The Hydrostatic and Hydrodynamic Volumes of Polyols in Aqueous Solutions and Their Sweet Taste

The tastes and solution properties of sugar alcohols were studiedin an attempt to illuminate the mechanism of sweet taste chemoreception.The SMURF method was used to measure taste time-intensity ofaqueous solutions of sugar alcohols and the results were interpretedusing the Stevens power function and kinetic parameters. Theapparent molar volumes, apparent specific volumes, partial molarvolumes, partial specific volumes and intrinsic viscositiesof the solutions were studied. Apparent molar volume reflectsthe size of the molecule in a hydrostatic state whereas intrinsicviscosity gives a measure of the size of the molecules in ahydrodynamic state. Generally the apparent molar volumes ofthe polyols are 6–13% greater than those of the parentsugars, indicating less interaction with the water structure.Apparent specific volume values can predict taste quality, andthe average apparent specific volume for the sugar alcoholsstudied fits within the central part of the sweet range, i.e.0.5–0.68 cm³/g, which accords with their ability to elicita pure sweet taste response. Intensities and persistences ofsweetness in the polyols followed the same trend as intrinsicviscosities. Chem. Senses 22: 149–161, 1997.     

Taste preference thresholds for food-associated sugars in the squirrel monkey (Saimiri sciureus)

The purpose of this study was to determine taste preference thresholds for four different food-associated sugars inSaimiri sciureus. Using a two-bottle test three male squirrel monkeys were found to significantly prefer 10 mM sucrose, 40 mM fructose, 90 mM glucose, and 100 mM lactose over tap water. Presentation of suprathreshold sugar solutions led to marked concentration-dependent and monotonically increasing polydipsia. The results showed the squirrel monkey to prefer lower sugar concentrations compared to other non-human primates and thus support the assumption that this species may use sweetness as a criterion for food selection.     

Modeling of the Psychophysical Response Curves Using the Grand Canonical Ensemble in Statistical Physics

This paper aims to investigate the peripheral mechanism of taste perception by the use of the grand canonical ensemble in statistical physics. It allows a better understanding of this process and its interpretation at a microscopic level. The experimental part allowed us to obtain psychophysical curves relative to four nutritive sweeteners (sucrose, fructose, glucose, and maltitol). These curves represent the intensity of sweetness as a function of sugar concentration in water. A Sensory Measuring Unit for Recording Flux (SMURF) device is used to obtain intensity–time curves for each of the studied sweeteners. To model these curves we have established the expressions of some models using grand canonical ensemble formalism in statistical physics and applying some simplification approaches. The fitting of the psychophysical data with statistical models by numerical simulation demonstrates a good correlation between the models and the experimental curves. Some physicochemical parameters interfere in the expression of the established models. These parameters are classified in two categories: on one hand, the steric aspect, which is manifested by the density of taste receptor site, and the number of molecules per receptor site and on the other hand, an energetic aspect illustrated by the concentration at half saturation, which gives indirectly the sweet molecule-receptor site energy of interaction.     

Genetic Sensitivity to 6-n-Propylthiouracil (PROP) and Hedonic Responses to Bitter and Sweet Tastes

Genetically mediated sensitivity to the bitter taste of 6-n-propylthiouracil(PROP) has been associated with greater acuity for bitter andfor some sweet tastes. Thus far, few studies have explored therelationship between PROP taste sensitivity and hedonic responsesto bitter and sweet. In this study, 87 normal-weight young womenwere divided into PROP non-tasters (n = 18), regular tasters(n = 49), and supertasters (n = 20), based on their PROP detectionthresholds and the scaling of five suprathreshold solutionsof PROP and NaCl. Non-tasters had thresholds >1.8 x 10^–4mol/l PROP. Supertasters had thresholds <3.2 x 10^–5mol/l PROP and PROP/NaCl ratios >1.70. As expected, dislikeof the bitter taste of PROP was determined by its perceivedintensity, which was greater among supertasters than among regulartasters or non-tasters. Significant correlations were observedbetween PROP taste thresholds and the sum of intensity ratings(r = –0.61) and between summed intensity and summed hedonicratings (r = –0.80). PROP taste sensitivity was weaklylinked to enhanced perception of sweet taste, but did not predicthedonic responses to sucrose or to saccharin solutions. Giventhat the dislike of PROP solutions is determined by their perceivedintensity, hedonic responses to PROP solutions may provide arapid way of screening for PROP taster status. Chem. Senses22: 27–37, 1997.     

Genetic dimorphism in the taste sensitivity to trehalose inDrosophila melanogaster

Summary A quantitative behavioral assay was developed for the measurement of taste responses to sugars inDrosophila. The amount of the intake of a sugar solution was measured colorimetrically after homogenization of flies which had consumed sugar solutions mixed with a food-dye. A two-choice method was utilized to determine the taste sensitivity to sugars. Two kinds of sugar solutions were marked with either blue or red food-dye and placed alternately in the wells of a micro test plate. Flies were allowed to choose between the two sugar solutions. By classifying and counting the coloured flies, the relative taste sensitivity could be determined. Employing these methods, a genetic dimorphism in the taste sensitivity to trehalose was found among some laboratory strains ofDrosophila melanogaster. No difference in the taste sensitivity to glucose, fructose and sucrose was found between the trehalose high-sensitivity (T-1) and the low-sensitivity (Oregon-R) strains. Trehalose concentration equivalent to 2 mmol/1 sucrose, in terms of stimulating activity, was 57 mmol/1 inOregon-R and was 10 mmol/1 inT-1. Genetic analysis showed that theTre gene, whose locus is closely linked tocx (13.6) on theX chromosome, is responsible for the difference in the taste sensitivity to trehalose.     

Validation of a handheld display device for an expandable labeled magnitude scale (LMS)

Palmtop computers provide a possible avenue for the convenient collection of subjective ratings from individuals outside of a fixed laboratory setting. One disadvantage of these computers is the small size of their display screens, which may reduce the resolution of responses available as compared with standard display screens. One plausible solution to this problem is to use a scale that expands contingent on an initial response made by the subject, so that the final response is made from a scale with finer resolution. To validate this approach, we compared taste intensity judgments of six sucrose solutions (0.03, 0.06, 0.12, 0.24, 0.48, and 0.96 M), using a labeled magnitude scale either presented in expandable form on a palmtop computer (Palm scale) or in conventional (nonexpandable) form on a standard 17' PC monitor (PC scale). Twenty-four subjects rated all six sucrose solutions thrice, using both scale types, the different scales being used on different days of testing. The scales led to very similar taste intensity ratings at all but the lowest concentration, which was rated less intense on the Palm scale. The Palm scale was used with slightly less precision than the PC scale for the weakest solution concentrations. In summary, the responses of the two scales were similar enough to validate the use of the expandable scale on the palmtop computer outside the laboratory setting.     

Apparent molar volumes of sugars and their significance in sweet taste chemoreception

The apparent molar volumes (V) of selected sugars in 10–50%aqueous solutions have been determined at temperatures rangingfrom 20 to 40°C. The V values obtained accord well withmolecular weight of solute, but vary with molarity, particularlyat the higher temperatures studied. These changes may be ascribableto solute/solute and solute/solvent interactions which may inturn influence the sweet properties of the sugars. Althoughthe apparent molar volumes determined show no obvious relationshipto published sweetness values, their conversion to parachorsemphasises the manner in which attractive interations betweensugar motecules might mediate taste chemoreception.     

Effects of pharmacologic reductions in salivary flow on judgments of suprathreshold taste stimuli

The effects of short term salivary flow reductions on suprathresholdjudgments of taste intensity were measured using both a seriesof taste solutions and a comparable series of tastants driedon a filter paper base. Decreases in salivary flow were producedby the oral administration of either Elavil^®, Benadryl^®or atropine. The pharmacologic agents produced a 25 –82% reduction in salivary flow during the period that tastetesting occurred but no measurable effects on perceived tasteintensity were found. The exponents of power functions describingmolar concentration and perceived intensity were unchanged aswas the spread in perceived intensity between aqueous and drystimuli. Significant relationships between individual differencesin salivary flow and suprathreshold taste parameters also failedto emerge.     

Salt as an oral irritant

The temporal characteristics of oral irritation produced byNaCl and KCl were investigated in two experiments. Subjectswere exposed to 0.4 and 0.8 M solutions of both salts at therate of once per min for 15 min. No water rinses were allowedbetween sips. The results showed that the irritation producedby NaCl increased in intensity as a function of number of exposures.In contrast, the intensity of the salt taste remained approximatelyconstant over the 15 min period. The relative contribution ofirritation to the sensation of saltiness therefore increasedover time. The same pattern of results was found for 0.8 M butnot for 0.4 M KCl. The growth in perceived intensity of saltirritation with repeated exposures may be attributable to thephenomenon of ‘sensitization’ that is a characteristicof some nociceptive afferents. Overall, the results demonstratethat salts produce perceptible sensations of irritation at concentrationstypically used in psychophysical studies of salt taste, andthat this apparently non-gustatory component of saltiness vanesdirectly with both concentration and duration of exposure.     

Amiloride Effects on Taste Quality: Comparison of Single and Multiple Response Category Procedures

Although there is compelling evidence that amiloride reducesthe intensity of Na⁺ and Li⁺ salts in humans, its effects onsaltiness are conflicting. Many salts elicit not only a saltytaste but also one or more side tastes (sweetness, sournessor bitterness). Some studies have shown a suppression of saltinessby amiloride; others show no effect on saltiness but a significantreduction in sourness. In the experiments demonstrating a reductionof saltiness, subjects estimated only saltiness; in those showingan amiloride effect on sourness and not saltiness, subjectsestimated all qualities on each trial. The present study examinesthe role of the psychophysical method in these conflicting results.We have investigated the effects of amiloride on taste qualityby modifying only the instructions to the subjects, keepingall other variables constant. One group of subjects (intensity-only)gave magnitude estimates of the overall intensity of a LiCIconcentration series. A second group (salty-only) was instructedto estimate the saltiness of the stimuli, and a third group(sour-only) estimated their sourness. Finally, a fourth group(profile) rated all of the taste qualities on each stimuluspresentation, using a modified taste profile method. The ratingsof all groups were made comparable by the use of 0.1 mM quinine-HCIas a modulus. When subjects used only one response category,amiloride reduced their estimates (of intensity, saltiness orsourness), but if subjects attended to all four qualities, amiloridespecifically reduced the sourness of LJCI and had no significanteffect on its saltiness. Comparison of the saltiness estimatesof the salty-only group to the sum of the salty and sour estimatesof the profile group demonstrated that subjects combined thesesensations when presented with only one response alternative.To reveal the effect of amiloride on a specific quality of asalt, the psychophysical method must allow subjects to attendto all qualities on each trial. These data and previous resultssuggest that apical Na⁺ channels on the taste receptor cellmembrane mediate the sourness but not the saltiness of Na⁺ andLi⁺ salts. Chem. Senses 22: 267–275, 1997.     

Interactions in caffeine-sucrose and coffee-sucrose mixtures: evidence of taste and flavor suppression

Taste–taste and flavor–taste interactions (suppression)in caffeine–sucrose and coffee–sucrose mixtureswere determined. Similar interactions for both types of mixturesshowed an extended hypoadditivity effect for overall taste orflavor intensity (percentage of suppression about 30–40%).Futhermore, mutual suppression among the components has beendetermined. Firstly, the physical intensity of the suppressivecomponent controls the amount of suppression of the other component.Thus, the suppression of bitterness and coffee flavor qualitiesincrease when sucrose levels increase, and similarly, the suppressionof sweetness increases when caffeine or coffee levels rise.Secondly, the magnitude of suppression depends upon the qualityof the suppressive component. Comparisons of the reciprocalactions were made at similar subjective intensities of the mixture'sconstituents in isolation. The results showed that, at similarperceived intensities, caffeine bitterness or coffee flavorwere suppressed by sucrose but sweetness was not affected bycaffeine or coffee.     

A test of seasonal responses to sugars in four populations of the termite Reticulitermes flavipes

Several studies have shown that Reticulitermes termites prefer food with certain types of sugars. However, the specific sugars that were preferred by the termites in each study differed. The difference between the results of these studies might be explained by differences between populations or changes in feeding responses during the active season. To address these variables, we examined the feeding response to a food source food containing glucose, sucrose, or xylose versus a food source without sugar in several populations of termites and observed whether these responses changed during the year. Termites were collected from colonies from four field sites in Missouri during the spring (May and June), summer (July and August), and fall (September and October) and tested for their response to all three sugars under laboratory conditions. Results show there are distinct differences in response to sugars between populations but only a slight seasonal effect.     

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.     

Phosphorylation of SMURF2 by ATM exerts a negative feedback control of DNA damage response

Timely repair of DNA double-strand breaks (DSBs) is essential to maintaining genomic integrity and preventing illnesses induced by genetic abnormalities. We previously demonstrated that the E3 ubiquitin ligase SMURF2 plays a critical tumor suppressing role via its interaction with RNF20 (ring finger protein 20) in shaping chromatin landscape and preserving genomic stability. However, the mechanism that mobilizes SMURF2 in response to DNA damage remains unclear. Using biochemical approaches and MS analysis, we show that upon the onset of the DNA-damage response, SMURF2 becomes phosphorylated at Ser³⁸⁴ by ataxia telangiectasia mutated (ATM) serine/threonine kinase, and this phosphorylation is required for its interaction with RNF20. We demonstrate that a SMURF2 mutant with an S384A substitution has reduced capacity to ubiquitinate RNF20 while promoting Smad3 ubiquitination unabatedly. More importantly, mouse embryonic fibroblasts expressing the SMURF2 S384A mutant show a weakened ability to sustain the DSB response compared with those expressing WT SMURF2 following etoposide treatment. These data indicate that SMURF2-mediated RNF20 ubiquitination and degradation controlled by ataxia telangiectasia mutated–induced phosphorylation at Ser³⁸⁴ constitutes a negative feedback loop that regulates DSB repair.     

Changes in Taste Perception Following Mental or Physical Stress

Taste perception depends not only on the chemical and physicalproperties of tastants, but may also depend on the physiologicaland psychological conditions of those who do the tasting. Inthis study, the effects of mood state on taste sensitive wasevaluated in humans who were exposed to conditions of mentalor physical fatigue and tension. Taste responses to quininesulfate (bitter), citric acid (sour) and sucrose (sweet) weretested. The intensity of the taste sensations were recordedby a computerized time-intensity (TI) on-line system. Subjectsperformed mental tasks by personal computer or physical tasksby ergometer for 10–40 min. Before and after these sessions,the duration of the after-taste and the intensity of the sensationof taste were recorded by the TI system, and in addition, psychologicalmood states were evaluated with POMS (Profile of Mood State).TI evaluation showed that after the mental tasks, the perceivedduration of bitter, sour and sweet taste sensations was shortenedrelative to the control. Total amount of bitterness, sournessand sweetness was also significantly reduced. Furthermore, themaximum intensity of bitterness was significantly reduced. Therewere no significant differences in bitterness and sweetnesssensations following physical tasks. However, relative to beforethe physical task, the duration of the after-taste of sournesswas significantly shortened by the physical task. After thephysical task, the buffering capacity of saliva was significantlyincreased. Thus mental and physical tasks alter taste perceptionin different ways; the mechanisms underlying these changes remainto be determined. Chem. Senses 21: 195–200, 1996.     

Taste Responses in the Nucleus of the Solitary Tract in Saccharin-preferring and Saccharin-averse Rats

A minority of rats consistently reject the taste of sodium saccharinat concentrations that the majority find palatable. We choserats that selected either water (WP), or 0.03 M NaSaccharin(SP) in two-bottle preference tests and monitored single unitresponses to a range of taste qualities in the nucleus of thesolitary tract. WP rats gave significantly greater responsesto Na/Li salts and QHCI. Their responses to sugars were equalto those from SP rats. Total activity to NaSaccharin did notdiffer between the two groups, but its distribution across thethree identified neuron types did. The response was skewed fromone in which sugar (S) and sodium salt (N) participated nearlyequally (SP) to one dominated by the activity of N cells andnearly devoid of an S cell contribution (WP rats). Accordingly,the response profile for NaSaccharin was correlated nearly aswell with those of the sugars (+ 0.60) as with the Na/Li salts(+ 0.73) in SP rats, but was reshaped in WP rats to be nearlyidentical with those of the salts (+ 0.85) and unlike sugars(+ 0.30). In their heightened sensitivity to stimuli that humanscall salty and bitter, and in their rejection of the complextaste of NaSaccharin, WP rats showed many of the characteristicsof human tasters of PTC/PROP. Chem. Senses 21: 147–157,1996.     

Concentrations of NaCl and sucrose: equality in perceived taste intensity

Results from previous studies suggest that sucrose and NaClsolutions have an equal perceived taste intensity when the molarconcentration of sucrose is 1.5–1.75 times the molar concentrationof NaCl. However, according to other studies, sucrose and NaClsolutions taste equally strong when their molar concentrationsare about equal. This issue was further pursued using the methodof constant stimuli, where subjects matched the perceived tasteintensity of NaCl solutions to five sucrose references and viceversa. The results concur with previous findings that sucroseand NaCl solutions have equal perceived taste intensities whenthe molar concentration of sucrose is 1.5–1.75 times themolar concentration of NaCl.