Differential Perception of Caffeine Bitter Taste Depending on Smoking Status

Taste impairment may be associated with tobacco smoking. We assessed taste recognition and intensity among healthy middle-aged current smokers (N?=?94, 21 %), former smokers (N?=?48, 11 %) and non-smokers (N?=?309, 69 %) recruited on a voluntary basis among hospital staff. By means of a whole-mouth gustatory test, participants tasted one concentration of the four basic tastes (NaCl 34 mM, sucrose 58 mM, acetic acid 60 mM, caffeine 1.5 mM for salty, sweet, sour and bitter tastes, respectively) and completed a questionnaire for taste recognition and intensity (ranging from 0 to 10). The recognition of salty, sweet and sour tastes was not influenced by smoking status. Bitter taste recognition was wrong among 13.4, 19.8 and 26.5 % of non-smokers, current smokers and former smokers, respectively (p?=?0.043). The adjusted odds ratio (95 % confidence interval) of correct bitter taste recognition was 0.31 (0.14–0.69) among former and 0.74 (0.35–1.55) among current smokers (p?=?0.016), compared to non-smokers while adjusting for gender, age, year of assessment and bitter taste intensity. The distribution of caffeine’s bitter taste intensity was bimodal regardless of the smoking status. The differential perception of caffeine’s bitter taste by current and former smokers is likely to be caused by a toxic process. As taste impairment persists in former smokers, the bioaccumulation of some tobacco/combustion products might be responsible for the disequilibrium in taste buds regeneration.     

Taste responses in patients with Parkinson's disease

OBJECTIVE: Preclinical studies indicate that dopaminergic transmission in the basal ganglia may be involved in processing of both pleasant and unpleasant stimuli. Given this, the aim of the present study was to assess taste responses to sweet, bitter, sour, and salty substances in patients with Parkinson's disease (PD). METHODS: Rated intensity and pleasantness of filter paper discs soaked in sucrose (10-60%), quinine (0.025-0.5%), citric acid (0.25-4.0%), or sodium chloride (1.25-20%) solutions was evaluated in 30 patients with PD and in 33 healthy controls. Paper discs soaked in deionised water served as control stimuli. In addition, reactivity to 100 ml samples of chocolate and vanilla milk was assessed in both groups. Taste detection thresholds were assessed by means of electrogustometry. Sociodemographic and neuropsychiatric data, including cigarette smoking, alcohol consumption, tea and coffee drinking, depressive symptoms, and cognitive functioning were collected. RESULTS: In general, perceived intensity, pleasantness, and identification of the sucrose, quinine, citric acid, or sodium chloride samples did not differ between the PD patients and controls. Intensity ratings of the filter papers soaked in 0.025% quinine were significantly higher in the PD patients compared with the control group. No inter-group differences were found in taste responses to chocolate and vanilla milk. Electrogustometric thresholds were significantly (p = 0.001) more sensitive in the PD patients. CONCLUSIONS: PD is not associated with any major alterations in responses to pleasant or unpleasant taste stimuli. Patients with PD may present enhanced taste acuity in terms of electrogustometric threshold.     

Pilot Experiment: the Effect of Added Flavorants on the Taste and Pleasantness of Mixtures of Glycerol and Propylene Glycol

Introduction

The US Food and Drug Administration banned most “sweet” flavorants for use in cigarettes due to the concern that sweet flavors appeal to young, beginning smokers. However, many of the same flavors, including fruity and confection-associated aromas (e.g., vanilla), are still used in e-cigarettes. Sweet flavors may have a number of effects, including enhancement of the taste of other ingredients. The current work focused on the impact of model flavorants on the taste of a mixture of propylene glycol and vegetable glycerine, solvents used in most e-cigarettes and related products.

Methods

A device delivered mixtures of propylene glycol and vegetable glycerine into the mouth in parallel with puffs of clean air (control) or odorized air. Aromas included two “fruity” esters (“pineapple” and “banana”), two confection-associated aromas (“vanilla” and “caramel/malty”), menthol (not a “sweet” aroma, but commonly used in e-cigarettes), and a “burnt” aroma not expected to enhance flavor. Twenty young adults, aged 18–25, rated the sweetness, bitterness, and pleasantness of all stimuli (within-subjects design).

Results

Both fruity aromas significantly enhanced sweetness, both confection-associated aromas significantly enhanced pleasantness, and the caramel/malty aroma significantly reduced bitterness. Menthol and the “burnt” aroma had no measurable effects on the taste of solvent mixtures.

Conclusion

Some flavorants modulated the taste of solvents commonly used in e-cigarettes in ways consistent with an enhanced sensory profile.

Implications

If similar effects occur in actual products, improved flavor profiles could facilitate continued use, particularly in non-smokers experimenting with e-cigarettes and related products.

     

Species differences in polysaccharide and sugar taste preferences

This study compared the polysaccharide and sugar taste preferences of humans and four rodent species (laboratory rats, Rattus norvegicus; Golden Syrian hamsters, Mesocricetus auratus; Mongolian gerbils, Meriones unguiculatus; Egyptian spiny mice, Acomys cahirinus). In Experiment 1 human subjects rated the pleasantness, sweetness, and flavor intensity of polysaccharide (Polycose), sucrose, and maltose solutions at concentrations of 0.0125 M to 0.4 M, and 1% to 32% concentrations. At the higher molar concentrations Polycose was rated as less sweet and less pleasant than the sucrose and maltose solutions; there were no differences in the flavor intensity ratings. With the percent concentrations Polycose was rated as less sweet and less flavorable as the sucrose and maltose solutions; there were no reliable differences in the pleasantness ratings. In Experiment 2, the Polycose, sucrose, and maltose preferences of rats, hamsters, gerbils, and spiny mice were compared using 24 hr two-bottle tests (saccharide vs. water) at concentrations of 0.001 M, 0.005 M, 0.01 M, and 0.1 M. In general, the rats displayed stronger preferences for Polycose and maltose than did the other three species. In addition, the gerbils showed a stronger Polycose preference at the 0.1 M concentration than did the hamsters and spiny mice, and the spiny mice display a weaker preference for sucrose than did the other three species. Within species comparisons revealed that all four species displayed preferences for Polycose that were as strong or stronger than their preferences for sucrose and maltose. With only a few exceptions, male and female rodents did not differ in their saccharide preferences. Thus, while rats show the most robust Polycose preference of the four rodent species, all four species were attracted to the taste of polysaccharides. Humans, on the other hand, reported that Polycose solutions were unpleasant. The results suggest that rodents have taste receptors for starch-derived polysaccharides that humans lack.     

Taste perception abnormalities after acute stroke in postmenopausal women

The study aims to elucidate the characteristics of post-stroke taste dysfunction in postmenopausal women. Taste function in 120 consecutive postmenopausal women with acute (< 7 days) stroke was compared with that of age-matched control subjects (n = 109). The agents used were: sodium chloride for saltiness, sucrose for sweetness, glacial acetic acid for sourness and quinine hemisulfate for bitterness. Detection and recognition thresholds were performed by the three-stimulus drop technique. Taste threshold values beyond two standard deviations of normal were considered “abnormal”. For postmenopausal women after acute stroke, abnormal detection thresholds for the ability to taste sweetness, saltiness, sourness and bitterness were found in 33%, 21%, 35% and 30% of women, respectively, and abnormal recognition thresholds were found in 40%, 34%, 42% and 33% of women respectively. The taste dysfunction occurred ipsilaterally, contralaterally or bilaterally, and was not related to the side or location of the lesion. Large (>2 cm) lesions were more frequently associated with sweet and salty taste dysfunction than small lesions (p < 0.05). Follow-up examination in 23 patients at 24 to 31 months (mean 27 months) after the initial evaluation showed that the taste abnormality persisted in 8 (35%) patients. Taste perception abnormalities are common and often persistent in stroke patients. The dysfunction can occur ipsilaterally, contralaterally or bilaterally.     

Taste–Odor Integration in Espresso Coffee

Espresso coffee samples were freshly prepared with 10% sucrose, 0.0143% sucralose (equivalent in sweetness to 10% sucrose), or unsweetened, each with and without nondairy creamer. A sensory panel rated the intensities of “malty,” “caramel,” “roasty,” and “coffee-like.” The concentrations of flavor chemicals associated with the latter three sensations (Furaneol, 2-ethyl-3,5-dimethyl [EDM] pyrazine, and 2-furfuryl thiol, respectively) were determined by gas chromatography, using solid-phase microextraction sampling of coffee headspace. Furaneol and furfuryl thiol were essentially unaffected by creamer addition, but the more nonpolar EDM pyrazine was greatly reduced. The malty, caramel, roasty, and coffee-like flavor intensities were not significantly affected by creamer addition. This appears to be a case of disconnect between the absence of an odorant and perception. Furaneol, furfuryl thiol, and EDM pyrazine concentrations were unaffected by adding either sweetener. The malty sensation was the same with and without added sweetener. The roasty and coffee-like ratings both decreased to similar extents in the samples with the two added sweeteners. The ratings for caramel were considerably increased, again to a similar extent, by both sweeteners. Since the added sweeteners were both nonvolatile, this is clearly a case where taste affected odor perception.     

The perception of affective touch in Parkinson's disease and its relation to small fibre neuropathy

Affective touch sensation is conducted by a sub‐class of C‐fibres in hairy skin known as C‐Tactile (CT) afferents. CT afferents respond maximally to gentle skin stroking at velocities between 1 and 10 cm/s. Parkinson's disease (PD) is characterised by markedly reduced cutaneous C‐fibres. It is not known if affective touch perception is influenced by C‐fibre density and if affective touch is impaired in PD compared to healthy controls. We predicted that perceived pleasantness to gentle stroking in PD would correlate with C‐afferent density and that affective touch perception would be impaired in PD compared to healthy controls. Twenty‐four PD patients and 27 control subjects rated the pleasantness of brush stroking at an optimum CT stimulation velocity (3 cm/s) and two sub‐optimal velocities (0.3 and 30 cm/s). PD patients underwent quantification of C‐fibre density using skin biopsies and corneal confocal microscopy. All participants rated a stroking velocity of 3 cm/s as the most pleasant with significantly lower ratings for 0.3 and 30 cm/s. There was a significant positive correlation between C‐fibre density and pleasantness ratings at 3 and 30 cm/s but not 0.3 cm/s. Mean pleasantness ratings were consistently higher in PD patients compared to control subjects across all three velocities. This study shows that perceived pleasantness to gentle touch correlates significantly with C‐fibre density in PD. The higher perceived pleasantness in PD patients compared to controls suggests central sensitisation to peripheral inputs, which may have been enhanced by dopamine therapy.     

On-line psychophysical data acquisition and event-related fMRI protocol optimized for the investigation of brain activation in response to gustatory stimuli

An experimental method for event-related functional magnetic resonance imaging that allows for the presentation of several chemosensory stimuli in the oral cavity during the same run, the collection of psychophysical measures (intensity or pleasantness) during the presentation of the stimuli, and the analysis of the data in an event-related fashion are described. The automatic pumps used to present taste stimuli allowed for multiple tastes to be delivered in small amounts under computer control. Psychophysical ratings of pleasantness or intensity were collected after each presentation of a taste stimulus and water, with the general labeled magnitude scale, using a joystick that controlled the movement of an arrow on the visual display. Performing these cognitive tasks required that the participant remained focused, and aided in the interpretation of the data collected. The perceived pleasantness differed across stimuli for all conditions; however, pleasantness ratings for the same stimulus displayed consistency, over the duration of the run and before each scan on separate days. Activation in response to sucrose and caffeine while the participant rated pleasantness was found in the insula, frontal operculum, rolandic operculum and orbitofrontal cortex which is consistent with previous taste fMRI studies.     

Olfaction and taste processing in autism.

BACKGROUND: Autism is often associated with sensory symptoms, but few studies have examined chemosensory functions in this population. We examined olfactory and taste functioning in individuals with autism to characterize chemosensory processing and test competing hypotheses about underlying brainstem versus cortical abnormalities. METHODS: Twenty-one participants (10-18 years) with autism were compared with 27 well-matched control participants with typical development. Taste identification was tested via sucrose, NaCl, citric acid, and quinine solutions applied to standard locations on the anterior tongue. Taste detection thresholds were established in the same regions with electrogustometry, and olfactory identification was evaluated with "Sniffin' Sticks." RESULTS: Participants with autism were significantly less accurate than control participants in identifying sour tastes and marginally less accurate for bitter tastes, but they were not different in identifying sweet and salty stimuli. Taste detection thresholds via electrogustometry were equivalent. Olfactory identification was significantly worse among participants with autism. CONCLUSIONS: True differences exist in taste and olfactory identification in autism. Impairment in taste identification with normal detection thresholds suggests cortical, rather than brainstem dysfunction. Further research is needed to determine the neurologic bases of olfactory and taste impairments, as well as the relationship of chemosensory dysfunction to other characteristics of autism.     

The Influence of “Tastiness” and “Healthiness” Labels in Cheese Flavor Perception

Tastiness and healthiness labels are known to influence consumer expectations, acceptance, attention, and hedonic ratings regarding the food so labeled. Surprisingly, few studies have focused on flavor perception in relation to these labels. Thus, the present study rated the perceived intensity of flavors in Comté and Emmental cheeses in three groups named “tastiness group,” “healthiness group,” and “control group” (without label). Results showed a significant effect of the label with Comté cheese, i.e., the intensity of perceived flavors was rated higher with a “tastiness” label than with either no label or with a “healthiness” label and higher with no label than with a “healthiness” label. Furthermore, no significant difference in relation to label was observed in the case of Emmental cheese. Additionally, the effect of label on flavor perception appeared to be strongly dependent on age. These findings are discussed in terms of the possible subsequent influence of changed perception on eating behavior.     

Sweet and Bitter Taste Perception of Women During Pregnancy

Introduction

Changes in sweet and bitter taste perception during pregnancy have been reported in a limited number of studies leading, however, to inconclusive results. The current study aimed to investigate possible differences in perceived intensity and liking of sweetness and bitterness between pregnant and nonpregnant women.

Methods

Forty-six pregnant and 45 nonpregnant women evaluated taste intensity and liking of five samples of each of four different products: two sweet (cake and apple + berry juice) and two bitter (salad and grapefruit juice). Product samples varied in sweetness and bitterness, respectively. Pregnant women completed also a self-administered questionnaire on changes in sweet and bitter taste perception due to pregnancy.

Results

Perceived intensity of sweetness and bitterness was not different between pregnant and nonpregnant women for any of the products. However, the liking of the least sweet apple + berry juice was significantly higher, and the optimal preferred sugar content was significantly lower in pregnant compared to nonpregnant women. With regards to self-report, pregnant women who reported higher sensitivity in sweet or bitter taste did not have significantly different intensity scores from those with no self-reported changes. The apple + berry juice sample highest in sugar content was liked less by pregnant women who reported higher sensitivity toward sweet taste compared to those who reported no change.

Conclusion

This study provides evidence that pregnant women may prefer lower sugar content in a juice mixture compared to nonpregnant women. Future research should focus on the possible occurrence of this phenomenon in other beverages and foods, as well.

     

It’s in the eye of the beholder: selective attention to drink properties during tasting influences brain activation in gustatory and reward regions

Statements regarding pleasantness, taste intensity or caloric content on a food label may influence the attention consumers pay to such characteristics during consumption. There is little research on the effects of selective attention on taste perception and associated brain activation in regular drinks. The aim of this study was to investigate the effect of selective attention on hedonics, intensity and caloric content on brain responses during tasting drinks. Using functional MRI brain responses of 27 women were measured while they paid attention to the intensity, pleasantness or caloric content of fruit juice, tomato juice and water. Brain activation during tasting largely overlapped between the three selective attention conditions and was found in the rolandic operculum, insula and overlying frontal operculum, striatum, amygdala, thalamus, anterior cingulate cortex and middle orbitofrontal cortex (OFC). Brain activation was higher during selective attention to taste intensity compared to calories in the right middle OFC and during selective attention to pleasantness compared to intensity in the right putamen, right ACC and bilateral middle insula. Intensity ratings correlated with brain activation during selective attention to taste intensity in the anterior insula and lateral OFC. Our data suggest that not only the anterior insula but also the middle and lateral OFC are involved in evaluating taste intensity. Furthermore, selective attention to pleasantness engaged regions associated with food reward. Overall, our results indicate that selective attention to food properties can alter the activation of gustatory and reward regions. This may underlie effects of food labels on the consumption experience of consumers.     

Taste Identification in Adults with Autism Spectrum Conditions

Sensory issues are widely reported in Autism Spectrum Conditions (ASC). Since taste perception is one of the least studied senses in ASC we explored taste identification in adults with ASC (12 males, 11 females) compared to control participants (14 males, 12 females). 'Taste strips' were used to measure taste identification overall, as well as bitter, sour, sweet and salty tastes. Results revealed lower taste scores overall in the ASC group, as well as for bitter, sour and sweet tastes. Salty taste scores did not differ between the groups. Examining error types showed that adults with ASC more often misidentified a taste as salty or as no taste. Future studies should investigate underlying mechanisms of taste identification difficulties in ASC.     

Chemospecific deficits in taste sensitivity following bilateral or right hemispheric gustatory cortex lesions in rats

Our prior studies showed bilateral gustatory cortex (GC) lesions significantly impair taste sensitivity to salts (NaCl and KCl) and quinine (“bitter”) but not to sucrose (“sweet”). The range of qualitative tastants tested here has been extended in a theoretically relevant way to include the maltodextrin, Maltrin, a preferred stimulus by rats thought to represent a unique taste quality, and the “sour” stimulus citric acid; NaCl was also included as a positive control. Male rats (Sprague–Dawley) with histologically confirmed neurotoxin-induced bilateral (BGCX, n = 13), or right (RGCX, n = 13) or left (LGCX, n = 9) unilateral GC lesions and sham-operated controls (SHAM, n = 16) were trained to discriminate a tastant from water in an operant two-response detection task. A mapping system was used to determine placement, size, and symmetry (when bilateral) of the lesion. BGCX significantly impaired taste sensitivity to NaCl, as expected, but not to Maltrin or citric acid, emulating our prior results with sucrose. However, in the case of citric acid, there was some disruption in performance at higher concentrations. Interestingly, RGCX, but not LGCX, also significantly impaired taste sensitivity, but only to NaCl, suggesting some degree of lateralized function. Taken together with our prior findings, extensive bilateral lesions in GC do not disrupt basic taste signal detection to all taste stimuli uniformly. Moreover, GC lesions do not preclude the ability of rats to learn and perform the task, clearly demonstrating that, in its absence, other brain regions are able to maintain sensory-discriminative taste processing, albeit with attenuated sensitivity for select stimuli.     

Variable Branching Characteristics of Peripheral Taste Neurons Indicates Differential Convergence

Taste neurons are functionally and molecularly diverse, but their morphologic diversity remains completely unexplored. Using sparse cell genetic labeling, we provide the first reconstructions of peripheral taste neurons. The branching characteristics across 96 taste neurons show surprising diversity in their complexities. Individual neurons had 1–17 separate arbors entering between one and seven taste buds, 18 of these neurons also innervated non-taste epithelia. Axon branching characteristics are similar in gustatory neurons from male and female mice. Cluster analysis separated the neurons into four groups according to branch complexity. The primary difference between clusters was the amount of the nerve fiber within the taste bud available to contact taste-transducing cells. Consistently, we found that the maximum number of taste-transducing cells capable of providing convergent input onto individual gustatory neurons varied with a range of 1–22 taste-transducing cells. Differences in branching characteristics across neurons indicate that some neurons likely receive input from a larger number of taste-transducing cells than other neurons (differential convergence). By dividing neurons into two groups based on the type of taste-transducing cell most contacted, we found that neurons contacting primarily sour transducing cells were more heavily branched than those contacting primarily sweet/bitter/umami transducing cells. This suggests that neuron morphologies may differ across functional taste quality. However, the considerable remaining variability within each group also suggests differential convergence within each functional taste quality. Each possibility has functional implications for the system.SIGNIFICANCE STATEMENT Taste neurons are considered relay cells, communicating information from taste-transducing cells to the brain, without variation in morphology. By reconstructing peripheral taste neuron morphologies for the first time, we found that some peripheral gustatory neurons are simply branched, and can receive input from only a few taste-transducing cells. Other taste neurons are heavily branched, contacting many more taste-transducing cells than simply branched neurons. Based on the type of taste-transducing cell contacted, branching characteristics are predicted to differ across (and within) quality types (sweet/bitter/umami vs sour). Therefore, functional differences between neurons likely depends on the number of taste-transducing cells providing input and not just the type of cell providing input.     

Intact hedonic responses to sweet tastes in autism spectrum disorder

The Sweet Taste Test (STT) is a standardized measure designed to index the ability to detect differences in sweet tastes (sweet taste sensitivity) and hedonic responses to sweet tastes (sweet taste liking). Profiles of response on the STT suggest enhanced hedonic responses to sweet tastes in psychiatric disorders characterized by dysfunctional reward processing systems, including binge-eating disorders and substance use disorders, and a putative mechanism governing STT responses is the brain opioid system. The present study examined STT responses in 20 adults with autism spectrum disorder (ASD) and 38 healthy control adults. There were no differences in sweet taste sensitivity or hedonic response to sweet tastes between the ASD and control groups. Within the ASD sample, ASD symptom severity was associated with sweet taste sensitivity, but not hedonic response to sweet taste. Results may ultimately shed light on brain opioid system functioning in ASD.     

Rebaudioside A and Rebaudioside D Bitterness do not Covary with Acesulfame-K Bitterness or Polymorphisms in TAS2R9 and TAS2R31

In order to reduce calories in foods and beverages, the food industry routinely uses non-nutritive sweeteners. Unfortunately, many are synthetically derived, and many consumers have a strong preference for natural sweeteners, irrespective of the safety data on synthetic non-nutritive sweeteners. Additionally, many non-nutritive sweeteners elicit aversive side tastes, such as bitter and metallic, in addition to sweetness. Bitterness thresholds of acesulfame-K (AceK) and saccharin are known to vary across bitter taste receptor polymorphisms in TAS2R31. Rebaudioside A (RebA) has been shown to activate hTAS2R4 and hTAS2R14 in vitro. Here, we examined the bitterness and sweetness perception of natural and synthetic non-nutritive sweeteners. In a follow-up to a previous gene association study, participants (n?=?122) who had been genotyped previously rated sweet, bitter, and metallic sensations from RebA, rebaudioside D (RebD), aspartame, sucrose, and gentiobiose in duplicate in a single session. For comparison, we also present sweet and bitter ratings of AceK collected in the original experiment for the same participants. At similar sweetness levels, aspartame elicited less bitterness than RebD, which was significantly less bitter than RebA. The bitterness of RebA and RebD showed wide variability across individuals, and bitterness ratings for these compounds were correlated. However, RebA and RebD bitterness did not covary with AceK bitterness. Likewise, single-nucleotide polymorphisms (SNPs) shown previously to explain the variation in the suprathreshold bitterness of AceK (rs3741845 in TAS2R9 and rs10772423 in TAS2R31) did not explain the variation in RebA and RebD bitterness. Because RebA activates hT2R4 and hT2R14, an SNP in TAS2R4 previously associated with variation in bitterness perception was included here; there are no known functional SNPs for TAS2R14. In the present data, a putatively functional SNP (rs2234001) in TAS2R4 did not explain the variation in RebA or RebD bitterness. Collectively, these data indicate that the bitterness of RebA and RebD cannot be predicted by AceK bitterness, reinforcing our view that bitterness is not a simple monolithic trait that is high or low in an individual. This also implies that consumers who reject AceK may not find RebA and RebD aversive, and vice versa. Finally, RebD may be a superior natural non-nutritive sweetener to RebA, as it elicits significantly less bitterness at similar levels of sweetness.