes included age, sex, smoking history, and alcohol history.

RESULTS

Among the 488 patients with OD, 93 (19.1%) showed GD and 395 (80.9%) had normal gustatory function. Only 25 (9.8%) among 254 individuals with normosmia showed GD. Analyses of these frequencies revealed a significant association between OD and GD. In addition, the taste score was significantly lower in patients with OD than individuals with normosmia. The frequency of GD was significantly higher in patients with PTOD (53.6%) than in those with OD of other aetiologies (sinonasal disease, 6.7%; PIOD, 13.0%; others, 24.4%). In the multivariate analysis, age ≥55 years and PTOD were associated with a high frequency of GD among patients with OD.

CONCLUSIONS

The current study show that GD is significantly associated with OD. In particular, GD is more common in patients with PTOD than in those with OD of other aetiologies.

Human Oral Sensitivity to and Taste Modulation by 3-Mercapto-2-Methylpentan-1-ol

Introduction

3-Mercapto-2-methylpentan-1-ol (3 M) is a key onion flavor (aroma), but past sensory work has focused primarily on ortho-nasal presentation. A series of experiments was conducted to characterize human sensitivity to oral 3 M solutions, then determine how 3 M impacts perception of basic tastes.

Methods

Detection thresholds were measured for a food grade, racemic mixture using a forced-choice staircase procedure (n = 19). Recognition was measured by presenting a single stimulus per trial (3 M, vanillin, or water), with "onion," "vanilla," or "water" as responses (n = 18). Supra-threshold intensity (n = 20) was measured for various concentrations using the general labeled magnitude scale (gLMS). Odor-taste interactions were studied using mixtures of 3 M and exemplars of basic tastes. Participants rated the intensity of basic tastes, or both taste and aroma, using the gLMS (n ranged from 10 to 15). All stimuli were in aqueous solution.

Results

Participants detected oral 3 M at about 0.90 ppb and recognized 3 M as "onion" at about 5 ppb. Supra-threshold intensity increased roughly as a cumulative logistic function of concentration. 3 M enhanced the rated savory intensity of monosodium glutamate, but did not enhance the dominant qualities of exemplars of the other four basic tastes. Under a response-context more favorable to an analytic approach, savory enhancement was reduced but not eliminated. Savory enhancement was eliminated with nose-clips.

Conclusions

Oral sensitivity was lower than previous retronasal studies would suggest, but roughly consistent with concentrations in cooked allium varieties. Oral 3 M selectively enhanced savory intensity, an effect likely due to retronasal aroma rather than taste or mouthfeel.

Implication

3 M is a promising candidate aroma to enhance or impart a savory flavor.

Cortical Hub for Flavor Sensation in Rodents

The experience of eating is inherently multimodal, combining intraoral gustatory, olfactory, and somatosensory signals into a single percept called flavor. As foods and beverages enter the mouth, movements associated with chewing and swallowing activate somatosensory receptors in the oral cavity, dissolve tastants in the saliva to activate taste receptors, and release volatile odorant molecules to retronasally activate olfactory receptors in the nasal epithelium. Human studies indicate that sensory cortical areas are important for intraoral multimodal processing, yet their circuit-level mechanisms remain unclear. Animal models allow for detailed analyses of neural circuits due to the large number of molecular tools available for tracing and neuronal manipulations. In this review, we concentrate on the anatomical and neurophysiological evidence from rodent models toward a better understanding of the circuit-level mechanisms underlying the cortical processing of flavor. While more work is needed, the emerging view pertaining to the multimodal processing of food and beverages is that the piriform, gustatory, and somatosensory cortical regions do not function solely as independent areas. Rather they act as an intraoral cortical hub, simultaneously receiving and processing multimodal sensory information from the mouth to produce the rich and complex flavor experience that guides consummatory behavior.

Odor-Taste-Texture Interactions as a Promising Strategy to Tackle Adolescent Overweight

The adolescence period is characterized by a considerable risk to weight gain due to the high consumption of food rich in sugar. A promising strategy to reduce sugar consumption may lie in exploiting the ability of our senses to interact to each other (cross-modal interactions). The aims were to investigate the cross-modal interactions and gustatory function in normal-weight and overweight adolescents. Fifty adolescents (25 overweight and 25 normal-weight) were involved. Subjects rated liking and attribute intensity in pudding samples obtained by adding vanilla aroma (0.1%; 0.3%), butter aroma (0.05%; 0.1%) or a thickener agent (1%; 1.5%) to a base formulation. The gustatory function was also measured through the “taste strips” methodology. Overweight adolescents were found to have a significantly (p < 0.001) worse ability to correctly identify all tastes. Cross-modal interactions occurred differently according to their body mass index, with a significant increase (p < 0.05) in sensory desirable characteristics (e.g., sweet and creaminess) due to aroma addition, especially in overweight subjects. Furthermore, butter aroma significantly increased hedonic responses only in overweight subjects. Tricking our senses in the way of perceiving sensory attributes could be a promising strategy to develop innovative food formulations with a reduced sugar amount, which will lead to a potential decrease in caloric intake and help to tackle the obesity epidemic.

E-Nose and Olfactory Assessment: Teamwork or a Challenge to the Last Data? The Case of Virgin Olive Oil Stability and Shelf Life

Electronic nose (E-nose) devices represent one of the most trailblazing innovations in current technological research, since mimicking the functioning of the biological sense of smell has always represented a fascinating challenge for technological development applied to life sciences and beyond. Sensor array tools are right now used in a plethora of applications, including, but not limited to, (bio-)medical, environmental, and food industry related. In particular, the food industry has seen a significant rise in the application of technological tools for determining the quality of edibles, progressively replacing human panelists, therefore changing the whole quality control chain in the field. To this end, the present review, conducted on PubMed, Science Direct and Web of Science, screening papers published between January 2010 and May 2021, sought to investigate the current trends in the usage of human panels and sensorized tools (E-nose and similar) in the food industry, comparing the performances between the two different approaches. In particular, the focus was mainly addressed towards the stability and shelf life assessment of olive oil, the main constituent of the renowned “Mediterranean diet”, and nowadays appreciated in cuisines from all around the world. The obtained results demonstrate that, despite the satisfying performances of both approaches, the best strategy merges the potentialities of human sensory panels and technological sensor arrays, (i.e., E-nose somewhat supported by E-tongue and/or E-eye). The current investigation can be used as a reference for future guidance towards the choice between human panelists and sensorized tools, to the benefit of food manufacturers.

Effective Connectivity in the Human Brain for Sour Taste, Retronasal Smell, and Combined Flavour

The anterior insula and rolandic operculum are key regions for flavour perception in the human brain; however, it is unclear how taste and congruent retronasal smell are perceived as flavours. The multisensory integration required for sour flavour perception has rarely been studied; therefore, we investigated the brain responses to taste and smell in the sour flavour-processing network in 35 young healthy adults. We aimed to characterise the brain response to three stimulations applied in the oral cavity—sour taste, retronasal smell of mango, and combined flavour of both—using functional magnetic resonance imaging. Effective connectivity of the flavour-processing network and modulatory effect from taste and smell were analysed. Flavour stimulation activated middle insula and olfactory tubercle (primary taste and olfactory cortices, respectively); anterior insula and rolandic operculum, which are associated with multisensory integration; and ventrolateral prefrontal cortex, a secondary cortex for flavour perception. Dynamic causal modelling demonstrated that neural taste and smell signals were integrated at anterior insula and rolandic operculum. These findings elucidated how neural signals triggered by sour taste and smell presented in liquid form interact in the brain, which may underpin the neurobiology of food appreciation. Our study thus demonstrated the integration and synergy of taste and smell.

Flavor Enhancement in Daily Life of Patients with Olfactory Dysfunction

Introduction

Patients with olfactory dysfunction report deterioration of taste due to loss of flavor, leading to less food enjoyment, alterations in dietary behaviors and stress. The aim of this study was to introduce flavor enhancement to investigate its acceptance and possible effects on quality of life.

Methods

In this prospective, controlled, randomized, single-blinded, cross-over pilot study, we recruited 30 olfactory dysfunction patients, of which 16 were hyposmic and 14 anosmic. After single-blinded triangle flavor discrimination test, flavor drops were randomized either in high or low concentration for 14 days and vice versa for another 14 days. Records included a daily diary and the questionnaire of olfactory disorders.

Results

Usage rates were excellent with 82.2% of all days, while drops were mainly used for breakfast (44.6%, p < 0.05). Hyposmics used flavor enhancement on significantly more days (median = 14) compared to anosmics (median = 11, p = 0.0094). QOD improved in 12 patients to a meaningful extent.

Conclusions

In this pilot study, we show that flavor enhancement is feasible accompanied by high compliance and acceptance in olfactory dysfunction patients. Flavor drops were used regardless of low or high concentrations with no adverse events noted.

Implications

Our findings give rise to further studies illuminating the possible advantages of flavor enhancement in patients with olfactory disorders.

What Is the Relationship between the Presence of Volatile Organic Compounds in Food and Drink Products and Multisensory Flavour Perception?

This narrative review examines the complex relationship that exists between the presence of specific configurations of volatile organic compounds (VOCs) in food and drink products and multisensory flavour perception. Advances in gas chromatography technology and mass spectrometry data analysis mean that it is easier than ever before to identify the unique chemical profile of a particular food or beverage item. Importantly, however, there is simply no one-to-one mapping between the presence of specific VOCs and the flavours that are perceived by the consumer. While the profile of VOCs in a particular product undoubtedly does tightly constrain the space of possible flavour experiences that a taster is likely to have, the gustatory and trigeminal components (i.e., sapid elements) in foods and beverages can also play a significant role in determining the actual flavour experience. Genetic differences add further variation to the range of multisensory flavour experiences that may be elicited by a given configuration of VOCs, while an individual’s prior tasting history has been shown to determine congruency relations (between olfaction and gustation) that, in turn, modulate the degree of oral referral, and ultimately flavour pleasantness, in the case of familiar foods and beverages.

Aroma of Icewine: A Review on How Environmental, Viticultural, and Oenological Factors Affect the Aroma of Icewine

The aroma of a wine is mostly driven by not only the factors in the vineyard, such as the grape variety and harvest time, but also the fermentation process. Icewine is a unique, intensely sweet wine made from late harvested grapes that have frozen naturally on the vine. Different from normal table wines, the grapes used in icewine naturally undergo a dehydration process and freeze-thaw cycles, and the must for icewine making has to be pressed from frozen grapes. This pressing process leaves water behind as ice crystals and allows the grape juice to be concentrated with more sugars, acids, and other dissolved solids, resulting in a slower than normal fermentation. These special procedures can lead to a unique aroma characteristic of icewine. This review delves into recent advances in chemical compounds related to icewine aroma characteristics and addresses how changes in these aroma characteristics and composition are influenced by environmental, viticultural, and oenological factors in the vineyard and winery. Deficiencies in previous studies and future trends related to the flavor science of icewine were also briefly addressed.

Taste and Smell Function in Head and Neck Cancer Survivors

Survivors of head and neck squamous cell cancers (HNSCC) frequently complain of taste dysfunction long after radiation therapy is completed, which contradicts findings from most sensory evaluation studies that predict dysfunction should resolve few months after treatment. Therefore, it remains unclear whether taste and smell function fully recovers in HNSCC survivors. We evaluated HNSCC survivors (n = 40; age 63 ± 12 years, mean ± standard deviation) who received radiation therapy between 6 months and 10 years before recruitment and compared their responses to those of a healthy control group (n = 20) equivalent in age, sex, race, smoking history, and body mass index. We assessed regional (tongue tip) and whole-mouth taste intensity perception using the general Labeled Magnitude Scale and smell function using the University of Pennsylvania Smell Identification Test (UPSIT). To determine possible differences between groups in retronasal smell perception, we used solutions of sucrose with strawberry extract, citric acid with lemon extract, sodium chloride in vegetable broth, and caffeine in coffee and asked participants to rate perceived smell and taste intensities with and without nose clips. We found groups had similar UPSIT and taste intensity scores when solutions were experienced in the whole mouth. However, HNSCC survivors were less likely to identify low concentrations of bitter, sweet, or salty stimuli in the tongue tip relative to healthy controls. Our findings suggest persistent and subtle localized damage to the chorda tympani or to the taste buds in the fungiform papillae of HNSCC survivors, which could explain their sensory complaints long after completion of radiotherapy.

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.

Subthreshold chemesthetic stimulation can enhance flavor lastingness of a soft chewable candy

In addition to taste and aroma components of a flavor, FEMA GRAS approved chemesthetic flavor ingredients deliver a trigeminal experience or chemesthetic effect and provide a third dimension to overall flavor experience. In this study, we explored the impact of chemesthetic stimulation on dynamic flavor perception, acceptability and salivation, with two base flavors (mint, watermelon), using a soft chewable candy as a model food. Each base flavor was augmented with three increasing levels of a mixture of chemesthetic flavor ingredients, which provided a cooling sensation; subthreshold, detection threshold, and supra-threshold levels. Thirty-six panelists were asked to rate the perceived flavor intensity of each sample during eating and after swallowing using time intensity analysis. Lastingness after swallowing was measured as the time for the flavor intensity to drop below 25% of the maximum intensity perceived during chewing. Compared with the control, the addition of chemesthetic flavor ingredients increased the perceived flavor intensity during chewing and the flavor lastingness after swallowing for both mint and watermelon flavor. These effects started from the addition of subthreshold concentration of chemesthetic flavor ingredients and further increased with increasing the concentration of chemesthetic flavor ingredients added. By adding the subthreshold concentration of chemesthetic flavor ingredients, the flavor lastingness was increased by 32% for mint flavor and 22% for watermelon flavor. The acceptability of these weak-flavored soft chewable candy test samples was significantly increased towards 'just right' with increasing concentrations of chemesthetic flavor ingredients, even at subthreshold level. However, chew time and saliva flow rate were not affected by the addition of chemesthetic flavor ingredients. The increased flavor lastingness by the addition of chemesthetic flavor ingredients could therefore be explained by perceptual interaction between chemesthesis and flavor perception.

Determination of Retronasal Olfactory Threshold Values

OBJECTIVES/HYPOTHESIS

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.

STUDY DESIGN

Prospective, descriptive and methodological study.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:1608-1614, 2021.

Odor-Taste Interactions in Food Perception: Exposure Protocol Shows No Effects of Associative Learning

Repeated exposure can change the perceptual and hedonic features of flavor. Associative learning during which a flavor's odor component is affected by co-exposure with taste is thought to be central in this process. However, changes can also arise due to exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of exposure without taste by repeatedly presenting one odor together with sucrose and a second odor alone. Sixty individuals attended two testing sessions separated by a 5-day Exposure Phase during which the stimuli were presented as flavorants in chewing gums that were chewed three times daily. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the notion that food preferences are modulated by exposure, odor pleasantness increased between the sessions independently of whether the odor (basil or orange flower) had been presented with or without sucrose. However, we found no evidence of associative learning in any of the tasks. In addition, exploratory equivalence tests suggested that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that the hypothesized effects of associative learning are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to evaluate the relative support for these explanations and, if experimental conditions can be identified that reliably produce such effects, to identify factors that regulate the formation of new odor-taste associations.

Perspective: Measuring Sweetness in Foods, Beverages, and Diets: Toward Understanding the Role of Sweetness in Health

Various global public health agencies recommend minimizing exposure to sweet-tasting foods or beverages. The underlying rationale is that reducing exposure to the perception of sweet tastes, without regard to the source of sweetness, may reduce preferences for sweetness, added sugar intake, caloric intake, and body weight. However, the veracity of this sequence of outcomes has yet to be documented, as revealed by findings from recent systematic reviews on the topic. Efforts to examine and document the effects of sweetness exposure are needed to support evidence-based recommendations. They require a generally agreed-upon methodology for measuring sweetness in foods, beverages, and the overall diet. Although well-established sensory evaluation techniques exist for individual foods in laboratory settings, they are expensive and time-consuming, and agreement on the optimal approach for measuring the sweetness of the total diet is lacking. If such a measure could be developed, it would permit researchers to combine data from different studies and populations and facilitate the design and conduct of new studies to address unresolved research questions about dietary sweetness. This narrative review includes an overview of available sensory techniques, their strengths and limitations, recent efforts to measure the sweetness of foods and diets across countries and cultures, and a proposed future direction for improving methods for measuring sweetness toward developing the data required to support evidence-based recommendations around dietary sweetness.

Adaptive weighting of taste and odor cues during flavor choice

Colloquially referred to as "taste," flavor is in reality a thoroughly multisensory experience. Yet, a mechanistic understanding of the multisensory computations underlying flavor perception and food choice is lacking. Here, we used a multisensory flavor choice task in rats to test specific predictions of the statistically optimal integration framework, which has previously yielded much insight into cue integration in other multisensory systems. Our results confirm three key predictions of this framework in the unique context of flavor choice behavior, providing novel mechanistic insight into multisensory flavor processing.NEW & NOTEWORTHY The authors demonstrate that rats make choices about which flavor solution (i.e., taste-odor mixture) to consume by weighting the individual taste and odor components according to the reliability of the information they provide about which solution is the preferred one. A similar weighting operation underlies multisensory cue combination in other domains and offers novel insight into the computations underlying multisensory flavor perception and food choice behavior.

Factors affecting flavor perception in space: Does the spacecraft environment influence food intake by astronauts?

The intention to send a crewed mission to Mars involves a huge amount of planning to ensure a safe and successful mission. Providing adequate amounts of food for the crew is a major task, but 20 years of feeding astronauts on the International Space Station (ISS) have resulted in a good knowledge base. A crucial observation from the ISS is that astronauts typically consume only 80% of their daily calorie requirements when in space. This is despite daily exercise regimes that keep energy usage at very similar levels to those found on Earth. This calorie deficit seems to have little effect on astronauts who spend up to 12 months on the ISS, but given that a mission to Mars would take 30 to 36 months to complete, there is concern that a calorie deficit over this period may lead to adverse effects in crew members. The key question is why astronauts undereat when they have a supply of food designed to fully deliver their nutritional needs. This review focuses on evidence from astronauts that foods taste different in space, compared to on Earth. The underlying hypothesis is that conditions in space may change the perceived flavor of the food, and this flavor change may, in turn, lead to underconsumption by astronauts. The key areas investigated in this review for their potential impact on food intake are the effects of food shelf life, physiological changes, noise, air and water quality on the perception of food flavor, as well as the link between food flavor and food intake.

Experience Informs Consummatory Choices for Congruent and Incongruent Odor-Taste Mixtures in Rats

Experience is an essential factor informing food choice. Eating food generates enduring odor-taste associations that link an odor with a taste's quality and hedonic value (pleasantness/unpleasantness) and creates the perception of a congruent odor-taste combination. Previous human psychophysical experiments demonstrate that experience with odor-taste mixtures shapes perceptual judgments related to the intensity, familiarity, and pleasantness of chemosensory stimuli. However, how these perceptual judgments inform consummatory choice is less clear. Using rats as a model system and a 2-bottle brief-access task, we investigated how experience with palatable and unpalatable odor-taste mixtures influences consummatory choice related to odor-taste congruence and stimulus familiarity. We found that the association between an odor and a taste, not the odor's identity or its congruence with a taste, informs consummatory choice for odor-taste mixtures. Furthermore, we showed that the association between an odor and a taste, not odor neophobia, informs consummatory choice for odors dissolved in water. Our results provide further evidence that the association between an odor and a taste, after odor-taste mixture experience, is a fundamental feature guiding consummatory choice.

Experience-Dependent c-Fos Expression in the Mediodorsal Thalamus Varies With Chemosensory Modality

The mediodorsal thalamus is a higher order thalamic nucleus critical for many cognitive behaviors. Defined by its reciprocal connections with the prefrontal cortex, the mediodorsal thalamus receives strong projections from chemosensory cortical areas for taste and smell, gustatory cortex and piriform cortex. Recent studies indicate the mediodorsal thalamus is involved in experience-dependent chemosensory processes, including olfactory attention and discrimination and the hedonic perception of odor-taste mixtures. How novel and familiar chemosensory stimuli are represented within this structure remains unclear. Here, we compared the expression of c-Fos in the mediodorsal thalami of rats familiar with an odor, a taste, or an odor-taste mixture with those that sampled the stimuli for the first time. We found that familiar tastes or odor-taste mixtures induced significantly greater c-Fos expression in the mediodorsal thalamus than novel tastes or odor-taste mixtures, whereas novel odors induced greater c-Fos expression than familiar odors. These experience-dependent and modality-specific differences in c-Fos expression may relate to the behavioral relevance of the chemosensory stimulus, including odor neophobia. In a two-bottle brief-access preference task, rats preferred water to isoamyl acetate-odorized water over multiple days. However, after experience with isoamyl acetate mixed with sucrose (odor-taste mixture), the preference for water was eliminated. These findings demonstrate that experience with chemosensory stimuli modulates responses in the mediodorsal thalamus, suggesting this structure plays an integral role in communicating behaviorally relevant chemosensory information to higher order areas to guide food-related behaviors.

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.

Effect of flavor on neuronal responses of the hypothalamus and ventral tegmental area

Although it is well known that food intake is affected by the palatability of food, the actual effect of flavoring on regulation of energy-homeostasis and reward perception by the brain, remains unclear. We investigated the effect of ethyl-butyrate (EB), a common non-caloric food flavoring, on the blood oxygen level dependent (BOLD) response in the hypothalamus (important in regulating energy homeostasis) and ventral tegmental area (VTA; important in reward processes). The 16 study participants (18-25 years, BMI 20-23 kg/m²) drank four study stimuli on separate visits using a crossover design during an fMRI setup in a randomized order. The stimuli were; plain water, water with EB, glucose solution (50gram/300 ml) and glucose solution with EB. BOLD responses to ingestion of the stimuli were determined in the hypothalamus and VTA as a measure of changes in neuronal activity after ingestion. In the hypothalamus and VTA, glucose had a significant effect on the BOLD response but EB flavoring did not. Glucose with and without EB led to similar decrease in hypothalamic BOLD response and glucose with EB resulted in a decrease in VTA BOLD response. Our results suggest that the changes in neuronal activity in the hypothalamus are mainly driven by energy ingestion and EB does not influence the hypothalamic response. Significant changes in VTA neuronal activity are elicited by energy combined with flavor.

Different Olfactory Percepts Evoked by Orthonasal and Retronasal Odorant Delivery

The Duality of Smell hypothesis suggests odorants delivered orthonasally elicit different sensations compared with those delivered retronasally despite activating the same receptors in the olfactory epithelium. Presently, we investigated this further using a matching paradigm free from odorant or semantic memory bias. Subjects were asked to evaluate an aroma delivered in one condition (orthonasal or retronasal delivery) and match the same aroma from 4 unknowns evaluated in the same or different delivery conditions. Panelists matched flavors in 4 delivery conditions: orthonasal-orthonasal, retronasal-retronasal, retronasal-orthonasal, and orthonasal-retronasal. For orthonasal presentation, panelists smelled samples using their nostrils, and for retronasal presentation, panelists swallowed aqueous flavors. In Experiment 1, panelists were instructed to match familiar flavors (banana, grape, orange, raspberry). In Experiments 2 and 3, panelists used the same experimental design with either 4 unfamiliar flavors (kinnow, longan, pawpaw, prunus) or 4 distinct subtypes of a strawberry flavor (woody, green, ripe, candy). In Experiment 1, the number of correct matches in each condition did not significantly differ suggesting stability in the perceptual construct across delivery routes. However, in Experiments 2 and 3, significantly more samples were correctly matched in the orthonasal-orthonasal and retronasal-retronasal conditions compared with the retronasal-orthonasal or orthonasal-retronasal conditions suggesting aroma perception is dependent on delivery route. Additionally, across the 4 delivery methods, the ability to correctly match flavors decreased as flavor familiarity decreased or similarity increased and may reflect the different cognitive strategies employed by subjects when matching these stimuli. Our results suggest odorant percepts are route-dependent and consistent with the Duality of Smell phenomenon.

Mammalian Taste Cells Express Functional Olfactory Receptors

The peripheral taste and olfactory systems in mammals are separate and independent sensory systems. In the current model of chemosensation, gustatory, and olfactory receptors are genetically divergent families expressed in anatomically distinct locations that project to disparate downstream targets. Although information from the 2 sensory systems merges to form the perception of flavor, the first cross talk is thought to occur centrally, in the insular cortex. Recent studies have shown that gustatory and olfactory receptors are expressed throughout the body and serve as chemical sensors in multiple tissues. Olfactory receptor cDNA has been detected in the tongue, yet the presence of physiologically functional olfactory receptors in taste cells has not yet been demonstrated. Here we report that olfactory receptors are functionally expressed in taste papillae. We found expression of olfactory receptors in the taste papillae of green fluorescent protein-expressing transgenic mice and, using immunocytochemistry and real-time quantitative polymerase chain reaction experiments, the presence of olfactory signal transduction molecules and olfactory receptors in cultured human fungiform taste papilla (HBO) cells. Both HBO cells and mouse taste papilla cells responded to odorants. Knockdown of adenylyl cyclase mRNA by specific small inhibitory RNA and pharmacological block of adenylyl cyclase eliminated these responses, leading us to hypothesize that the gustatory system may receive olfactory information in the periphery. These results provide the first direct evidence of the presence of functional olfactory receptors in mammalian taste cells. Our results also demonstrate that the initial integration of gustatory and olfactory information may occur as early as the taste receptor cells.

Associations between olfactory pathway gene methylation marks, obesity features and dietary intakes

Background

Olfaction is an important sense influencing food preferences, appetite, and eating behaviors. This hypothesis-driven study aimed to assess associations between olfactory pathway gene methylation signatures, obesity features, and dietary intakes.

Methods

A nutriepigenomic analysis was conducted in 474 adults from the Methyl Epigenome Network Association (MENA) project. Anthropometric measurements, clinical data, and serum metabolic profiles of the study population were obtained from structured databases of the MENA cohorts. Habitual dietary intake was assessed using a validated semiquantitative food frequency questionnaire. DNA methylation was measured in circulating white blood cells by microarray (Infinium Human Methylation 450 K BeadChips). FDR values (p < 0.0001) were used to select those CpGs that showed the best correlation with body mass index (BMI) and waist circumference (WC). Pathway analyses involving the characterization of genes involved in the olfactory transduction system were performed using KEGG and pathDIP reference databases.

Results

Overall, 15 CpG sites at olfactory pathway genes were associated with BMI (p < 0.0001) and WC (p < 0.0001) after adjustments for potential confounding factors. Together, methylation levels at the15 CpG sites accounted for 22% and 20% of the variability in BMI and WC (r² = 0.219, p < 0.001, and r² = 0.204, p < 0.001, respectively). These genes encompassed olfactory receptors (OR4D2, OR51A7, OR2T34, and OR2Y1) and several downstream signaling molecules (SLC8A1, ANO2, PDE2A, CALML3, GNG7, CALML6, PRKG1, and CAMK2D), which significantly regulated odor detection and signal transduction processes within the complete olfactory cascade, as revealed by pathway enrichment analyses (p = 1.94 × 10^–10). Moreover, OR4D2 and OR2Y1 gene methylation patterns strongly correlated with daily intakes of total energy (p < 0.0001), carbohydrates (p < 0.0001), protein (p < 0.0001), and fat (p < 0.0001).

Conclusions

The results of this study suggest novel relationships between olfactory pathway gene methylation signatures, obesity indices, and dietary intakes.

Differential Effects of BMI on Brain Response to Odor in Olfactory, Reward and Memory Regions: Evidence from fMRI

：Obesity has reached epidemic proportions, motivating research into the underlying mechanisms. Olfaction is a powerful mediator of food consumption, and obesity has been associated with altered olfactory sensitivity. The current study used an event-related functional magnetic resonance imaging (fMRI) to examine the central processing of odor in humans to gain insight into the effect of the body mass index (BMI) on the neural processes involved in rating the pleasantness of a food odor during a hunger state and in a satiety state. We hypothesized that, during the hedonic evaluation of food odor, BMI would be associated with differences in brain activation within olfactory and higher order processing areas important for perception, reward, and memory. We report novel findings of a dissociation between the relationship between BMI and activation in reward areas and in olfactory and odor memory areas, i.e., activation in reward areas decreased as BMI increased, whereas activation in primary olfactory and memory regions increased as BMI increased. A greater BMI is associated with decreased activation in the reward and frontal regions, supporting a blunted reward response in obesity. These findings have important potential implications for decision making, response inhibition, and reward-based behaviors that may play key roles as causal and maintenance factors in obesity. In contrast, a greater BMI is associated with an increased activation in the primary olfactory and memory areas, which was observed during a hunger state. These results raise the speculative hypothesis that high BMI may be associated with hyperactivation in the olfactory and memory areas, and that over time, the resulting excitotoxic effects may contribute to neurodegenerative changes in these areas.

Visual-Olfactory Interactions: Bimodal Facilitation and Impact on the Subjective Experience

Odors are inherently ambiguous and therefore susceptible to redundant sensory as well as context information. The identification of an odor object relies largely on visual input. Thus far, it is unclear whether visual and olfactory stimuli are indeed integrated at an early perceptual stage and which role the congruence between the visual and olfactory inputs plays. Previous studies on visual-olfactory interaction used either congruent or incongruent information, leaving it open whether nuances of visual-olfactory congruence shape perception differently. We aimed to answer 1) whether visual-olfactory information is integrated at early stages of processing, 2) whether visual-olfactory congruence is a gradual or dichotomous phenomenon, and 3) whether visual information influences bimodal stimulus evaluation and odor identity. We found a bimodal response time speedup that is consistent with parallel processing according to race models. Subjectively, pleasantness of bimodal stimuli increased with increasing congruence, and orange images biased odor composition toward orange. Visual-olfactory congruence was perceived in gradual and distinct categories, consistent with the notion that congruence is a gradual phenomenon. Together, the data provide evidence for bimodal facilitation consistent with parallel processing of the visual and olfactory stimuli, and that visual-olfactory interactions influence various levels of the subjective experience.

Effects of Varying the Color, Aroma, Bitter, and Sweet Levels of a Grapefruit-Like Model Beverage on the Sensory Properties and Liking of the Consumer

Color, aroma, sweet, and bitter tastes contribute to the sensory perception of grapefruit juice. Consumers differ about liking grapefruit. A reason is the bitter taste that characterize the fruit. The objective was to determine the effect of varying the color (red or yellow), aroma (two levels), bitterness (three levels), and sweetness (three levels) of a grapefruit-like model beverage, on consumers’ liking and perception of its sensory properties. The sensory profiles of thirty-six grapefruit-like beverages, created on the basis of a factorial design, has been described. Consumers rated their liking of color, aroma, and flavor of the twelve most diverse beverages. Bitter and sweet levels of the beverages had a significant effect on the flavor and aftertaste attributes. Aroma concentration had a significant effect on the majority of the sensory attributes. Color had a significant effect on perception of some of the aroma attributes, as well as the grapefruit’s flavor intensity. Consumers liked the red beverages more than the yellow ones, and those with low aroma over the high aroma intensity. Consumers preferred the low bitter/high sweet beverages. Pungent and grapefruit aroma were found to be negative drivers for liking of the aroma. Sweet and citrus flavors were found to be positive drivers and sour and bitter flavors were found to be negative drivers of flavor-preferences (or liking) of the tested beverages.

Interactions of Lemon, Sucrose and Citric Acid in Enhancing Citrus, Sweet and Sour Flavors

Flavorants such as lemon extract that activate olfactory receptors may also evoke or enhance flavor qualities such as sour and sweet that are typically considered gustatory. Similarly, flavorants such as sucrose and citric acid that activate gustatory receptors may enhance flavors such as citrus that are typically considered olfactory. Here, we ask how lemon extract, sucrose, and citric acid, presented separately and together, affect sweet, sour, and citrus flavors. We accomplished this by testing, in the same 12 subjects, lemon extract and sucrose (Experiment 1), lemon extract and citric acid (Experiment 2), and lemon extract, sucrose, and citric acid (Experiment 3). Results showed that both lemon extract and citric acid increased the ratings of citrus and sour intensity. Lemon extract did not affect sweet, but citric acid did, mainly in Experiment 3. Sucrose systematically increased only sweet intensity and modulated the effect of lemon extract on sour. The most robust multiquality effect was the enhancement of sour by lemon extract. These outcomes suggest, first, a role played by experience with the statistical associations of gustatory and olfactory flavorants and, second, that lemon flavor is complex, having citrus and sour qualities that may not be fully separable in perception.