Keast RSJ, Roper J. A complex relationship among chemical concentration, detection threshold, and suprathreshold intensity of bitter compounds. Chem Senses 32, 245-253
ABSTRACT 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.
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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 . Previous human taste-test studies and briefaccess mouse studies have also shown that the minimal effective concentration of 6-PTU is ∼10 −4 M   . "
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.01/2015; 2015:1-9. DOI:10.1155/2015/403919
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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. "
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.Chemosensory Perception 12/2014; 7(3-4):147-157. DOI:10.1007/s12078-014-9166-3 · 1.37 Impact Factor
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- "To ensure that differences in perception were specific to taste sensations and not differences in how the scales were used, the adults were asked to use the gLMS to rate the heaviness of 6 opaque, sand-filled jars of differing weights. Heaviness ratings were then used to normalize taste intensity ratings using previously described methods (Keast and Roper 2007). "
ABSTRACT: Sweeteners are often added to liquid formulations of drugs but whether they merely make them better tasting or actually reduce the perception of bitterness remains unknown. In a group of children and adults, we determined whether adding sucrose to urea, caffeine, denatonium benzoate, propylthiouracil (PROP), and quinine would reduce their bitterness using a forced-choice method of paired comparisons. To better understand individual differences, adults also rated each solution using a more complex test (general Labeled Magnitude Scale [gLMS]) and were genotyped for the sweet taste receptor gene TAS1R3 and the bitter receptor TAS2R38. Sucrose suppressed the bitterness of each agent in children and adults. In adults, sucrose was effective in reducing the bitterness ratings from moderate to weak for all compounds tested, but those with the sensitive form of the sweet receptor reported greater reduction for caffeine and quinine. For PROP, sucrose was most effective for those who were genetically the most sensitive, although this did not attain statistical significance. Not only is the paired comparison method a valid tool to study how sucrose improves the taste of pediatric medicines among children but knowledge gleaned from basic research in bitter taste and how to alleviate it remains an important public health priority.Chemical Senses 11/2014; 40(1). DOI:10.1093/chemse/bju053 · 3.28 Impact Factor