Modern psychophysics and the assessment of human oral sensation

Comparing Taste Perception Across Modalities in Healthy Adults: Liquids Versus Dissolvable Taste Strips

Taste stimulation has rehabilitative value in dysphagia management, as it activates salient underlying afferent pathways to swallowing which may evoke feedforward effects on swallow biomechanics. Despite its potential beneficial effects on swallow physiology, taste stimulation's clinical application is limited for persons unsafe to orally consume food/liquid. This study aimed to create edible, dissolvable taste strips matched to flavor profiles previously used in research assessing taste's effects on swallowing physiology and brain activity, and to evaluate how similar their perceived intensity and hedonic, or palatability, ratings were between their liquid counterparts. Plain, sour, sweet-sour, lemon, and orange flavor profiles were custom-made in taste strips and liquid modalities. The generalized Labeled Magnitude Scale and hedonic generalized Labeled Magnitude Scale were used to assess intensity and palatability ratings for flavor profiles in each modality. Healthy participants were recruited and stratified across age and sex. Liquids were rated as more intense than taste strips; however, there was no difference in palatability ratings between the modalities. There were significant differences across flavor profiles in intensity and palatability ratings. Collapsed across liquid and taste strip modalities, pairwise comparisons revealed all flavored stimuli were rated as more intense than the plain profile, sour was perceived as more intense and less palatable than all other profiles, and orange was rated as more palatable than sour, lemon, and plain tastants. Taste strips have useful implications for dysphagia management, as they could offer safe and patient-preferred flavor profiles to potentially provide advantageous swallowing and neural hemodynamic responses.

The Effect of Genetic Taste Status on Swallowing: A Literature Review

PURPOSE

Swallowing and taste share innervation pathways and are crucial to nutritive intake. Individuals vary in their perception of taste due to factors such as genetics; however, it is unclear to what extent genetic taste status influences swallowing physiology and function. The purpose of this review article is to provide background on genetic taste status, review the evidence on the association between genetic taste status and swallowing, and discuss research and clinical implications.

METHOD

A comprehensive literature review was conducted using search terms related to swallowing and genetic taste status. Studies were included if they investigated the main effect of genetic taste status on swallowing or the interaction of genetic taste status with other variables. Studies were grouped by participant population (healthy participants or persons with a swallowing disorder), swallowing-related outcome measure, and method of genetic taste status measurement.

RESULTS

The results were mixed, with five of 10 reviewed studies reporting a statistically significant main or interaction effect on swallowing. Most studies included healthy participants, with only one study investigating participants with dysphagia. Additionally, swallowing-related outcome measures and methods of determining genetic taste status varied greatly between studies conducted on separate cohorts.

CONCLUSIONS

Few studies have incorporated genetic taste status as a variable in swallowing research, and results are mixed. Future research on sensation and swallowing should consider the potential effect of genetic taste status and follow standardized procedures for its determination. Despite the limited evidence, clinicians may consider how individual differences in perception shape swallowing outcomes.

Taste and Smell Disorders in Cancer Treatment: Results from an Integrative Rapid Systematic Review

Taste and smell disorders (TSDs) are common side effects in patients undergoing cancer treatments. Knowing which treatments specifically cause them is crucial to improve patients' quality of life. This review looked at the oncological treatments that cause taste and smell alterations and their time of onset. We performed an integrative rapid review. The PubMed, PROSPERO, and Web of Science databases were searched in November 2022. The article screening and study selection were conducted independently by two reviewers. Data were analyzed narratively. Fourteen studies met the inclusion criteria and were included. A high heterogeneity was detected. Taste disorders ranged between 17 and 86%, while dysosmia ranged between 8 and 45%. Docetaxel, paclitaxel, nab-paclitaxel, capecitabine, cyclophosphamide, epirubicin, anthracyclines, and oral 5-FU analogues were found to be the drugs most frequently associated with TSDs. This review identifies the cancer treatments that mainly lead to taste and smell changes and provides evidence for wider studies, including those focusing on prevention. Further studies are warranted to make conclusive indication possible.

The effect of taste on swallowing: A scoping and systematic review

Consuming foods and liquids for nutrition requires the coordination of several muscles. Swallowing is triggered and modified by sensory inputs from the aerodigestive tract. Taste has recently received attention as a potential modulator of swallowing physiology, function, and neural activation; additionally, taste impairment is a sequela of COVID-19. This review presents factors impacting taste and swallowing, systematically summarizes the existing literature, and assesses the quality of included studies. A search was conducted for original research including taste stimulation, deglutition-related measure(s), and human participants. Study design, independent and dependent variables, and participant characteristics were coded; included studies were assessed for quality and risk of bias. Forty-eight articles were included after abstract and full-text review. Synthesis was complicated by variable sensory components of stimuli (taste category and intensity, pure taste vs. flavor, chemesthesis, volume/amount, consistency, temperature), participant characteristics, confounding variables such as genetic taster status, and methods of measurement. Most studies had a high risk of at least one type of bias and were of fair or poor quality. Interpretation is limited by wide variability in methods, taste stimulation, confounding factors, and lower-quality evidence. Existing studies suggest that taste can modulate swallowing, but more rigorous and standardized research is needed.

Capsaicin burn increases thickness discrimination thresholds independently of chronic chili intake

The trigeminal nerve transduces both chemical irritation and textural sensations suggesting that perception in one may influence perception in the other. Little is known about how the oral burn of capsaicin may affect texture sensitivity. The aim of this study was to determine the effect of burning sensations on thickness discrimination thresholds in liquid foods assessed by consumers who vary in habitual spicy food intake. Forty-seven Caucasian participants (31 females and 16 males; mean age: 25.0 ± 5.7 yrs; mean BMI: 21.5 ± 2.6 kg/m²) were recruited in the Netherlands. Chili pepper intake frequency and preference for chili peppers and spicy foods were assessed using questionnaires. Perceived burn and disliking/liking of bouillon soups thickened with xanthan gum (concentrations ranging from 0.06 to 0.21 g/mL; viscosity at 50 s^-1 (η_50s-1) ranging from 11 to 48 mPas) containing varying amounts of capsaicin (0, 1, or 10 ppm) were determined using generalized scales (gLMS and gDOL). Estimates of thickness discrimination thresholds were determined using the 2-Alternative Forced Choice ascending staircase method. Capsaicin was applied in two ways: (i) capsaicin was added directly to the soups or (ii) a pre-rinse of a capsaicin solution was held in mouth before evaluating soups without capsaicin. As expected, frequent chili pepper consumers reported significantly lower burn intensity and higher hedonic ratings compared to infrequent consumers. Thickness discrimination thresholds (i.e., BET expressed as Δη_50s-1) increased significantly from 11.3 mPas at 0 ppm to 16.1 mPas at 1 ppm (42% increase) to 21.4 mPas at 10 ppm capsaicin (89% increase) on average across all participants. Similar modification of thickness discrimination thresholds were observed regardless of whether capsaicin was added to the soup or was applied as a pre-rinse. No significant differences in thickness discrimination thresholds were observed between infrequent and frequent chili consumers. We conclude that oral burn caused by capsaicin affects thickness discrimination independently of reported chili pepper intake. Also, we suggest the ability of capsaicin to alter thickness discrimination may be due to increased neural noise, attentional effects or cross-modal interactions.

Phenol-Rich Food Acceptability: The Influence of Variations in Sweetness Optima and Sensory-Liking Patterns

The consumption of phenol-rich foods is limited by their prominent bitterness and astringency. This issue has been addressed by adding sweet tastes, which suppress bitterness, but this is not a complete solution since individuals also differ in their preference for sweetness. In this study, we aimed at identifying groups of consumers differing in sweetness optima and sensory-liking patterns. To this end, increasing concentrations of sucrose were added to a chocolate pudding base. This allowed us to (1) investigate if individual differences in sensory responses are associated with different sweet liking optima in a product context, (2) define the psychological and oro-sensory profile of sweet liker phenotypes derived using a product context, and (3) assess if individuals differing in sweet liking optima differ also in consumption and liking of phenol-rich foods and beverages as a function of their sensory properties (e.g., sweeter vs. more bitter and astringent products). Individuals (1208; 58.4% women, 18–69 years) were characterised for demographics, responsiveness to 6-n-propylthiouracil (PROP), personality traits and attitudes toward foods. Three clusters were identified based on correlations between sensory responses (sweetness, bitterness and astringency) and liking of the samples: liking was positively related to sweetness and negatively to bitterness and astringency in High and Moderate Sweet Likers, and the opposite in Inverted U-Shaped. Differences between clusters were found in age, gender and personality. Furthermore, the Inverted-U Shaped cluster was found to have overall healthier food behaviours and preferences, with higher liking and consumption of phenol-rich vegetables and beverages without added sugar. These findings point out the importance of identifying the individual sensory-liking patterns in order to develop more effective strategies to promote the acceptability of healthy phenol-rich foods.

Factors affecting detection of bimodal sour-savory mixture and inter-individual umami taste perception

While basic taste interactions have been the subject of many research studies, there is one combination where data is limited in the literature: sour and umami. This combination is universal in culinary preparations and of key interest to the food industry. Therefore, the primary goal of the present study is to assess how increasing concentrations of acidity (citric acid) affect, if at all, the intensity of a constant concentration of umami (monosodium glutamate, MSG). The secondary goal is to investigate other possible factors in umami taste perception. Here, a crowdsourced cohort of 734 individuals (age range 8-81) tasted and rated the intensity of 50 mM MSG alone, and in combination with citric acid at varying concentrations (1.25 mM, 6.25 mM, 31.25 mM). Participants were also genotyped for the single nucleotide polymorphism rs34160967 in the T1R1 gene. The results show a significant decrease in the intensity perception of umami as sour concentration increases (low: p = 0.005, medium: p < 0.001, high: p < 0.001). Situational factors such as participant hunger level and time since last eating also have a significant effect on umami intensity perception. Neither the biological factors of sex, age, and ancestry appear to play a role in umami perception, nor does variation in gene TAS1R1 at rs34160967. These new data contribute to the growing field of taste and sensory interaction by giving evidence that sour suppresses umami taste perception in bi-model samples.

Regional Variation of Bitter Taste and Aftertaste in Humans

Despite widespread and persistent myths of a tongue map, all 5 prototypical taste qualities are sensed over the entire tongue. However, modern psychophysical data also suggest there may be more nuanced differences in suprathreshold intensity across oral loci, especially for bitterness. Here, we test whether bitter stimuli matched for whole-mouth intensity differ in perceived intensity across regions of the oral cavity in 2 experiments. Experiment 1 consisted of a whole-mouth sip and spit approach and Experiment 2 consisted of a spatial taste test using cotton swabs. In Experiment 1, participants (n = 63) rated overall intensity of 3 bitter solutions at 5 different loci (front, middle, back of tongue; roof of mouth; and lip). Temporal effects were explored using in-mouth and aftertaste ratings. In Experiment 2, participants (n = 48) rated the intensity of quinine and Tetralone solutions after solutions were painted on fungiform, circumvallate, and foliate papillae with a swab. After the spatial taste test, participants completed a questionnaire on self-reported beer intake. Analysis of variance results of both experiments show a significant locus by stimulus interaction, suggesting different bitterants were perceived differently across the various loci. This result was apparently driven by low-intensity ratings for Tetralone on the anterior tongue. Aftertaste ratings in Experiment 1 also revealed significant temporal effects: ratings on the anterior tongue decreased for all bitterants and ratings for quinine decreased at all loci. Reasons for these effects are not known but may suggest differential expression of bitter taste receptors or differences in bitter agonist-receptor binding affinity across tongue regions.

Patient-reported taste change assessment questionnaires used in the oncology setting: A narrative review

PURPOSE

Patient-reported questionnaires to assess taste changes (TC) among patients with cancer and the common domains or aspects assessed by those questionnaires are identified in this narrative review. Taste changes are a prevalent symptom experienced by patients with cancer that impact food choice and enjoyment, reduce food intake, and diminish quality of life. Appropriate assessment is essential to detect and manage this symptom.

METHOD

A systematic search of relevant databases between 1999 and 2018 yielded 1959 articles; 38 articles were included in the review.

RESULTS

Seventeen questionnaires designed specifically to assess patient-reported taste changes among patients with cancer are described in the review. Seven domains were identified among the questionnaires; the most frequently assessed domain was the description of the taste change in 14 questionnaires). Timeframe, scoring, number of items and domains, and item phrasing varied greatly among questionnaires and the approach to domain and item evaluation was inconsistent. Comprehensive questionnaires (n = 7) assessed five or more domains to characterize the taste change experience. The majority of questionnaires have been cited only once or twice.

CONCLUSION

Patient-reported taste change assessment in oncology has been achieved by a large number of diverse questionnaires; no standard tool or approach is used. Development of a question bank of validated or standardized taste change modules or items may strengthen the consistency and applicability of research in this area.

A Systematic Review of Taste Differences Among People With Eating Disorders

BACKGROUND

Eating disorders are a significant cause of morbidity and mortality. The etiology and maintenance of eating-disorder symptoms are not well understood. Evidence suggests that there may be gustatory alterations in patients with eating disorders.

OBJECTIVE

This article systematically reviews research assessing gustatory differences in patients with anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED).

METHOD

A systematic review was performed, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, examining taste and eating disorders. We reviewed electronic databases and identified 1,490 peer-reviewed English-language studies. Of these, 49 met inclusion criteria.

RESULTS

Studies employed psychophysical measures (n = 27), self-reported questionnaires (n = 5), and neuroimaging techniques (i.e., electroencephalography, functional magnetic resonance imaging; n = 17). Psychophysical studies showed that individuals with BN, in general, had greater preference for sweetness than healthy controls, and those with AN had a greater aversion for fat than controls. In neuroimaging studies, findings suggested that predictable administration of sweet-taste stimuli was associated with reduced activation in taste-reward regions of the brain among individuals with AN (e.g., insula, ventral, and dorsal striatum) but increased activation in BN and BED.

DISCUSSION

To our knowledge, this systematic review is the first to synthesize literature on taste differences in AN, BN, and BED. The inconsistency and variability in methods used across studies increased difficulties in comparing studies and disease processes. Further studies with well-defined population parameters are warranted to better understand how taste varies in patients with eating disorders.

Putting out the fire - Efficacy of common beverages in reducing oral burn from capsaicin

Capsaicin is classically considered an irritant, due to the warming and burning sensations it elicits. Widespread consumption of chilis suggests many individuals enjoy this burn, but these sensations can be overwhelming if the burn is too intense. While substantial folklore exists on the ability of specific beverages to mitigate capsaicin burn, quantitative data to support these claims are generally lacking. Here, we systematically tested various beverages for their ability to reduce oral burn following consumption of capsaicin in tomato juice. Participants (n = 72, 42 women, 30 men) rated the burn of 30 mL of spicy tomato juice on a general Labeled Magnitude Scale (gLMS) immediately after swallowing, and again every 10 s for 2 min. On 7 of 8 trials, a test beverage (40 mL) was consumed after tomato juice was swallowed, including: skim milk, whole milk, seltzer water, Cherry Kool-Aid, non-alcoholic beer, cola, and water. Participants also answered questions regarding intake frequency and liking of spicy food. Initial burn of tomato juice alone was rated below "strong" but above "moderate" on a gLMS and continued to decay over the 2 min to a mean just above "weak". All beverages significantly reduced the burn of the tomato juice. To quantify efficacy over time, area under the curve (AUC) values were calculated, and the largest reductions in burn were observed for whole milk, skim milk, and Kool-Aid. More work is needed to determine the mechanism(s) by which these beverages reduce burn (i.e., partitioning due to fat, binding by protein, or sucrose analgesia). Present data suggest milk is the best choice to mitigate burn, regardless of fat context, suggesting the presence of protein may be more relevant than lipid content.

Rheological parameters of saliva in comparison with taste examination

BACKGROUND

It is generally unknown if taste sensitivity is dependent upon saliva viscosity. The rheological properties of saliva result from many factors and it has been shown to behave as a non-Newtonian fluid whose viscosity decreases with increasing shear rate. Taste sensitivity may be quantitatively assayed by electro-gustometry.

OBJECTIVES

The aim of this work was to compare saliva rheological properties, obtained with a rotary-oscillating rheometer, to quantitative measures of taste sensitivity, using electro-gustometry.

METHODS

Saliva samples were taken from 27 healthy non-smoking donors - 7 men and 20 women aged 18-65 years (mean age - 37 years). After thresholds of taste sensation were measured, the saliva samples were taken and characterized in terms of their rheological properties and pH. Saliva viscosity was measured in the order of decreasing shear rate in the range 100-0.01 s-1. Viscoelastic properties were examined under constant frequency oscillations (with f = 0.5 Hz) and with decreasing shear effective amplitude γeff'.

RESULTS AND CONCLUSIONS

Saliva viscosity was found to decrease with increasing shear rate and varied with time. Analysis of the dependence of the viscosity values of saliva and components of complex viscosity did not show a significant correlation with taste sensation. A dependency of taste sensation on pH could not be discerned due to the narrow range of naturally occurring pH.

Use of Adult Sensory Panel to Study Individual Differences in the Palatability of a Pediatric HIV Treatment Drug

PURPOSE

The recommended first-line treatment for young children infected with HIV includes the liquid formulation of the co-formulated protease inhibitors lopinavir/ritonavir (Kaletra® [Abbott Laboratories, Chicago, Illinois]). Clinical reports indicate that some children readily accept the taste of Kaletra, whereas others strongly reject it, which can deter therapeutic adherence and outcomes.

METHODS

As a proof-of-concept approach, a sensory panel of genotyped adults was used to document the range of individual differences in the taste and palatability (hedonics) of the liquid formulation of Kaletra and other taste stimuli, including common excipients. Panelists rated taste sensations using generalized labeled magnitude scales to determine genotype-phenotype relationships. Several months later, the panelists were retested to assess response reliability.

FINDINGS

Not all panelists had the same sensory experience when tasting Kaletra. Palatability ratings varied widely, from moderate like to strongest imaginable dislike, and were reliable over time. The more irritating and bitter Kaletra tasted, the more disliked by the panelist. The more they disliked the taste of Kaletra, the more they disliked the taste of its excipient ethanol and the bitter stimulus denatonium. Those who experienced less bitter and sweeter taste sensations had a different genetic signature than the other panelists. Bitterness and irritation ratings of Kaletra varied by the orphaned bitter receptor gene (TAS2R60), whereas sweetness ratings of Kaletra varied according to the cold receptor gene (TRPM8), which is activated by menthol, an excipient of Kaletra. Neither genotype related to ratings for ethanol or denatonium, however.

IMPLICATIONS

The use of a sensory panel holds promise as a first step in determining the nature of individual differences in the palatability of existing pediatric drug formulations and sources of variation. In this era of personalized medicine, the need is great to develop psychophysical tools to determine which drugs will show variation in acceptance by children and whether patterns of individual variation in taste as assessed by adults mirror those of young patients. ClinicalTrials.gov identifier: NCT01841710.

Effect of cigarette smoke on gustatory sensitivity, evaluation of the deficit and of the recovery time-course after smoking cessation

BACKGROUND

Study results have shown that chronic exposure to cigarette smoke affects the taste function in humans. However, neither the quantitative impact on taste sensitivity nor the time-course of taste recovery on stopping smoking have been precisely examined.

METHODS

The experimental design included 2 phases, (i) a case-control phase comparing the taste sensitivity level measured by Electrogustometric (EGM) thresholds from various parts of the tongue (locus) between smokers (n = 83) and non-smokers (n = 48), (ii) a follow-up study looking at the taste sensitivity recovery in smokers after smoking cessation (n = 24) and compared with non-smokers.

RESULTS

Smokers exhibited significantly lower taste sensitivity than non-smokers - the higher the nicotine dependence (Fagerström scores), the lower the taste sensitivity. After smoking cessation, EGM thresholds decreased progressively, and reached the taste sensitivity range of non-smokers depending on locus and time. After 2 weeks a recovery could be observed on the 3 Tip and the 2 edge loci; the recovery in the posterior loci was complete after 9 weeks, and in the dorsal loci recovery was observed only after 2 months or more.

CONCLUSIONS

Smoking cessation does lead to a rapid recovery of taste sensitivity among smokers, with recovery time found to differ based on the sensitivity of loci of the tongue. The use of EGM could potentially be explored as a motivational tool for smoking cessation.

Psychophysical Evaluation of Sweetness Functions Across Multiple Sweeteners

Sweetness is one of the 5 prototypical tastes and is activated by sugars and non-nutritive sweeteners (NNS). The aim of this study was to investigate measures of sweet taste function [detection threshold (DT), recognition threshold (RT), and suprathreshold intensity ratings] across multiple sweeteners. Sixty participants, 18–52 years of age (mean age in years = 26, SD = ±7.8), were recruited to participate in the study. DT and RT were collected for caloric sweeteners (glucose, fructose, sucrose, erythritol) and NNS (sucralose, rebaudioside A). Sweetness intensity for all sweeteners was measured using a general Labeled Magnitude Scale. There were strong correlations between DT and RT of all 4 caloric sweeteners across people (r = 0.62–0.90, P < 0.001), and moderate correlations between DT and RT for both of the NNS (r = 0.39–0.48, P < 0.05); however, weaker correlations were observed between the DT or RT of the caloric sweeteners and NNS (r = 0.26–0.48, P < 0.05). The DT and RT of glucose and fructose were not correlated with DT or RT of sucralose (P > 0.05). In contrast, there were strong correlations between the sweetness intensity ratings of all sweeteners (r = 0.70–0.96, P < 0.001). This suggests those caloric sweeteners and NNS access at least partially independent mechanisms with respect to DT and RT measures. At suprathreshold level, however, the strong correlation between caloric sweeteners and NNS through weak, moderate, and strong intensity indicates a commonality in sweet taste mechanism for the perceived intensity range.

Nonnutritive sweeteners are not supernormal stimuli

BACKGROUND

It is often claimed that nonnutritive sweeteners (NNS) are 'sweeter than sugar', with the implicit implication that high-potency sweeteners are supernormal stimuli that encourage exaggerated responses. This study aimed to investigate the perceived sweetness intensity of a variety of nutritive sweeteners (sucrose, maple syrup and agave nectar) and NNS (acesulfame-K (AceK), rebaudioside A (RebA), aspartame and sucralose) in a large cohort of untrained participants using contemporary psychophysical methods.

METHODS

Participants (n=401 total) rated the intensity of sweet, bitter and metallic sensations for nutritive sweeteners and NNS in water using the general labeled magnitude scale.

RESULTS

Sigmoidal dose-response functions were observed for all stimuli except AceK. That is, sucrose follows a sigmoidal function if the data are not artifactually linearized via prior training. More critically, there is no evidence that NNS have a maximal sweetness (intensity) greater than sucrose; indeed, the maximal sweetness for AceK, RebA and sucralose were significantly lower than that for concentrated sucrose. For these sweeteners, mixture suppression due to endogenous dose-dependent bitter or metallic sensations appears to limit maximal perceived sweetness.

CONCLUSIONS

In terms of perceived sweetness, NNS cannot be considered supernormal stimuli. These data do not support the view that NNS hijack or overstimulate sweet receptors to produce elevated sweet sensations.

The effect of barium on perceptions of taste intensity and palatability

Barium may affect the perception of taste intensity and palatability. Such differences are important considerations in the selection of dysphagia assessment strategies and interpretation of results. Eighty healthy women grouped by age (younger, older) and genetic taste status (supertaster, nontaster) rated intensity and palatability for seven tastants prepared in deionized water with and without 40 % w/v barium: noncarbonated and carbonated water, diluted ethanol, and high concentrations of citric acid (sour), sodium chloride (salty), caffeine (bitter), and sucrose (sweet). Mixed-model analyses explored the effects of barium, taster status, and age on perceived taste intensity and acceptability of stimuli. Barium was associated with lower taste intensity ratings for sweet, salty, and bitter tastants, higher taste intensity in carbonated water, and lower palatability in water, sweet, sour, and carbonated water. Older subjects reported lower palatability (all barium samples, sour) and higher taste intensity scores (ethanol, sweet, sour) compared to younger subjects. Supertasters reported higher taste intensity (ethanol, sweet, sour, salty, bitter) and lower palatability (ethanol, salty, bitter) than nontasters. Refusal rates were highest for younger subjects and supertasters, and for barium (regardless of tastant), bitter, and ethanol. Barium suppressed the perceived intensity of some tastes and reduced palatability. These effects are more pronounced in older subjects and supertasters, but younger supertasters are least likely to tolerate trials of barium and strong tastant solutions.

A high throughput in vivo assay for taste quality and palatability

Taste quality and palatability are two of the most important properties measured in the evaluation of taste stimuli. Human panels can report both aspects, but are of limited experimental flexibility and throughput capacity. Relatively efficient animal models for taste evaluation have been developed, but each of them is designed to measure either taste quality or palatability as independent experimental endpoints. We present here a new apparatus and method for high throughput quantification of both taste quality and palatability using rats in an operant taste discrimination paradigm. Cohorts of four rats were trained in a modified operant chamber to sample taste stimuli by licking solutions from a 96-well plate that moved in a randomized pattern beneath the chamber floor. As a rat's tongue entered the well it disrupted a laser beam projecting across the top of the 96-well plate, consequently producing two retractable levers that operated a pellet dispenser. The taste of sucrose was associated with food reinforcement by presses on a sucrose-designated lever, whereas the taste of water and other basic tastes were associated with the alternative lever. Each disruption of the laser was counted as a lick. Using this procedure, rats were trained to discriminate 100 mM sucrose from water, quinine, citric acid, and NaCl with 90-100% accuracy. Palatability was determined by the number of licks per trial and, due to intermediate rates of licking for water, was quantifiable along the entire spectrum of appetitiveness to aversiveness. All 96 samples were evaluated within 90 minute test sessions with no evidence of desensitization or fatigue. The technology is capable of generating multiple concentration-response functions within a single session, is suitable for in vivo primary screening of tastant libraries, and potentially can be used to evaluate stimuli for any taste system.

Direct comparison of the generalized Visual Analog Scale (gVAS) and general Labeled Magnitude Scale (gLMS)

Hundreds of studies have used the generalized Labeled Magnitude Scale (gLMS) to collect intensity data. Recent work on generalized affective scales like the Labeled Affective Magnitude (LAM) scale and Labeled Hedonic Scale (LHS) suggest a substantial proportion of participants fail to use the entire range of generalized scales, marking only at the adjective labels. This categorical behavior (i.e., clustering) is not limited to affective ratings, as it is well known anecdotally among users of the gLMS. One way to stop this behavior would be to retain a generalized top anchor and cross modal orientation procedure while stripping away the internal adjectives. Several published studies have already used this variant, the generalized Visual Analog Scale (gVAS). Because there are no reports directly comparing the gVAS and gLMS head to head, we did so in two experiments. In Experiment 1, participants (n=87) were randomized to 1 of 3 conditions to test effects of scaling instructions and scale structure. In Experiment 2, participants (n=58) assessed perceived ease of use and resolving power for each scale in a two-session crossover design. gLMS data showed evidence of categorical behavior, while gVAS data did not. Explicitly instructing participants to rate between adjectives did not reduce this behavior. The gLMS was easier to use according to participants, but resulted in non-normal data due to clustering near the adjective labels. gVAS data did not show categorical behavior, as there are no adjectives to cluster around, but the gVAS sacrifices semantic information about the magnitude of response. Regardless of scale type, participants felt the cross-modal orientation procedure helped them understand how to use the scale. Both scales were able to discriminate between sucrose samples in a concentration series. Relative tradeoffs between the two methods suggest the choice of one scale over the other depends on the specific goals and context of the project.

Evidence of hearing loss in a 'normally-hearing' college-student population

We report pure-tone hearing threshold findings in 56 college students. All subjects reported normal hearing during telephone interviews, yet not all subjects had normal sensitivity as defined by well-accepted criteria. At one or more test frequencies (0.25-8 kHz), 7% of ears had thresholds ≥25 dB HL and 12% had thresholds ≥20 dB HL. The proportion of ears with abnormal findings decreased when three-frequency pure-tone-averages were used. Low-frequency PTA hearing loss was detected in 2.7% of ears and high-frequency PTA hearing loss was detected in 7.1% of ears; however, there was little evidence for 'notched' audiograms. There was a statistically reliable relationship in which personal music player use was correlated with decreased hearing status in male subjects. Routine screening and education regarding hearing loss risk factors are critical as college students do not always self-identify early changes in hearing. Large-scale systematic investigations of college students' hearing status appear to be warranted; the current sample size was not adequate to precisely measure potential contributions of different sound sources to the elevated thresholds measured in some subjects.

Evidence of hearing loss in a 'normally-hearing' college-student population

We report pure-tone hearing threshold findings in 56 college students. All subjects reported normal hearing during telephone interviews, yet not all subjects had normal sensitivity as defined by well-accepted criteria. At one or more test frequencies (0.25-8 kHz), 7% of ears had thresholds ≥25 dB HL and 12% had thresholds ≥20 dB HL. The proportion of ears with abnormal findings decreased when three-frequency pure-tone-averages were used. Low-frequency PTA hearing loss was detected in 2.7% of ears and high-frequency PTA hearing loss was detected in 7.1% of ears; however, there was little evidence for 'notched' audiograms. There was a statistically reliable relationship in which personal music player use was correlated with decreased hearing status in male subjects. Routine screening and education regarding hearing loss risk factors are critical as college students do not always self-identify early changes in hearing. Large-scale systematic investigations of college students' hearing status appear to be warranted; the current sample size was not adequate to precisely measure potential contributions of different sound sources to the elevated thresholds measured in some subjects.

Vegetable Intake in College-Aged Adults Is Explained by Oral Sensory Phenotypes and TAS2R38 Genotype

Taste and oral sensations vary in humans. Some of this variation has a genetic basis, and two commonly measured phenotypes are the bitterness of propylthiouracil (PROP) and the number of fungiform papillae on the anterior tongue. While the genetic control of fungiform papilla is unclear, PROP bitterness associates with allelic variation in the taste receptor gene, TAS2R38. The two common alleles are AVI and PAV (proline, alanine, valine, and isoleucine); AVI/AVI homozygotes taste PROP as less bitter than heterozygous or homozygous PAV carriers. In this laboratory-based study, we determined whether taste of a bitter probe (quinine) and vegetable intake varied by taste phenotypes and TAS2R38 genotype in healthy adults (mean age=26 years). Vegetable intake was assessed via two validated, complementary methods: food records (Food Pyramid servings standardized to energy intake) and food frequency questionnaire (general intake question and composite vegetable groups). Quinine bitterness varied with phenotypes but not TAS2R38; quinine was more bitter to those who tasted PROP as more bitter or had more papillae. Nontasters by phenotype or genotype reported greater consumption of vegetables, regardless of type (i.e., the effect generalized to all vegetables and was not restricted to those typically thought of as being bitter). Furthermore, nontasters with more papillae reported greater vegetable consumption than nontasters with fewer papillae, suggesting that when bitterness does not predominate, more papillae enhance vegetable liking. These findings suggest that genetic variation in taste, measured by multiple phenotypes or TAS2R38 genotype, can explain differences in overall consumption of vegetables, and this was not restricted to vegetables that are predominantly bitter.

Epidemiological studies of taste function: discussion and perspectives

Efforts to quantify the public health impact of chemosensation present significant challenges, including a strong need for testing methods suitable for field assessment. This discussion highlights several promising approaches to the population-based study of taste function; it also identifies key principles that should be considered when adapting laboratory-based taste tests for field use.

Optimizing oral medications for children

BACKGROUND

Active pharmaceutical ingredients that taste bitter and/or irritate the mouth and throat are aversive to children as well as many adults. Effective methods of avoiding unpleasant tastes for adults (eg, encapsulating the medicine in pill, capsule, or tablet form) are problematic because many children cannot or will not swallow these. The unpalatable flavor of the medicine can thwart the benefits of even the most powerful of drugs. Failure to consume medication may do the child harm and can even be life-threatening.

OBJECTIVES

This article provides an overview of the current knowledge of the sensory capabilities and preferences of children as it relates to flavor, defined here as the combined input of taste, smell, and chemical irritation. The methods used to evaluate flavor perception in children are reviewed. Recent scientific advances are summarized that shed light on why the bitter taste of oral pharmaceuticals is an ongoing formulation problem and how discoveries of novel flavor molecules and modulators of bitter tastes hold considerable promise for the future. Alternative methods for evaluation of the palatability of medicines are described.

METHODS

The Eunice Kennedy Shriver National Institute of Child Health and Human Development sponsored a Pediatric Formulation Initiative workshop on December 6 and 7, 2005, in Bethesda, Maryland. Information for this article was gathered from literature reviews that were then discussed during this workshop as well as during several conference calls with the Taste and Flavor Working Group members. Terms for the MEDLINE search (1970-2007) included infant, children, taste, olfaction/smell, flavor, chemical senses, palatability, sensory testing, pharmaceutical, and medicines.

RESULTS

Children have well-developed sensory systems for detecting tastes, smells, and chemical irritants, and their rejection of unpalatable medications is a reflection of their basic biology. Sugars, salt, and other substances reportedly reduce the bitterness of several pharmaceuticals. Adding pleasant flavor volatiles such as bubble gum may help induce children to consume a medicine, but such volatile compounds are not effective in suppressing the strong bitter tastes associated with some medications. Also, because individual experiences and culture mainly determine which odors are attractive, a universally appealing volatile flavoring agent may be difficult to identify. Sensory panelists who are sensitive to the pediatric palate, which is different from adults, and new techniques involving animal models, isolated parts of the receptor cells, and even electronic devices that detect taste and flavor are among the tools that may be used to evaluate the palatability of medications and predict compliance among pediatric populations.

CONCLUSIONS

Although there are no easy solutions to this dilemma, children's acceptance of many medicines can be improved by applying the knowledge gleaned from basic research in the chemical senses. Further development and validation of sensory methods will provide a better understanding of the sensory world of the child. This understanding, combined with new technologies and results of animal model studies, will enhance drug acceptance and compliance in pediatric populations. A better understanding of the scientific basis for distaste and how to ameliorate it is a public health priority.