Chem. Senses 28: 219-229,
2003
© Oxford University Press 2003
Effect of Repeated Presentation on Sweetness Intensity of Binary and Ternary Mixtures of Sweeteners
Department of Psychiatry, Duke University Medical Center, Durham, NC 27710 1 The NutraSweet Company, Chicago, IL 60654, USA
Correspondence to be sent to: Susan S. Schiffman, Department of Psychiatry, Duke University Medical Center, 54212 Woodhall Building, Box 3259, Durham, NC 27710, USA. e-mail: sss{at}acpub.duke.edu
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Abstract |
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The purpose of the present study was to determine the effect of repeated presentation of the same sweet stimulus on sweetness intensity ratings. The sweet stimuli tested in this study were binary and ternary blends of 14 sweeteners that varied widely in chemical structure. A trained panel evaluated the sweetness intensity over four sips of a given mixture presented at 30 s intervals. The individual components in the binary sweetener combinations were intensity-anchored with 5% sucrose, while the individual sweeteners in the ternary mixtures were intensity-anchored with 3% sucrose (according to formulae developed previously). Each self-mixture was also evaluated (e.g. acesulfame-K—acesulfame-K). The main finding of this study was that mixtures consisting of two or three different sweeteners exhibited less reduction in sweetness intensity over four repeated sips than a single sweetener at an equivalent sweetness level. Furthermore, ternary combinations tended to be slightly more effective than binary combinations at lessening the effect of repeated exposure to a given sweet stimulus. These findings suggest that the decline in sweetness intensity experienced over repeated exposure to a sweet stimulus could be reduced by the blending of sweeteners.
Key words: bulk sweeteners, high potency, repeated presentation, sweeteners, synergism
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Introduction |
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Prolonged uninterrupted application of a taste stimulus to the tongue reduces the responsivity to that stimulus (McBurney, 1969
). This
phenomenon is termed adaptation. Continuous prolonged exposure of the tongue
to a variety of taste stimuli has been studied in humans
(McBurney, 1966;
DuBose et al., 1977;
Lawless and Skinner, 1979;
DuBose and Meiselman, 1979;
Meiselman and Buffington,
1980; Bujas et al.,
1991) and in animals (Smith et al.,
1975,
1978;
Schiffman et al.,
1992) using a gravity flow system that delivers a constant stream
of a taste solution over the dorsal tongue surface. In real-life eating
situations, however, tastes of a single substance are seldom prolonged but
rather are interrupted by short time intervals between bites or sips. The
effect of repeated exposure to a single stimulant (with short interruptions)
on taste intensity ratings differs from that of prolonged continuous flow in
that it may involve some degree of taste system recovery from adaptation. For
example, the sweetness of sucrose decreased less over time when consumed
intermittently in water (Schiffman et
al., 1994) or in sweetened yogurt
(Theunissen et al.,
2000b) than with uninterrupted application to the tongue by
gravitational flow (DuBose and Meiselman,
1979) or by filter paper (Gent
and McBurney, 1978; Theunissen et al.,
2000a,b).
This smaller reduction in sweetness with repeated tasting is presumably the
result of two processes: adaptation and recovery.
The biochemical mechanisms by which adaptation occurs at the receptor level
in the taste system are not known but desensitization of the sweet taste
receptor (Schiffman et al.,
1994), intracellular cascades that involve protein kinase A
(Varkevisser and Kinnamon,
2000), or inositol phospholipid hydrolysis, intracellular
Ca2+ mobilization and protein kinase C-mediated phosphorylation
(Ozaki and Amakawa, 1992) may
play a role. The rate or degree of adaptation can also be modified by a number
of factors, such as extracellular citrate ions
(Ogawa and Caprio, 1999),
extracellular tannic acid (Schiffman
et al., 1994) and other components in a mixture with
sweet taste compounds (Schiffman et al.,
1995,
2000). Mouth movements that
move solution away from receptors have also been reported to interfere with
the adaptation process (Theunissen and
Kroeze, 1996; Theunissen
et al., 2000a).
The sweetness intensity of a number of sweeteners has been shown to
decrease after repeated tasting over a 2 min interval
(Schiffman et al.,
1994). High-potency sweeteners (such as aspartame, saccharin or
acesulfame-K) tended to exhibit more reduction in sweetness over time than
bulk sweeteners (such as sucrose)
(Schiffman et al.,
1994; Froloff et al.,
1998). The absolute reduction in sweetness intensity over time,
however, tends to vary depending upon the concentration and type of sweetener.
One potential method that may blunt the reduction in responsivity with
repeated tasting, especially for high potency sweeteners, is combining lower
concentrations of two or more sweeteners in mixtures. It was hypothesized in
this study that mixtures of sweeteners would show less reduction in sweetness
over time than a single sweetener in part because each component of the
mixture would be used at lower concentrations and hence produce less
adaptation. Use of sweetener mixtures may also utilize different biochemical
mechanisms that could potentially reduce the impact of adaptation.
In this study, repeated tastes of binary and ternary blends of sweeteners
were presented to trained taste panelists to determine the effect on sweetness
intensity ratings. The binary and ternary blends of stimuli tested in this
study represented a broad spectrum of molecular types, from common
carbohydrate sweeteners such as sucrose and fructose to several high-potency
sweeteners such as aspartame and sucralose. These data on sweetener blends
were compared with a previous research paper by Schiffman et al.
(Schiffman et al.,
1994) in which a single sweetener was studied using the same
protocol.
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Subjects
A trained panel of 17 subjects, 10 males and 7 females, participated in the
study [for details of panel training see DuBois et al.
(DuBois et al.,
1991)]. The minimum number of subjects who participated in any
given session was 10, and the maximum number of subjects was 16. The mean age
of the subjects was 48 ± 12 years. All subjects were from the Duke
University or Durham, NC community. Subjects were paid for their
participation. The study was approved by the Duke University Medical Center
Institutional Review Board for Human Subjects.
Stimuli
Binary blends
Binary combinations of the following 14 food grade sweeteners were tested:
three sugars (fructose, glucose, sucrose), three terpenoid glycosides
[Highstevia RA (a commercial stevia blend), monoammonium glycyrrhizinate,
rebaudioside-A], two N-sulfonylamides (acesulfame-K, sodium
saccharin), two polyhydric alcohols (mannitol, sorbitol), one chlorodeoxysugar
(sucralose), one dipeptide derivative (aspartame), one protein (thaumatin) and
one sulfamate (sodium cyclamate). The sugars and polyhydric alcohols are
defined as bulk sweeteners, and the glycosides, sulfonylamides,
chlorodeoxysugar, dipeptide, protein and sulfamate are high-potency
sweeteners. The sweeteners were dissolved in deionized water. The two
sweeteners in any given mixture were anchored in sweetness intensity to
sucrose, i.e. tested at levels expected to be equisweet with a given
concentration of sucrose (Schiffman et
al., 1994). Each sweetener was tested at a concentration
expected to be equivalent in intensity with 5% sucrose [according to formulae
developed by DuBois et al. (DuBois
et al., 1991)]. Table
1 lists the concentrations of sweeteners tested in the study of
binary blends. All possible combinations of these 14 sweeteners were tested in
binary mixtures, including self-mixtures (e.g. 5% sucrose + 5% sucrose). The
abbreviations used for each sweetener throughout the paper are also given in
Table 1.
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Ternary blends
The following eight food grade sweeteners were tested: two sugars
(fructose, sucrose), two N-sulfonylamides (acesulfame-K, sodium
saccharin), one chlorodeoxysugar (sucralose), one dipeptide derivative
(aspartame), one protein (thaumatin) and one terpenoid glycoside (Highstevia
RA). The sweeteners were dissolved in deionized water. Each sweetener was
tested at a concentration expected to be equivalent in intensity with 3%
sucrose [according to formulae developed by DuBois et al.
(DuBois et al.,
1991)]. Table 1
lists the concentrations of sweeteners tested in this study, as well as the
abbreviations used for each sweetener in this study. All possible combinations
of the eight sweeteners were tested in ternary mixtures, including
self-mixtures (e.g. 3% sucrose + 3% sucrose + 3% sucrose).
Procedure
The procedure used for repeated tasting in this study is similar to the one
used in a previous study by this laboratory
(Schiffman et al.,
1994). It is designed to quantify any changes in sweetness
intensity that may occur with repeated tasting in a controlled laboratory
setting using psychophysical procedures with a trained panel. The order of
presentation of the blends was randomized with two sweetener blends tested at
each taste panel session. Each mixture was presented four consecutive times
with 30 s between each sample. A given sweetener was not tested in more than
one of the two mixtures in a session. Panelists were not told that each set of
four samples was actually the same sample repeated four times. The
presentation order of the samples was the same for all panelists. Panelists
were asked to give sweetness, bitterness and sourness intensity ratings for
each sample. The sample size was 
10–15 ml of solution served in 30
ml plastic medicine cups. Each of the four samples of a given mixture was
coded with a different random three-digit number.
Prior to evaluating the samples, each trained panelist tasted basic taste
references, according to the method described by DuBois et al.
(DuBois et al., 1991).
These included six sweet references: 2 sweet (2% sucrose), 5 sweet (5%
sucrose), 7.5 sweet (7.5% sucrose), 10 sweet (10% sucrose), 12 sweet (12%
sucrose) and 15 sweet (16% sucrose). These sucrose standards have been used in
previous studies (Schiffman et al.,
1994,
1995;
Portmann and Kilcast, 1996;
Hutteau et al.,
1998). Panelists also tasted two bitter references, labeled 2
bitter (0.02% caffeine) and 4 bitter (0.03% caffeine), and one sour reference,
labeled 2 sour (0.01% citric acid). These concentrations cover the range of
bitter and sour components typically found in the sweeteners we have tested.
Concentrations used for the bitter and sour references were based upon
previous evaluations by a portion of the current panelists, as well as other
trained panelists.
Panelists refrained from eating or drinking anything other than water for 30 min prior to the tasting session. During each taste session, the panelists swirled a given sample around in their mouths for 5 s and then expectorated. Immediately following expectoration of a sample, the experimenter began timing 30 s. During this 30 s, the panelists completed the three ratings scales (sweet, bitter and sour intensity) for the sample on Toshiba laptop computer units using CSA software (Computerized Sensory Analysis, Version 4.3, Compusense Inc., 1994). The intensity of an attribute was noted by making a mark with a light pen on a 15-point line scale, which was anchored at 0, 1.5, 3, 4.5, 6, 7.5, 9, 10.5, 12, 13.5 and 15. After the 30 s expired, the panelists sipped the second sample and swirled it for 5 s. This procedure was repeated for the third and fourth samples. The experimenter instructed the panelists when to sip, expectorate and rate each sample using a stopwatch to time the intervals. The panelists did not rinse with water, eat crackers or re-taste their references during the ‘repeated sips’ procedure for a given mixture. After the fourth sample of a mixture was evaluated, the experimenter set the timer for 5 min. During this time delay, subjects rinsed their mouths thoroughly with deionized water and, if necessary, ate unsalted-top crackers to rid their mouths of lingering attributes of previous samples. This procedure was repeated with a second mixture in four consecutive samples.
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Results |
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Analysis of variance—binary mixtures
General linear models (GLMs) were estimated (using SAS statistical software for Windows Version 8) to examine whether binary mixtures of sweeteners exhibit more, the same or less decline in sweetness intensity with repeated sips than their constituent self-mixtures. The GLM procedure uses the method of least squares to fit general linear models including analysis of variance when group means are not equal. For each binary mixture comparison, the binary mixture was compared with the average of its two self-mixtures. Any subject who did not participate in all three conditions (evaluations of the binary mixture and both self-mixtures) was excluded from analysis, so that the data could be analyzed using a within-subjects design. This was done to prevent possible unequal weighting of values in the self-mixture and mixture conditions. GLMs were estimated examining the effect of stimulus (mixture versus average of the constituent self-mixtures), sip (sip 1 through sip 4) and stimulus x sip effects.
There was an effect of stimulus for 53 out of 91 of binary mixtures. For all significant stimulus effects, the binary mixtures exhibited higher overall sweetness intensity ratings across four sips than the average of self-mixtures. There was a significant effect of sip for virtually all of the binary mixtures as well as self-mixtures in which the mean sweetness intensity decreased over the four repeated sips. The only binary mixtures that did not have significant sip effects (i.e. did not decrease over the four sips) were glu–man, glu–sor and glu–tha.
There was a stimulus x sip interaction for the following binary mixtures: ace–MAG, apm–cyc, cyc–fru, cyc–glu, cyc–MAG, cyc–man, cyc–sac, cyc–sor, cyc–sucr, cyc–tha, fru–MAG, fru–reb, fru–sac, fru–sucr, MAG–reb, reb–sucr and sac–tha. Figure 1 depicts the sweetness intensity ratings (based on least squares means) for sip 1 through sip 4 for those binary mixtures exhibiting a significant stimulus x sip interaction, as well as the least squares means for the ratings of their respective constituent self-mixtures. Least squares means are the most unbiased estimates of means when using GLM.
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For binary mixtures in which there was a stimulus x sip interaction, the following comparisons were made: binary mixture sip 1 versus self-mixture sip 1, binary mixture sip 1 versus binary mixture sip 4 and self-mixture sip 1 versus self-mixture sip 4. Sweetness intensity ratings of mixtures for sip 1 were higher than those for sip 1 of the average of the constituent self-mixtures for the following binary blends with significant stimulus x sip interactions: apm–cyc, cyc–fru, cyc–glu, cyc–sac, cyc–sor, cyc–sucr, fru–sac, fru–sucr and reb–sucr (for cyc–tha, the opposite was true). Significant reduction in sweetness intensity ratings from sip 1 to sip 4 occurred in all binary mixtures (with a significant stimulus x sip interaction), as well as their constituent self-mixtures. For all significant stimulus x sip effects, the binary mixtures exhibited less decline in sweetness ratings over four sips than the average of their constituent self-mixtures.
Analysis of variance—ternary mixtures
General linear models were also estimated to examine whether ternary mixtures of sweeteners exhibit more, the same or less reduction in sweetness intensity with repeated sips than their constituent self-mixtures. For each ternary mixture comparison (e.g. ace–suc–tha), the sweetness intensity of the mixture was compared with the average sweetness intensity of its three constituent self-mixtures (e.g. ace–ace–ace, suc–suc–suc, tha–tha–tha). Only those panelists who participated in all three conditions (evaluating the ternary mixture and all three constituent self-mixtures) were included in the analysis. General linear models (GLM) were estimated examining the effect of stimulus (mixture versus average of the constituent self-mixtures), sip (sip 1 through sip 4) and stimulus x sip interactions.
There was an effect of stimulus for 39 out of 56 ternary mixtures. For all significant stimulus effects, the ternary mixtures exhibited higher overall sweetness intensity ratings than the average of the three self-mixtures. There was an effect of sip for almost all of the ternary mixtures evaluated in which mean sweetness intensity declined over four repeated sips. The only ternary blends that did not have a significant effect of sip were ace–suc–tha, apm–sac–ste, apm–ste–tha, apm–suc–tha, sac–ste–tha and suc–sucr–tha.
There was a stimulus x sip interaction for the following ternary mixtures: ace–apm–fru, ace–apm–sac, ace–apm–tha, ace–fru–ste, ace–sucr–tha, apm–fru–ste, apm–fru–sucr, apm–fru–tha, apm–sac–ste, fru–sac–ste, fru–sac–suc, fru–sac–sucr, fru–sac–tha, fru–ste–tha, fru–suc–sucr, fru–suc–tha, fru–sucr–tha, sac–ste–suc, sac–ste–tha, sac–suc–sucr and sac–sucr–tha. Figure 2 shows the mean sweetness intensity ratings for sip 1 through sip 4 of each ternary mixture (based on least squares means) with a significant stimulus x sip interaction and the mean of its constituent self-mixtures.
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For ternary mixtures in which there was a stimulus x sip interaction, the following comparisons were made: ternary mixture sip 1 versus self-mixture sip 1, ternary mixture sip 1 versus ternary mixture sip 4 and self-mixture sip 1 versus self-mixture sip 4. Sweetness intensity ratings of mixtures for sip 1 were higher than those for sip 1 of the average of the constituent self-mixtures for the following ternary mixtures with a significant stimulus x sip interaction: ace–apm–fru, ace–apm–sac, ace–apm–tha, ace–fru–ste, ace–sucr–tha, apm–fru–ste, apm–fru–tha, apm–sac–ste, fru–sac–ste, fru–sac–tha and sac–sucr–tha (for fru–ste–tha, the opposite was true). Significant reduction in sweetness intensity from sip 1 to sip 4 occurred in 13 out of 21 ternary mixtures, with significant stimulus x sip interactions (ace–apm–fru, ace–apm–sac, apm–fru–ste, apm–fru–sucr, apm–fru–tha, fru–sac–ste, fru–sac–suc, fru–sac–tha, fru–suc–sucr, fru–suc–tha, fru–sucr–tha, sac–suc–sucr, sac–sucr–tha). All of the constituent self-mixtures demonstrated a significant decline in sweetness intensity ratings from sip 1 to sip 4. For all significant stimulus x sip interactions, the ternary mixtures exhibited less decline in sweetness ratings over four sips than the average of their constituent self-mixtures.
Percentage decreases in sweetness for binary and ternary mixtures
Percentage decreases in sweetness intensities from sip 1 to sip 4 were calculated in both the binary and ternary mixture studies. Figure 3 compares the mean percent decline of each binary blend versus the mean percent decline for the corresponding self-mixtures for the following sweeteners: acesulfame-k, aspartame, fructose, glucose, MAG, mannitol, rebaudioside-A, Na saccharin, sorbitol, Highstevia, sucrose, sucralose and thaumatin, respectively. The range in percentage decrease of all binary blends was 6.5% (man–sor) to 52.6% (ace–sac). For 87% of binary mixtures, the mean percent decrease in sweetness intensity was numerically lower than the percent decrease of their respective self-mixtures. Some binary blends differed greatly in the percentage they declined in sweetness across sips relative to the mean of their constituent self-mixtures (e.g. the cyc–tha blend differed by 27.7 percentage points). For a small proportion (11% of the binary mixtures), the percent decrease from sip 1 to sip 4 in comparison to that of the mean of the constituent self-mixtures was minimal (within 1%). The sweeteners that exhibited the greatest mean difference between decline in sweetness of blends and corresponding self-mixtures were Na cyclamate (19.5%), thaumatin (11.4%) and acesulfame-K (10.6%).
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Figure 4 compares mean percent decline of each ternary blend with the mean of its constituent self-mixtures for acesulfame-K, aspartame, fructose, Na saccharin, Highstevia, sucrose, sucralose and thaumatin, respectively. All but one of the ternary mixtures (apm–ste–tha) decreased in intensity from sip 1 to sip 4. The ternary mixture with the greatest percent decline from sip 1 to sip 4 was ace–sac–sucr at 32.9%. For ternary blends, 98% of mixtures had a numerically lower percent decline in sweetness ratings from sip 1 to sip 4 compared with their corresponding self-mixtures. Furthermore, the decrease in sweetness for 61% of ternary sweetener blends differed 15 or more percentage points from their self-mixtures. All of the sweeteners tested in ternary blends, with the exception of sucrose blends, differed to a large degree from the self-mixtures in the amount of decline in sweetness from sip 1 to sip 4.
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Discussion |
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The purpose of the present study was to determine if the blending of sweeteners in either binary or ternary combinations would influence sweetness intensity ratings over the course of repeated sips. The findings indicate that the mixing of sweeteners in both binary and ternary combinations results in a smaller decrement in sweetness intensity with repeated sips relative to use of a single sweetener (Schiffman et al., 1994
). When sweetness intensity ratings of mixtures are
compared with the corresponding mean intensity ratings of constituent
self-mixtures (e.g. ace–apm versus the mean of ace–ace and
apm–apm for binary mixtures), the percent decline from sip 1 to sip 4
was reduced for the vast majority of both binary and ternary blends. For
stimulus mixtures in which a stimulus x sip interaction occurred, the
rate of decline in sweetness intensity was lower for blends of different
sweeteners than self-mixtures (see Figures
1 and
2). Nineteen percent (19%) of
binary mixture blends and 37.5% of the ternary mixture blends had a
significant stimulus x sip interaction. These significant interactions
indicate that combining lower concentrations of two or more sweeteners in
blends can blunt the reduction in sweetness that occurs with repeated
sips.
For blends for which there was a reduction in percentage decrease in
sweetness intensity rating but no stimulus x sip interaction, the
reduction could be an artifact of the shape of the intensity functions for
each sweetener or actual synergy among the individual components. The shape of
the psychophysical functions for unmixed components has been shown to play a
role in the sweetness intensity of mixtures for a variety of sweet compounds
(DeGraaf and Frijters, 1987,
1988;
DeGraaf et al., 1987;
Frijters and DeGraaf, 1987;
Frijters and Oude Ophuis,
1983; McBride,
1988; Schifferstein,
1995,
1996). Synergism has been
shown to occur for some of the sweetener combinations tested here (Schiffman
et al., 1995,
2000). Synergism occurs when
the intensity of the mixture is greater than the theoretical sum of the
intensities of the individual components
(Frank et al., 1989;
Ayya and Lawless, 1992;
Verdi and Hood, 1993;
Birch, 1996). The analysis of
variance indicated that there was an effect of stimulus (blends versus
self-mixtures) for the majority of binary and ternary mixtures. For all
significant stimulus effects, the binary and ternary mixtures exhibited higher
overall sweetness intensity ratings than the average of the self-mixtures.
Thus, the binary and ternary blends had higher sweetness intensity over the
four sips compared with the self-mixtures. For example, if a binary sweetener
blend started at an intensity of 12 at sip 1 (rather than the expected 10,
i.e. 5 sweetness plus 5 sweetness) and the average of its corresponding
self-mixtures started at an intensity of 10, and both decreased with the same
slope to intensities of 9 and 7 respectively after four sips, the percentage
decrease in sweetness for the blend [i.e. (12–9)/12 or 25%] would be
less than for the average of the self-mixtures [i.e. (10—7)/10 or 30%].
Thus, smaller percentage changes in responsivity to mixtures over four sips
(when no stimulus x sip interaction was found) may be a numerical
consequence of the higher initial sweetness intensities resulting from either
the psychophysical functions or the synergy of the individual components.
Ternary combinations tended to be even more effective than binary combinations in blunting the reduction in sweetness with repeated sips. A comparison of binary and ternary mixtures involving only the sweeteners that were tested in both studies (acesulfame-K, aspartame, fructose, Na saccharin, stevioside, sucralose, sucrose and thaumatin) yielded the following results. The average decrease in sweetness after four sips for the ternary mixtures involving these eight sweeteners (excluding self-mixtures) was 14.5%, whereas the average decrease for binary mixtures for the eight sweeteners (excluding self-mixtures) was 23.0%. (The average decrease in sweetness after four sips for both binary and ternary self-mixtures involving these eight sweeteners was 31%.) For example, binary blends containing fructose experienced 7.9% less decline in sweetness on average than its self-mixtures while ternary blends containing fructose experienced 18.7% less than its corresponding self-mixtures. Binary blends containing thaumatin experienced on average 11.4% less decline in sweetness than its self-mixtures while ternary blends containing thaumatin experienced 19.6% less than its corresponding self-mixtures. Binary blends containing acesulfame-K experienced on average 10.6% less decline in sweetness than its self-mixtures while ternary blends containing acesulfame-K experienced 17.5% less than its corresponding self-mixtures. Reduced blunting of sweetness with repeated sips for ternary blends relative to binary blends may occur because they are accessing a greater variety of receptor types at lower concentrations for each component sweetener in the mixture.
Sucrose was the sweetener that demonstrated the smallest sweetness
reduction from the first to the fourth sip in binary, ternary and self-mixture
blends. Sucrose (and other bulk sweeteners) are thought to activate a wide
variety and number of sweet receptor types
(Faurion et al.,
1980; Schiffman et al.,
1981,
1986;
Tonosaki and Funakoshi, 1989),
while high-potency sweeteners are thought to activate a more limited number of
receptor types. However, it should be noted here that biochemical
investigations of sweetener receptors are still in their infancy. To date only
one human sweetener receptor type has been isolated
(Nelson et al.,
2001). This receptor is a G-protein-coupled receptor that is a
hetero-dimer T1R2/T1R3.
The binary mixture with the greatest percentage decrease in sweetness
(ace–sac) was present in several ternary mixtures, which also displayed
significant sweetness reduction (ace–fru–sac,
ace–sac–ste, ace–sac–sucr and
ace–sac–tha). Previous studies have hypothesized that acesulfame-K
and Na saccharin may activate the same receptor type because they cross-adapt
(Schiffman et al.,
1981) and are not synergistic with one another
(Schiffman et al.,
1995).
Overall, this study shows that the reduction in sweetness intensity with
repeated sips could be reduced if multiple sweeteners are included in the
mixture. However, our understanding of the mechanisms involved in this
blunting of taste awaits further discoveries in biochemistry, molecular
biology and genetics. Recent molecular cloning studies have led to the
identification of a number of taste receptor cell-specific G-protein-coupled
receptors (GPCRs) (Adler et al.,
2000; Chandrashekar et
al., 2000; Kitagawa
et al., 2001; Li
et al., 2001;
Montmayeur et al.,
2001; Max et al.,
2001; Nelson et al.,
2001). These studies are a major step toward understanding the
variety of receptors that are involved in the complicated molecular mechanisms
of taste transduction.
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Accepted February 13, 2003
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