Bitter taste of saccharin related to the genetic ability to taste the bitter substance 6-n-propylthiouracil.

Bitter taste thresholds for 6-n-propylthiouracil are bimodally distributed, dividing subjects into tasters and nontasters. Their taste worlds differ with regard to the sweetness of sucrose and saccharin and to the bitterness of saccharin. These differences suggest that nontasters tend to perceive less bitterness in saccharin at concentrations used in beverages.

Sweet taste of water induced by artichoke (Cynara scolymus).

Exposure of the tongue to artichoke can make water taste sweet. Two major active components of artichoke are the salts of chlorogenic acid and cynarin. The sweetening of substances by temporarily modifying the tongue, rather than by adding a substance sweet in itself, may provide an alternative to currently used nonnutritive sweeteners.

Taste of water in the cat: effects on sucrose preference.

Electrophysiological recordings show that water is not tasteless to cats. Also, unlike most mammals, cats appear indifferent to sucrose, but this may be because the taste of the sucrose is masked by the taste of the water in which it is dissolved. When the water taste is suppressed by the addition of small amounts of sodium chloride, cats take sucrose avidly.

Bitter taste markers explain variability in vegetable sweetness, bitterness, and intake.

Intake of vegetables falls short of recommendations to lower risk of chronic diseases. Most research addresses bitterness as a sensory deterrent to consuming vegetables. We examined bitter and sweet sensations from vegetables as mediators of vegetable preference and intake as well as how these tastes vary with markers of genetic variation in taste (3.2 mM 6-n-propylthiouracil bitterness) and taste pathology (1.0 mM quinine bitterness, chorda tympani nerve relative to whole mouth). Seventy-one females and 39 males (18-60 years) reported prototypical tastes from and preference for Brussels sprouts, kale and asparagus as well as servings of vegetables consumed, excluding salad and potatoes. Intensity and hedonic ratings were made with the general Labeled Magnitude Scale. Data were analyzed with multiple linear regression and structural equation modeling. Vegetable sweetness and bitterness were independent predictors of more or less preference for sampled vegetables and vegetable intake, respectively. Those who taste PROP as most bitter also tasted the vegetables as most bitter and least sweet. The spatial pattern of quinine bitterness, suggestive of insult to chorda tympani taste fibers, was associated with less bitterness and sweetness from vegetables. Via structural equation modeling, PROP best explained variability in vegetable preference and intake via vegetable bitterness whereas the quinine marker explained variability in vegetable preference and intake via vegetable bitterness and sweetness. In summary, bitterness and sweetness of sampled vegetables varied by taste genetic and taste function markers, which explained differences in preference for vegetables tasted in the laboratory as well as overall vegetable intake outside the laboratory.

Supertasting, earaches and head injury: genetics and pathology alter our taste worlds.

Family studies using thresholds showed that PROP (6-n-propylthiouracil) tasting is produced by a dominant allele, T. Nontasters have two recessive alleles and tasters have one or two dominant alleles. The bitterness of suprathreshold PROP and anatomical criteria subdivide tasters into medium and supertasters. Supertasters may be TT tasters, but this has yet to be demonstrated. Supertasters preceive the greatest bitterness and sweetness from many stimuli as well as the greatest oral burn from alcohol and capsaicin. Women are more likely than men to be supertasters. Otitis media and head trauma can alter taste and thus PROP classifications, complicating studies on PROP genetics. Some subjects with a history of otitis media show taste reductions, but others show enhanced tastes and appear to have more taste buds per fungiform papilla. Subjects with head trauma show reduced tastes on some oral loci, but there is evidence that severe reductions on the front of the tongue ameliorate reductions at the circumvallate papillae on the back of the tongue by a release of inhibition mechanism.

The psychophysics of taste.

Modern psychophysical studies of sensory systems have produced new insight into sensory function and new techniques that have application to the clinical evaluation of taste. Most previous taste evaluation has been done with threshold measures that are subject to a variety of problems and that also fail to provide an accurate picture of suprathreshold sensitivity. The scaling of suprathreshold intensity reflects a patient's taste world more accurately than thresholds.

Taste. Robust across the age span?

The prevalence of taste loss over a discrete area of the tongue or palate is unknown; however, we have identified discrete losses in three etiological groups: head trauma, upper respiratory infection, and bulimia. We have now identified discrete losses in elderly subjects. To summarize, elderly subjects show elevated taste thresholds for some taste stimuli. Mild dysgeusia may act as a masking stimulus that makes taste thresholds appear to be elevated, and this may be more common in the elderly than the young. Discrete taste losses occur more often among the elderly than the young but usually go unnoticed (although these losses may contribute to elevated thresholds when the test procedure stimulates an area of loss). When the samples are at high concentrations, when the subject judges total intensity rather than typical quality, and when the whole mouth is used to do the tasting, the taste responses of elderly subjects look much like those of the young. Two factors contribute to the failure of people to notice localized taste loss. First, there appear to be mutually inhibitory connections between various taste loci such that if taste input from one area is blocked, the inhibition from that area is also blocked. This results in increases in perceived taste from the other areas. Second, a blank spot for taste can go unnoticed because taste is poorly localized. We can demonstrate this with an illusion. If a taste solution is painted from an area with receptors into an area that does not have receptors, the taste sensation seems to invade the area with no receptors. We suggest that a similar phenomenon may occur with areas from which receptors are lost. This localization illusion could then prevent a subject from noticing that an area has lost taste function. The discovery of discrete taste losses in a population of elderly subjects suggests that earlier failures to find substantial taste losses with age may reflect the redundancy of the taste system. This possibility raises the question of what functions taste subserves that require this kind of redundancy. The taste system appears to be "hard wired" to maintain the constancy of perceived intensity even if substantial taste areas are damaged. This constancy suggests that taste is serving important biological functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Taste changes across pregnancy.

UNLABELLED: We examined taste intensity and preference in 46 pregnant and 41 healthy female controls enrolled in the Yale Pregnancy Study (J. Rodin, PI). Pregnant females were tested non-pregnant (non-pg) and during the first, second and third trimesters; controls, at corresponding time intervals. Subjects rated intensity of and preference for a three-member concentration series of NaCl, sucrose, citric acid (CA), and quinine hydrochloride (QHCl) on a labeled line ('nothing' at the left, 'extremely' at 80%). Variance differences between groups were tested with the F distribution (p < 0.05). Controls had significantly greater variance among overall intensity ratings than pregnant females, most pronounced for QHCl. Controls did not have highest variance among overall hedonic ratings, but did have highest variance for sweet and QHCl ratings. Within pregnancy analyses were tested with the Friedman two-way ANOVA. Significant intensity changes occurred for moderate NaCl and QHCL concentrations (p < 0.005). For NaCl, intensity fell from non-pg and first trimester to second and third trimesters. For QHCl, intensity rose from non-pg to first trimester, and fell from first to second and third trimesters. In the hedonic ratings, significant changes occurred for top concentrations of NaCl (p < 0.05) and 0.001 M CA (p < 0.001), and moderate QHCl (p < 0.005). NaCl preference rose from non-pg to third trimester. Preference for CA fell from non-pg to first trimester and then rose from first to second and third trimesters. QHCl became less disliked from non-pg and first trimester to third trimester. SUMMARY: taste intensity and hedonic variance in controls may associate with menstrual hormone fluctuations. Pregnant women were aligned in pregnancy stage which may explain the lower variance. Taste intensity and hedonic changes across pregnancy could serve to support healthy pregnancy outcomes: increases in bitter intensity in first trimester to protect against ingesting poisons; changes in NaCl, sour and bitter preference later in pregnancy to support ingesting a varied diet.

PROP (6-n-propylthiouracil) supertasters and the saltiness of NaCl.

Taste blindness to phenylthiocarbamide (PTC) and its chemical relative 6-n-propylthiouracil (PROP) was discovered in the 1930s. Family studies showed that those who could not taste PTC/PROP (nontasters) carried two recessive alleles. In recent years, we have classified tasters into two groups: medium (PROP is moderately bitter) and supertasters (PROP is intensely bitter). With our classification, approximately 25% of Americans are nontasters, 50%, medium tasters, and 25%, supertasters. Studies showed that supertasters form a cohesive group. Anatomical studies showed that supertasters have the most fungiform papillae. Psychophysical studies showed that supertasters perceive the most intense bitterness and sweetness from a variety of compounds, the most intense burn from oral irritants, and the most intense tactile sensations from viscous solutions. Oral burn and touch are presumably perceived to be the most intense to supertasters because taste buds in fungiform papillae are innervated by the trigeminal nerve (pain, touch) as well as the chorda tympani nerve (taste). The psychophysical scaling method used was magnitude matching with NaCl as the control modality. With this method, subjects rated the intensities of a series of NaCl and PROP solutions. The assumption that the taste of NaCl did not vary with PROP status allowed comparisons of the bitterness of PROP across subjects. Early magnitude matching studies, using sound as the control, had suggested that this assumption was reasonable. However, recent studies challenged that conclusion. Larger samples with more diverse populations, using sound as the control, showed that the taste of NaCl varied with PROP bitterness; supertasters perceived the strongest taste and nontasters, the weakest. Thus our earlier conclusions were conservative because differences between nontasters, medium tasters, and supertasters were concealed by using NaCl as a standard. Using magnitude matching with sound as the standard, or using the Green scale, which employs intensity labels, we found that the differences between PROP groups are larger. Note that the association between PROP status and salt taste is interesting in itself, since variability in salt taste may have important nutritional consequences.

Comparison of the Green scale versus magnitude estimation for taste perception.

The Green scale is a new psychophysical method that is simple for subjects to use, but its relation with magnitude estimation has yet to be fully characterized. In comparing the consistency between the Green scale and magnitude estimation, we found that the former seems to provide a psychological oral sensation measurement that is different from the latter method. A simple correction formula can be derived.

Psychophysical measurement of 6-n-propylthiouracil (PROP) taste perception.

The ability to taste 6-n-propylthiouracil (PROP) is genetically determined. PROP tastes moderately bitter to 'medium tasters' (MT), intensely bitter to 'supertasters' (ST), and tasteless to 'nontasters' (NT). The psychophysical method used to characterize PROP status should capture the entire range of perception, while minimizing context, ceiling and other effects. Magnitude estimation successfully captures the variability in PROP perception, but requires normalization and may be difficult to conduct in industrial settings. Two labeled scales were tested as part of three separate studies (S1, S2 and S3) to measure perceived intensity of PROP and sweeteners. All studies included reportedly healthy volunteers aged 21-62 years recruited at Cultor Food Science in Groton, CT. In S1 [n = 163 (55 males, 108 females)], subjects rated perceived intensity of PROP-saturated paper and sucrose (1.0 M) on the Labeled Magnitude (Green) Scale (LMS) [labeled line with descriptors (no taste--strongest imaginable)]. In S2 [n = 152 (49 males, 103 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on the LMS. In S3 [n = 136 (48 males, 88 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on a 9-point category scale (1 = not at all; 9 = extremely). In all experiments, water rinses were included between each tastant and PROP was the final stimulus. Statistical analyses included descriptive statistics, regression analysis, and ANOVA. In S1 and S2, those with higher PROP perception perceived sucrose more intensely [(S1: r = 0.32; p < 0.001); (S2: r = 0.25; p < 0.01)]. A higher frequency of females were ST than males. Also, the PROP effect on sweet perception was most evident in female ST. This apparent sex difference may be the result of hormonal variation associated with menstruation. As well, in S1 and S2 subjects aged 20-40 years, females had significantly greater variance among sucrose intensity ratings than males (F = 3.66; p < 0.01), which may be due to hormonal changes with menses. The S3 results failed to show either the positive correlation between PROP and sucrose perception or the sex difference. Thus of the two labeled scales, the LMS appears to be better for assessing PROP perception, as it is continuous and also minimizes ceiling effects. Future research will extend these studies by including sucrose and high intensity sweetener concentration series.

A taste illusion: taste sensation localized by touch.

Taste sensations appear to come from all over the inner surface of the mouth, yet the taste receptors are restricted to relatively small particular areas of the oral surface. In addition, even if a relatively large (e.g., one half) proportion of the taste field is damaged, subjective taste experience may be unaffected. The touch system contributes to this constancy because taste sensations appear to be localized by touch. If a taste solution is painted from the side of the tongue (an area of low receptor density) past the tip (an area of high receptor density) and on to the second side, the taste sensation begins weak, gets stronger at the tip, and retains much of its intensity. The strong taste from the tip follows the tactile path of the stimulus sweep. This illusion occurs for all four stimuli tested: sucrose, sodium chloride, citric acid, and quinine hydrochloride.

Taste synergism between monosodium glutamate and disodium 5'-guanylate.

The examples of "synergism" reported in the taste literature fit the common definition of the term but may merely reflect normal additivity in the taste system. That is, the perceived intensities of these "synergistic" mixtures exceed the sums of the perceived intensities of the unmixed taste components (addition of perceived intensities), but do not exceed the perceived intensities predicted by adding along the expandng psychophysical functions which describe the unmixed taste components (stimulus addition). True synergism requires that the perceived intensity of a mixture be greater than that predicted by both types of additivity. Subjects used magnitude estimation to judge the perceived intensity of unmixed monosodium glutamate and disodium 5'-guanylate and mixtures of these two taste substances. The mixtures showed synergism according to both crtieria. The robustness of this phenomenon is striking; for all subjects the taste mixtures showed true synergism. True synergism in taste is an extremely rare phenomenon.

Bitterness suppression as revealed by split-tongue taste stimulation in humans.

QHCl-sucrose and QHCl-NaCl mixtures administered to the anterior part of the human tongue led to substantial bitterness suppression as determined by the method of magnitude estimation. In the QHCl-sucrose condition components separated by the tongue's midline and those spatially mixed produced equal amounts of bitterness suppression. However, the QHCl-NaCl mixture produced significantly more bitterness suppression with the spatially mixed than with the spatially separated stimulus components. It is concluded that bitterness suppression in mixtures with sucrose occurs centrally and in mixtures with NaCl both peripherally and centrally.

PTC/PROP tasting: anatomy, psychophysics, and sex effects.

Taste worlds of humans vary because of taste blindness to phenylthiocarbamide (PTC) and its chemical relative, 6-n-propylthiouracil (PROP). We review early PTC studies and apply modern statistical analyses to show that a higher frequency of women tasted PTC crystals, and were tasters (threshold classification). In our laboratory, scaling of PROP bitterness led to the identification of a subset of tasters (supertasters) who rate PROP as intensely bitter. Supertasters also perceive stronger tastes from a variety of bitter and sweet substances, and perceive more burn from oral irritants (alcohol and capsaicin). The density of taste receptors on the anterior tongue (fungiform papillae, taste buds) correlate significantly with perceived bitterness of PROP and support the supertaster concept. Psychophysical data from studies in our laboratory also show a sex effect; women are supertasters more frequently. The anatomical data also support the sex difference; women have more fungiform papillae and more taste buds. Future investigations of PTC/PROP tasting and food behaviors should include scaling to identify supertasters and separate sex effects.

Effects of temperature on the perceived sweetness of sucrose.

The sweetness of sucrose depends on the temperature as well as the concentration of a solution. The main effect is that relatively low concentrations gain sweetness as temperature increases. This effect diminishes with progressively higher concentration and finally becomes negligible at about 0.5 M. At this concentration the various functions that relate perceived sweetness to concentration for various temperatures converge. The mechanism of the taste-temperature interaction is speculative, but the interaction is large enough to be of practical interest in the perception of common foods and beverages as well as a variable to be strictly controlled in taste experiments. An examination of method of tasting showed that swallowing stimuli did not substantially increase perceived sweetness.

Olfactory and taste sensitivity in children with cystic fibrosis.

Psychophysical experiments measured both olfactory sensitivity to 1-butanol and sodium chloride and taste sensitivity to sodium chloride in normal children and in children with cystic fibrosis. The sensitivity of the children with cystic fibrosis fell within the normal range. These results stand in contrast to those of Henkin and Powell, who found children with cystic fibrosis to be hypersensitive to both olfactory and taste stimuli. Apparent hypersensitivity to taste stimuli could have resulted from the adapting effects of the relatively high level of sodium in the saliva of children with cystic fibrosis. If the contaminating effects of saliva are removed, children with cystic fibrosis yield, on the average, a taste threshold identical to that of normal children. There appears to be no simple explanation for why Henkin and Powell found hypersensitivity to odorants. The present results indicate that, in fact, children with cystic fibrosis display a slight hyposensitivity to odorants.

Effect of anesthesia of the chorda tympani nerve on taste perception in humans.

Individuals who have sustained considerable damage to parts of the taste system often fail to experience changes in everyday taste experience. The two halves of the tongue are independently innervated: the chorda tympani (branch of the facial or VIIth cranial nerve) innervating the anterior two-thirds and the glossopharyngeal (IXth cranial nerve) innervating the posterior one-third. Anesthesia of the chorda tympani nerve on one side produced increased taste intensities for some stimuli on the area innervated by the glossopharyngeal nerve on the other side. Because this effect occurs across the midline and taste projects ipsilaterally, the effect must occur in the central nervous system (CNS). This supports Halpern and Nelson's release-of-inhibition hypothesis that the area to which the chorda tympani projects in the CNS must normally inhibit that of the glossopharyngeal nerve. Anesthesia of the chorda tympani abolishes that inhibition and leads to perception of increased taste intensities from areas innervated by the glossopharyngeal nerve.

Anesthesia of the chorda tympani nerve and taste phantoms.

The chorda tympani nerve innervates the anterior two-thirds and the glossopharyngeal nerve, the posterior one-third, of each side of the tongue. Previous work showed that anesthesia of one chorda tympani increased the perceived intensity of quinine applied to an area innervated by the contralateral glossopharyngeal nerve, but decreased the perceived intensity of NaCl applied to an area innervated by the ipsilateral glossopharyngeal nerve. The data presented here corroborate that earlier finding and show that if both chorda tympani nerves are anesthetized, the taste of quinine is intensified and the taste of NaCl diminished at areas innervated by the glossopharyngeal on both sides of the tongue. In about 40% of the subjects, tastes occurred in the absence of stimulation (we call these tastes phantoms). The phantoms were usually localized to the posterior tongue contralateral to the anesthesia and they were abolished when a topical anesthetic was applied to the area where they were perceived. Phantoms like these may be a source of clinical dysgeusia in patients with localized taste damage. The phantoms may result because the anesthesia releases inhibition normally occurring between the central projection areas of different taste nerves.