RELATIONSHIPS BETWEEN BITTER TASTE SENSITIVITY AND CONSUMPTION OF BITTER SUBSTANCES

The effect of consumption of bitter taste substances (caffeine and beer) to bitter taste sensitivity was examined by 19 healthy adults. For individual taste sensitivity, detection thresholds were used on 6 bitter substances (caffeine, iso-alpha-acids: beer bittering agents, quinine sulfate, L-tryptophan, L-phenylalanine and glycyl-L-phenylalanyl-L-phenylalanine) and 3 non-bitter substances (L-aspartic acid, aspartame and NaCl). Nonusers of caffeine had significantly higher sensitivity (lower threshold) for caffeine compared to moderate and heavy users. Slight consumers of beer had significantly higher sensitivity for iso-alpha-acids relative to heavy users of beer, Iso-alpha-acids were not detected in saliva in acute dosing test by using 6 subjects. The correlations between thresholds of 6 bitter substances were calculated. Significant correlations (p < 0.01) were noted in 2 cases between caffeine and quinine, and iso-alpha-acids and L-trypothan. These data suggest the significant relation between individual bitter taste sensitivity and the consumption of caffeine and beer (iso-alpha-acids).     

A RESEARCH NOTE: COMPARISON OF TIME-INTENSITY AND THRESHOLD MEASURES FOR DETERMINING BITTER TASTE SENSITIVITY OF CAFFEINE USER AND NONUSER

Two taste sensitivity measures (detection threshold and time-intensity [T/I]) were applied to evaluate bitter taste sensitivity of caffeine in both caffeine nonusers (n = 12) and users (n=12, caffeine consumption level; > 300mg/day). Taste thresholds of caffeine were significantly different between nonusers and users in two test sessions (p < 0.01 in first and p < 0.05 in second). In T/I measures, only the difference in peak height was observed between the two groups in one of two test sessions. The other two measures, half width and area of T/I curves showed no significant difference.     

INFLUENCE OF COLOR ON TASTE THRESHOLDS

Increasing molar concentrations of sweet, sour, bitter and saltywere evaluated in colorless and colored (red, green, yellow)water solutions by 28 untrained students. Green color statisticallyincreased sweet taste threshold sensitivity while yellow colordecreased taste sensitivity. Red color did not affect the tastesensitivity of sweet. In the case of sour, both yellow and greencolors decreased sensitivity with red having no affect. Redcolor decreased bitter taste sensitivity with yellow and greencolor having no effect. No significant differences due to coloraffected salty taste sensitivity. Thus, psychological colorassociation can alter reports of certain basic taste sensations. ^*Scientific Series Paper Number 1764 of the Colorado State UniversityExperiment Station.     

USE OF THE RECEIVER OPERATING CHARACTERISTIC IN THE STUDY OF TASTE PERCEPTION

Studies of the Receiver Operating Characteristic (ROC) for taste are reviewed and new data on its shape are presented. What evidence there is suggests that ROCs for taste conform to the normal-normal equal variance model of signal detection theory. Few ROCs for taste have been reported, probably because the large number of trials required by detection theory makes the task arduous for subjects in taste experiments. However, pooling ratings from several subjects and estimating the parameters of the pooled ROC by jackknife techniques circumvents that problem to some extent. Because experiments on taste are often based on a small number of trials, it is especially useful to determine the standard errors of ROC parameters. Methods for estimating these standard errors, including that of the area measure, p(A), are therefore presented.     

Individual differences in the chemical senses: is there a common sensitivity?

Taste, smell, and chemical irritation (so-called trigeminal sensation) combine in our daily experience to produce the supramodal sensation of flavor, are processed by partly overlapping neural mechanisms, and show functional interconnectivity in experiments. Given their collaboration in flavor formation and the well-established connections between these senses, it is plausible that polymodal detection mechanisms might contribute to individual differences in measured sensitivity. One would expect the existence of a general chemosensory sensitivity factor to result in associations among taste, smell, and trigeminal stimulation thresholds. Measures of 5 detection thresholds from all the chemical senses were assessed in the same group of young healthy subjects (n=57). An unbiased principal components analysis (PCA) yielded a 2-component solution. Component 1, on which taste thresholds loaded strongly, accounted for 29.4% of the total variance. Component 2, on which the odor and trigeminal lateralization thresholds loaded strongly, accounted for 26.9% of the total variance. A subsequent PCA restricted to a 3-component solution cleanly separated the 3 sensory modalities and accounted for 75% of the total variance. Thus, though there may be a common underlying factor that determines some individual differences in odor and trigeminal lateralization thresholds, a general chemical sensitivity that spans chemosensory modalities seems unlikely.     

TASTE ACUITY IN THE ELDERLY: THE IMPACT OF THRESHOLD, AGE, GENDER, MEDICATION, HEALTH AND DENTAL PROBLEMS

This study was designed to assess taste threshold and investigate the effect of age, dental problems, health disorders/diseases and multiple medications on the distortion of taste and to determine if the loss of taste increases with age. One hundred seven elderly from rural congregate feeding sites and senior centers in Northern Alabama volunteered to participate in this study. Water solutions of varying concentrations for sweet, salty, sour, and bitter were prepared to determine recognition thresholds and test the effect of other factors on the ability to taste. A questionnaire was administered to each elderly volunteer to assess overall health. Results indicated that there was no significant age difference for the basic taste sensations, except for sweetness. Gender, dental problems, health disorders, diseases and multiple uses of medications did not significantly affect taste threshold. The basic was a decrease in taste threshold independent of any extraneous factors.     

CROSS-MODAL ADDITIVITY OF TASTE AND SMELL

Subjects were simultaneously given subthreshold levels of taste and odor stimuli, delivered orally, for both a commonly paired and an uncommonly paired taste–odor combination. Results indicate cross‐modal summation of subthreshold concentrations of both taste–odor pairs when the olfactory stimulus is delivered orally. Results of control studies suggest that the summation was indeed across modalities, and not due to the taste of the odor compound or the smell of the taste compounds. Furthermore, results indicate that regardless of taste–odor pair commonness, taste and smell can combine in a completely additive fashion (i.e., at threshold detectability when both stimuli are presented simultaneously at 50% threshold level) if the taste–odor pair is presented orally. In several instances, but not all, measured probabilities exceeded those predicted by probability summation, indicating that hyperadditive mixing often occurs, but there do seem to be individual differences. Cross‐modal summation, regardless of taste–odor pair commonness, has broader implications for the development of foods, beverages and pharmaceuticals, especially in masking undesirable tastes and smells.     

NEUROPHYSIOLOGY AND HUMAN TASTE SENSATIONS

Taste sensations are of primary importance in food flavor. Any attempt to synthesize chemically the flavor of a natural food involves mainly taste active compounds. Many distinct taste sensations can be identified as associated with food compounds. Thirteen different taste sensations are discussed herein. These different taste sensations are differentiated on the basis of stimulus chemistry and peripheral nerve conveying the taste information. Neurophysiological examination of the peripheral nerves involved in taste reveals that the sensory neurons can, in any species, be subdivided into distinct neural groups. These different neural groups respond to distinct classes of chemicals and often display different neurophysiological characteristics. Altogether in four different species, nine functional neural taste groups can be distinguished. In many cases, these neural groups can be taken as analogs for the neural groups assumed to underly human taste sensations. Distinct human taste sensations can be considered to arise from the excitation or inhibition of different neural groups. For certain human taste sensations there are no animal neural analog groups; and for certain neural groups there are no analog human sensations.     

NaCl taste thresholds in 13 inbred mouse strains

Molecular mechanisms of salty taste in mammals are not completely understood. We use genetic approaches to study these mechanisms. Previously, we developed a high-throughput procedure to measure NaCl taste thresholds, which involves conditioning mice to avoid LiCl and then examining avoidance of NaCl solutions presented in 48-h 2-bottle preference tests. Using this procedure, we measured NaCl taste thresholds of mice from 13 genealogically divergent inbred stains: 129P3/J, A/J, BALB/cByJ, C3H/HeJ, C57BL/6ByJ, C57BL/6J, CBA/J, CE/J, DBA/2J, FVB/NJ, NZB/BlNJ, PWK/PhJ, and SJL/J. We found substantial strain variation in NaCl taste thresholds: mice from the A/J and 129P3/J strains had high thresholds (were less sensitive), whereas mice from the BALB/cByJ, C57BL/6J, C57BL/6ByJ, CE/J, DBA/2J, NZB/BINJ, and SJL/J had low thresholds (were more sensitive). NaCl taste thresholds measured in this study did not significantly correlate with NaCl preferences or amiloride sensitivity of chorda tympani nerve responses to NaCl determined in the same strains in other studies. To examine whether strain differences in NaCl taste thresholds could have been affected by variation in learning ability or sensitivity to toxic effects of LiCl, we used the same method to measure citric acid taste thresholds in 4 inbred strains with large differences in NaCl taste thresholds but similar acid sensitivity in preference tests (129P3/J, A/J, C57BL/6J, and DBA/2J). Citric acid taste thresholds were similar in these 4 strains. This suggests that our technique measures taste quality-specific thresholds that are likely to represent differences in peripheral taste responsiveness. The strain differences in NaCl taste sensitivity found in this study provide a basis for genetic analysis of this phenotype.     

Visual sensitivity in the squirrel monkey

Several indices of visual sensitivity have been obtained from behavioral experiments conducted on the squirrel monkey (Saimiri sciureus). In this species, the photopic spectral sensitivity functions determined by increment-threshold and flicker discrimination procedures are substantially different; the involvement of two different neural processes in the two tasks is suggested. When tested similarly, the thresholds for rod and cone-based vision are not substantially different for squirrel monkeys and humans; however, above cone threshold, for a 500 nm test light, increment threshold is some 0.3 to 0.4 log₁₀ units higher for the squirrel monkey. Rod saturation has also been demonstrated to occur in the squirrel monkey.     

The influence of temperature on the threshold values of primary tastes

The threshold values of taste substances are influenced by severalfactors. To learn about the effect of the temperature on stimulus,recognition and terminal thresholds, these threshold valueswere determined for sucrose, sodium chloride, caffeine, quininehydrochloride, citric and tartaric acid at temperatures of 10,20, 40 and 60°C in a panel of 19 tasters. The individualvalues were found to vary over a wide range, resulting in arelatively large standard deviation of the mean threshold values.A temperature-dependence was found for the stimulus and recognitionthresholds which was different for the different taste substances.The stimulus and recognition thresholds are lowest in the temperaturerange of 20 to 40°C. The threshold values increase withincreasing temperature, and except for citric acid, significantand highly significant differences existed particularly between20 and 60°C, whereas statistically verifiable results couldnot be obtained between 10 and 20°C. There was no verifiabletemperature dependence either for the terminal thresholds. Theterminal thresholds were found to lie rather in a relativelynarrow concentration range and to be largely independent ofthe temperature. The results suggest that in warm dishes andbeverage more taste substances are required to produce the sametaste intensity. A dependence of the individual thresholds uponage, sex and smoking habits could not be found.     

Comparing sensory experience in bitter taste perception of phenylthiocarbamide within and between human twins and singletons: intrapair differences in thresholds and genetic variance estimates

BACKGROUND: Quantitative genetic studies revealed that not all of the phenotypic variance in PTC taste perception is heritable. AIM: To study quantitative variations in PTC tasting ability in twins and to estimate heritability of PTC taste perception on the taste of twin data on males and females sexes separately. SUBJECTS AND METHODS: The data for PTC taste sensitivity following the classic method of Harris & Kalmus (1949) were collected on a sample of 141 twin pairs (66 MZ and 75 DZ) and 275 singletons (128 males and 147 females) from Chandigarh, India. Genetic analyses were performed following Christian (1979), Donner (1986) and Sham (1998). RESULTS: Frequency of non-tasters was similar in twins (33 %) and singletons (32 %), but significant sex differences were observed. No differences were found between zygosities for mean thresholds. Similarly, no evidence of variance heterogeneity and environmental covariance was seen between zygosities. Since no basic assumption of the twin method was found violated, within-pair estimates of genetic variance would be unbiased. These estimates were highly significant in both males and females. However, dominance and additive components of genetic variance were found to differ between sexes. CONCLUSION: PTC thresholds do not seem to be significantly affected by environmental factors as no variance inequality was observed between twin zygosities. Intensity of bitterness (scalar dimensions) of PTC is a separate trait having no commonality with the genetic basis of recognition threshold for PTC tasting ability. The receptors recognizing bitter taste are different from the receptors determining intensity of taste. The absolute difference between co-twins in PTC thresholds can be used as a simple tool in the twin zygosity diagnosis. The results show that none of the MZ co-twins had manifested difference of more than 3 in their PTC threshold.     

Fat taste in humans: Sources of within- and between-subject variability

Non-esterified fatty acids (NEFA) are reportedly detectable through taste mechanisms in the human oral cavity. However, wide variability has been observed in NEFA taste sensitivity between and within subjects as well as across research groups. Some of this variability may be due to the hydrophobic nature of the NEFA and the methods used to make stimuli emulsions. As NEFA are poorly soluble in water, emulsification is necessary for delivery of stimuli to taste receptors. However, properties of emulsions may also be detected by somatosensory cues complicating attribution of sensory findings to taste. Additionally, learning (improved test performance) has been observed when using traditional tests for measuring sensitivity to NEFA, which may contribute greatly to within-subject variability if not standardized. Factors such as sex, diet, and BMI have been proposed to affect NEFA taste sensitivity, but the degree to which these individual factors influence NEFA detection thresholds remains to be fully established. Improved knowledge of stimulus properties and individual sensory capabilities will be needed to further evaluate the posited taste component to human oral fat detection. Progress in this area should facilitate the translation of findings on how NEFA taste may contribute to or reflect food choice and chronic disease risk.     

Taste Sensitivity and Aging: High Incidence of Decline Revealed by Repeated Threshold Measures

Contrary to what has often been said about the subject, declinein taste sensitivity with aging characterizes virtually everybodyand is not the artificial result of averaging large losses ofa minority with negligible losses of a majority. This assertionis supported by six repeated measures of sucrose thresholdsin each of 15 older (over 64 years) and 15 younger (under 27years) adult subjects. Threshold was determined by a proceduresimilar to past studies and with the same results: much scatterand considerable overlap between the thresholds of younger andolder subjects. A quite contrasting picture emerges, however,when each subject's six threshold determinations are averaged.Averaging shrinks the individual differences among subjects,as well as the over-lap between younger and older subjects.Although virtually all elderly subjects now revealed taste weakness,reliable individual differences in degree of weakness aboundamong them, suggesting various individual rates of physiologicalaging. In contrast young persons exhibit greater uniformityof sensitivity. These findings were brought out by inter-testcorrelations, which were much higher for the older subjects;i.e. an older subject who tended to score high (low) on onetest tended to score high (low) on the other tests. The studyconfirms the tenuous nature of brief threshold tests as indicesof personal sensitivity as found earlier also in olfactory thresholdsand in concurrent measurement of two-point touch thresholdsin the present study. This revealed correlated losses betweenrepeated taste and touch thresholds from the same 15 older subjects,unrelated to their exact chronological age. Chem. Senses 20:451–459, 1995.     

RECEPTIVE FIELDS OF CAT TASTE FIBERS

The receptive fields of 25 cat chorda tympani taste fibers weremapped by the application of taste solutions to individual fungiformpapillae on the tongue. Chemical stimulation of other siteson the tongue was ineffective. The receptive fields were ingeneral small and discrete, but could extend for distances ofmore than 5 mm with one or more unresponsive papillae interposedbetween responsive papillae. Since most fibers branched andinnervated at least 2 fungiform papillae (mean 2.7), it waspossible to stimulate 2 papillae within a fiber's receptivefield independently. The two sets of taste receptors innervatedby a given fiber had similar relative chemical sensitivity.Therefore, branches of a taste fiber are not connected at randomto the various kinds of taste receptor cells.     

TASTE GROUP THRESHOLDS AND SENSORY EVALUATION OF SPANISH WINE VINEGARS

Wine vinegar is a product obtained from wine acidification which contains at least 5% by wt. of acetic acid, in general without any additives or colorings.
Aspects studied in this work include: the determination of the taste group thresholds (geometric mean of the individual best-estimate thresholds "BET") of two different acids (citric and acetic acids) in aqueous solution and spanish vinegars produced from table and sherry wines. The results obtained suggest that wine vinegar can be considered something more than just an acidulant agent.
In order to evaluate differences among wine vinegars, discriminant tests for twenty-five spanish vinegars (sherry, table and flavored vinegars) were applied. Six of the twelve attributes freely chosen by assessors allowed grouping of the spanish wine vinegars according to their sensory aspects.     

Psychophysical and neurophysiological hearing thresholds in the bat <Emphasis Type="Italic">Phyllostomus </Emphasis><Emphasis Type="Italic">discolor</Emphasis>

Absolute hearing thresholds in the spear-nosed bat Phyllostomus discolor have been determined both with psychophysical and neurophysiological methods. Neurophysiological data have been obtained from two different structures of the ascending auditory pathway, the inferior colliculus and the auditory cortex. Minimum auditory thresholds of neurons are very similar in both structures. Lowest absolute thresholds of 0 dB SPL are reached at frequencies from about 35 to 55 kHz in both cases. Overall behavioural sensitivity is roughly 20 dB better than neural sensitivity. The behavioural audiogram shows a first threshold dip around 23 kHz but threshold was lowest at 80 kHz (−10 dB SPL). This high sensitivity at 80 kHz is not reflected in the neural data. The data suggest that P. discolor has considerably better absolute auditory thresholds than estimated previously. The psychophysical and neurophysiological data are compared to other phyllostomid bats and differences are discussed. S. Hoffmann, L. Baier, F. Borina contributed equally to this work.     

Are human taste thresholds similar on the right and left sides of the tongue?

The human tongue is a relatively symmetrical anatomical structure and is generally assumed functionally equivalent on both sides. Experimental evaluation of this assumption is complicated by the fact that psychophysical measurements tend to vary considerably across testing sessions. To address functional laterality, we determined the detection thresholds of six right-handed and six left-handed subjects for Na saccharin, NaCl, citric acid and quinine HCl. Five pairs of interwoven, left and right unilateral thresholds were obtained for each taste stimulus in 12 subjects (n = 480 separate thresholds). In most cases mean sensitivity based on multiple measurements was found to be laterally symmetrical, however, we observed a few cases of lateral asymmetry of both general and compound-specific sensitivity. Threshold values were found to vary considerably across sessions, consistent with the test-retest variability previously reported for whole mouth thresholds. We conclude that taste threshold sensitivity is equivalent on the left and right anterior tongue for most individuals. Given the occasional exceptions to this rule, however, it is advisable to employ a counterbalanced design for any experimental or clinical testing protocol in which treatments are applied asymmetrically to the tongue.     

Assessing gustatory detection capabilities using preference procedures

Two-bottle preference tests have often been used to make inferencesabout gustatory thresholds. The validity of such inferencesdepends on the extent to which taste differences produce differentialfluid consumptions from the bottles. If equal amounts are consumeddespite perceived gustatory dissimilarity, inaccurate thresholdestimates result. Modifications of common preference-test procedures,interacting with tastant properties and genetic variation, disclosedinstances of such non-discrimination among inbred strains ofmice. With an hedonically neutral to mildly unpalatable tastant(sodium cyclamate), taste-aversion conditioning yielded lowerthresholds. With a palatable tastant (maltose), testing withoutprior conditioning usually indicated lower thresholds. Descendingconcentration series produced lower thresholds than ascendingconcentration series, for both palatable (sucrose) and neutral(cyclamate) tastants. Previous experience with the tastantselevated preference scores, yielding lower thresholds with palatabletastants (sucrose, maltose) and higher thresholds with an unpalatabletastant (sucrose octaacetate). Within-strain discrepancies betweenthresholds indicated by the different methods were often large(2–3 log molar concentration steps). Amongstrain differencesof comparable magnitude, both in preferences and threshold estimates,were found for sucrose, maltose and cyclamate.