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PubMed1994

Structural basis for bitterness based on Rabdosia diterpenes.

Bitterness of naturally occurring substances seems to be due to a balance between the "bitter unit" and the hydrophobic portions of the molecule. The study based on the Rabdosia diterpenes indicates that the bitter unit consists of a proton donor DH group and a proton acceptor A group. In addition to this DH-A unit, an A-A unit may also be possible. The bitter compounds could enter the molecular structure of the receptor site with the bitter unit oriented into the aqueous phase by hydrogen bonding and the hydrophobic portion aligned into the lipid phase by dispersion forces.

Animals↗
PubMed1994

Influences on acceptance of bitter foods and beverages.

Bitterness is generally viewed as an undesirable attribute of foods and beverages, yet segments of the population regularly ingest items with a prominent bitter taste. The influence of taste sensitivity, exposure, selected personality traits (i.e., neophobia, variety seeking, sensation seeking) and pharmacological reactivity on alcohol and caffeine consumption, two widely consumed bitter substances, was assessed in 20 healthy adults (10 male, 10 female). Self-reported alcohol use was positively correlated with measured ethanol taste detection threshold and pharmacological reactivity (self-reported behavioral effects). The latter accounted for 23% of the variance in alcohol intake. Caffeine intake was significantly associated with personality traits. Sensation seeking status and self-reported reactivity to caffeine accounted for 46% of the variance in caffeine intake. Pleasantness ratings for novel bitter and sour foods were unaffected by 10 exposures whereas increased ratings were given to sweet and salty items. Variation in the influence of these factors between individuals and across products may explain individual differences in the acceptability and use of foods and beverages containing alcohol, caffeine and other bitter compounds.

Adult↗
PubMed2006

Functional expression of mammalian bitter taste receptors in Caenorhabditis elegans.

Bitter taste has evolved as a central warning signal against the ingestion of potentially toxic substances appearing in the environment. The molecular events in the perception of bitter taste start with the binding of specific water-soluble molecules to G protein-coupled receptors (GPCR) called T2Rs and expressed at the surface of taste receptor cells. The functional characterisation of T2R receptors is far from been completed due to the difficulty to functionally express them in heterologous systems. Taking advantage of the parallelisms between the Caenorhabditis elegans (C. elegans) and mammalian GPCR signalling pathways, we developed a C. elegans-based expression system to express functional human and rodent GPCRs of the T2R family. We generated transgenic worms expressing T2Rs in ASI chemosensory neurons and performed behavioural assays using a variety of bitter tastants. As a proof of the concept, we generated transgenic worms expressing human T2R4 or its mouse ortholog T2R8 receptors, which respond to two bitter tastants previously characterised as their functional ligands, 6-n-propyl-2-thiouracil and denatoniun. As expected, expression of human T2R4 or its mouse ortholog T2R8 in ASI neurons counteracted the water-soluble avoidance to 6-n-propyl-2-thiouracil and denatoniun observed in control wild-type worms. The expression in ASI neurons of human T2R16, the ligand of which, phenyl-beta-d-glucopyranoside, belong to a chemically different group of bitter tastants, also counteracted the water-soluble avoidance to this compound observed in wild-type worms. These results indicate that C. elegans is a suitable heterologous expression system to express functional T2Rs providing a tool to efficiently search for specific taste receptor ligands and to extend our understanding of the molecular basis of gustation.

Animals↗
PubMed2005

Hypoglycemic effects of steroidal sapogenins isolated from Jamaican bitter yam, Dioscorea polygonoides.

In this study, three steroidal sapogenins (Delta3 diosgenin, diosgenin, and pennogenin) and the phytosterols, stigmasterol and beta-sitosterol were isolated from Jamaican bitter yam, Dioscorea polygonoides. Their effects on fasting blood glucose and intestinal amylase and ATPases in streptozotocin-induced diabetic rats were studied. The diabetic rats (fed supplemented and unsupplemented diets) lost weight significantly compared to the normal group. There was a significant increase in the activity of alpha-amylase in the proximal region of the small intestinal mucosa of diabetic rats fed sapogenin extract or commercial diosgenin. However, this did not result in increased fasting blood glucose. Instead, supplementation of the diet with bitter yam sapogenin extract significantly decreased fasting blood glucose compared to the diabetic group. Supplementation of the diet with bitter yam sapogenin extract or commercial diosgenin significantly reduced Na+-K+-ATPase activity in all three regions compared to the diabetic control group. Commercial diosgenin supplementation resulted in a significant increase in Ca2+ ATPase activity in proximal region compared to the diabetic control and bitter yam sapogenin extract groups. The effect of bitter yam sapogenin extract or commercial diosgenin on intestinal Na+-K+-ATPase activity could account for their hypoglycemic properties. However, there was adverse effect on the body weight.

Adenosine Triphosphatases↗
PubMed2004

The distinctiveness of ionic and nonionic bitter stimuli.

The diverse chemical structures of stimuli that are bitter to humans suggest a need for multiple bitter receptors. Reactions of golden hamsters (Mesocricetus auratus) to 1 mM quinine hydrochloride, 3 mM denatonium benzoate, 180 mM magnesium sulfate, 30-100 mM caffeine, and 1-1.5 mM sucrose octaacetate (SOA) were studied to address whether there are multiple sensations elicited by bitter stimuli. Methods included behavioral generalization of LiCl-induced conditioned taste aversions (CTAs), intake preference tests, and electrophysiological recordings from the chorda tympani (CT) nerve. The five compounds, all bitter to humans, were all innately aversive to hamsters. CTA for the ionic quinine.HCl, denatonium benzoate, and MgSO(4) mutually cross-generalized and these ionic compounds were effective CT stimuli. Yet, the hamsters were much less sensitive to denatonium than humans, requiring a 100,000 times higher concentration for detection. CTA for nonionic caffeine and SOA did not cross-generalize to quinine or the other two ionic stimuli and these nonionic compounds were not effective CT stimuli. SOA and caffeine may elicit aversive reflexes or systemic reactions rather than taste sensations in the animals. Thus, the three ionic and two nonionic compounds form separate aversive stimulus classes in hamsters, neither of which appears to be a close homologue of the human bitter taste.

Animals↗
PubMed2004

Relating ionisation of calcium chloride in saliva to bitterness perception.

Saliva plays a role in the perception of bitter, sour and salty tastes that are presumed to be derived from the concentration of free cations or anions ions dissolved in saliva. The role of ionisation of calcium in bitter taste was studied by determining binding in vitro mixture of saliva and protein solutions and in spit. In vitro, the addition of whey to calcium chloride solutions increased the calcium binding, pH and viscosity. The addition of saliva to these mixtures, the increased calcium binding and the induced small changes in viscosity and pH were thought not to contribute significantly to bitterness perception. Nonstimulated saliva, at pH 7.5, contained about 5 mM calcium, of which about one third was ionised. The bitter threshold of fully ionised calcium chloride in water varied between 1 and 15 mM among individuals. In spit, after tasting whey, ionised calcium was found to have increased at low, but decreased at high, calcium concentrations and varied 30% among individuals. Bitterness was related, on average, to the concentration of ionised calcium and not to the total concentration of calcium in spit. A general explicative model based on the composition of bulk saliva is discussed in relation to perception threshold and the likely importance of saliva from von Ebner's gland.

Adult↗
PubMed2000

T2Rs function as bitter taste receptors.

Bitter taste perception provides animals with critical protection against ingestion of poisonous compounds. In the accompanying paper, we report the characterization of a large family of putative mammalian taste receptors (T2Rs). Here we use a heterologous expression system to show that specific T2Rs function as bitter taste receptors. A mouse T2R (mT2R-5) responds to the bitter tastant cycloheximide, and a human and a mouse receptor (hT2R-4 and mT2R-8) responded to denatonium and 6-n-propyl-2-thiouracil. Mice strains deficient in their ability to detect cycloheximide have amino acid substitutions in the mT2R-5 gene; these changes render the receptor significantly less responsive to cycloheximide. We also expressed mT2R-5 in insect cells and demonstrate specific tastant-dependent activation of gustducin, a G protein implicated in bitter signaling. Since a single taste receptor cell expresses a large repertoire of T2Rs, these findings provide a plausible explanation for the uniform bitter taste that is evoked by many structurally unrelated toxic compounds.

Afferent Pathways↗
PubMed2002

Prediction of the bitterness of single, binary- and multiple-component amino acid solutions using a taste sensor.

The purpose of this study was to develop a quick, quantitative, prediction method for the determination of the bitterness of solutions containing one or more of five amino acids (L-isoleucine, L-leucine, L-valine, L-phenylalanine, and L-tryptophan), using an artificial taste sensor. The bitterness of various solutions containing different concentrations (1, 3, 10, 30, and 100 mM) of five amino acids, singly and in combination, was estimated using a multichannel taste sensor and compared with the results of human gustatory sensation tests with nine volunteers. The relative response electric potential patterns were similar for all five amino acids. Large sensor outputs were observed in channels 1-4 (which are negatively charged) while there were no responses in channels 5-8 (positively charged). The sensor output for channel 1, which was the largest output value, was used for prediction of bitterness. The change of membrane potential caused by adsorption (CPA), which corresponds to aftertaste, could not be used as an explanatory variable since the adsorption of the amino acids to the sensor membrane was weak and CPA values were small. The bitterness intensity scores for single, binary, and multi-component amino acid solutions, could be easily predicted on the basis of the sensor output value of channel 1 using regression analysis. Principal component analysis of the sensor output data suggested that the sourness, astringency and/or smell of the solutions also played a role in the perception of bitterness.

Amino Acids↗
PubMed2006

Relation between bitter taste sensitivity and incidence or intensity of propofol injection pain.

BACKGROUND AND OBJECTIVE: In human beings, pain and taste perception are two major sensory inputs. We investigated whether increasing bitter taste sensitivity would increase intensity or incidence of pain associated with propofol, and whether there is a relationship between bitter sensitivity and venepuncture pain. METHODS: One hundred (50 males, 50 females) American Society of Anesthesiologists Grade I adults undergoing elective surgery were included in this study. Determination of the taste thresholds employed a series of propylthiouracil solutions. The filter paper disk method was used to measure the taste threshold. A 20-G intravenous (i.v.) cannula was inserted in the dorsum of the non-dominant hand. Venepuncture pain was assessed by using a numerical rating scale (NRS; 0, no pain and 10, extreme pain). Propofol 10 mL (100 mg) was injected over 30 s. Assessment of pain with i.v. propofol was made using a 4-point scale: 0, no pain; 1, mild pain; 2, moderate pain; 3, severe pain. RESULTS: The NRS score of venepuncture pain was 2.8 +/- 1.5. Sixty patients had pain during propofol injection. There was statistically significant correlation between bitter sensitivity and propofol injection pain, and between bitter sensitivity and venepuncture pain (P < 0.05). CONCLUSIONS: We conclude that increased bitter taste sensitivity correlates with increased intensity or incidence of propofol injection pain and NRS of venepuncture pain.

Adult↗
PubMed2002

Relationship between cyanogenic compounds in kernels, leaves, and roots of sweet and bitter kernelled almonds.

The relationship between the levels of cyanogenic compounds (amygdalin and prunasin) in kernels, leaves, and roots of 5 sweet-, 5 slightly bitter-, and 5 bitter-kernelled almond trees was determined. Variability was observed among the genotypes for these compounds. Prunasin was found only in the vegetative part (roots and leaves) for all genotypes tested. Amygdalin was detected only in the kernels, mainly in bitter genotypes. In general, bitter-kernelled genotypes had higher levels of prunasin in their roots than nonbitter ones, but the correlation between cyanogenic compounds in the different parts of plants was not high. While prunasin seems to be present in most almond roots (with a variable concentration) only bitter-kernelled genotypes are able to transform it into amygdalin in the kernel. Breeding for prunasin-based resistance to the buprestid beetle Capnodis tenebrionis L. is discussed.

Amygdalin↗
PubMed2005

Evaluation of bitter masking flavanones from Herba Santa (Eriodictyon californicum (H. and A.) Torr., Hydrophyllaceae).

Products made from Herba Santa (Eriodictyon californicum (H. & A.) Torr.) have been used as bitter remedies for some pharmaceutical applications for many years, but they are actually too aromatic to be useful for many food or pharmaceutical applications. In sensory studies flavanones homoeriodictyol (1), its sodium salt (1-Na), sterubin (2), and eriodictyol (4) could significantly decrease the bitter taste of caffeine without exhibiting intrinsic strong flavors or taste characteristics. Further investigations on 1-Na elicited a broad masking activity between 10 and 40% toward different chemical classes of bitter molecules (e.g. salicin, amarogentin, paracetamol, quinine) but not toward bitter linoleic acid emulsions. For caffeine and amarogentin, dose-response studies were performed; the masking activity toward bitter taste for both compounds reached a plateau at higher concentrations of 1-Na. Due to these facts, homoeriodictyol sodium salt (1-Na) seems to be a very interesting new taste modifier for food applications and pharmaceuticals.

Eriodictyon↗
PubMed2005

Direct spectrophotometric determination of bitterness in virgin olive oil without prior isolation by pH gradient.

Bitter taste, an organoleptic characteristic of virgin olive oil, has been related to phenolic compound composition. The usual method to assess this attribute is by a sensorial panel of tasters, while in the laboratory; methods based on physicochemical properties have been assayed as K225, the most widely used one. However, a direct determination of bitterness in virgin olive oil is useful for quality-control purposes. The proposed method is supported by the observable spectral change undergone by the compounds responsible for bitterness as pH varied. This measurement was carried out directly in the oil, without prior isolation of bitter analytes. The difference of absorbance between alkaline and neutral medium showed a highly significant correlation (r = 0.988, p < 0.0001) with the conventional parameter (K225). The method was rapid, required a small sample, allowed direct determination of bitterness in virgin olive oil, and could be easily automated.

Hydrogen-Ion Concentration↗
PubMed2006

Quantitative structure-activity relationship study of bitter peptides.

A database consisting of 224 di- to tetradecapeptides and five amino acids was compiled to study quantitative structure-activity relationships of bitter peptides. Partial least-squares regression-1 analysis was conducted using the amino acid three z-scores and/or three parameters (total hydrophobicity, residue number, and log mass values) as X-variables and bitterness values (log 1/T where T is the bitterness threshold) as Y-variables. Using the three parameters only, significant models (p < 0.001) were obtained describing the entire data set as well as data subsets, except that comprised only of octa- to tetradecapeptides. For data sets comprising different peptide lengths, the models were improved by including the three z-scores at the N-terminal and C-terminal positions. Correlation coefficients for bitterness prediction of 48 dipeptides and 12 pentapeptides were 0.75 (RMSEP = 0.53) and 0.90 (RMSEP = 0.48), respectively. Bulky hydrophobic amino acids at the C terminus and bulky basic amino acids at the N terminus were highly correlated to bitterness.

Amino Acid Sequence↗
PubMed1999

Influence of L-cysteine on the formation of bitter-tasting aminohexose reductones from glucose and L-proline: identification of a novel furo[2,3-b]thiazine.

Thermal treatment of a 1 + 1 mixture of glucose and L-proline led to the development of an intense bitter taste being reflected in high amounts of the bitter-tasting bispyrrolidino- (1) and pyrrolidinohexose reductones (2) formed. Heating the reaction mixture in the presence of L-cysteine drastically reduced the amounts of these aminohexose reductones and, thereby, the intensity of the bitter taste. Studies on the mechanism of the cysteine-induced reduction of the bitter taste revealed that the precursor of the aminohexose reductones, the hexose-derived acetylformoin (3), reacted more easily with L-cysteine to form the 7-hydroxy-4a,6-dimethyl-2H,3H,4aH-furo[2,3-b]thiazine (4), a previousely unknown Maillard reaction product, than with L-proline to the aminohexose reductones 1 and 2, thereby blocking the formation of bitter-tasting compounds.

Chromatography, High Pressure Liquid↗
PubMed1997

Response of pigs to bitter-tasting compounds.

Two-bottle preference tests were done to determine whether pigs detect bitter-tasting compounds. Four standard bitter compounds and nine bitter-tasting pharmaceutical compounds were tested. Pigs detect and avoid taste compounds that humans perceive as bitter-tasting. A dose-response to varying concentrations of bitter tastants can be measured.

Animals↗
PubMed2000

An In vitro assay useful to determine the potency of several bitter compounds.

Gustducin and transducin are guanine nucleotide binding regulatory proteins (G proteins) expressed in taste receptor cells and implicated in transducing taste cell responses to certain compounds that humans consider bitter or sweet. These G proteins can be activated in vitro by taste receptor-containing membranes plus any of several bitter compounds. This activation can be monitored using limited trypsin digestion, sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Scanning of the autoradiograms enables one to quantitate the level of activation (defined as an activation index), obtain dose-response profiles and estimate the potency of the tastant. This assay may provide a useful substitute for, or adjunct to, the time-consuming human psychophysical analysis and costly animal studies typically used in taste sensory analysis. It may be used to identify and determine the concentration-response function of many bitter components of oral pharmaceuticals and food ingredients. A potential limitation of the assay is that only about half of all bitter compounds tested demonstrated in vitro activity, perhaps due to the presence of multiple transduction pathways. Nevertheless, the rapid throughput and microsample handling capability of this assay make it an ideal method to screen for high-potency bitterness inhibitors.

Animals↗
PubMed2001

Reduction of saltiness and bitterness after a chlorhexidine rinse.

Chronic rinsing with chlorhexidine, an oral-antiseptic, has been shown to decrease the saltiness of NaCl and the bitterness of quinine. The effect of acute chlorhexidine on taste has not been investigated. The purpose of the present study was to examine the effect of acute chlorhexidine rinses on taste intensity and quality of 11 stimuli representing sweet, salt, sour, bitter and savory. All stimuli were first matched for overall intensity so the effects of chlorhexidine would be directly comparable across compounds. As a control treatment, the bitter taste of chlorhexidine digluconate (0.12%) was matched in intensity to quinine HCl, which was found to cross-adapt the bitterness of chlorhexidine. Subjects participated in four experimental conditions: a pre-test, a quinine treatment, a chlorhexidine treatment, and a post-test condition, while rating total taste intensity and taste qualities in separate test sessions. Relative to the quinine treatment, chlorhexidine was found to decrease the salty taste of NaCl, KCl and NH4Cl, and not to significantly affect the tastes of sucrose, monosodium glutamate (MSG), citric acid, HCl and the taste of water. The bitter taste of urea, sucrose octa-acetate and quinine were suppressed after chlorhexidine rinses relative to water rinses, but were only marginally suppressed relative to quinine rinses. Potential mechanisms are discussed.

Adult↗
PubMed2002

Bitter taste of saccharin and acesulfame-K.

The relationships among suprathreshold taste responses to acesulfame-K, Na-saccharin and 6-n-propylthiouracil (PROP) were examined in two studies. In the first study, the labeled magnitude scale was used with the high anchor labeled as 'strongest imaginable oral sensation' and in the second study, it was labeled as 'strongest imaginable sensation of any kind'. Results from the two procedures were similar. Individual differences among 65 subjects were seen in bitter responses to acesulfame-K and saccharin. Bitter responses to acesulfame-K ands accharin were positively correlated, but showed no significant relationship with responses to PROP bitterness or with PROP taster groups. Saccharin and acesulfame-K may share a common mechanism for bitter taste reception and transduction, one that varies across individuals and is different from mechanisms mediating bitter responses to PROP. Changing the instructions of the labeled magnitude scale induced a context effect. Ratings of sweetness referenced to the 'strongest imaginable sensationof any kind' were lower than ratings referenced to just oral sensations.

Adult↗