Bitter taste intensity: the effect of tastant and thiourea taster status

Thiourea tasters and nontasters did not significantly differin their ratings of intensity of caffeine or quinine HCl, butsignificant group x concentration interactions were noted fordenatonium benzoate, sucrose octaacetate and urea.     

Residual family resemblance for PTC taste sensitivity

Summary Complex segregation analysis reveals no evidence for incomplete dominance, polygenic variation, or an effect of family environment on PTC sensitivity. Estimates of gene frequency and displacement from a phenotypic trichotomy agree closely with conventional values for the dichotomy of tasters vs. nontasters.     

Evolution of phenylthiocarbamide taster trait in Mysore, South India

BACKGROUND:

The ability to taste phenylthiocarbamide (PTC), a bitter chemical has long been known to be a heritable trait, which is being widely used for both genetic and anthropological studies. The frequency of taster and non-taster allele is found to vary in different populations.

AIMS AND OBJECTIVE:

To investigate the frequency of taster trait in Mysore, South India.

MATERIALS AND METHODS:

The present investigation was conducted in Mysore, South India during 2002 - 2003. About 3282 subjects irrespective of age, sex, religion, food habits, socio-economic status were randomly selected from various parts of the city and a total of 180 families, which included Christian (50), Hindu (61) and Muslim (69) were screened from different localities of the city. Harris and Kalmus method was used to assess the PTC taster and nontaster phenotype.

RESULTS:

It was found that tasters were significantly more frequent than nontasters in all the four categories. The incidence of tasters was more in unbiased category (85%) and less in Muslim category (58%). Investigations on PTC tasting in the families of three different religious groups revealed that the tasters were significantly more frequent than nontasters. It was also found that heterozygous father or mother for the taster genes with nontaster partner had taster and nontaster progenies in the ratio 1.0: 1.54 indicating the deviation in the segregation pattern of test cross.

CONCLUSION:

In Mysore, tasters are more frequent than nontasters. Variation in the frequency of nontaster allele in the religious groups could be due to inbreeding.     

Sweet taste receptor gene variation and aspartame taste in primates and other species

Aspartame is a sweetener added to foods and beverages as a low-calorie sugar replacement. Unlike sugars, which are apparently perceived as sweet and desirable by a range of mammals, the ability to taste aspartame varies, with humans, apes, and Old World monkeys perceiving aspartame as sweet but not other primate species. To investigate whether the ability to perceive the sweetness of aspartame correlates with variations in the DNA sequence of the genes encoding sweet taste receptor proteins, T1R2 and T1R3, we sequenced these genes in 9 aspartame taster and nontaster primate species. We then compared these sequences with sequences of their orthologs in 4 other nontasters species. We identified 9 variant sites in the gene encoding T1R2 and 32 variant sites in the gene encoding T1R3 that distinguish aspartame tasters and nontasters. Molecular docking of aspartame to computer-generated models of the T1R2 + T1R3 receptor dimer suggests that species variation at a secondary, allosteric binding site in the T1R2 protein is the most likely origin of differences in perception of the sweetness of aspartame. These results identified a previously unknown site of aspartame interaction with the sweet receptor and suggest that the ability to taste aspartame might have developed during evolution to exploit a specialized food niche.     

COMPARISON OF NEW AND EXISTING METHODS FOR THE CLASSIFICATION OF INDIVIDUALS ACCORDING TO 6-N PROPYLTHIOURACIL (PROP) TASTER STATUS

We developed an alternative method for the determination of 6-n propylthiouracil (PROP) taster status that is based on the comparison of intensity ratings of PROP solutions with intensity ratings of visual, tactile, and kinesthetic (physical) stimuli. We then compared the classification obtained with this method to those derived from traditional approaches. One hundred and forty-two subjects rated the perceived intensity of 0.000032, 0.00018, 0.00032, 0.0018, and 0.0032 M PROP, and 0.01, 0.032, 0.1, 0.32, and 1.0 M NaCl, as well as five levels each of perceived roughness of sandpaper, grayness of shades, and thickness of honey and water mixtures on the Labeled Magnitude Scale (LMS). Ratings for 0.00032 M PROP and 0.1 M NaCl were also compared in a one solution test. Subjects were classified as PROP nontasters, tasters or supertasters by all three procedures. Seventy-six percent of panelists were classified in a similar way by the physical stimuli and NaCl procedures, while 70% percent of panelists were classified similarly by the physical stimuli procedure and the one solution test, as well as by the NaCl procedure and the one solution test. Only 65% of panelists were classified similarly by all three procedures. Further, in replicate ratings of PROP solutions, supertasters' evaluations of PROP at all concentration levels decreased significantly (P < 0.01) from the first to the second rating. It is evident from these findings that the method used to determine PROP taster status can greatly influence the outcome of any investigation of PROP taster status on other phenotypes.     

Inherited Taste Sensitivity to 6‐n‐Propylthiouracil in Diet and Body Weight in Children

Objective: Negative associations between the inherited ability to taste the bitter compound 6‐n‐propylthiouracil (PROP) and preference for fat and body weight have been observed in adults. This study tested the relationships among the ability to taste PROP, reported food intake, and body weight in young children. Research Methods and Procedures: Fifty‐three 4‐ to 5‐year‐old children were classified as tasters (N = 35) or nontasters (N = 18) of PROP using a standard screening solution. Anthropometric measures were taken in the laboratory. Mothers completed questionnaires to assess their child's food intake and their own dieting behaviors. Results: Nontaster boys had higher weight‐for‐height percentiles than taster boys (77th vs. 56th percentile, respectively), but the relationship was opposite for girls (p ≤ 0.05). Nontasters reportedly consumed a higher percentage of their daily energy from protein (p ≤ 0.01), mainly as high‐fat meat products. Tasters reportedly consumed a higher percentage of their daily energy from sugars (p ≤ 0.05), mainly in the form of brownies, doughnuts, cookies, soft drinks, and juice drinks. There were no differences between tasters and nontasters for reported intake of grains, fruits, vegetables, dairy products, or discretionary fats. Discussion: This study is the first, to our knowledge, to report weight differences in children as a function of their PROP status. Genetic taste factors seem to play a role in the development of dietary patterns and weight differences in young children, but the nature of these relationships may vary with gender.     

Magnitude-matching: the measurement of taste and smell

In the method of magnitude-matching, subjects try to judge intensitiesof sensations from two or more modalities on a single, commonscale. Using responses to one modality as a standard makes itpossible to compare subjects' suprathreshold perceptions onthe other, test modality. A series of ten experiments revealedthe following: (i) magnitude-matching ‘works’: withboth loudness of tones and lightness of grays as standards,tasters versus nontasters of 6-n-prophylthiouracil (PROP) (asdefined by a threshold criterion) show much greater responceto suprathreshold PROP and slightly greater response to surcose;(ii) though superior to rating-scale judgements of sensory intensitymade without reference to a second modality, magnitude-matchingis not, however, flawless: the cross-modality matching relationproduced by a set of magnitude-matches depends systematicallyon the contextual sets of stimulus levels presented for judgement;(iii) with taste as the standard, old versus young subjectsshowed only a 25% decrement in responce to the odor intensityof butanol when both groups recieved the same physical (concentration)levels, but a >50% decrement in responce when both groupsrecieved about the same perceptual levels; (iv) magnitude-matchesare much the same whether subjets make their judgements on abounded rating-scale or an open-ended magnitude-estimation scale:and (v) loudness, lightness and odor intensity serve about equallyin magnitude-matching with taste intensity.     

PROP (6-n-Propylthiouracil) tasting and sensory responses to caffeine,sucrose, neohesperidin dihydrochalcone and chocolate

The genetically determined ability to taste 6-n-propylthiouracil (PROP) has been linked with lowered acceptance of some bitter foods. Fifty-four women, aged 18-30 years, tasted and rated PROP-impregnated filter paper and seven solutions of PROP. Summed bitterness intensity ratings for PROP solutions determined PROP taster status. Respondents also tasted five sucrose and seven caffeine solutions, as well as seven solutions each of caffeine and PROP that had been sweetened with 0.3 mmol/l neohesperidin dihydrochalcone (NHDC). Respondents also rated three kinds of chocolate using 9-point category scales. PROP tasters rated caffeine solutions as more bitter than did non-tasters and liked them less. PROP tasters did not rate either sucrose or NHDC as more sweet. The addition of NHDC to PROP and caffeine solutions suppressed bitterness intensity more effectively for tasters than for non-tasters and improved hedonic ratings among both groups. PROP tasters and non-tasters showed the same hedonic response to sweetened caffeine solutions and did not differ in their sensory responses to chocolate. Genetic taste markers may have only a minor impact on the consumption of such foods as sweetened coffee or chocolate.     

Marked Increase in PROP Taste Responsiveness Following Oral Supplementation with Selected Salivary Proteins or Their Related Free Amino Acids

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by ¹H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.¹H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.     

Genetic sensitivity to bitter taste of 6-n Propylthiouracil: A useful diagnostic aid to detect early childhood caries in pre-school children

PURPOSE:

Genetic factor to bitter taste perception appears to be largely mediated by the TAS2R38 gene. The insensitivity to bitter compounds like 6-n-propylthiouracil (PROP) is mediated by this gene. PROP, a pharmacological drug used in treatment of Graves’ disease, proved to be useful tool in determining the genetic sensitivity levels to bitter and sweet taste. The purpose of this study is to show much simpler PROP sensitivity technique for the clinical examiner and its application as a diagnostic aid in Early Childhood Caries (ECC) detection among preschool children.

MATERIALS AND METHODS:

A total of 119 children belonging to the age group of 36 to 71 months of both sexes, were recruited from A. J. Institute of Dental Sciences, Mangalore (Karnataka). PROP sensitivity test was carried out to determine the inherent genetic ability to taste a bitter or sweet substance. This study used simpler scaling method to find out genetic sensitivity to bitter taste; one who tasted bitter as taster and one who was not able to differentiate/tasted like paper as non-taster. A questionnaire was provided to evaluate their dietary habits and caries experience was recorded. Collected data were tabulated and subjected to statistical analysis.

RESULTS:

In the total of 119 children the mean dmfs was definitely higher in non-taster children compared to tasters. The tasters had a mean dmfs value of 9.5120 (S.D. 7.0543) and non-tasters had a value of 7.7250 (S.D. 8.33147), which was statistically significant. The results suggested that there was increase in caries experience among the group of non-tasters as compared to tasters. Tasters tended to be sweet dislikers and non-tasters tended to be sweet likers. On the whole, tasters had a bad dentition as compared to non tasters.

CONCLUSION:

The PROP sensitivity test (filter paper test) proved to be a useful diagnostic tool in determining the genetic sensitivity levels of bitter taste. The knowledge of a child''s taste perception can help us in identifying the children who are at higher risk for ECC.     

RELATIONSHIP OF PROP (6-N-PROPYLTHIOURACIL) TASTER STATUS WITH THE BODY MASS INDEX AND FOOD PREFERENCES OF FILIPINO ADULTS

The study determined the 6-n-propylthiouracil (PROP) status of Filipino adults and how it relates to their body mass indices (BMI) and food preferences. Self-reported food preference checklists were administered to 100 male and female adults aged 18–60, classified according to BMI. Increasing concentrations of PROP and NaCl solutions were rated in labeled magnitude scale to establish the PROP taster status of the selected respondents. The Filipino adult respondents were composed of 12% nontasters, 45% medium tasters and 43% supertasters. No association ( P >  0.05) between BMI and PROP taster status was found. Sweet-tasting foods were the most preferred and bitter-tasting foods were the least preferred within each taster status. Furthermore, medium tasters and supertasters had the highest acceptance for meats, fish and poultry, and least acceptance for beverages, which were mostly bitter. Decreased preferences for fats and oils, sugars and confectionery, and beverages were correlated ( P <  0.05) with responsiveness to PROP.

PRACTICAL APPLICATIONS

The research provides a general baseline data of the PROP taster status of Filipino adults. The findings from this study can be used as a reference and can be compared to similar studies conducted in other countries. Likewise, the information from the study can add to the scarce data for taste genetics specifically for the Asian population. The relationship of PROP taster status with body mass index and food preferences can be a guide in the design of products and dietary plans. Likewise, the study would be a means to understand why people vary in liking for particular food items and how these can be reflected in their food consumption and nutritional status.     

Adiposity in Middle‐aged Women is Associated with Genetic Taste Blindness to 6‐n‐Propylthiouracil

Objective: Taste blindness to the bitterness of 6‐n‐propylthiouracil (PROP) may be a genetic marker for food preferences and dietary choices that ultimately influence body weight. A previous study in middle‐aged women showed that those who were taste blind to PROP (i.e., nontasters) had higher BMIs than those with the greatest sensitivity to PROP (i.e., supertasters). This study tested the hypothesis that the nontaster phenotype was associated with greater adiposity in middle‐aged women. Research Methods and Procedures: Forty women with a mean BMI of 26.6 ± 1.3 kg/m² and a mean age of 41.8 ± 1.8 years were recruited from the local community. They were classified as nontasters (n = 8), medium tasters (n = 18), or supertasters (n = 14) of PROP using a filter paper screening procedure. Anthropometric measures included height, weight, body fatness, triceps skinfold thickness, and waist circumference. Dietary restraint and disinhibition were also measured to assess cognitions associated with body weight. Results: BMI was 6.2 units higher in nontaster women compared with supertaster women (29.7 ± 0.9 vs. 23.5 ± 0.9, respectively; p < 0.05). Body fatness (p < 0.01) and triceps skinfold thickness (p < 0.05) were also higher in these women. Waist circumference showed a trend in the appropriate direction. Although disinhibition was associated with greater adiposity, the relation between PROP status and adiposity was not altered after controlling for disinhibition. Discussion: The PROP nontaster phenotype was strongly associated with several measures of adiposity in middle‐aged women. These data confirm our previous findings and suggest that the PROP polymorphism may be a reliable indicator of weight gain susceptibility.     

Effect of high altitude on sensitivity to the taste of phenylthiocarbamide

Sensitivity to the taste of phenylthiocarbamide (PTC) was studied using the Harris-Kalmus method in healthy human volunteers at sea level and then subsequently at an altitude of 3500 m over a period of 3 weeks, after which they were brought back to sea level. Blood sugar, insulin and blood cortisol levels were estimated weekly. The results indicated that, out of 51 subjects studied, 26 (55%) were PTC tasters at sea level. Eight of those unable to taste PTC at sea level tested as tasters at high altitude, and 2 of them reverted to being non-tasters on return to sea level. In the blood, an increase in cortisol and blood insulin levels was seen without any significant change in sugar levels. All the changes recorded at high altitude tended to return to basal values after re-induction to sea level. The study suggests that high-altitude hypoxia in some way, possibly involving changes in hormonal profile among other factors, causes an alteration in sensitivity to the taste of PTC, resulting in some of the individuals shifting to lower PTC sensitivity. Received: 24 November 1999 / Accepted: 25 January 2000     

Effect of slowly increasing elastic load on breathing in conscious humans

Because the detection of added loads is a function of the step change in load relative to background level of load (Weber's law), we reasoned that detection may be delayed if the load is increased in very small steps over a protracted period. This would permit the study of subliminal load responses over a greater range than would otherwise be possible. In 13 healthy males, an external elastic load (delta E) was added in very small steps (load increased every few seconds) such that delta E increased from zero to 6.0 cmH2O/l in 18 min. Each subject underwent a control study in which an identical protocol was followed but no load was added. Five subjects sensed the load after a variable period of load application. Their results were discarded. In the remaining eight subjects, there was no perception of increased load throughout the 18 min. By comparison with the control studies in the same subjects, there was a progressive reduction in tidal volume and breath duration with loading. To assess the response to an increase in load associated with perception, in five of the eight "nonsensers" the load was suddenly doubled (delta E = 6 cmH2O/l) at the end of the 18 min of progressive nonsensed loading. This evoked perception in all subjects and was associated with highly variable responses in tidal volume and breath duration. We conclude that tachypnea associated with elastic loading in conscious humans is a reflex response that is facilitated by consciousness but does not require perception.     

The control of the proventriculus in the honeybee (Apis mellifera carnica L.) II. Feedback mechanisms

The mechanisms underlying the control of solution transport rates through the proventriculus in foraging honeybees were investigated in individuals trained to collect defined amounts of sugar solutions. Following feeding, bees were injected either with metabolisable (glucose, fructose, trehalose), or non-metabolisable (sorbose) sugars, in order to distinguish between haemolymph osmolarity and haemolymph sugar levels as factors controlling the solution transport rates through the proventriculus. After a fixed period, workers were dissected in order to measure crop content and haemolymph sugar titers. Between feeding and dissection, the metabolic rate of every investigated forager was measured using open-flow respirometry. Bees injected with metabolisable sugars 15 min after feeding were observed to reduce their solution transport rates through the proventriculus, but injection of non-metabolisable sugars had no influence on them. This suggests that the solution transport rate through the proventriculus is controlled by the concentration of metabolisable compounds in the haemolymph, and not by the haemolymph osmolarity. A period of 10 min after injection of metabolisable sugars was enough to observe reduced solution transport rates. However, if bees were injected only 5 min after feeding, no reduced solution transport rates were observed 10 min after injection.     

Toxicity of the Taste Testing Compound Phenylthiocarbamide

THE genetic polymorphism in human taste acuity for phenylthiocarbamide (phenylthiourea, PTC) and related compounds is widely used in practical demonstrations at most educational levels. The Nuffield O-level biology text¹ advises that PTC papers be prepared from 0.13% PTC solution, but PTC solutions or crystals are often used to distinguish “tasters” and “non-tasters”.