The effectiveness of different sweeteners in suppressing citric acid sourness

The exact mechanism that causes taste suppression in a perceptually heterogeneous mixture, and the locus of that mechanism, are as yet unknown. The present study was designed to explore the idea that mixture suppression is a perceptual phenomenon and not the result of physical, chemical, or receptor-substance interactions. An investigation was carried out as to whether perceptually similar taste stimuli give rise to the same sensory interactions when mixed with a substance of a different taste quality. In the first study, five different sweeteners (sucrose, fructose, aspartame, saccharin, and sorbitol) were matched in perceived sweetness intensity, in order to obtain five perceptually similar stimuli. Every equisweet sweetener concentration was mixed with each of four citric acid concentrations. In a second study, the sourness-suppressing effects of two sweeteners, sucrose and aspartame, were compared at four different concentration levels. Sourness scale values of unmixed citric acid, the unmixed sweeteners, and the citric acid/sweetener mixtures were assessed with a functional measurement approach in combination with a two-stimulus procedure. The equisweet sweeteners were equally effective in suppressing the perceived sourness intensity of citric acid over the concentration range used. The side tastes of the sweeteners, if present, did not have a substantial effect on the degree of sourness suppression.     

Water taste in man

Taste quality and intensity shifts following adaptation to NaCl, quinine hydrochloride, sucrose and HCl were investigated in 10 Ss. In each of four sessions, Ss were adapted to water and two concentrations of one taste solution and gave magnitude estimates and quality judgments for a series of concentrations of that solution. Adapting to water produced magnitude estimates which increased with increasing concentration. Quality judgments were typical, e.g., “salty” for NaCl. Adapting to moderate concentrations of taste solutions generally produced magnitude estimates of zero at the adapting concentrations and increasing values for higher and lower (sub-adapting) concentrations. Sub-adapting tastes were atypical. Adaptation to NaCl and sucrose produced bitter sub-adapting tastes and adaptation to HCl and quinine hydrochloride produced sweet sub-adapting tastes. Water, as the lowest sub-adapting “concentration”, produced the largest sub-adapting tastes.     

Effects of context on sweet and bitter tastes: unrelated to sensitivity to PROP (6-n-propylthiouracil).

In a double-shifting context paradigm, subjects gave magnitude estimates of the perceived intensity of qualitatively dissimilar taste substances (saccharin and quinine, sucrose and quinine) or qualitatively similar ones (saccharin and sucrose), with each pair of substances taking on different contextual sets of concentrations in different sessions. The dissimilar pairs produced substantial differential effects of context (e.g., a particular concentration of saccharin or sucrose was judged more intense than a particular quinine in one contextual setting, less intense in another), but the similar pair did not. This result accords with the hypothesis that differential context effects depend on qualitative similarity. Contrary to expectations, however, the magnitude of the context effect did not differ in tasters and nontasters of the bitter substance 6-n-propylthiouracil (PROP), groups previously shown to differ in sensitivity to bitterness in saccharin. Similarity judgments suggest that saccharin and sucrose were qualitatively alike for all subjects, regardless of sensitivity to PROP.     

Effects of context on sweet and bitter tastes: Unrelated to sensitivity to PROP (6-npropylthiouracil)

In a double-shifting context paradigm, subjects gave magnitude estimates of the perceived intensity of qualitatively dissimilar taste substances (saccharin and quinine, sucrose and quinine) or qualitatively similar ones (saccharin and sucrose), with each pair of substances taking on different contextual sets of concentrations in different sessions. The dissimilar pairs produced substantial differential effects of context (e.g., a particular concentration of saccharin or sucrose was judged more intense than a particular quinine in one contextual setting, less intense in another), but the similar pair did not. This result accords with the hypothesis that differential context effects depend on qualitative similarity. Contrary to expectations, however, the magnitude of the context effect did not differ in tasters and nontasters of the bitter substance 6-n-propylthiouracil (PROP), groups previously shown to differ in sensitivity to bitterness in saccharin. Similarity judgments suggest that saccharin and sucrose were qualitatively alike for ail subjects, regardless of sensitivity to PROP.     

Perceptual changes in taste mixtures

Three studies were conducted to quantify perceptual changes that occur when sapid chemicals are tasted in mixture solutions. The primary effect when mixing sweetness (glucose or fructose) with salt (NaCl), sour (citric acid), or bitter (quinine sulfate) was to reduce the intensity of each taste in the mixture. The reduction was not equal for the two components, although the overall (total) taste intensity of the mixture appeared to be approximately 50% of the sum of the intensities of the unmixed components. Mixtures of sweet and salt developed an “unblended” or “clashing” taste, in which the components alternated in attempting to dominate the taste percept. Sweet mixed with either sour or bitter blended in almost all proportions. The “flavor” of sweetness in mixtures differed from that of simple sugar sweetness, suggesting that the presence of a second taste modified the qualitative aspect of sweetness. The magnitude of change in sweetness quality depended upon the sugar being rated, and upon the quality and intensity of the second, or modifying, taste.     

Perception of sweetness and bitterness in different vehicles

In the present study, we investigated taste-taste, taste-vehicle, and simultaneous taste-vehicle-taste mixtures. Subjects made estimates of the sweetness and bitterness of 27 stimuli. Sucrose (292, 585, and 1170 mM), caffeine (13, 26, and 52 mM), and binary mixtures of low (292-13 mM), middle (585-26 mM), and high (1170-52 mM) levels of both components were dispersed in water, carboxymethylcellulose (CMC) 1% w/v, and gelatin 6% w/v. The sweetness and bitterness of the sucrose-vehicle-caffeine combinations were significantly weaker than the respective sucrose-vehicle and caffeine-vehicle combinations. The emerged mutual suppressive effects were asymmetrical and persisted when both tastants were presented in CMC and gelatin. Moreover, the increase in vehicle consistency and the simultaneous addition of another taste reduced the perceived intensity of a taste either presented alone or dissolved in water. For both sweetness and bitterness, the total taste suppression observed was always significant.     

Effects of taste quality and intensity on oral perception of viscosity

Oral assessments of viscosity were obtained with the method of magnitude estimation. Subjects judged the viscosity of a series of aqueous solutions thickened to one of six viscosity levels (1–2025 centistokes) with a food-grade gum, sodium carboxymethylcellulose. The solutions contained one of several concentrations of caffeine, citric acid, sodium chloride, or sucrose. The presence of taste substances significantly altered the perception of solution viscosity for only the thickest solutions. Increasing concentrations of citric acid and sodium chloride produced progressive decreases in perceived viscosity, and increasing sucrose concentrations produced small increases in perceived viscosity. Caffeine did not affect judgments of solution viscosity. The most likely explanation for these findings is that subjects detected differences in the Newtonian behavior of the thickened solutions, differences that were produced by the addition of taste substances.     

Age-related differences in the pleasantness of chemosensory stimuli

Modest decrements in both taste threshold sensitivity and, more recently, suprathreshold sensitivity have been associated with the aging process. The present study was designed to investigate the existence of changes in preference for various concentrations of single tastes and of the same single tastes in more complex chemosensory mixtures. In this study, 300 participants from three different age groups (18-26, 32-45, over 65) rated for pleasantness four concentrations of sodium chloride, sucrose, and citric acid presented in both aqueous and beverage bases. Results showed significant effects of age, stimulus background, stimulus, concentration, and of several interactions, and they suggest that elderly subjects find salt and sugar pleasanter at higher concentrations than younger subjects do.     

Perceptual integration of tertiary taste mixtures

Integration psychophysics was used to explore the taste perception of mixtures of sucrose, fructose, and citric acid. Three levels of each stimulus were varied in a 3 x 3 x 3 factorial design. Subjects rated total intensity, sweetness, and acidity of the 27 mixtures on graphic rating scales. Consistent with earlier work, the perceived total intensity of the tertiary mixtures was found to be dictated by the intensity of the (subjectively) stronger component alone (i.e., either the integrated sweetness or the acidity, whichever was the more intense). In contrast, the sweetness and acidity of the mixture were susceptible to mutual suppression: Sweetness suppressed acidity, acidity suppressed sweetness. There was, however, a difference between sucrose and fructose in their interactions with citric acid, fructose being the more susceptible to suppression. This selectivity of suppression indicates that the two sweetnesses could not have been inextricably integrated. Implications for taste coding are discussed, and the findings are reconciled in terms of two separate coding mechanisms: one for taste intensity, another for taste quality.     

Sweet odours and sweet tastes are conflated in memory

Certain odours and certain tastes appear to share common perceptual properties. One example is sweetness, a perceptual experience that results from stimulation of taste receptors on the tongue typically by sugars. The experiment here examined for evidence of this perceptual similarity using a novel and indirect test. Participants were exposed six times each, to three odours (strawberry, caramel, and oregano) and three tastes (sucrose, saline, and citric acid). Following a 10-min interval, participants were given a surprise frequency estimation task, in which they had to judge how often each stimulus had occurred. If sweet-smelling strawberry and caramel odours really do share this perceptual characteristic in common with sweet tasting sucrose, then frequency estimates for sucrose should be overestimated relative to non-sweet tastes. Not only was this observed, but frequency estimates for sweet tastes were also found to correlate with (1) evaluations from a later test of similarity between these sweet smells and sucrose, and (2) the degree to which these odours smelled sweet. These findings suggest a shared perceptual feature between such odours and sucrose - sweetness - under conditions where no judgment of perceptual quality was required.     

Aging is associated with increased Weber ratios

To investigate whether age-associated changes in the human taste system are quality-specific, we compared young and elderly subjects’ suprathreshold discrimination abilities for caffeine and sucrose. The method of constant stimuli was used to obtain just noticeable differences and Weber ratios. The elderly generated larger Weber ratios than did the young for both the medium and high concentrations of caffeine, but not for the low concentration. For example, a 74% increase in .005 M caffeine was required to obtain a perceptible difference for the elderly, whereas a 34% increase produced a perceptible difference for the young. The Weber ratios for sucrose did not differ for the two age groups. The results of this study indicate that age-associated changes in the taste system are quality-specific.

     

EMG activities of facial and chewing muscles of human adults in response to taste stimuli

To evaluate facial expression patterns induced by different taste stimuli, electromyograms (EMG) of the facial and chewing muscles of 12 healthy university students, aged 20 to 23 years, were analyzed. Sucrose (sweet), NaCl (salty), citric acid (sour), quinine-HCl (bitter), monosodium glutamate (MSG; umami), homogentisic acid (harsh), tannic acid (astringent), and capsaicine (pungent) were the taste stimuli used. Rating scale tests were made to assess the hedonics (pleasantness) of the taste stimuli. EMG responses of the corrugator supercilii, venter frontalis, orbicularis oculi, depressor anguli, and digastricus muscles to capsaicine, tannic, acid, and citric acid showed larger amplitudes than to NaCl, MSG, homogentisic acid, and sucrose. Increases in EMG responses for most facial and chewing muscles for the taste solutions had significant negative correlations to the solutions' hedonic scale values. Most facial and chewing muscles of adult humans therefore showed greater responses to disliked than to preferred or less preferred tastes.     

Reliability of magnitude matching

In each of four experimental sessions, each of 16 subjects gave magnitude estimates of the taste intensities of NaCl and the loudness of noise on a single, common scale--the method of magnitude matching. In all sessions, the intensity levels of the noises were identical; but in two sessions, the concentrations of NaCl were low, and in two they were high. Cross-modality matches (magnitude matches) between NaCl and noise were derived from the judgments, revealing two main findings: First, given constant NaCl concentrations, individual subjects showed reliably different magnitude matches. Second, changing the NaCl concentrations (context) strongly affected the magnitude matches. These findings suggest that magnitude matching may be useful in assessing interindividual as well as intergroup differences, though caution must be taken to minimize effects of context: Context effects are pervasive; they suggest the presence of a complex relativistic process operating when people judge the intensities of qualitatively different stimuli.     

Aging is associated with increased Weber ratios for caffeine, but not for sucrose

To investigate whether age-associated changes in the human taste system are quality-specific, we compared young and elderly subjects' suprathreshold discrimination abilities for caffeine and sucrose. The method of constant stimuli was used to obtain just noticeable differences and Weber ratios. The elderly generated larger Weber ratios than did the young for both the medium and high concentrations of caffeine, but not for the low concentration. For example, a 74% increase in .005 M caffeine was required to obtain a perceptible difference for the elderly, whereas a 34% increase produced a perceptible difference for the young. The Weber ratios for sucrose did not differ for the two age groups. The results of this study indicate that age-associated changes in the taste system are quality-specific.     

Detection of heteroquality taste mixtures

Detection thresholds were measured for sweet (sucrose), salty (sodium chloride), sour (citric acid), and bitter (quinine hydrochloride) and for the 11 possible mixtures of these four substances. These 11 mixtures (6 binary, 4 ternary, and 1 quaternary) all turned out to be stimulus additive, in the sense that a person could reliably detect mixtures whose individual components are weaker than their unmixed thresholds. Tastants too weak to be perceived alone can thus make impact when in mixtures. The threshold concentration for a given compound was reduced in approximate proportion to the number of compounds added to it. This liberal heteroquality additivity contests the widespread belief that heteroquality mixtures (different chemicals evoking different qualities) are nonadditive and homoquality mixtures (different chemicals evoking the same quality) are additive. Heteroquality additivity emerges on appropriate definition of the subject’s task by forced choice (unavailable to earlier investigators), in order to skirt methodological pitfalls. Operating together, homoand heteroquality additivity may concomitantly enable a person to sense natural mixtures of hosts of weak constituents, such as drinking water. In this regard, gustatory mixtures may function much as do mixtures of frequencies in audition and mixtures of gaseous compounds in olfaction.     

Both perceptual and conceptual factors influence taste-odor and taste-taste interactions

Observers are often asked to make intensity judgments for a sensory attribute of a stimulus that is embedded in a background of “irrelevant” stimulusdimensions. Under some circumstances, these background dimensions of the stimulus can influence intensity judgments for the target attribute. For example, judgments of sweetness can be influenced by the other taste or-odor qualities of a solution (Frank & Byram, 1988; Kamen et al., 1961). Experiments 1 and 2 assessed the influence of stimulus context, instructional set, and reference stimuli on cross-quality interactions in mixtures of chemosensory stimuli. Experiment 1 demonstrated that odor-induced changes in sweetness judgments were dramatically influenced when subjects rated multiple attributes of the stimulus as compared with when they judged sweetness alone. Several odorants enhanced sweetness when sweetness alone was judged, while sweetness was suppressed for these same stimuli when total-intensity ratings were broken down into ratings for the sweetness, saltiness, sourness, bitterness, and fruitiness of each solution. Experiment 2 demonstrated a similar pattern of results when bitterness was the target taste. In addition, Experiment 2 showed that the instructional effects applied to both taste-odorand taste-taste mixtures. It was concluded that the taste enhancement and suppression observed for taste-odor and taste-taste mixtures are influenced by (1) instructional sets which influence subjects’ concepts of attribute categories, and (2) the perceptual similarities among the quality dimensions of the stimulus.     

Taste-taste,odor-odor,and taste-odor mixtures: Greater suppression within than between modalities

Subjects judged the intensities of the component qualities of two taste stimuli [sucrose (S) and NaCl (N)], two odor stimuli [citral (C) and anethole (A)], and the mixtures of these stimuli [taste-taste (SN), odor-odor (CA), and taste-odor (SC, NC, SA, and NA)]. The within-modality mixtures, taste-taste and odor-odor, produced greater suppression of perceived intensity than did the between-modality mixtures, taste-odor. However, taste-odor mixtures also produced a significant amount of suppression of perceived intensity when compared with the individual taste and odor stimuli. The data are discussed with respect to peripheral and central mechanisms in mixture suppression.     

Odor intensity of mixed and unmixed stimuli under environmentally realistic conditions

Subjects judged the odor intensity of single odorants and binary mixtures of fixed or varying proportions presented in the atmosphere of an environmental chamber. The subjects were exposed to the vapors either continuously (15 min) or periodically (once a minute for 15 min). As found previously, the mixtures smelled less intense than predicted from the simple sum of their unmixed components. The degree of hypoadditivity proved about the same for the four pairs of odorants studied, but varied from periodic to continuous exposure. Periodic exposure led to a greater departure from simple additivity and confirmed the presence of the phenomenon of compromise whereby the mixture can smell less intense than its stronger component alone. Continuous exposure led to a closer approximation to simple additivity and exhibited no compromise. Nevertheless, the behavior seen under continuous exposure apparently derived from a tendency for mixtures to exhibit less adaptation than their components. Whereas mixtures may seem to lack potency relative to their unmixed components, they may in fact compensate for any deficiency in momentary intensity through an increase in durability.     

Incomplete taste adaptation to different concentrations of salt and sugar solutions

Two concentrations each of sodium chloride and sucrose solutions were used as stimuli in a study examining taste adaptation. Twenty subjects were presented a 3-min continuous flow of each taste stimulus over the anterior dorsal tongue surface, and periodically gave magnitude estimates of its intensity. The degree of adaptation was greater for the less concentrated solutions than for the more concentrated ones, but the majority of subjects did not adapt completely to any of the stimuli. This result, which is consistent with other reports from this laboratory, is discussed in terms of individual differences among subjects and in relation to recent taste research based on completely adapted subjects.     

An Examination of Sex and Masculinity/Femininity as Related to the Taste Sensitivity of Japanese Students

The purpose of the present study was to examine the influences of gender differences and masculinity–femininity on taste thresholds and food preferences. The participants were 108 Japanese undergraduate students (44 men and 64 women); their mean age was 19.6 years (SD = 1.3). Their detection and recognition thresholds for caffeine and sucrose were measured. Multiple regression analyses showed that women tended to have a lower detection threshold for caffeine than men did. The recognition threshold for caffeine was positively associated with scores for masculinity. For men, masculinity may be associated with smoking and drinking behavior, thereby resulting in a lower sensitivity for bitterness. Masculinity and femininity related to food preferences are also discussed.