In health and illness: does taste remain consistent? Exploring the influence of inflammation on taste perception through a systematic review and meta-analysis.

OBJECTIVE: Dysgeusia is characterized by a loss of taste perception, leading to malnutrition. This situation affects inflammatory conditions such as respiratory and neurological conditions, obesity, cancer, chemotherapy, aging, and many others. To date, there is not much information on the prevalence and risk of dysgeusia in an inflammatory condition; also, it is unclear which flavor is altered. MATERIALS AND METHODS: We systematically searched three databases from January 2018 to January 2023. Participants were children, adults, or elderly persons with an inflammatory condition and evaluated taste loss. A random effects model was used for statistical analysis to calculate the pooled odds ratio with its corresponding 95.0% confidence interval to estimate the probability of taste alteration (dysgeusia) in an inflammatory condition. RESULTS: The data allowed us to conduct a systematic review, including 63 original articles and 15 studies to perform the meta-analysis. The meta-analysis indicated a heterogenicity of 84.7% with an odds ratio of 3.25 (2.66-3.96), indicating a significant risk of Alzheimer's disease, SARS-CoV-2, chemotherapy, and rhinosinusitis. CONCLUSIONS: Inflammatory conditions and taste alterations are linked. Dysgeusia is associated with a higher risk of malnutrition and poorer general health status, especially in vulnerable populations.

Biophysical investigations using atomic force microscopy can elucidate the link between mouthfeel and flavour perception.

Food texture, along with taste and odour, is an important factor in determining food flavour. However, the physiological properties of oral texture perception require greater examination and definition. Here we explore recent trends and perspectives related to mouthfeel and its relevance in food flavour perception, with an emphasis on the biophysical point of view and methods. We propose that atomic force microscopy, combined with other biophysical techniques and more traditional food science approaches, offers a unique opportunity to study the mechanisms of mouthfeel at cellular and molecular levels. With this knowledge, food composition could be modified to develop healthier products by limiting salt, sugar, fat and calories while maintaining sensory qualities and consumer acceptance.

Change in taste sensation after orthognathic surgery.

OBJECTIVE: The objective of this study was to evaluate the effect of orthognathic surgery on taste sensation. MATERIALS AND METHODS: Thirty-five patients scheduled to undergo Le Fort I osteotomy (LFIO), sagittal split ramus osteotomy (SSRO), and bimaxillary surgery (BMS) were evaluated by administering localized and whole-mouth taste tests preoperatively and postoperatively at months 1, 3, and 6. The patients were asked to identify the quality of four basic tastes applied to six locations on the palate and tongue and to rate the taste intensities they perceived. Taste recognition thresholds and taste intesity scores were evaluted according to operation groups and follow-ups. RESULTS: There were significant decreases in the quinine HCl recognition thresholds at the postoperative follow-ups compared to the preoperative in LFIO patients (p = 0.043). There were significant decreases in sucrose taste intensity scores in the right posterolateral part of the tongue at months 3 and 6 compared to preoperative in SSRO patients (p = 0.046), and significant increases in quinine HCL taste intensity scores in the right and left anterior parts of the tongue at month 6 compared to preoperative in LFIO patients (p < 0.05). CONCLUSION: Taste perception is affected due to potential damage to the chemosensory nerves during orthognathic surgical procedures. Generally, non-significant alterations have been observed in taste perception after orthognathic surgery, except for significant alterations in bitter and sweet taste perceptions. CLINICAL RELEVANCE: Maxillofacial surgeons should be aware of taste perception change after orthognathic surgery procedures and patients should be informed accordingly. THE TRIAL REGISTRATION NUMBER (TRN): NCT06103422/Date of registration: 10.17.2023 (retrospectively registered).

Does presbygeusia really exist? An updated narrative review.

This review critically assessed the existence of presbygeusia, i.e., the impairment in taste perception occurring in the elderly, as a natural part of the aging process and its potential clinical implications. Several factors might contribute to age-related taste alterations (TAs), including structural changes in taste buds, alterations in saliva composition, central nervous system changes, and oral microbiota dysbiosis. A comprehensive literature review was conducted to disentangle the effects of age from those of the several age-related diseases or conditions promoting TAs. Most of the included studies reported TAs in healthy elderly people, suggesting that presbygeusia is a relatively frequent condition associated with age-related changes in the absence of pathological conditions. However, the impact of TAs on dietary preferences and food choices among the elderly seems to be less relevant when compared to other factors, such as cultural, psychological, and social influences. In conclusion, presbygeusia exists even in the absence of comorbidities or drug side effects, but its impact on dietary choices in the elderly is likely modest.

Locus Ceruleus Dynamics Are Suppressed during Licking and Enhanced Postlicking Independent of Taste Novelty.

Attending to salient sensory attributes of food, such as tastes that are new, displeasing, or unexpected, allows the procurement of nutrients without food poisoning. Exposure to new tastes is known to increase norepinephrine (NE) release in taste processing forebrain areas, yet the central source for this release is unknown. Locus ceruleus norepinephrine neurons (LC-NE) emerge as a candidate in signaling salient information about taste, as other salient sensory stimuli (e.g., visual, auditory, somatosensation) are known to activate LC neurons. To determine if LC neurons are sensitive to features of taste novelty, we used fiber photometry to record LC-NE activity in water-restricted mice that voluntarily licked either novel or familiar substances of differential palatability (saccharine, citric acid). We observed that LC-NE activity was suppressed during lick bursts and transiently activated upon the termination of licking and that these dynamics were independent of the familiarity of the substance consumed. We next recorded LC dynamics during brief and unexpected consumption of tastants and found no increase in LC-NE activity, despite their responsiveness to visual and auditory stimuli, revealing selectivity in LC's responses to salient sensory information. Our findings suggest that LC activity during licking is not influenced by taste novelty, implicating a possible role for non-LC noradrenergic nuclei in signaling critical information about taste.

Evolutionary origins of bitter taste receptors in jawed vertebrates.

Taste is a sense that detects information about nutrients and toxins in foods. Of the five basic taste qualities, bitterness is associated with the detection of potentially harmful substances like plant alkaloids. In bony vertebrates, type 2 taste receptors (T2Rs), which are G-protein-coupled receptors (GPCRs), act as bitter taste receptors1,2. In vertebrates, six GPCR gene families are described as chemosensory receptor genes, encoding taste receptor families (T1Rs and T2Rs) and olfactory receptor families (ORs, V1Rs, V2Rs, and TAARs). These families of receptors have been found in all major jawed vertebrate lineages, except for the T2Rs, which are confined to bony vertebrates3. Therefore, T2Rs are believed to have emerged later than the other chemosensory receptor genes in the bony vertebrate lineage. So far, only the genomes of two cartilaginous fish species have been mined for TAS2R genes, which encode T2Rs4. Here, we identified novel T2Rs in elasmobranchs, namely selachimorphs (sharks) and batoids (rays, skates, and their close relatives) by an exhaustive search covering diverse cartilaginous fishes. Using functional and mRNA expression analyses, we demonstrate that their T2Rs are expressed in the oral taste buds and contribute to the detection of bitter compounds. This finding indicates the early origin of T2Rs in the common ancestor of jawed vertebrates.

The Obese Taste Bud study: Objectives and study design.

AIMS: Taste modifies eating behaviour, impacting body weight and potentially obesity development. The Obese Taste Bud (OTB) Study is a prospective cohort study launched in 2020 at the University of Leipzig Obesity Centre in cooperation with the HI-MAG Institute. OTB will test the hypothesis that taste cell homeostasis and taste perception are linked to obesity. Here, we provide the study design, data collection process and baseline characteristics. MATERIALS AND METHODS: Participants presenting overweight, obesity or normal weight undergo taste and smell tests, anthropometric, and taste bud density (TBD) assessment on Day 1. Information on physical and mental health, eating behaviour, physical activity, and dental hygiene are obtained, while biomaterial (saliva, tongue swap, blood) is collected in the fasted state. Further blood samples are taken during a glucose tolerance test. A stool sample is collected at home prior to Day 2, on which a taste bud biopsy follows dental examination. A subsample undergoes functional magnetic resonance imaging while exposed to eating-related cognitive tasks. Follow-up investigations after conventional weight loss interventions and bariatric surgery will be included. RESULTS: Initial results show that glycated haemoglobin levels and age are negatively associated with TBD, while an unfavourable metabolic profile, current dieting, and vegan diet are related to taste perception. Olfactory function negatively correlates with age and high-density lipoprotein cholesterol. CONCLUSION: Initial findings suggest that metabolic alterations are relevant for taste and smell function and TBD. By combining omics data from collected biomaterial with physiological, metabolic and psychological data related to taste perception and eating behaviour, the OTB study aims to strengthen our understanding of taste perception in obesity.

Learning enhances representations of taste-guided decisions in the mouse gustatory insular cortex.

Learning to discriminate overlapping gustatory stimuli that predict distinct outcomes-a feat known as discrimination learning-can mean the difference between ingesting a poison or a nutritive meal. Despite the obvious importance of this process, very little is known about the neural basis of taste discrimination learning. In other sensory modalities, this form of learning can be mediated by either the sharpening of sensory representations or the enhanced ability of "decision-making" circuits to interpret sensory information. Given the dual role of the gustatory insular cortex (GC) in encoding both sensory and decision-related variables, this region represents an ideal site for investigating how neural activity changes as animals learn a novel taste discrimination. Here, we present results from experiments relying on two-photon calcium imaging of GC neural activity in mice performing a taste-guided mixture discrimination task. The task allows for the recording of neural activity before and after learning induced by training mice to discriminate increasingly similar pairs of taste mixtures. Single-neuron and population analyses show a time-varying pattern of activity, with early sensory responses emerging after taste delivery and binary, choice-encoding responses emerging later in the delay before a decision is made. Our results demonstrate that, while both sensory and decision-related information is encoded by GC in the context of a taste mixture discrimination task, learning and improved performance are associated with a specific enhancement of decision-related responses.

Metabolic sensing in AgRP regulates sucrose preference and dopamine release in the nucleus accumbens.

Hunger increases the motivation for calorie consumption, often at the expense of low-taste appeal. However, the neural mechanisms integrating calorie-sensing with increased motivation for calorie consumption remain unknown. Agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus sense hunger, and the ingestion of caloric solutions promotes dopamine release in the absence of sweet taste perception. Therefore, we hypothesised that metabolic-sensing of hunger by AgRP neurons would be essential to promote dopamine release in the nucleus accumbens in response to caloric, but not non-caloric solutions. Moreover, we examined whether metabolic sensing in AgRP neurons affected taste preference for bitter solutions under conditions of energy need. Here we show that impaired metabolic sensing in AgRP neurons attenuated nucleus accumbens dopamine release in response to sucrose, but not saccharin, consumption. Furthermore, metabolic sensing in AgRP neurons was essential to distinguish nucleus accumbens dopamine response to sucrose consumption when compared with saccharin. Under conditions of hunger, metabolic sensing in AgRP neurons increased the preference for sucrose solutions laced with the bitter tastant, quinine, to ensure calorie consumption, whereas mice with impaired metabolic sensing in AgRP neurons maintained a strong aversion to sucrose/quinine solutions despite ongoing hunger. In conclusion, we demonstrate normal metabolic sensing in AgRP neurons drives the preference for calorie consumption, primarily when needed, by engaging dopamine release in the nucleus accumbens.

Relationship between olfactory and gustatory functions: The Iwaki health promotion project 2019.

OBJECTIVE: Olfactory and gustatory functions are important sensory aspects in humans. Although they are believed to influence each other, their interrelationship is not well understood. In this study, we aimed to investigate the relationship between the olfactory and gustatory functions based on the results of a large-scale epidemiological study (Iwaki Health Promotion Project) of the general local population. METHODS: We analyzed 565 participants who underwent taste and olfactory tests in the 2019 Iwaki Project. Gustatory function was tested for four taste qualities (sweet, sour, salty, and bitter) using whole-mouth taste tests. Olfactory function was tested using the University of Pennsylvania Smell Identification Test modified for Japanese (UPSIT-J). We evaluated sex-related differences between olfactory and gustatory functions and the effects of various factors on olfactory identification using multivariate analysis. Furthermore, we compared the percentage of accurate UPSIT-J responses between the normal and hypogeusia groups. We also analyzed the effects of taste and olfactory functions on eating. RESULTS: Olfactory and gustatory functions were lower in men than in women. Among the four taste qualities, salty taste was the most closely associated with olfactory identification ability, with lower olfactory scores of salty taste in the hypogeusia group than in the normal group. Moreover, the hyposmia group had higher daily salt intake than the normal olfaction group in women. CONCLUSION: These results suggest that olfactory identification tests may be useful in predicting elevated salt cognitive thresholds, leading to a reduction in salt intake, which may contribute to hypertension prevention.

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.

Demystifying wine expertise through the lens of imagination: Descriptions and imagery vividness across sensory modalities.

For most untrained novices, talking about wine or imagining the smells and flavours of wine is difficult. Wine experts, on the other hand, have been found to have better imagery for wine, and are also more proficient in describing wine. Some scholars have suggested that imagery and language are based on similar underlying processes, but no conclusive evidence has been found regarding mental imagery and language production. In this study, we examined the relationship between imagery and language use in both novices and experts. In an online experiment, wine experts and novices were asked to imagine the colour, smell, taste and mouthfeel of wines in different situations, and were asked to rate the vividness of the imagined experience as well as describe it with words. The results show that experts differ from novices on a number of linguistic measures when describing wine, including the number of words used, the type of words used, the concreteness of those words, and the adjective to noun ratio. Similarly, imagery for wine was more vivid in wine experts compared to novices in the modalities of smell, taste, and mouthfeel, in alignment with previous work. Surprisingly, we found that no single linguistic variable significantly predicted the reported vividness of wine imagery, neither in experts nor in novices. However, the linguistic model predicted imagery vividness better using data from experts compared to novices. Taken together, these findings underscore that imagery and language are different facets of wine cognition.

The gustin gene variation at rs2274333 and PROP taster status affect dietary fat perception: a stepwise multiple regression model study.

Gustin, a trophic factor for taste bud development, and its polymorphism at rs2274333 influence taste perception of 6-n-propylthiouracil (PROP) and fungiform papillae (FP) density. The PROP taster status affects dietary fat sensing and body composition. However, there is a paucity of research on the gustin genotype with dietary fat perception, PROP tasting ability, and body mass index (BMI). Thus, taste sensitivity to fat and bitterness was evaluated in 178 healthy individuals. The general labeled magnitude scale was used to determine suprathreshold taste intensity ratings, whereas the alternative forced choice approach was used to estimate the taste-sensing ability. The FP density was assessed by applying blue-colored food dye over the anterior region of the tongue. Restriction fragment length polymorphism was used to detect the genetic polymorphism (rs2274333) in the carbonic anhydrase VI (CA-VI) gene. Fisher's chi-square analysis showed that the CA-VI genotype and allelic frequencies significantly correlated (p<0.001) with the PROP taster status and BMI. Healthy individuals with AA genotypes of the CA-VI polymorphism and PROP super-tasters demonstrated stronger gustatory sensitivity for linoleic acid (LA) with greater FP density in comparison to individuals with AG/GG genotypes and other PROP taster groups. Stepwise forward multiple regression analysis indicates that BMI and PROP taster status significantly influence the LA sensing ability. The suprathreshold intensity rating for LA was also significantly impacted by PROP taster status and CA-VI genotypes, with a variation of 73.3%. Overall, our findings show a relationship between the taste papillae environment and the CA-VI genetic mutation at rs2274333, which influenced the gustatory preference for dietary fat and bitter taste.

Predicting and improving complex beer flavor through machine learning.

The perception and appreciation of food flavor depends on many interacting chemical compounds and external factors, and therefore proves challenging to understand and predict. Here, we combine extensive chemical and sensory analyses of 250 different beers to train machine learning models that allow predicting flavor and consumer appreciation. For each beer, we measure over 200 chemical properties, perform quantitative descriptive sensory analysis with a trained tasting panel and map data from over 180,000 consumer reviews to train 10 different machine learning models. The best-performing algorithm, Gradient Boosting, yields models that significantly outperform predictions based on conventional statistics and accurately predict complex food features and consumer appreciation from chemical profiles. Model dissection allows identifying specific and unexpected compounds as drivers of beer flavor and appreciation. Adding these compounds results in variants of commercial alcoholic and non-alcoholic beers with improved consumer appreciation. Together, our study reveals how big data and machine learning uncover complex links between food chemistry, flavor and consumer perception, and lays the foundation to develop novel, tailored foods with superior flavors.

From Molecular Dynamics to Taste Sensory Perception: A Comprehensive Study on the Interaction of Umami Peptides with the T1R1/T1R3-VFT Receptor.

The research on the umami receptor-ligand interaction is crucial for understanding umami perception. This study integrated molecular simulations, sensory evaluation, and biosensor technology to analyze the interaction between umami peptides and the umami receptor T1R1/T1R3-VFT. Molecular dynamics simulations were used to investigate the dissociation process of seven umami peptides with the umami receptor T1R1/T1R3-VFT, and by calculating the potential mean force curve using the Jarzynski equation, it was found that the binding free energy of umami peptide is between -58.80 and -12.17 kcal/mol, which had a strong correlation with the umami intensity obtained by time intensity sensory evaluation. Through correlation analysis, the dissociation rate constants (0.0126-0.394 1/s) of umami peptides were found to have a great impact on umami perception. The faster the dissociation rate of umami peptides from receptors, the stronger the perceived intensity of the umami taste. This research aims to elucidate the relationship between the umami peptide-receptor interaction and umami perception, providing theoretical support for the exploration of umami perception mechanisms.

Rethinking Sweetener Discovering: Multiparameter Modeling of Molecular Docking Results between the T1R2-T1R3 Receptor and Compounds with Different Tastes.

Molecular docking has been widely applied in the discovery of new sweeteners, yet the interpretation of computational results sometimes remains difficult. Here, the interaction between the T1R2-T1R3 sweet taste receptor and 66 tasting compounds, including 26 sweet, 19 bitter, and 21 sour substances was investigated by batch molecular docking processes. Statistical analysis of the docking results generated two novel methods of interpreting taste properties. Quantitative correlation between relative sweetness (RS) and docking results created a multiparameter model to predict sweetness intensity, whose correlation coefficient r = 0.74 is much higher than r = 0.17 for the linear correlation model between sweetness and binding energy. The improved correlation indicated that docking results besides binding energy contain undiscovered information about the ligand-protein interaction. Qualitative discriminant analysis of different tasting molecules generated an uncorrelated linear discriminant analysis (UDLA) model, which achieved an overall 93.1% accuracy in discriminating the taste of molecules, with specific accuracy for verifying sweet, bitter, and sour compounds reaching 88.0%, 92.1%, and 100%. These unprecedented models provide a unique perspective for interpreting computational results and may inspire future research on sweetener discovery.

Seeing is misbelieving: Consumers wrongly believe that unhealthy food tastes better when there is more of it.

Recent studies have shown that people can believe that unhealthy foods taste better, even if healthy and unhealthy foods are equally as tasty. Specifically, when tasty and unhealthy foods are frequent in one context but rare in another, people perceive unhealthy foods to taste better, even if health and taste are unrelated. Given that people often consume food in one context, the current study investigated whether false beliefs about the health-taste relationship in foods can also occur in just one single context, in which either healthy or unhealthy foods are predominant, when there is no contrasting context where the respective other food is predominant. In two experiments (N = 342), we presented participants with pictures of meals from a single context and varied the frequency of healthy and unhealthy foods between participants. Although healthy and unhealthy foods tasted equally as good, participants believed that (un)healthy foods tasted better when there were more of them. This research demonstrates that health-taste beliefs might be changed by increasing the relative frequency of healthy foods in the environment overall, not by just offering some healthy and tasty foods.

Identification and Validation of Key Genes Related to Preferred Flavour Profiles in Australian Commercial Papaya (Carica papaya L.).

Commercial papaya varieties grown in Australia vary greatly in taste and aroma. Previous profiling has identified undesirable 'off tastes' in existing varieties, discouraging a portion of the population from consuming papayas. Our focus on enhancing preferred flavours led to an exploration of the genetic mechanisms and biosynthesis pathways that underlie these desired taste profiles. To identify genes associated with consumer-preferred flavours, we conducted whole RNA sequencing and de novo genome assembly on papaya varieties RB1 (known for its sweet flavour and floral aroma) and 1B (less favoured due to its bitter taste and musty aroma) at both ripe and unripe stages. In total, 180,368 transcripts were generated, and 118 transcripts related to flavours were differentially expressed between the two varieties at the ripe stage. Five genes (cpBGH3B, cpPFP, cpSUS, cpGES and cpLIS) were validated through qPCR and significantly differentially expressed. These genes are suggested to play key roles in sucrose metabolism and aromatic compound production pathways, holding promise for future selective breeding strategies. Further exploration will involve assessing their potential across broader germplasm and various growth environments.

Influence of taste sensitivity on preference and sensory perception of mezcal.

The perception of orosensory stimuli, which includes flavor, can vary between individuals. These individual variations in oral sensations can be due to genetic factors and it would appear that they can predict food liking and consumption. The most studied source of variation is related to bitter taste perception associated with 6-n-propylthiouracil (PROP) responsiveness. In this context, humans can be classified as non-tasters (NT), medium tasters (MT) and supertasters (ST). Evidence suggests that genetic variation in bitter taste perception contributes to differences in the level of irritation caused by alcohol perception in solutions. The aim of this investigation was to study the bitter taste sensitivity among a group of mezcal consumers and its relationship with sensory perception and preference through PROP taster status. The tests were carried out in the state of Oaxaca in Mexico. A total of 83 mezcal consumers were classified by their PROP taster status and were asked to provide sensory descriptors for five mezcal samples and rate them according to the level of liking. The three-solution test was used to classify the subjects as NT, MT, and ST, while a Multiple Factor Analysis (MFA) was used to visualize the sensory descriptors provided by these three groups. The proportion of MT subjects was 16%, while the proportion of NT and ST was 34 and 51%, respectively. The MT provided higher liking ratings for at least three mezcal samples. According to MFA, the mezcal samples were organized in a similar configuration along the two dimensions. However, NT mentioned a limited number of simple terms (strong flavor, tasteless, burning in the mouth) to describe the samples, whereas ST used a more complex vocabulary (astringent, smoky, scratchy aftertaste). These data suggest that the preference for mezcal samples was similar for non-taster and supertasters, but there are indications that the sensory perception of mezcal differs between groups.