Genetic sensitivity to the bitter taste of phenylthiocarbamide and 6-n-propylthiouracil (PROP) is a well-studied human trait. It has been hypothesized that this phenotype is a marker for individual differences in taste perception that influence food preferences and dietary behavior with subsequent links to body weight and chronic disease risk. Steady progress has been made over the past several decades in defining the involvement of this phenotype and its underlying gene, TAS2R38, in this complex behavioral pathway. However, more work needs to be done to fully determine its overall nutritional and health significance. The primary goal of this review is to assess our current understanding of the role of the PROP bitter taste phenotype in food selection and body weight in both children and adults. A brief history of the field is included and controversies surrounding the use of different PROP screening methods are addressed. The contribution of other receptors (both bitter and nonbitter) to human taste variation is also discussed.

Nutritional Implications of Genetic Taste Variation: The Role of PROP Sensitivity and Other Taste Phenotypes

Accumulating evidence suggests dietary fatty acids (FAs) may be sensed in the oral cavity. However, the effective cues have not been characterized. In particular, influences from other sensory cues have hampered identification of an independent gustatory contribution. Experiment 1 examined techniques to minimize the formation of FA oxidation products and improve the homogeneity of water/lipid emulsions to be used as stimuli in Experiment 2, a psychophysical study to determine FA detection thresholds in humans. Through sonication of chilled samples held in polypropylene labware and the addition of 0.01% ethylenediaminetetraacetic acid, calcium disodium salt, homogenous emulsions of unoxidized linoleic and oleic FAs were obtained. Spectrophotometric analysis revealed no oxidation product formation over a 24-h period. Coupled with these techniques, a masking approach was used to minimize other sensory cues imparted from linoleic, oleic, and stearic FAs. Concentration ranges from 0.00028% to 5% (w/v) were prepared in mixtures with 5% mineral oil (w/v) and 5% gum acacia (w/v) to mask lubricity and viscosity effects, respectively. Testing was conducted under red light with nares blocked to eliminate visual and olfactory cues. Oral rinses with 20 ppm capsaicin were administered to desensitize participants to selected irritation effects prior to remeasuring linoleic acid detection thresholds. To determine if the effective stimulus was an oxidation product, oxidized linoleic acid was included among the test stimuli. Detection thresholds were obtained using a 3-alternative, forced-choice ascendingconcentration presentation procedure. The mean detection threshold for linoleic acid pre-desensitization was 0.034 ± 0.008%, for linoleic acid post-desensitization was 0.032 ± 0.007%, for oleic 0.022 ± 0.003%, for stearic 0.032 ± 0.005%, and oxidized linoleic 0.025 ± 0.005%. The results suggest that linoleic, oleic, stearic, and oxidized linoleic acids are detectable in the oral cavity of humans with minimal input from the olfactory, capsaicin, and viscosity-assessing tactile systems.

/pdf/evidence-for-human-orosensory-taste-sensitivity-to-free-50z02fprle.pdf

Evidence for Human Orosensory (Taste?) Sensitivity to Free Fatty Acids

The bad taste of medicines: overview of basic research on bitter taste.

Check-all-that-apply questions: Influence of attribute order on sensory product characterization

Objective: Variation in the bitter-taste receptor gene, TAS2R38 confers the ability to taste 6-n-propylthiouracil (PROP) The objective of this study was to relate TAS2R38 haplotypes and PROP-tasting phenotypes to adiposity in a genetically isolated population We hypothesized that the nontaster phenotype would be associated with higher BMI and waist circumference (WC) in females, and that dietary restraint would mediate this relationship



Methods and Procedures: Participants were 540 healthy inhabitants of the genetically isolated village of Carlantino in southern Italy who were 15–89 years of age at the time of the study Haplotype analyses were performed and PROP tasting was assessed using a filter paper method Height, weight, and WC were measured and restrained eating was assessed using a brief questionnaire



Results: Nontaster females had higher BMI and WC than females who were phenotypic tasters, and this relationship was specific to females with low dietary restraint Regression analysis showed that BMI declined by 17 units across taster groups in females when the model included the PROP by restraint interaction PROP phenotype was not significantly associated with WC in the regression models Polymorphisms in TAS2R38 were not associated with BMI or WC in females Neither TAS2R38 haplotype nor PROP phenotype was strongly related to BMI or WC in males



Discussion: These data support previous findings of a relation between the nontaster phenotype and higher BMI in females that is modified by dietary restraint Assessment of PROP phenotypes might provide unique information about adiposity that is not captured by haplotype analysis alone

https://onlinelibrary.wiley.com/doi/pdf/10.1038/oby.2008.357

Variation in the Bitter‐taste Receptor Gene TAS2R38, and Adiposity in a Genetically Isolated Population in Southern Italy

Development of brief methods to classify individuals by PROP taster status.

Assessment of Different Methods for 6-n-Propylthiouracil Status Classification

A total of 450 consumers participated in a test to determine whether question- naire length, presence of key diagnostic questions or serving position affected their hedonic discrimination among yellow cakes. Consumers evaluated four yellow cakes representing a 2 x 2 factorial design of texture andflavorflaws. They used one of the following six questionnaires: only a 9-point hedonic scale, a 9-point hedonic scale with open end questions, and four others comprising a 2 x 2 factorial design with two levels of questionnaire length and two levels of questionnaire completeness. Neither the presence of key attribute questions nor the length of the questionnaire affected the value or the sensitivity of the judges' overall liking scores. Samples tasted first received higher hedonic scores than those same samples tasted second through fifth. Judges could discriminate among the samples on the basis of overall liking best when samples were tasted fourth or fifth. 'Published as paper

Carol M. Christensen

Papers

Development of brief methods to classify individuals by PROP taster status.

Assessment of Different Methods for 6-n-Propylthiouracil Status Classification

Effect of questionnaire design and the number of samples tasted on hedonic ratings