Taste Detection Thresholds Research Articles

The relationship between PTC taster status and taste thresholds in young adults

The aim of this study was to compare taste detection and recognition thresholds of young males and females, and young phenylthiocarbamide (PTC) "tasters" and "nontasters" for stimuli representing sweet, sour, bitter, salty, and umami classes of taste sensations. Thirty-eight men and 37 women (mean [SD] age = 24.5 [2.5] years) were classified as PTC tasters and nontasters according to their PTC recognition thresholds. Detection and recognition thresholds for the non-PTC stimuli were determined using a 2-alternative, forced choice procedure. The detection thresholds for quinine-HCl and sucrose and the recognition threshold for quinine-HCl were significantly higher in the PTC nontasters than in the tasters. The PTC threshold showed significant correlations with detection or recognition thresholds for sucrose, sodium chloride, quinine-HCl, and monosodium glutamate. The sucrose recognition threshold was lower in women than in men. In this study, gender and PTC taster status were found to be associated with thresholds for sucrose and quinine-HCl.

Depressive symptoms and taste reactivity in humans

Animal studies suggest that induction of depression-like states may alter preference for sweet tastants. A major goal of the present study was to search for correlations between depressive symptoms measured by the Beck Depression Inventory (BDI) and taste responses to sweet and bitter substances. Thirty-three nonclinical volunteers rated intensity and pleasantness of chocolate and vanilla milk as well as of sucrose- and quinine-soaked filter paper disks. Reactivity to citric acid (sour) and sodium chloride (salty) was also tested with the paper disk methodology. Taste detection thresholds were assessed by means of electrogustometry. A weak inverse relationship was found between the BDI scores (range: 3–33) and rated intensity of paper disks soaked in 60% sucrose. No correlations were found between depressive symptoms and intensity, pleasantness or identification of the other samples. Similarly, there was no relationship between the BDI scores and responses to chocolate and vanilla milk. BDI scores were not associated with electrogustometric thresholds. These data suggest that depressive symptoms may not influence taste reactivity in nonclinical population.

Evaluation of the taste contribution of theaflavins in black tea infusions using the taste activity concept

The contribution of theaflavins to the astringent taste of black tea infusions has been investigated. The major benzotropolons theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate, theaflavin-3,3′-digallate, and theaflavic acid were synthetically prepared by enzymatic oxidation of binary mixtures of the corresponding flavan-3-ols, purified by high-speed countercurrent chromatography, and then sensorially evaluated by means of a comparative duo test. The sensory analysis revealed that the theaflavins imparted a mouth-coating, astringent, and long-lasting oral sensation at the very back of the throat, and demonstrated the theaflavins to have by far lower oral thresholds than the astringent catechins; for example, the threshold concentration of theaflavin (0.016 mmol/L) is by a factor of 33 and 58 lower than those of its precursors epigallocatechin and epicatechin, respectively. In order to study the importance of these theaflavins as contributors to tea astringency, these benzotropolons were quantified in tea infusions and taste activity values were calculated from the quotient of their concentration in tea and their taste detection thresholds. Relating the taste activity values of the individual theaflavins to the overall astringency of the teas revealed that the theaflavins accounted for less than 0.1% of the overall astringency of the teas investigated. In consequence, the theaflavin concentration seems not to be a suitable measure for taste quality of tea infusions.

Association between plasma zinc concentration and zinc kinetic parameters in premenopausal women.

The objective of this study was to measure relationships between plasma zinc (Zn) concentrations and Zn kinetic parameters and to measure relationships of Zn status with taste acuity, food frequency, and hair Zn in humans. The subjects were 33 premenopausal women not taking oral contraceptives and dietary supplements containing iron and Zn. Main outcomes were plasma Zn concentrations, Zn kinetic parameters based on the three-compartment mammillary model using 67Zn as a tracer, electrical taste detection thresholds, and food frequencies. Lower plasma Zn was significantly (P < 0.01) associated with smaller sizes of the central and the lesser peripheral Zn pools, faster disappearance of tracer from plasma, and higher transfer rate constants from the lesser peripheral pool to the central pool and from the central pool to the greater peripheral pool. The break points in the plasma Zn-Zn kinetics relationship were found between 9.94 and 11.5 micromol/l plasma Zn. Smaller size of the lesser peripheral pool was associated with lower frequency of beef consumption and higher frequency of bran breakfast cereal consumption. Hypozincemic women with plasma Zn <10.7 micromol/l or 700 ng/ml had decreased thresholds of electrical stimulation for gustatory nerves. Our results based on Zn kinetics support the conventional cutoff value of plasma Zn (10.7 micromol/l or 700 ng/ml) between normal and low Zn status.

Oral amiloride treatment decreases taste sensitivity to sodium salts in C57BL/6J and DBA/2J mice.

Sodium taste transduction is thought to occur via an amiloride-sensitive, sodium-selective pathway and an amiloride-insensitive, cation nonselective, anion-dependent pathway(s). It has been shown by others that amiloride, an epithelial sodium channel (ENaC) blocker, significantly reduces the chorda tympani nerve response to lingually applied NaCl in C57BL/6 (B6) mice but not in DBA/2 (D2) mice, suggesting that the latter strain might not possess functional ENaCs in taste receptor cells. We psychophysically measured and compared taste detection thresholds of NaCl and sodium gluconate (NaGlu) prepared with and without 100 microM amiloride in these two strains (eight/strain). Mice were trained and tested in a two-response operant signal detection procedure conducted in a gustometer. Surprisingly, no strain effect was found for the detection thresholds of both salts (approximately 0.05-0.06 M). Moreover, these thresholds were increased by almost an order of magnitude by amiloride adulteration of the solutions. This marked effect of amiloride on sodium detection thresholds suggests that ENaCs are necessary for normal sensitivity to sodium salts in both strains. In addition, because NaGlu is thought to stimulate primarily the amiloride-sensitive pathway, especially at low concentrations, the similarity of NaCl and NaGlu thresholds (r > 0.81 both strains) suggests that ENaCs are also sufficient to support the detection of sodium in weak solutions by B6 and D2 mice.

A New Whole-mouth Gustatory Test Procedure: II. Effects of Aging, Gender and Smoking

Taste detection and recognition thresholds for the 4 basic tastes were measured in 670 healthy subjects using a new whole-mouth method in which test solutions of the 4 basic tastes were diluted 1 : 1 with distilled water successively in 13 steps. The taste thresholds were measured by spraying a 1 ml aliquot of solution into the mouth, starting with the lowest concentration, and asking the subject to swallow and note if a taste was detected and, if so, which one. The mouth was rinsed with distilled water only between different taste test solutions. Multiple comparison analysis showed a clear age-related increase in thresholds for salty, sour and bitter tastes for subjects in their eighth decade of life. From the third decade onwards, female subjects had significantly lower thresholds compared to males for sour taste in about half of the age groups and for salty and bitter tastes in some age groups. In contrast, for 18- and 19-year-old subjects, the gustatory thresholds of male subjects were lower than those of female subjects. Regarding smoking, male smokers in their third decade had significantly higher thresholds for bitter taste compared to male non-smokers in this age group.

Functional recovery of taste sensitivity to sodium chloride depends on regeneration of the chorda tympani nerve after transection in the rat.

Chorda tympani nerve (CT) transection (CTX) raises sodium chloride (NaCl) taste detection threshold, but the effect of CT regeneration on NaCl threshold is unknown. This experiment examined whether CT regeneration supports normal NaCl threshold in the rat. Thresholds were measured with a 2-lever operant procedure. Thresholds increased more than 1 order of magnitude after CTX regardless of recovery period length. Postsurgical thresholds in rats with regenerated CTs did not differ from presurgical values. Stimulus adulteration with amiloride raised thresholds in rats with intact or regenerated CTs by about 1 order of magnitude but did not raise thresholds beyond postsurgical levels in rats with transected CTs. Thus, the regenerated CT supports normal NaCl threshold, which is raised by amiloride. Because thresholds remained elevated 62 days after CTX when regeneration was prevented, compensatory processes alone cannot support normal NaCl threshold.

Effect of Tricyclic Antidepressants on Taste Responses in Humans and Gerbils

One of the side effects of antidepressant pharmacotherapy reported clinically is impairment of the sense of taste. In this study, the taste effects of four tricyclic antidepressant compounds (clomipramine HCl, desipramine HCl, doxepin HCl, and imipramine HCl) were evaluated experimentally by topical application of the drugs to the tongue. Taste detection threshold concentrations for all four medications ranged from 0.1 mM to 0.2 mM in young persons but were elevated by as much as 7.71 times that in elderly individuals who were taking no concurrent medications. Each compound had a predominantly bitter taste with other qualities including metallic, sour, and sharp-pungent. In addition, each tricyclic antidepressant at concentrations from 1 mM to 5 mM blocked responses to a wide range of taste stimuli in both humans and gerbils. The differential suppression of other tastes by tricyclic antidepressants at the level of the taste receptors may contribute to the clinical reports of dysgeusia and hypogeusia.

Role of saliva in the maintenance of taste sensitivity.

Saliva is the principal fluid component of the external environment of the taste receptor cells and, as such, could play a role in taste sensitivity. Its main role includes transport of taste substances to and protection of the taste receptor. In the initial process of taste perception, saliva acts as a solvent for taste substances; salivary water dissolves taste substances, and the latter diffuse to the taste receptor sites. During this process, some salivary constituents chemically interact with taste substances. For example, salivary buffers (e.g., bicarbonate ions) decrease the concentration of free hydrogen ions (sour taste), and there are some salivary proteins which may bind with bitter taste substances. Another effect of saliva on taste transduction is that some salivary constituents can continuously stimulate the taste receptor, resulting in an alteration of taste sensitivity. For example, the taste detection threshold for NaCl is slightly above the salivary sodium concentrations with which the taste receptor is continuously stimulated. In contrast, saliva protects the taste receptor from damage brought about by dryness and bacterial infection, and from disuse atrophy via a decrease in transport of taste stimuli to the receptor sites. This is a long-term effect of saliva that may be related to taste disorders. These various effects of saliva on the taste perception differ depending on the anatomical relationship between the taste buds and oral openings of the ducts of the salivary glands. Many taste buds are localized in the trenches of the foliate and circumvallate papillae, where the lingual minor salivary glands (von Ebner's glands) secrete saliva. Taste buds situated at the surface of the anterior part of the tongue and soft palate are bathed with the mixed saliva secreted mainly by the three major salivary glands.

Development of taint and odour in cellulosic carton-board packaging systems

Unsaturated lipids exist in carton-board used for food packaging and can be the precursors of odorous compounds. The linoleic acid component may be in the form of a free acid, an alkyl ester derivative or a triglyceride. Oxidation proceeds via a free radical route to produce aldehydes, ketones, alcohols, furans, lower fatty acids, alkenes and alkanes, the majority of which are odorous. The aldehydes, in particular, have very low odour and taste detection thresholds, needing to be present only in very small amounts in a packaging material to cause a taint problem. Static headspace GC/MS analyses have identified a number of odorous compounds formed from the oxidation reactions. These oxidation reactions are affected to various extents by a number of factors that include temperature and the presence of photosensitising agents. Ultra-violet (UV) curable inks are commonly used in the printing of cellulosic carton-board packaging materials. These inks contain photoinitiators that have the potential to affect the rate and the extent of oxidation of unsaturated lipids, resulting in the formation of odorous compounds within the cellulosic carton-board matrix.

Amiloride increases sodium chloride taste detection threshold in rats.

The epithelial sodium-channel blocker amiloride has been shown to inhibit sodium responses in the 7th cranial nerve of the rat. In the signal detection task used in this study, amiloride (100 microM) treatment raised the NaCl threshold by approximately 1 log10 unit. The inhibition constant for amiloride was 1 microM at 0.013 M NaCl. Because the NaCl intake of adult rats has been shown to be related to the level of dietary NaCl exposure early in development, rats were exposed by way of maternal diet to 1 of 3 diets (0.1% NaCl, n = 8; 1.0% NaCl, n = 8; 3.0% NaCl, n = 9) from conception through weaning, to determine whether this treatment affects taste sensitivity. At Postnatal Day 30, rats were placed on 1.0% NaCl chow. This treatment did not affect NaCl detection or amiloride sensitivity in adulthood. The amiloride-induced shifts in NaCl sensitivity functions imply that the transcellular sodium transduction pathway is necessary for normal NaCl detection in the rat.

Amiloride increases sodium chloride taste detection threshold in rats.

Amiloride increases sodium chloride taste detection threshold in rats.

Effects of a Pressure Surround on the Regional Taste Detection Threshold for Sodium Chloride

The question as to whether tactile stimulation alters proximal taste function in humans has never been answered, despite the suggestion of anatomical and physiological associations between somatosensory and gustatory function in a number of species. In this study, we established NaCl detection thresholds for a 25 mm2 anterior tongue region on four test occasions in each of 12 men and 12 women. Testing was performed using the Regional Automated Taste Testing System (RATTS), a device that allows for accurate temporal and spatial presentation of tastants to the lingual surface. On each test occasion, a different negative pressure (vacuum suction) was applied around the stimulus presentation field of the glass stimulation device (i.e. 40, 50, 60 and 70 mmHg). The order of presentation of the vacua was systematically counterbalanced among subjects across sessions using 4 x 4 Latin square sequences. Neither the vacua nor their order of presentation meaningfully altered the taste threshold values, even though the higher vacua produced persistent discernible discomfort in most subjects. On average, taste thresholds tended to be marginally lower in women than in men. These data indicate that static vacuum-induced tactile stimulation around a discrete anterior taste field has no meaningful influence on NaCl detection threshold sensitivity.

The Effect of Naltrexone on Taste Detection and Recognition Threshold

Eighteen healthy female volunteers were administered 50 mg naltrexone in a double-blind, placebo control study. Relative taste detection and recognition thresholds for sweet, salty, sour and bitter taste and liking for and perception of sucrose solutions were determined at baseline and 1 hour after administration of naltrexone. Naltrexone did not alter relative taste detection and recognition thresholds for any of the four tastes or perception of sweetness. However, a significant, but slight, decrease in liking for sucrose solutions occurred after naltrexone administration. These findings suggest that opioid-dependent intake is independent of changes in taste perception in humans.

Alterations of Chemosensory Function in End-Stage Liver Disease

Taste and smell dysfunction has been documented in patients with both acute and chronic liver disease. The purpose of this study was to determine if chemosensory function is improved after restoration of hepatic function with liver transplantation. Nine subjects (seven women and two men) with end-stage liver disease participated in the study. Taste and smell detection and recognition thresholds were determined before and after transplantation. A significant improvement in detection of the taste of sodium chloride and the odor of phenethyl alcohol was found after transplantation. These findings may have clinical significance in food choices and nutritional status of these patients.

Chorda tympani nerve transection, but not amiloride, increases the KCl taste detection threshold in rats.

Chorda tympani nerve transection, but not amiloride, increases the KCl taste detection threshold in rats.

Chorda tympani nerve transection, but not amiloride, increases the KCl taste detection threshold in rats.

Water-restricted rats were trained to press one lever after KCl presentation and the other lever after distilled water. Water reinforcement was given after each correct response, and a time-out followed each incorrect response. Rats were trained and tested on KCl stimuli of varying concentrations. Threshold was defined as the KCl concentration corresponding to 1/2 the maximum asymptote of performance for each rat. The geometric mean KCl detection threshold for all rats was 0.033 M KCl. Rats that had the chorda tympani nerve (CT) bilaterally transected showed an average increase in KCl threshold of approximately 0.60 log10 units, whereas sham-operated rats showed no change. Control rats retested with 100 microM amiloride added to all KCl concentrations and water displayed no change in threshold. These results suggest that although the CT contributes significantly to the rat's sensitivity to KCl, amiloride-sensitive taste transduction pathways do not.

Taste Sensitivity Is Altered in Patients with Chronic Renal Failure Receiving Continuous Ambulatory Peritoneal Dialysis

Decreased taste sensitivity may be one of the many factors influencing the poor nutritional status of many patients with chronic renal failure. Several studies examining taste in chronic uremic and hemodialysis (HD) patients indicate decreased sensitivity; continuous ambulatory peritoneal dialysis (CAPD) patients, however, warrant investigation. The aim of this study was to determine if the taste detection threshold for each of the four tastes (sweet, salty, sour and bitter) differs between CAPD patients and age and sex matched controls with normal renal function. The thresholds were determined using Cornsweet's staircase technique for increasing and decreasing stimulus concentration, in which the subject's response determines the next concentration to be tested. A forced-choice design using three samples was used to help minimize bias. The taste detection threshold for the CAPD patients was significantly higher than that of the controls for sodium chloride (salty)(P = 0.001) and quinine (bitter) (P = 0.01). This information may be useful when designing dietary supplements and devising meal plans to help patients consume nutritionally adequate diets.

Genetic Sensitivity to 6- N-Propylthiouracil (prop) and Sensory Acceptance of Soy Products and Japanese Green Tea.

LEARNING OUTCOME: Sensory acceptance of functional foods, with reputed cancer preventive properties, such as soy products and Japanese green tea, may be influenced by genetic sensitivity to the bitter taste of PROP. Subjects were 53 young women (ages 20-45 y) recruited from the University of Michigan community. Taste detection thresholds for 6- n-propylthiouracil (PROP) were determined using the method of solutions. The subjects also tasted 5 suprathreshold solutions each of PROP and NaCl. Separation of subjects into nontasters (n=14), regular tasters (n=27) and supertasters (n=12) of PROP was based on PROP detection thresholds and mean response ratios to PROP as compared to NaCl solutions. The subjects also tasted a range of soy products including tofu, miso, plain soy milk and vanilla-flavored soy milk, as well as five different concentrations of Japanese green tea presented at room temperature. The most concentrated tea sample used 2.25 g of tea per 50 ml water, infused over a 5 min period. Taste intensity ratings were recorded using 9-point category scales, while acceptability ratings were based on a 9-point hedonic preference scale. Results showed that tasters and supertasters of PROP found tofu less acceptable than did nontasters, and to the contrary, preferred sweetened vanilla-flavored soy milk. PROP tasters rated Japanese green tea as more bitter than did nontasters. Rated acceptance of green tea decreased as bitterness increased. In past studies, genetically mediated sensitivity to PROP predicted lower acceptance of grapefruit juice. Since potentially chemopreventive flavonoids in soy products and green tea also have a bitter taste, avoidance of bitter foods may alter eating habits and reduce dietary exposure to foods known to alter cancer risk. Supported by NCI grant CA61680 and funds from the Michigan Soybean Promotion Board.

A computer-controlled electrogustometer for the estimation of evoked taste thresholds

Reliable taste detection thresholds in humans are difficult to obtain for either research or clinical purposes because ordinary taste stimuli cannot be generated and presented by means of a computer. However, in investigations of taste dysfunction, electrical taste stimulation (electrogustometry) is sometimes employed. Minute anodal direct currents are applied manually to the tongue, giving rise to an acid taste experience through the liberation of protons into the saliva. This experience accords with recent findings on the mechanisms underlying sour taste perception. The device described here is a safe and accurate constant-current device, operating under computer control at very low amperages, making it possible to apply modern psychophysical procedures to the measurement of evoked taste thresholds.