A Complex Relationship among Chemical Concentration, Detection Threshold, and Suprathreshold Intensity of Bitter Compounds

School of Exercise and Nutrition Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia.
Chemical Senses (Impact Factor: 3.16). 04/2007; 32(3):245-53. DOI: 10.1093/chemse/bjl052
Source: PubMed


Detection thresholds and psychophysical curves were established for caffeine, quinine-HCl (QHCl), and propylthiouracil (PROP)
in a sample of 33 subjects (28 female mean age 24 ± 4). The mean detection threshold (±standard error) for caffeine, QHCl,
and PROP was 1.2 ± 0.12, 0.0083 ± 0.001, and 0.088 ± 0.07 mM, respectively. Pearson product–moment analysis revealed no significant
correlations between detection thresholds of the compounds. Psychophysical curves were constructed for each bitter compound
over 6 concentrations. There were significant correlations between incremental points of the individual psychophysical curves
for QHCl and PROP. Regarding caffeine, there was a specific concentration (6 mM) below and above which the incremental steps
in bitterness were correlated. Between compounds, analysis of psychophysical curves revealed no correlations with PROP, but
there were significant correlations between the bitterness of caffeine and QHCl at higher concentrations on the psychophysical
curve (P < 0.05). Correlation analysis of detection threshold and suprathreshold intensity within a compound revealed a significant
correlation between PROP threshold and suprathreshold intensity (r = 0.46–0.4, P < 0.05), a significant negative correlation for QHCl (r = −0.33 to −0.4, P < 0.05), and no correlation for caffeine. The results suggest a complex relationship between chemical concentration, detection
threshold, and suprathreshold intensity.

    • "These relationships can be neatly accounted for by the common TAS2R activation profiles for these bitter substances (quinine and quassia TAS2R4, -10,-14, and -46; quinine and gentian TAS2R4, -39, -43, and -46; quinine and caffeine TAS2R7, -10, -14, -43, and -46; TAS2R43 and -46 are activated by caffeine and gentian. This cluster of compounds showed no relationship to the PROP taste status, in the case of quinine confirming previous observations (Hall et al. 1975; Bartoshuk 1979; Keast and Roper 2007). Consistent with our hypothesis, we did not see any correlation between caffeine taste intensity scores and PTC or PROP, as these compounds activate different TAS2Rs. "
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    ABSTRACT: The human population displays high variation in taste perception. Differences in individual taste sensitivity may also impact on nutrient intake and overall appetite. A well-characterized example is the variable perception of bitter compounds such as 6-n-propylthiouracil (PROP) and phenylthiocarbamide (PTC), which can be accounted for at the molecular level by polymorphic variants in the specific type 2 taste receptor (TAS2R38). This phenotypic variation has been associated with influencing dietary preference and other behaviors, although the generalization of PROP/PTC taster status as a predictor of sensitivity to other tastes is controversial. Here, we proposed that the taste sensitivities of different bitter compounds would be correlated only when they activate the same bitter taste receptor. Thirty-four volunteers were exposed to 8 bitter compounds that were selected based on their potential to activate overlapping and distinct repertoires of TAS2Rs. Taste intensity ratings were evaluated using the general Labeled Magnitude Scale. Our data demonstrate a strong interaction between the intensity for bitter substances when they activate common TAS2Rs. Consequently, PROP/PTC sensitivity was not a reliable predictor of general bitter sensitivity. In addition, our findings provide a novel framework to predict taste sensitivity based on their specific T2R activation profile. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail:
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    • "Multiple T2R family members (at least T2R-1, -4, and -38) in humans are known to detect 6-PTU [34, 44, 45], and these genes are the most conserved between humans and rodents [12]. Previous human taste-test studies and briefaccess mouse studies have also shown that the minimal effective concentration of 6-PTU is ∼10 −4 M [31] [46] [47]. "
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    ABSTRACT: The primary function of the gastrointestinal (GI) tract is the extraction of nutrients from the diet. Therefore, the GI tract must possess an efficient surveillance system that continuously monitors the luminal content for beneficial or harmful compounds. Recent studies have shown that specialized cells in the intestinal lining can sense changes in this content. These changes directly influence fundamental GI processes such as secretion, motility, and local blood flow via hormonal and/or neuronal pathways. Until recently, most studies examining the control of ion transport in the colon have focused on neural and hormonal regulation. However, study of the regulation of gut function by the gut chemosensory system has become increasingly important, as failure of this system causes dysfunctions in host homeostasis, as well as functional GI disorders. Furthermore, regulation of ion transport in the colon is critical for host defense and for electrolytes balance. This review discusses the role of the gut chemosensory system in epithelial transport, with a particular emphasis on the colon.
    Full-text · Article · Apr 2015
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    • "Less work has been done on other prototypical tastes, but they are also thought to vary subtly in different tongue areas, at least in regard to thresholds (Collings 1974). However, it should also be noted that thresholds and suprathreshold intensity are distinct phenotypes (e.g., Hayes and Keast 2011; Keast and Roper 2007) that may not generalize to each other. "
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    ABSTRACT: The sense of taste is often referred to as a 'nutritional gatekeeper', thought to have evolved to indicate energy sources and prevent ingestion of potential toxins. Fungiform papillae are structures on the anterior tongue in which taste buds are situated. They are concentrated at the tongue's tip and they can provide a useful estimate of overall taste bud density for taste research. Some reports suggest taste perception may differ subtly across tongue regions, irrespective of FP number. Other data show an association between taste intensity perception for the bitter compound 6-n-propylthiouracil (PROP) and FP density. However, contradictions exist in the literature, with more recent, larger studies suggesting little or no association between FP number and perceived taste intensity. Much research has examined the relation between FP density and PROP perception, while other tastes have been less thoroughly studied. Here, in a cohort of mainly Caucasian individuals, aged 18-45, recruited from the campus of a large rural university, we examined regional and whole-mouth taste intensities, and FP density using an updated method of a digital still photography method first described in 2005. We found regional differences in suprathreshold intensity. Although all taste sensations were experienced all over the tongue, once again disproving the mythical tongue map, we also observed bitter and umami taste perception to be significantly greater on the posterior tongue than on the anterior tongue. In contrast, there were no regional differences observed for sweet, salty or sour tastes. The relation of FP density to whole-mouth intensity of 6-n-propylthiouracil, and to the intensity of saltiness of NaCl, sweetness from sucrose or from Acesulfame-K, bitterness of quinine, or burning from capsaicin delivered to different regions of the tongue are also discussed.
    Full-text · Article · Dec 2014 · Chemosensory Perception
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