The neurocognitive bases of human multimodal food perception: sensory integration

Brain mechanisms of oral multisensory processing related to oral health: a systematic review of neuroimaging findings

AIM

Oral functions related to eating, including mastication, swallowing, and taste, are fundamentally a multisensory experience that relies on the crossmodal interaction of touch, gustation, temperature, pain, and proprioception. The brain mechanisms of oral multisensory processing related to eating have remained unknown.

METHODS

The current systematic review summarizes the findings from neuroimaging studies (mainly functional magnetic resonance imaging) focusing on the interaction of multiple sensory stimuli in human participants. Neuroimaging studies of human adults on the interaction between multiple sensory stimuli related to oral functions were identified and extracted via three electronic databases and reviewed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

RESULTS

Thirteen primary studies were eligible to be included in this review. Five studies investigated the interaction of intraoral (i.e., sensorimotor, taste, and noxious) stimuli. Six studies investigated the interaction between intraoral and extraoral (i.e., auditory, olfactory, and visual) stimuli. One study investigated the audio-visual interaction on dental fear, and another study investigated sensorimotor processing of eating tools. The studies showed great diversity in the experimental design of crossmodal interaction. Regarding the brain features related to the interaction, the somatosensory and motor regions were mostly reported in the studies.

CONCLUSIONS

The systematic review revealed a complex pattern of brain activation of oral multisensory processing, which can be attributed to the diversity in the experimental design of crossmodal interaction. The findings highlight the role of multisensory integration in maintaining oral health.

Perceived food value depends on display format, preference strength, and physical accessibility

In everyday life, dietary decisions are made in response to real foods, such as at the grocery store or cafe. In stark contrast, decision-making studies in the laboratory typically measure responses to food stimuli presented as two-dimensional pictures or computer images, with the assumption that artificial displays are adequate substitutes for their real-world counterparts. Yet accumulating evidence challenges this view, including studies showing that willingness-to-pay (WTP) is higher for foods displayed as real objects versus images -a phenomenon known as the "real object advantage" in valuation. Here, we examined whether the "real object advantage" is modulated by accessibility to the stimuli, subjective food preference, or interactions between these factors. Participants placed monetary bids on snack foods displayed as real objects or computer images. Critically, on half of the trials, a transparent barrier was positioned between the participant and the stimulus. Linear mixed-effects modeling analysis revealed that, overall, WTP was ∼7 % higher for foods displayed as real objects versus images; however, this effect emerged only for foods of moderate (but not strong) preference strength. WTP was also higher when the stimuli appeared unoccluded versus behind the barrier, but this was equally so for real objects and images, suggesting that the barrier's effect on valuation was not related to stimulus actability. Our findings suggest that while eliminating perceived barriers to a good can bolster valuation regardless of display format, presenting real foods may nevertheless increase valuation and encourage healthy dietary choices.

Perceptual Complexity as Normalized Shannon Entropy

Complexity is one of the most important variables in how the brain performs decision making based on esthetic values. Multiple definitions of perceptual complexity have been proposed, with one of the most fruitful being the Normalized Shannon Entropy one. However, the Normalized Shannon Entropy definition has theoretical gaps that we address in this article. Focusing on visual perception, we first address whether normalization fully corrects for the effects of measurement resolution on entropy. The answer is negative, but the remaining effects are minor, and we propose alternate definitions of complexity, correcting this problem. Related to resolution, we discuss the ideal spatial range in the computation of spatial complexity. The results show that this range must be small but not too small. Furthermore, it is suggested by the analysis of this range that perceptual spatial complexity is based solely on translational isometry. Finally, we study how the complexities of distinct visual variables interact. We argue that the complexities of the variables of interest to the brain's visual system may not interact linearly because of interclass correlation. But the interaction would be linear if the brain weighed complexities as in Kempthorne's λ-Bayes-based compromise problem. We finish by listing several experimental tests of these theoretical ideas on complexity.

The processing of shaking and standing improves the taste quality of summer black tea

Shaking and standing (SS) enhances the aroma intensity and quality of black tea (BT). However, its contribution to the taste remains unknown, and the interaction mechanism between the aroma and taste perception of black tea is also undisclosed. Here, the metabolomics and sensory evaluation-assisted flavor analysis were employed to investigate the changes in non-volatiles induced by SS, and the interaction mechanism between aroma and taste perception. SSBT exhibited considerable reduced bitterness and astringency intensities compared to BT. Notably, the concentrations of contributing compounds such as catechins, proanthocyanidins, theaflavins, anthocyanins, and flavonol glycosides were decreased in SSBT. Sensory experiments further revealed that nine floral and sweet odorants in SSBT exhibited odor-enhancing interactions. Molecular docking validated the binding affinity and interaction forces between mono/di-ligands and OR1G1/OR52D1. Furthermore, the presence of the nine odorants exerted inhibitory effects on the bitterness and astringency of SSBT. These findings provide a novel perspective on the formation of flavor in SSBT.

Gustatory-Visual Interaction in Human Brain Cortex: fNIRS Study

BACKGROUND

Many studies, for example, on taste-visual dissonance, have shown that the influence of the visual cortex on taste sensation is enormous. The presented work aims to investigate, using fNIRS, whether a taste stimulus, in this case, the taste of bitter, also causes stimulation of the visual cortex in the fNIRS study.

METHODS

fNIRS was used to examine 51 participants (204 examinations, 9996 records), collecting signals from the left hemisphere. Differences between the maximum and minimum changes in oxyHb concentrations (ΔoxyHb) for the areas of the brain cortex considered responsible for recording visual and gustatory signals were analyzed. Protocols I, II, III, and IV-activation with distillate water, coffee with lower concentration, reference (no stimulation), and coffee with higher concentration, respectively, were used.

RESULTS

We recorded high signals for teste activation on channels covering the gustatory cortex, which confirms the correctness of the choice of research method. As expected, a significant statistical difference was observed between protocols I, II, and IV and reference III (without stimulation). What seems important is the fact that we also received high signals for the channels 45-49, which cover the visual cortex. The statistical analysis shows no differences between protocols I, II, and IV (different taste activation-water, coffee A, and coffee B) for specific channels for analyzing regions of interest. As a result of the analysis of the correlation between the subjective bitterness assessment solutions and the signal ΔoxyHb height, it was observed that a statistically significant correlation, although weak, occurs only for 14 and gustatory channels, only for coffee with a higher concentration. Additionally, the only statistically significant difference between women and men was observed in Protocol I (water), where the ΔoxyHb signal was twice as high in women compared to men.

CONCLUSIONS

In conclusion, we can clearly state that the senses of sight and taste work closely together. Moreover, this cooperation is not one-sided: while visual activation influences taste perception, interestingly, a taste stimulus can also generate a hemodynamic response, activating the visual cortex.

The Impact of Artificial and Natural Additives in Meat Products on Neurocognitive Food Perception: A Narrative Review

The holistic sensory experience creates a unified perception that influences consumer memory. Consumer interest in clean label products underlines an accelerated trend towards products without artificial additives. From a sensory point of view, food appeal is significantly influenced by how additives actively participate in the organoleptic properties of the final product. This research aims to shed light on the impact of artificial and natural additives in meat products on neurocognitive food perception, which is essential for understanding how they influence the consumer's final decision and direct food trends. Different neural mechanisms involved in multimodal sensory integration confirm differences in perception of meat products containing artificial and natural additives. Analysis confirms that neurocognitive perception integrates organoleptic sensations to form a complete sensory experience. The encephalon simultaneously processes multimodally integrated stimuli from organoleptic properties, reaching the orbitofrontal cortex and other regions involved in the neuroprocessing of the final product. The reformulation and development of meat products need a detailed analysis of the impact of additives on sensory properties contributing to the shaping of consumption trends.

Cross-modal representation of chewing food in posterior parietal and visual cortex

Even though the oral cavity is not visible, food chewing can be performed without damaging the tongue, oral mucosa, or other intraoral parts, with cross-modal perception of chewing possibly critical for appropriate recognition of its performance. This study was conducted to clarify the relationship of chewing food cross-modal perception with cortex activities based on examinations of the posterior parietal cortex (PPC) and visual cortex during chewing in comparison with sham chewing without food, imaginary chewing, and rest using functional near-infrared spectroscopy. Additionally, the effects of a deafferent tongue dorsum on PPC/visual cortex activities during chewing performance were examined. The results showed that chewing food increased activity in the PPC/visual cortex as compared with imaginary chewing, sham chewing without food, and rest. Nevertheless, those activities were not significantly different during imaginary chewing or sham chewing without food as compared with rest. Moreover, subjects with a deafferent tongue dorsum showed reduced PPC/visual cortex activities during chewing food performance. These findings suggest that chewing of food involves cross-modal recognition, while an oral somatosensory deficit may modulate such cross-modal activities.

Flavor and taste recognition impairments in people with type 1 diabetes

BACKGROUND/OBJECTIVES

Adherence to dietary recommendations is a critical component in the management of type 1 diabetes (T1D). Taste and flavor significantly influence food choices. The aim of this study was to investigate taste sensitivity and flavor recognition ability in adults with T1D compared to healthy individuals.

SUBJECTS/METHODS

Seventy-two people with T1D and 72 matched healthy controls participated in the study. Participants underwent the gustometry test for sweet, sour, salty, and bitter tastes and the flavor test, which consisted of oral administration of aqueous aromatic solutions identifying 21 different compounds.

RESULTS

Participants with T1D had significantly lower flavor scores and gustometry scores than controls (p < 0.0001 and p = 0.0063, respectively). T1D individuals showed a lower perception of sour, bitter and salty tastes than controls, while the perception of sweet taste was similar. The sex differences and age-related decline in flavor perception observed in controls were not present in the participants with T1D. Neither BMI nor disease-related parameters such as fasting blood glucose on the day of the study, glycosylated hemoglobin, age at onset of diabetes, duration of diabetes, or type of insulin treatment (insulin pump or multiple daily injections) correlated with flavor and taste perception in the T1D participants.

CONCLUSIONS

Flavor and taste perception are impaired in adults with T1D, potentially affecting dietary adherence and food choices. This highlights the need for further research into the mechanisms underlying sensory changes in T1D and emphasizes the importance of targeted dietary interventions to improve health outcomes and quality of life in this population.

The impact of premature birth on auditory-visual processes in very preterm schoolchildren

Interactions between stimuli from different sensory modalities and their integration are central to daily life, contributing to improved perception. Being born prematurely and the subsequent hospitalization can have an impact not only on sensory processes, but also on the manner in which information from different senses is combined-i.e., multisensory processes. Very preterm (VPT) children (<32 weeks gestational age) present impaired multisensory processes in early childhood persisting at least through the age of five. However, it remains largely unknown whether and how these consequences persist into later childhood. Here, we evaluated the integrity of auditory-visual multisensory processes in VPT schoolchildren. VPT children (N = 28; aged 8-10 years) received a standardized cognitive assessment and performed a simple detection task at their routine follow-up appointment. The simple detection task involved pressing a button as quickly as possible upon presentation of an auditory, visual, or simultaneous audio-visual stimulus. Compared to full-term (FT) children (N = 23; aged 6-11 years), reaction times of VPT children were generally slower and more variable, regardless of sensory modality. Nonetheless, both groups exhibited multisensory facilitation on mean reaction times and inter-quartile ranges. There was no evidence that standardized cognitive or clinical measures correlated with multisensory gains of VPT children. However, while gains in FT children exceeded predictions based on probability summation and thus forcibly invoked integrative processes, this was not the case for VPT children. Our findings provide evidence of atypical multisensory profiles in VPT children persisting into school-age. These results could help in targeting supportive interventions for this vulnerable population.

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.

Theory of Food: Unravelling the Lifelong Impact of Childhood Dietary Habits on Adult Food Preferences across Different Diet Groups

The study investigates the behavioral manifestations of the "Theory of Food" (ToF), a novel theoretical framework centered on the early development of food perceptions. The ToF posits that childhood experiences with food shape cognitive networks influencing adult dietary choices. Stemming from the "Theory of Mind," the ToF hypothesizes that individuals construct an associative world of food images and representations mirroring the socio-cognitive world shaped by proper theory of mind development. The study, involving 249 healthy adults, employs the Cognitive Food Preference Questionnaire (CFPQ) and the Adult Food Preference Profile (AFPP) to explore the correlation between childhood and adult food preferences across diet groups (omnivores, vegetarians, and vegans). Results reveal robust correlations in omnivores, varied patterns in vegetarians, and mixed outcomes in vegans. Notably, omnivores show correlations in grains, fast food, dairy products, vegetables, meat, soft drinks, and snack consumption. Vegetarians exhibit correlations in grains, fast food, dairy products, vegetables, snacks, and, surprisingly, meat consumption. Vegans display correlations in grains, fast food, vegetables, and snacks. The study suggests that childhood dietary habits tend to influence adult food choices, offering insights for future research in the field of theory of food (ToF).

A quantitative information measure applied to texture perception attributes during mastication

We have calculated an entropy or information measure of previously reported experimentally determined temporal dominance of sensations (TDS) data of texture attributes for two sets of emulsion filled gels throughout the mastication cycle. The samples were emulsion filled gels and two-layered emulsion filled gels. We find that the entropy measure follows an average curve, which is different for each set. The specifics of the entropy curve may serve as a fingerprint for the perception of a specific food sample.

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.

The Interaction Relationship of Aroma Components Releasing with Saliva and Chewing Degree during Grilled Eels Consumption

The interaction perception between aroma and oral chewing during food consumption has always been a hot topic in exploring consumers' preferences and purchase desires. A chewing simulation system was set to find out the effect of key saliva components and chewing time on odorants released with grilled eel meat. Odor release did not always enhance with the degree of chewing, or the amount of saliva released. The breaking up of the tissue structure of the fish meat by the teeth encourages the release of odorants and the participation of saliva partially blocks this process. The release of pyrazine, alcohol, and acid compounds in grilled eel meat peaked within 20-60 s after chewing. Sufficient exposure of saliva to grilled eel meat will inhibit aromatic, ketone, ester, hydrocarbon, and sulfur compounds release. 3-methyl-2-butanol contributed to the subtle aroma differences that arise before and after eating grilled eel meat. Naphthalene, 2-acetylthiazole, 2-decenal, 2-undecanone, 5-ethyldihydro-2(3H)-furanone were the main odorants released in large quantities in the early stages of eating grilled eel and affected the top note. Consequently, the results provided the odorants information in aroma perception during grilled eel consumption and benefited the objective evaluation of grilled eel product optimization.

Dedicated odor-taste stimulation design for fMRI flavor studies

BACKGROUND

Flavor is a mental representation that results from the brain's integration of at least odor and taste, and fMRI can highlight brain-related areas. However, delivering stimuli during fMRI can be challenging especially when administrating liquid stimuli in supine position. It remains unclear how and when odorants are released in the nose and how to improve odorant release.

NEW METHOD

We used a proton transfer reaction mass spectrometer (PTR-MS) to monitor the in vivo release of odorants via the retronasal pathway during retronasal odor-taste stimulation in a supine position. We tested techniques to improve odorant release, including avoiding or delaying swallowing and velum open training (VOT).

RESULTS

Odorant release was observed during retronasal stimulation, before swallowing, and in a supine position. VOT did not improve odorant release. Odorant release during stimulation had a latency more optimal for fitting with BOLD timing than after swallowing.

COMPARISON WITH EXISTING METHOD(S)

Previous in vivo measurements of odorant release under fMRI-like conditions showed that odorant release occurred only after swallowing. On the contrary, a second study found that aroma release could occur before swallowing, but participants were sitting.

CONCLUSION

Our method shows optimal odorant release during the stimulation phase, meeting the criteria for high-quality brain imaging of flavor processing without swallowing-related motion artifacts. These findings provide an important advancement in understanding the mechanisms underlying flavor processing in the brain.

The psychological basis of reductions in food desire during satiety

Satiety-the reduced desire to eat, drink or have sex in their respective aftermath-is particularly important for feeding, where it assists energy balance. During satiety, the anticipated pleasure of eating is far less than the actual pleasure of eating. Here we examine two accounts of this effect: (i) satiety signals inhibit retrieval of pleasant food memories that form desirable images, allowing unpleasant memories into mind; (ii) feelings of fullness reflect what eating would be like now, negating the need for imagery. To test these accounts, participants undertook two tasks pre- and post-lunch: (i) judging desire for palatable foods either with or without imagery impairing manipulations; (ii) explicitly recollecting food memories. Impairing imagery reduced desire equally, when hungry and sated. Food-memory recollections became more negative/less positive when sated, with this correlating with changes in desire. These findings support the first account and suggest imagery is used when hungry and when sated to simulate eating, and that the content of these memory-based simulations changes with state. The nature of this process and its implications for satiety more generally are discussed.

Healthcare Professionals' Perceptions of Stabilized Edible Foam with Adults with Severe Dysphagia; an exploratory study: Use of stabilized edible foam with adults with dysphagia: Use of stabilized edible foam with adults with dysphagia

BACKGROUND

Improving the quality of life for individuals with severe dysphagia is a priority when considering new areas of dysphagia management, especially if this increases opportunities to participate in social activities associated with eating and drinking. Edible foam is widely researched and available in the food industry; however, the use of edible foam within the field of dysphagia remains unexplored. Despite no research published on effectiveness and safety, a commercial product currently on the market is widely distributed across both Europe and the UK, including 28 NHS Trusts, suggesting that it is increasingly being used in clinical practice.

AIMS

To explore the perceptions and experiences of healthcare professionals on the use of stabilized edible foam (SEF) with adults with severe dysphagia in order to inform areas for future research in this novel dysphagia intervention.

METHODS & PROCEDURES

Healthcare professionals were recruited using purposeful sampling and snowballing technique. A total of 56 healthcare professionals were initially approached, of which 10 completed the semi-structured interviews. Interview questions were developed from a topic guide and a pilot questionnaire.

OUTCOMES & RESULTS

Thematic analysis was used to identify three themes: potential impact, consideration of risk and perceived experiences. Overarching each of these themes was the element of the unknown.

CONCLUSIONS & IMPLICATIONS

Use of SEF with adults with dysphagia is in its infancy. Whilst results indicate that some clinicians are embracing this novel approach, others express concerns. Therefore, further research is needed, particularly in relation of direct experience of individuals and contra-indications.

WHAT THIS PAPER ADDS

What is already known on the subject The use of SEF with individuals with swallowing problems is a relatively novel area of dysphagia intervention in the UK. There are currently no published studies on its effectiveness and safety profile. What this paper adds to existing knowledge This study provides valuable preliminary work into the area of SEF and adults with severe dysphagia, capturing the experience and perceptions of healthcare professions who have an awareness of SEF. What are the potential or actual clinical implications of this work? Increasing clinicians and researcher's awareness of this novel area of dysphagia management.

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.

Insights into the flavor perception and enhancement of sodium-reduced fermented foods: A review

Salt (sodium chloride, NaCl) is a vital ingredient in fermented foods, which affects their safety, texture, and flavor characteristics. Recently, the demand for reduced-sodium fermented foods has increased, as consumers have become more health-conscious. However, reducing sodium content in fermented foods may negatively affect flavor perception, which is a critical quality attribute of fermented foods for both the food industry and consumers. This review summarizes the role of salt in the human body and foods and its role in the flavor perception of fermented foods. Current sodium reduction strategies used in the food industry mainly include the direct stealth reduction of NaCl, substituting NaCl with other chloride salts, and structure modification of NaCl. The odor-induced saltiness enhancement, application of starter cultures, flavor enhancers, and non-thermal processing technology are potential strategies for flavor compensation of sodium-reduced fermented foods. However, reducing sodium in fermented food is challenging due to its specific role in flavor perception (e.g., promoting saltiness and volatile compound release from food matrices, inhibiting bitterness, and changing microflora structure). Therefore, multiple challenges must be addressed in order to improve the flavor of low-sodium fermented foods. Future studies should thus focus on the combination of several strategies to compensate for the deficiencies in flavor resulting from sodium reduction.

Chemosensory Contributions of E-Cigarette Additives on Nicotine Use

While rates of smoking combustible cigarettes in the United States have trended down in recent years, use of electronic cigarettes (e-cigarettes) has dramatically increased, especially among adolescents. The vast majority of e-cigarette users consume "flavored" products that contain a variety of chemosensory-rich additives, and recent literature suggests that these additives have led to the current "teen vaping epidemic." This review, covering research from both human and rodent models, provides a comprehensive overview of the sensory implications of e-cigarette additives and what is currently known about their impact on nicotine use. In doing so, we specifically address the oronasal sensory contributions of e-cigarette additives. Finally, we summarize the existing gaps in the field and highlight future directions needed to better understand the powerful influence of these additives on nicotine use.

Improving the flavor of summer green tea (Camellia sinensis L.) using the yellowing process

Summer green tea (SGT) has poor flavor due to its high levels of bitterness and astringency. The present study aimed to improve the flavor of SGT using the yellowing process. The results showed that after the yellowing process, the sweetness and overall acceptability increased, and the content of gallated catechins and flavonol glycosides decreased by 30.2% and 27.4%, respectively, as did the bitterness and astringency of SGT. Yellowing caused a decrease in the concentration of some aroma compounds, such as (z)-3-hexen-1-ol, 1-hexanol, pentanal, heptanal and 1-octanol, which caused grassy, floral and fruity aromas. In contrast, the concentrations of 1-octen-3-ol, benzene acetaldehyde and β-ionone increased, which have mushroom and sweet aromas. Meanwhile, the sweetness and umami of SGT were enhanced by the addition of selected aroma compounds (1-octen-3-ol, benzene acetaldehyde and β-ionone), demonstrating that the yellowing process improves the flavor of SGT through odor-taste interactions.

A preliminary study on the impact of contextual information regarding the origin of food on consumers’ judgments and skin conductance responses

Explicit and implicit responses to food and beverage are known to be modulated by expectations generated by contextual factors. Among these, labelling regarding the country of origin has been systematically shown to impact on consumers' evaluations of products. However, it is not clear yet whether the presence of food origin biases also affects humans’ physiological (i.e., implicit) responses, as well as whether different conditions of sensory appreciation of products are equally influenced. The present preliminary study investigated the psychophysiological responses to food samples paired to labels of declared (i.e., Italy, Spain/Germany, EU) or undeclared origins. Food items (i.e., olives and cracker) were presented in visual or taste conditions to thirty Italian participants, whose behavioral (i.e., liking, willingness to buy, and estimated cost) and physiological (i.e., skin conductance responses) responses were collected. The results indicated that the food samples elicited stronger liking and willingness to buy responses by participants and were estimated as more expensive, when being firstly experienced through vision than taste. No differences in the physiological arousal state were found as a function of food origin or sensory condition of presentation.

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Explicit choices related to food are modulated by expectation generated by contextual factors.

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Labelling regarding the country-of-origin impacts the consumer evaluations of products.

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The study investigated the behavioral and psychophysiological responses to food products comparing different labelling.

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Food items were presented in visual or taste conditions.

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The sensory modalities and the labeling information affect the behavioral choice (but not the physiological response).

Taste of Fat and Obesity: Different Hypotheses and Our Point of View

Obesity results from a temporary or prolonged positive energy balance due to an alteration in the homeostatic feedback of energy balance. Food, with its discriminative and hedonic qualities, is a key element of reward-based energy intake. An alteration in the brain reward system for highly palatable energy-rich foods, comprised of fat and carbohydrates, could be one of the main factors involved in the development of obesity by increasing the attractiveness and consumption of fat-rich foods. This would induce, in turn, a decrease in the taste of fat. A better understanding of the altered reward system in obesity may open the door to a new era for the diagnosis, management and treatment of this disease.

The role of viscosity in flavor preference: plasticity and interactions with taste

The brain combines gustatory, olfactory, and somatosensory information to create our perception of flavor. Within the somatosensory modality, texture attributes such as viscosity appear to play an important role in flavor preference. However, research into the role of texture in flavor perception is relatively sparse, and the contribution of texture cues to hedonic evaluation of flavor remains largely unknown. Here, we used a rat model to investigate whether viscosity preferences can be manipulated through association with nutrient value, and how viscosity interacts with taste to inform preferences for taste + viscosity mixtures. To address these questions, we measured preferences for moderately viscous solutions prepared with xanthan gum using 2-bottle consumption tests. By experimentally exposing animals to viscous solutions with and without nutrient value, we demonstrate that viscosity preferences are susceptible to appetitive conditioning. By independently varying viscosity and taste content of solutions, we further show that taste and viscosity cues both contribute to preferences for taste + viscosity mixtures. How these 2 modalities are combined depended on relative palatability, with mixture preferences falling in between component preferences, suggesting that hedonic aspects of taste and texture inputs are centrally integrated. Together, these findings provide new insight into how texture aspects of flavor inform hedonic perception and impact food choice behavior.

Effects of psychological, sensory, and metabolic energy prime manipulation on the acute endocrine stress response in fasted women

The stress response supports survival through energy mobilization. Paradoxically, a low blood glucose level dampens the endocrine stress response, and sugar consumption prior to stress restores it. Thus, energy availability may play a causal role in the endocrine stress response. Yet, it has never been tested whether sweet taste or expectations towards a drink content modulate the stress response. We investigated the potential role of sweetness, energy load and expectations towards energy load of a drink consumed prior to stress in restoring stress reactivity after fasting. N = 152 women (meanage=21.53, sdage=2.61) participated in the Trier Social Stress Test for groups in the morning after an overnight fast. Prior to stress induction, participants consumed a drink containing saccharose (sugar, n = 51), an equally sweet drink containing non-caloric sweetener (sweetener, n = 46), or water (n = 56). Additionally, participants in the sugar and sweetener group (n = 97) were informed whether or not their drink contained any calories (energy prime), which was deceptive in 50% of the cases. Eight salivary cortisol (-30, -20, -10, 0, +12, +25, +35, +45 min) and three blood glucose samples (-30, 0, +25 min) were assessed throughout the experiment. The effects of the experimental manipulations on cortisol trajectories were tested using multilevel mixed models. We found that compared with water, sugar and sweetener both significantly increased cortisol stress reactivity and with comparable intensity. However, our sensitivity analysis revealed a significant effect of sugar on cortisol trajectories compared to water and to sweetener. Drink-induced changes in blood glucose concentration were not associated with increases in cortisol. The energy prime did not affect the stress response. Overall, we could replicate the boosting effect of sugar consumption in a female sample after 8 h of fasting. The specific contribution of sweet taste and metabolic hormones to this boosting effect should be tested more rigorously in sex-balanced designs in the future.

Olfaction in the Multisensory Processing of Faces: A Narrative Review of the Influence of Human Body Odors

A recent body of research has emerged regarding the interactions between olfaction and other sensory channels to process social information. The current review examines the influence of body odors on face perception, a core component of human social cognition. First, we review studies reporting how body odors interact with the perception of invariant facial information (i.e., identity, sex, attractiveness, trustworthiness, and dominance). Although we mainly focus on the influence of body odors based on axillary odor, we also review findings about specific steroids present in axillary sweat (i.e., androstenone, androstenol, androstadienone, and estratetraenol). We next survey the literature showing body odor influences on the perception of transient face properties, notably in discussing the role of body odors in facilitating or hindering the perception of emotional facial expression, in relation to competing frameworks of emotions. Finally, we discuss the developmental origins of these olfaction-to-vision influences, as an emerging literature indicates that odor cues strongly influence face perception in infants. Body odors with a high social relevance such as the odor emanating from the mother have a widespread influence on various aspects of face perception in infancy, including categorization of faces among other objects, face scanning behavior, or facial expression perception. We conclude by suggesting that the weight of olfaction might be especially strong in infancy, shaping social perception, especially in slow-maturing senses such as vision, and that this early tutoring function of olfaction spans all developmental stages to disambiguate a complex social environment by conveying key information for social interactions until adulthood.

Peri-threshold Trigeminal Stimulation with Capsaicin Increases Taste Sensitivity in Humans

Introduction

Taste perception is affected by trigeminal stimuli, i.e., capsaicin. This has been studied at suprathreshold concentrations. However, little is known about taste perception at threshold level in the presence of low concentration of capsaicin. The aim of the study was to explore whether taste sensitivity for sweet, sour, salt, bitter, and umami is modulated by the presence of capsaicin in the peri-threshold range.

Methods

Fifty-seven adults (age range 19–85 years; 32 women) with functional gustation participated in the study. Based on their perception of phenylthiocarbamide (PTC), the group was stratified into non-tasters (n = 20) and tasters (n = 37). Threshold for sweet (sucrose), sour (citric acid), salty (sodium chloride), bitter (quinine-hydrochloride), and umami (sodium-glutamate) tastes was estimated using a single-staircase paradigm (3-alternative forced choice; volume per trial 0.1 ml) with or without 0.9-µM capsaicin added. This capsaicin concentration had been determined in pilot studies to be in the range of oral perception thresholds.

Results

The addition of capsaicin produced lower taste thresholds for sweet, sour, salty, and bitter but not for umami. In contrast, neither PTC taster status nor sex affected these results.

Conclusion

The current results indicate that a low concentration of capsaicin increases gustatory sensitivity.

Implications

The current findings provide evidence supporting different effects of capsaicin on taste perception at threshold level. It has implications for boosting taste sensitivity or flavor enjoyment with low concentration of capsaicin.

Effect of brewing conditions on phytochemicals and sensory profiles of black tea infusions: A primary study on the effects of geraniol and β-ionone on taste perception of black tea infusions

As a worldwide popular drink, black tea has always been one of the main focuses of tea studies. However, few studies have addressed the flavor profiles and related components, and most researches were based on a single factor. This study investigated the effects of multiple brewing conditions (temperature, time, water/tea ratio, and particle size) on the phytochemicals (non-volatile and volatile compounds) and sensory profiles of black tea infusions through response surface methodology. The regression models describing the brewing of detected indexes were significant (p ≤ 0.01) and reliable (R² ≥ 0.902). The particle size led to the greatest variation of non-volatile compounds and presented negative correlations, while the water/tea ratio affected the composition of volatile compounds the most. Meanwhile, through the addition of the selected aroma compounds (geraniol and β-ionone), an enhancement of black tea infusion sweetness was observed, proved the existence of odor-taste interaction in black tea infusions.

Protein microspheres as structuring agents in lipids: potential for reduction of total and saturated fat in food products

Excess consumption of total and saturated fats is linked to the development of chronic diseases, such as obesity, heart disease, diabetes, and cancer. There is therefore considerable interest in the development of foods containing lower levels of total and saturated fats, but that still have the same desirable physicochemical and sensory characteristics as the original foods. Solid fats normally contribute a number of key functional attributes to foods due to their ability to form crystalline networks that alter texture (such as elasticity, plasticity, and spreadability) and appearance (such as opacity and creaminess). The aim of this review is to provide an overview and to discuss the potential applications of food proteins as fat structuring agents that may be able to offer some of the desirable attributes normally supplied by saturated and trans fats. Previous studies have shown that globular proteins (such as whey proteins) trapped inside water-in-oil emulsions form protein microspheres when they are thermally denatured, which leads to the creation of highly viscous or solid-like lipid phases, having higher rheological properties. These protein microspheres may therefore be useful for the development of reduced fat margarines and spreads with reduced level of saturated/trans-fat contents. © 2020 Society of Chemical Industry.

What Does the Taste System Tell Us About the Nutritional Composition and Toxicity of Foods?

One of the distinctive features of the human taste system is that it categorizes food into a few taste qualities - e.g., sweet, salty, sour, bitter, and umami. Here, I examined the functional significance of these taste qualities by asking what they tell us about the nutritional composition and toxicity of foods. I collected published data on the composition of raw and unprocessed foods - i.e., fruits, endosperm tissues, starchy foods, mushrooms, and meats. Sweet taste is thought to help identify foods with a high caloric or micronutrient density. However, the sweetest foods (fruits) had a relatively modest caloric density and low micronutrient density, whereas the blandest foods (endosperm tissues and meats) had a relatively high caloric and high micronutrient density. Salty taste is thought to be a proxy for foods high in sodium. Sodium levels were higher in meats than in most plant materials, but raw meats lack a salient salty taste. Sour taste (a measure of acidity) is thought to signify dangerous or spoiled foods. While this may be the case, it is notable that most ripe fruits are acidic. Umami taste is thought to reflect the protein content of food. I found that free L-glutamate (the prototypical umami tastant) concentration varies independently of protein content in foods. Bitter taste is thought to help identify poisonous foods, but many nutritious plant materials taste bitter. Fat taste is thought to help identify triglyceride-rich foods, but the role of taste versus mouthfeel in the attraction to fatty foods is unresolved. These findings indicate that the taste system provides incomplete or, in some cases, misleading information about the nutritional content and toxicity of foods. This may explain why inputs from the taste system are merged with inputs from the other cephalic senses and intestinal nutrient-sensing systems. By doing so, we create a more complete sensory representation and nutritional evaluation of foods.

Odor-Induced Saltiness Enhancement: Insights Into The Brain Chronometry Of Flavor Perception

Flavor perception results from the integration of at least odor and taste. Evidence for such integration is that odors can have taste properties (odor-induced taste). Most brain areas involved in flavor perception are high-level areas; however, primary gustatory and olfactory areas also show activations in response to a combination of odor and taste. While the regions involved in flavor perception are now quite well identified, the network's organization is not yet understood. Using a close to real salty soup model with electroencephalography brain recording, we evaluated whether odor-induced saltiness enhancement would result in differences of amplitude and/or latency in late cognitive P3 peak mostly and/or in P1 early sensory peak. Three target solutions were created from the same base of green-pea soup: i) with a "usual" salt concentration (PPS2), ii) with "reduced" salt (PPS1: -50%), and iii) with reduced salt and a "beef stock" odor (PPS1B). Sensory data showed that the beef odor produced saltiness enhancement in PPS1B in comparison to PPS1. As the main EEG result, the late cognitive P3 peak was delayed by 25 ms in the odor-added solution PPS1B compared to PPS1. The odor alone did not explain this peak amplitude and higher latency in the P3 peak. These results support the classical view that high-level integratory areas process odor-taste interactions with potential top-down effects on primary sensory regions.

Flavor identification inversely correlates with body mass index (BMI)

BACKGROUND AND AIMS

Dietary choices are influenced by several factors including physiological, social, or genetic factors. Among these, flavor is the most important determinant modulating food preferences. The aim of the present study was to assess flavor identification abilities in patients with obesity (Ob) in comparison with matched normal weight (NW) and over-weight (OW) subjects using a specific and validated chemosensory test.

METHODS AND RESULTS

The flavor test was administered to 140 Ob patients recruited in the obesity outpatient Unit at the Federico II University hospital and to the same number of NW and OW subjects matched by sex, age, and smoking habit. Flavor score (FS) inversely correlated with BMI. Median [Q1; Q3] FS was significantly higher in NW (14.5 [12; 16]) than in Ob (13 [10; 15] p < 0.001) and not significantly different from OW (14 [12; 16]) individuals. FS was also higher in OW than in Ob subjects (p < 0.005). When separated according to age quartiles, the BMI-related differences in FS were still significant in younger quartiles, while they were abolished in the older.

CONCLUSIONS

BMI is a critical factor modulating flavor identification, particularly in young subjects. Further investigations are needed to explore the precise mechanism and the causal relationship between body weight and olfactory dysfunctions.

CLINICALTRIAL ID

NCT03506074.

Audiovisual Crossmodal Correspondence between Bubbles' Size and Pouring Sounds' Pitch in Carbonated Beverages

Visual and auditory carbonation have been separately documented as being two sensory markers of perceived freshness in beverages. The aim of the present study is to investigate the cross-modal interactions between these two dimensions of carbonation. Three experiments focused on crossmodal correspondences between bubble size and pouring sound pitch, which have never been investigated with ecological stimuli. Experiment 1, using an implicit association test (IAT), showed a crossmodal correspondence between bubble size and pouring sound pitch. Experiment 2 confirmed this pitch-size correspondence effect by means of a Go/No-Go Association Task (GNAT). Experiment 3 investigated the mutual dependence between pitch, size, and spatial elevation as well as the influence of attentional factors. No dependence was found, however pitch-size correspondences were obtained only in the condition requiring attentional processes, suggesting that these effects might be driven by top-down influences. These results highlight the robustness of the pitch-size crossmodal correspondence across stimulus contexts varying in complexity. Thus, this correspondence might be fruitfully used to modulate consumers' perceptions and expectations about carbonated beverages.

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.

Altered grey matter volume in 'super smellers'

‘Super smellers‘ are those individuals who show a heightened sense of smell. Data on the structural neuroanatomy of this phenomenon are still missing. A voxel-based morphometry study was conducted in order to compare gray matter volume (GMV) in specific brain regions of the olfactory network (piriform/entorhinal cortex, orbitofrontal cortex, insula, hippocampus) between 25 male ‘super smellers’ and 20 normosmic men. Participants were assigned to these groups based on their scores on a standardized olfactory performance test. Relative to normosmic men, ‘super smellers’ showed increased GMV in the anterior insula and in the hippocampus (dentate gyrus). These regions are crucial for the integration of olfactory information as well as odor learning and odor memory. Moreover, positive correlations between hippocampal volume and olfactory performance were detected in both groups. Future research should elaborate on how much of the observed neuroanatomical pattern of ‘super smellers’ is genetic and how much of it reflects experienced-based GMV increase.

Orthonasal versus retronasal glomerular activity in rat olfactory bulb by fMRI

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