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This is the author’s final peer reviewed version of the item
published as:
Keast, Russell and Breslin, Paul A. S. 2003-03, An overview of binary taste-taste
interactions, Food quality and preference, vol. 14, no. 2, pp. 111-124.
Copyright : 2002, Elsevier Science Ltd.
An Overview of Binary Taste-Taste Interactions
Russell S. J. Keast and Paul A. S. Breslin
Monell Chemical Senses Center, 3500 Market St, Philadelphia, PA 19104
For Editorial Contact/Requests for Reprints:
Russell Keast
Monell Chemical Senses Center
3500 Market St
Philadelphia, PA, 19104
ph 215-898-0858
fax 215-898-2084
e-mail [email protected]
1
Abstract
The human gustatory system is capable of identifying five major taste qualities:
sweet, sour, bitter, salty and savory (umami), and perhaps several sub-qualities. This is a
relatively small number of qualities given the vast number and structural diversity of
chemical compounds that elicit taste. When we consume a food, our taste receptor cells
are activated by numerous stimuli via several transduction pathways. An important foodrelated taste question which remains largely unanswered is, How do taste perception’s
change when multiple taste stimuli are presented together in a food or beverage rather
than when presented alone? The interactions among taste compounds is a large research
area that has interested electrophysiologists, psychophysicists, biochemists, and food
scientists alike.
On a practical level, taste interactions are important in the development and
modification of foods, beverages or oral care products. Is there enhancement or
suppression of intensity when adding stimuli of the same or different qualities together?
Relevant psychophysical literature on taste-taste interactions along with selected
psychophysical theory is reviewed. We suggest that the position of the individual taste
stimuli on the concentration-intensity psychophysical curve (expansive, linear, or
compressive phase of the curve) predicts important interactions when reporting
enhancement or suppression of taste mixtures.
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Keywords
Taste psychophysics, food, sweet, sour, salty, umami, savory, bitter, suppression,
enhancement, taste mixtures
3
1.0
Introduction
Phylogenetic arguments for taste suggest that it evolved to identify nutritive foods
and potential toxins, thereby increasing the likelihood of survival and reproduction of
individuals who have these gustatory capabilities (Glendinning, 1994). Throughout the
evolution of animals, potential toxins had to be identified from within a complex matrix.
Perhaps this is why mixing a toxic, bitter stimulus with a sweet stimulus often results in a
bitter-sweet tasting solution. Surely, the taste system evolved under circumstances in
which it had to encode and identify complex mixtures of taste stimuli. Yet, noninteraction of taste mixture components is far from the rule. To the contrary, most taste
compounds interact perceptually and in a manner that follows an apparently complex set
of rules.
Decisions based on taste-taste interactions are part of everyday life: Will a wedge
of lemon improve the taste of my wheat beer? Is one teaspoon of sugar enough to
sweeten my coffee, and if I add two teaspoons will it double the sweetness? When
compounds eliciting tastes are mixed many outcomes are possible, including perceptual
enhancement & suppression, unmasking of a taste not initially observed, or possibly
chemical synthesis of a new taste. These outcomes and their potential implications for
taste transduction and food production have interested physiologists, psychophysicists,
and food scientists.
1.1
Outline and objectives
Taste-taste interactions are not well understood, partly because of contradictions
in the literature. The aim of this paper is to review the taste-taste interaction literature
4
taking into account factors that could lead to contradictions (Section 6.0), and to draw
general conclusions about how tastes interact with each other. This paper includes
sections on attributes of taste, analysis of psychophysical taste functions, and assessment
of factors that influence binary taste-taste interactions. The literature reviewed is limited
to taste solution admixtures, including similar quality and hetero-quality taste
interactions. In addition, we compare taste interactions in aqueous solutions to taste
interactions in food matrices. Finally, conclusions are discussed about the major factors
involved in taste interactions and future research directions are proposed.
1.2
Attributes of taste
There are four properties that make individual taste sensations unique: their
quality, intensity, temporal, and spatial patterns. The attribute “quality” is a descriptive
noun given to categorize sensations that taste compounds elicit; there are five major taste
quality descriptors: sweet, sour, salty, bitter, and umami/ savory. The quality of a taste
sensation is its single most important defining feature. We could not substitute sucrose
(sweet) for iso-α acids (bitter) in beer without rendering the beer a different beverage.
The attribute “intensity” is a measure of the magnitude of sensation(s) elicited by a
compound at a given time. The perceived intensity of a sapid compound may be plotted
against its concentration to produce a psychophysical function (Figure 1). Intensity is
also a key attribute. The difference in perceived intensity between 5ppm and 100ppm
iso-α acids in beer would be easily distinguished and render the stronger unpalatable.
The “temporal” pattern of a compound is related to the time course of the intensities
(McBride, 1976). For example, iso-α acids elicit a lingering bitterness, whereas urea’s
bitterness is relatively short in duration. Finally the “spatial” topography relates to the
5
location of taste sensations on the tongue and oral cavity (McBride, 1976). Iso-α acids
strongly stimulate bitterness on the back of the tongue and throat region leaving the
anterior portion of the tongue relatively unaffected, whereas quinine-HCl elicits
bitterness from the side to the back and front of the tongue. From this spatial pattern,
humans appear to be able to localize taste in the oral cavity, despite whole mouth
exposure.
1.3
Three levels of taste interactions
When assessing mixtures of taste eliciting compounds, three levels of interaction
must be taken into account: chemical interactions occurring in solution which may
directly affect taste perception (Shallenberger, 1993), secondary interactions between one
of the mixture components and the taste receptors/transduction mechanisms of the other
component (Lindemann, 2001), cognitive effects of different taste qualities being
perceived together in the mouth.
1.3.1
Chemical interactions
Chemical interactions can result in modified taste intensity or even the generation
of new qualities. They occur in a simple aqueous solution: an acid in combination with a
base will result in formation of a salt; weak attractive forces, such as hydrogen or
hydrophobic bonding, will result in altered structures; precipitation of the compounds
will render them weaker or tasteless.
1.3.2
Oral physiological interactions
When two compounds are mixed, there is potential for one compound to interfere
with taste receptor cells or taste transduction mechanisms associated with another
compound. For example, this type of peripheral interaction occurs between sodium salts
6
and certain bitter compounds. Sodium salts suppress the bitterness of selected
compounds (Bartoshuk,Rennert,Rodin & Stevens, 1982; Breslin & Beauchamp, 1995;
Frijters & Schifferstein, 1994; Keast & Breslin, 2002a). This suppression is a peripheral
oral effect (at the cellular/epithelial level) rather than a cognitive effect (central process).
To demonstrate the peripheral effect, Kroeze & Bartoshuk (1985) applied a bitter
stimulus to one side of the tongue and a sodium salt to the other side of the tongue (split
tongue methodology). The stimuli were applied independently and simultaneously. The
intensity of bitterness was only reduced when the stimuli were applied to the tongue in
mixture together, compared to independent simultaneous application of the two stimuli
on different sides of the tongue. This peripheral interaction between sapid compounds
could occur at a number of sites on or in the taste receptor cell (Keast,Breslin &
Beauchamp, 2001). Gillan (1982), when investigating sucrose-NaCl interaction,
performed a similar split tongue experiment, and found evidence for both peripheral and
cognitive interactions.
1.3.3
Cognitive interactions
Central processing during mixture identification is an integral part of taste. Taste
stimuli interact with taste transduction mechanisms in the oral cavity and afferent signals
are sent to the nucleus of the solitary tract, the first gustatory relay, and to upstream taste
processing regions of the brain where the signal is decoded and a taste sensations are
perceived. As a general heuristic, when two or more taste stimuli (above threshold) are
mixed together the intensity is less than the sum of the individual taste intensities. This is
called mixture suppression (Pangborn, 1960b). Mixture suppression has been extensively
reported in taste interaction research (Frank,van der Klaauw & Schifferstein, 1993;
7
Kroeze, 1982, 1990; Lawless, 1979a) and was effectively demonstrated by Kroeze et al.
(1985) using the split tongue methodology described above. Kroeze found suppression
of individual qualities, such as sweet and bitter, when the compounds were mixed,
regardless of whether the compounds were applied independently to either side of the
tongue, or together as a mixture. This demonstrated that suppression had a central
cognitive rather than just a peripheral oral effect. This conclusion is possible because the
two lateral halves of the tongue are neurologically independent until the ascending
neurons interact in the brain.
1.4
The psychophysical curve: Physical intensity vs. perceived intensity
Sensory organs located on surface regions of the body are responsible for
detecting different forms of energy in the environment. This energy comes into contact
with a receptor system (gustatory, olfactory, audition, vision) and is converted to an
electrical impulse, which is ultimately decoded as a percept at cortical levels. The two
variables can be plotted with the physical parameter (chemical concentration, energy
decibels, photon flux) on the x-axis against perceived intensity on the Y-axis. The final
shape of the plot is the psychophysical curve for the particular stimulus and
subject/population.
Sensory receptor systems responsible for detecting environmental cues vary in
structure, and therefore in their range of responsiveness. For example, the auditory
system has a basilar membrane in the cochlea of the ear that responds to changes in
pressure (sound waves). Different frequencies of sound waves (Hertz) produce maximal
activity at different positions along the basilar membrane. Thus, at a frequency of 10
kilohertz (kHz) and signal level of 20 decibels, a weak vibration will occur in a spot on
8
the basilar membrane and only a few hair cells and their fibers may respond. As the
decibel level increases (at 10kHz), hair cells that are unresponsive at 20 decibels, and are
ideally tuned to alternate frequencies (2-14 kHz), are recruited. The recruitment pattern
grows as the decibel level increases, and the growth is exponential over 80 decibels
(Figure 1, auditory psychophysical curve A). Unlike the auditory system which has a
capacity for perceived intensity to continue to grow with physical intensity up to the point
of physical damage to the receptor system, the taste system has a much more reserved
response to increases in chemical concentration. Recruitment may not be as general a
phenomenon in taste as it is in audition.
The taste system can be viewed as a modified enzyme system, in which the
receptor-taste compound activation is the fundamental limiting step for the remainder of
the system all the way through to perception. The rate of catalysis (in the taste system,
catalysis refers to activation of a taste transduction pathway) varies with the sapid
compound concentration. At a low concentration of sapid compound, the rise in intensity
is proportional to a rise in concentration. While at higher concentrations of sapid
compound, the perceived intensity may appear independent if the receptor system
becomes saturated and no further increases in perceived intensity are attained (for
selected compounds recruitment may occur and perceived intensity will continue to
increase over several orders of magnitude range in concentration, as seen with
denatonium benzoate). Figure 1 shows a compound following Michaelis-Menten-like
kinetics for the reaction, and the final shape of the curve resembling a hyperbole (curve
C). There is also the possibility that compounds may show sigmoidal functions. There
are only a few examples in the literature that show this accelerating function for
9
individual compounds. For example, an accelerating phase can be visualized in the
psychophysical curve of a number of sugars, including xylitol, sorbitol, and fructose
(Schiffman & Gatlin, 1993), and curves plotted for fructose and sucrose by McBride
(McBride, 1989). To our knowledge, the existence of a sigmoidal taste concentrationresponse function has yet to be investigated in a parametric manner within individuals.
However, Bartoshuk (1975) has proposed all three phases (compressive, linear,
expansive) exist for taste stimuli, although not for one stimulus.
A sigmoidally-shaped function for a taste-eliciting compound can be explained
via enzyme kinetics. The Michaelis-Menton model does not apply for all enzyme
reactions. In the case of a sigmoid curve, the binding of one substrate to an active site
can affect the binding of another substrate to a second active site within one system. If
the binding of substrates becomes co-operative, we would see an acceleration portion of a
curve (Stryer, 1988) (Figure 1, curve B sigmoid, acceleration at low intensity). This may
have implications for taste-taste interactions (see section 1.4.1).
1.4.1
A sigmoidal psychophysical curve; A model for taste mixture interactions
A simple sigmoidally-shaped psychophysical function for a hypothetical taste
mixture is illustrated in Figure 2. The sigmoid can be constructed as three separate
phases. The initial phase of the curve resembles an exponentially accelerating function in
which the perceived intensity grows faster than the concentration. The middle phase of
the curve follows a linear function with the intensity rising proportionally to the
concentration of the sapid compound/mixture. The final phase resembles an
exponentially decelerating function with a plateau of intensity corresponding to saturation
10
of receptors or maximum perceived intensity for that compound/mixture. Each of these
three phases can be described with Steven’s power law (Stevens1969).
I = kCn.
where I is the intensity of sensation, k is the constant and determines slope, C is the
concentration of the sapid compound, and n is the exponent associated with the
concentration-intensity shape of the line for the sapid compound at that phase. In the
expansive phase (exponent greater than one), doubling of a concentration, results in
greater than doubling of intensity. In the linear phase (exponent equal to one), increasing
a concentration, results in a proportional increase of intensity. At the compressive phase
(exponent less than one), doubling of a concentration results in less than doubling of
intensity.
We hypothesize that the sigmoidally-shaped function is an important feature in
taste-taste interactions. If the individual compounds of a mixture have psychophysical
curves that are hyperbole shape, mixing the two compounds may produce a sigmoid.
Figure 3 illustrates this point with theoretical compound A and B, both with hyperbolic
psychophysical curves that form a sigmoidal function when mixed 50:50, yet when both
are mixed we can observe a sigmoidal curve. The accelerating portion of the same-taste
quality function would be analogous to the allosteric effect of the two compounds on
receptor processes on a taste cell involved in taste transduction (see section 1.4). The
compressive phase would be due to the oral peripheral effect of saturation of the
receptors.
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There may also be oral peripheral interactions between two different taste
qualities, but rather than occurring at a receptor, interactions could occur between taste
cells (e.g. salt receptor cell adjacent to a sweet receptor cell) with activation of both cells
causing a potentiation of the afferent taste signal. Interactions between different taste
qualities could also occur within a taste cell (both sweet and salt receptors on the same
taste cell), where activation of multiple taste transduction pathways within the taste cell
results in signal potentiation.
The cognitive effect on the slope of a psychometric function cannot be
overlooked. Mixing of two very low taste intensities may produce combined taste
intensity greater than the sum. This effect may have nothing to do with any peripheral
interactions, but merely and effect of central processing. Also, at high intensity the
general phenomenon of mixture suppression has been extensively reported (1.3.3).
The majority of the binary taste-taste interaction literature reviewed in this paper
appears to follow sigmoidally shaped functions.
2.0
Same quality binary taste interactions
A great many compounds can elicit the same taste quality, for example iso-α
acids, L-tryptophan and quinine-HCl are all bitter, yet may activate unique taste
transduction pathways (Delwiche,Buletic & Breslin, 2001). Given that various receptors
and transduction mechanisms may exist for a single taste quality (Adler et al., 2000;
Chandrashekar et al., 2000; Lindemann, 2001; Nelson et al., 2001), it is possible that
mixtures of similar tasting substances will exhibit a variety of interactions via peripheral
intracellular mechanisms.
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2.1
Enhancement or suppression
There are a number of possible interactions when two compounds are mixed.
Accurate identification of linear or non-linear shifts is difficult from the literature.
Therefore, we will primarily refer to enhancement or suppression of intensity as general
terms. However, in situations where “synergy” was unequivocal, this term will be used
to describe the non-linear interactions.
Based on a common understanding in the literature, enhancement equates to
1+1>2, additivity to 1+1=2, and suppression to 1+1<2. This simple understanding of
enhancement or suppression can lead to spurious conclusions because people often fail to
consider that a compound’s concentration-response function is non-linear itself (Figure
2). Rifkin and Bartoshuk (1980) accurately described synergy between two compounds
by looking at the actual intensity of the mixed components, compared to self-addition.
Methods for assessing synergy are discussed in Section 6.2.1.
Figure 4 illustrates the types of interactions, both enhancement and suppression
that can occur to a psychophysical function of compound E when mixed with another
compound (D or F). Compound E is a bitter compound and the illustrated
psychophysical function is for the quality, bitter. When a fixed concentration of
compound D (same or different quality) is mixed with compound E, the psychophysical
function of E is shifted to the left and the slope increased, which illustrates that
compound D has an enhancing effect on the bitterness of E. Also, the linear part of the
psychophysical function of E could be left shifted without affecting slope (D1) (Figure 4
bottom). The asymptote may also be affected (D’); in this situation the maximum
13
attainable bitterness elicited by E is also increased. These scenarios show that compound
D enhanced the perceived bitterness of compound E at a given concentrations. Figure 4
also shows the effects on the bitterness of compound E when a fixed concentration of
compound F is added. Compound E’s psychophysical function is right shifted and the
slope decreased. Therefore, addition of F suppressed the bitterness of E. As well, the
psychophysical function can be right shifted without a change of slope (F1) (Figure 4
bottom). The asymptote may be affected, as shown by F’; in this situation F has blocked
the maximum achievable bitterness of E, as would be expected with a non-competitive
antagonist (See also section 6.2.1).
Studies investigating taste mixtures have often focused on compounds that elicit
different taste qualities. What follows is a brief summary of interactions between
compounds that elicit similar quality.
2.2
Sweet
The largest proportion of the literature investigating similar taste quality
interactions is for sweetness (Ayya & Lawless, 1992; Bartoshuk & Cleveland, 1977;
Cameron, 1947; De Graaf & Frijters, 1987; Frank,Mize & Carter, 1989; Kamen, 1959;
McBride, 1986, 1988; Moskowitz, 1973; Schifferstein, 1995, 1996; Schiffman et al.,
1995; Stone & Oliver, 1969; Yamaguchi,Yoshikawa,Ikeda & Ninomiya, 1970). Sweet
mixtures containing high intensity sweeteners tend to result in enhanced sweet intensity
and the term synergy is often used, but not uniformly. The clearest example of synergy
occurs with mixtures of aspartame and acesulfame K over a range of
intensity/concentrations and aspartame and saccharin at low intensities/concentrations
only. Overall, it appears the shape of the psychophysical function (Figure 2) predicts
14
whether enhancement or suppression will occur. At low intensity/concentrations
(corresponding to the expansive phase) reports of synergy are more common. At higher
intensity/concentrations (corresponding to linear of compressive phase) enhancement is
less common and suppression has been reported.
2.3
Umami
Monosodium glutamate (MSG) and the sodium salts of ribonucleotides disodium
5’-inosinate and guanylate exhibit synergy of umami/savory taste when mixed together
(Rifkin et al., 1980; Schiffman,Frey,Luboski,Foster & Erickson, 1991; Yamaguchi, 1967,
1991).
2.4
Salt
Breslin et al.(1995) examined a mixture of NaCl and KCl. At low concentration
saltiness was enhanced, while at higher concentrations it was suppressed.
2.5
Sour
When weak acids are mixed, the final sourness is less than predicted from the sum
of individual intensities (Bartoshuk et al., 1977), or additive (Moskowitz, 1974).
2.6
Bitter
When bitter compounds were mixed, the final bitterness was less than the
predicted sum of individual intensities (Bartoshuk et al., 1977). Urea suppressed the
bitterness of a variety of bitter compounds, while denatonium benzoate enhanced the
bitterness of some bitter compounds (Bournazel,Keast & Breslin, 2002; Keast,Bournazel
& Breslin, 2002b).
2.7
Conclusions
15
In general, same quality interactions are often predicted by a sigmoidal shaped
psychophysical function, with expansive, linear or compressive phases. The greater the
intensity/concentration the more reports of suppressive interactions. For two qualities,
sweet and umami/savory there is significant evidence of synergy of taste intensity (a
peripheral effect) when two compounds eliciting the same quality are mixed together.
3.0
Different quality binary taste interactions
When two compounds with different qualities are mixed, a number of interactions
may occur including non-monotonic (both enhancement and suppression) and
asymmetrical intensity shifts. Figure 5 shows the hypothetical psychophysical function
(bold black line) for sweet compound J (upper panel) and salty compound L (lower
panel), and the effects on sweetness and saltiness when the two compounds are mixed at
increasing concentrations along their individual functions. At low
intensity/concentration, the mixture resulted in an enhancement of sweetness and
suppression of saltiness. At moderate intensity/concentration, there is no effect on
sweetness and a slight increase in saltiness. High intensity/concentration mixing yielded
a suppression of sweetness and no effect on saltiness. Asymmetric effects occurred at all
concentrations; saltiness and sweetness are differentially affected. Also, the results were
non-monotonic; sweetness followed the predictions of expansive, linear and compressive
regions of the psychophysical function, while salty was suppressed at low concentration,
enhanced at moderate concentration and there was no effect at high concentration. The
point of this hypothetical exercise is to illustrate that the predictions based on a sigmoidal
function will not always be accurate.
16
It is important to note that what follows is a general review, and there will be
compound specific differences in interactions. The literature is often contradictory, and
in such cases we use the term ‘variable’. An explanation of why such variability exists is
discussed in section 6.0.
3.1
Umami/savory interactions
Woskow (1969) concluded that, sodium salts of 5’-ribonucleotides
(umami/savory quality) enhanced sweetness, enhanced saltiness at moderate
concentrations, while sourness and bitterness were suppressed. Kemp & Beauchamp
(1994) reported MSG had no influence on taste qualities at threshold levels, at
moderate/high concentrations of MSG, sweet and bitter were suppressed, and at a high
concentration of MSG, saltiness of NaCl was enhanced. Keast & Breslin (2002c) found
that MSG and adenosine mono-phosphate (Na+ salt) inhibited bitterness.
3.2
Sweet interactions
At low intensities/concentrations, which corresponds to the expansive phase of
the psychophysical function, the effect of binary mixtures of sweet tasting compounds
with other basic taste qualities is variable (reports of enhancement and suppression)
(Beebe-Center,Rogers,Atkinson & O'Connell, 1959; Breslin & Beauchamp, 1997;
Calvino,Garcia-Medina & Cometto-Muniz, 1990; Calvino & Garrido, 1991;
Curtis,Stevens & Lawless, 1984; De Graaf & Frijters, 1989; Frijters et al., 1994; Gillette,
1985; Kamen,Pilgrim,Gutman & Kroll, 1961; Kroeze, 1979; Kroeze et al., 1985;
Lawless, 1979a, 1982; Pangborn, 1960b, 1961, 1962, 1965; Prescott,Ripandelli &
Wakeling, 2001; Schifferstein, 1994b, 1997; Schifferstein & Frijters, 1993; Schifferstein
& Kleykers, 1996; Schiffman,Gill & Diaz, 1985; Schiffman et al., 1994; Schiffman et al.,
17
2000; Stevens, 1995; Stevens & Traverzo, 1997). At medium and high
intensities/concentrations sweet was generally suppressive of other basic tastes. At high
concentrations interactions between bitter and sour qualities with sweet is symmetrically
suppressive.
3.3
Salty interactions
Salt and sour mixtures symmetrically affect each others’ intensity with
enhancement at low intensity/concentrations and suppression or no effect at high
intensities/concentrations (Beebe-Center et al., 1959; Breslin et al., 1995, 1997; Breslin,
1996; De Graaf et al., 1989; Frank et al., 1993; Frijters et al., 1994; Gillette, 1985;
Kamen et al., 1961; Keast et al., 2002a, c; Kroeze, 1979, 1982; Kroeze et al., 1985;
Lawless, 1982; Pangborn, 1960b, 1962; Prescott et al., 2001; Schifferstein et al., 1993;
Schiffman et al., 1985; Stevens, 1995; Stevens et al., 1997). Bitterness is suppressed by
salt while salt taste is not affected by bitterness. Salt enhances sweetness at low
concentrations, has variable effects through the moderate intensity/concentration range,
and is suppressive or has no effect on sweetness at higher intensity/concentration.
Sweetness suppresses salty taste at moderate intensities.
3.4
Sour Interactions
Sour and salty mixtures symmetrically affect each others’ intensity with
enhancement at low intensity/concentrations and suppression or no effect at high
intensities/concentrations (Breslin, 1996; Curtis et al., 1984; Gillette, 1985; Kamen et al.,
1961; Pangborn, 1960b; Prescott et al., 2001; Schifferstein, 1994b, 1997; Schifferstein &
Frijters, 1990; Schifferstein et al., 1993; Schifferstein et al., 1996; Schiffman et al., 2000;
Stevens, 1995; Stevens et al., 1997). At low intensity/concentration sourness has variable
18
effects on sweetness, while at higher intensity/concentration mixtures of sour and sweet
are mutually suppressed. Mixtures of sour and bitter compounds enhance each other a
low intensity/concentration; at moderate intensity bitterness is suppressed and sourness
enhanced, while at high intensity/concentration sourness is suppressed and the effect on
bitterness is variable.
3.5
Bitter interactions
Bitter interactions are also highly variable (Breslin et al., 1995, 1997; Breslin,
1996; Calvino et al., 1990; Calvino et al., 1991; Frijters et al., 1994; Gillette, 1985;
Kamen et al., 1961; Keast et al., 2002a, c; Kroeze et al., 1985; Lawless, 1979a; Pangborn,
1960b; Prescott et al., 2001; Schifferstein et al., 1993; Schiffman et al., 1985; Schiffman
et al., 1994; Stevens, 1995). Bitterness is suppressed by salt while salty taste is not
affected by bitterness. Mixtures of bitter and sweet are variably affected at low
intensity/concentration, while mixtures at moderate and high intensity/concentrations are
mutually suppressive. At low intensity/concentration, mixtures of bitter with sour
compounds enhance each other, at medium intensity/concentration, sourness is enhanced
by bitterness and bitterness is suppressed by sour taste, and at high
intensity/concentration, sourness is suppressed by bitterness and bitterness is variably
affected by sour tasting compounds.
3.5
Conclusions
Figure 6 (a-c) summarizes generalizations about binary taste interactions of
different qualities. It is important to note that these are generalizations and that effects
will be compound specific. Due to the intensity/concentration influence of taste
19
interactions, there are three parts to the illustration, each corresponding to a region of a
psychophysical function: interactions of low perceived intensity corresponding to the
expansive phase (Figure 6A), moderate perceived intensity corresponding to the linear
phase (6B), and strong perceived intensity corresponding to the compressive phase (6C).
Umami was not included in Figure 6 as there is little symmetrical research investigating
heteroquality binary interactions with MSG [c.f., (Kemp & Beauchamp, 1994)].
In general, binary taste interactions follow the predictions of the different phases
of the psychophysical function (Figure 2) (Bartoshuk, 1975; Schifferstein et al., 1996).
This generalization does not address the many potential peripheral physiological
interactions that may occur. At low intensity/concentration enhancement is reported
more often, at moderate intensity/concentration there is a mix of enhancement,
suppression and linear interactions, while at high intensity/concentration suppression is
most common.
Regarding binary interactions, a number of potential combinations have yet to be
explored or have been given relatively little attention. Table 1 provides a subjective
rating on the extent of knowledge between possible binary combinations of taste eliciting
stimuli. Same quality interactions for sour, salty and bitter are poorly understood and
there is much research needed on interactions between sour, bitter and salty compounds.
Sweetness is the only quality that appears to be moderately well studied.
4.0
Trinary or more complex taste mixtures
4.1
Thresholds
20
Stevens (1997) investigated detection thresholds in complex mixtures and found
integration across all tastes (taste thresholds for compounds were reduced when other
qualities were added). This was true of all 24 compounds eliciting four qualities (sweet,
sour, salty, bitter) tested. When two compounds around threshold (very low to low
intensity) are mixed, their thresholds are mutually reduced (i.e., sensitivity increased).
4.1
Suprathreshold
Peripheral interactions have an influence in multi-component mixtures. Breslin et
al. (1997) examined the interaction between Na acetate, sucrose and urea. They asked,
What happens if a sodium salt is added to the bitter-sweet mixture, given that sodium
salts inhibit bitterness and bitterness and sweetness are mutually suppressive? The results
showed that addition of sodium to a bitter-sweet mixture suppressed the bitterness. As
the intensity of bitterness decreased, sweetness was enhanced due to release from
cognitive suppression of the bitterness. This three-taste interaction illustrates how
peripheral and central cognitive effects can interact.
In earlier research, Bartoshuk (1975) examined perceived quality intensity of
sweet, sour, salty and bitter eliciting compounds singularly and in mixture with each
other. With the exception of sour, subsequent additions of taste eliciting substances
caused a decrease in quality intensity, for example, bitterness decreased when the sweet
compound was added, decreased further when the salt compound was added, decreased
further when the sour component was added. Bartoshuk explained the suppression was
due to compressive functions for the compounds tested; however, the compressive
function of the sour compound did not cause any subsequent decrease in sour intensity
21
when other sapid compounds were added. Relative to binary taste mixtures, trinary or
more complicated interactions have been studied even less.
5.0
Effect of matrices
If iso-α acids are added to a complex matrix like beer, provided the concentration
is high enough, bitterness will be elicited or increased. Or if a teaspoon of sugar is added
to coffee, it will become sweeter. Psychophysics of taste compounds in aqueous
solutions can help our understanding of taste interactions in more complex vehicles, since
there are many examples of complex matrices behaving as predicted from simple aqueous
solutions.
The most influential researcher in the area of taste in various matrices or food
systems was Pangborn (Pangborn, 1960a, b, 1961, 1962, 1965, 1987; Pangborn,Berg &
Hansen, 1963; Pangborn & Chrisp, 1964a; Pangborn,Gibbs & Tassan, 1978; Pangborn &
Hansen, 1963; Pangborn,Ough & Chrisp, 1964b; Pangborn & Trabue, 1964c, 1967;
Pangborn,Trabue & Szczesniak, 1973). Pangborn and colleagues performed a series of
experiments in the early 1960’s investigating sucrose, citric acid and NaCl taste
interrelationships. Several different food matrices were used, e.g., pear nectar (Pangborn,
1960b), tomato juice (Pangborn et al., 1964a), and lima bean puree (Pangborn et al.,
1964c). The results from the food matrix generally supported results from the same
author in aqueous media (Pangborn, 1960b, 1961, 1962).
Calvino,Garcia-Medina & Cometto-Muniz (1990) investigated bitter-sweet
interaction in water and also in a coffee matrix. In line with the expansive, linear,
22
compressive model for psychophysical function, the authors found that the greater the
intensity/concentration of sweet, bitter or coffee flavor, the greater their suppressive
ability over the other component/s. For example, bitterness and coffee flavor were
suppressed when sucrose was added, and vice versa.
In a separate study investigating taste effects of thickeners, Calvino,GarciaMedina,Cometto-Muniz & Rodriguez (1993) investigated bitter-sweet perception in
water, with the addition of either a carbohydrate based thickener, or a protein based
gelling agent. The carbohydrate or protein had no influence on mutual suppression of the
bitter-sweet mixture. However, increasing the viscosity of the solution resulted in
suppression of taste intensity (Arabie & Moskowitz, 1971; Christensen, 1980;
Kokini,Bistany,Poole & Stier, 1982; Pangborn et al., 1978; Pangborn et al., 1973; Stone
& Oliver, 1966).
Breslin et al, (1997) demonstrated that sodium salt suppressed bitterness and also
increased sweetness by releasing it from the mixture suppression exerted by the
bitterness. This was demonstrated in food matrices: Gillette (1985) reported that addition
of NaCl to three soups decreased bitterness and increases sweetness, while Fuke &
Konosu (1991) reported that addition of umami tasting 5’-ribonucleotides (which
suppress bitterness) reduced bitterness and increased sweetness in an artificial prawn
extract.
Psychophysical research has shown that certain umami/savory quality compounds
act synergistically together to (Rifkin et al., 1980; Schiffman et al., 1991; Yamaguchi,
1967, 1991), (a) enhance salt taste (Kemp et al., 1994; Woskow, 1969; Yamaguchi,
1987), (b) enhance sweet taste (Woskow, 1969), and (c) suppress bitterness (Keast et al.,
23
2002c; Kemp et al., 1994; Woskow, 1969).
In a review of Japanese research on a
variety of foods, Fuke et al. (1991) concluded that glutamic acid and 5’-ribonucleotides
in the presence of sodium were required to produce characteristic tastes of foods. This
included enhancement of umami/savory, salty, and sweet taste and suppression of
bitterness.
Apart from the primary taste response of adding a compound (NaCl increasing
saltiness), the secondary and tertiary results such as suppressions, release of suppression,
or enhancements can often be predicted. Of course, in food there are other aspects to take
into account, for example aroma and somatosensory properties, but these topics are too
vast to include in the present review. There are parallels between simple solutions used
in psychophysical studies and the more complex food matrices. However, sapid
compounds added to a matrix may behave differently than predicted, and matrix effects
should not be underestimated. Overall, the aqueous taste psychophysical literature is
directly relevant to the food and oral care industry.
6.0
Sources of variability in taste psychophysical literature
Human psychophysical studies have investigated mixture interactions as early as
1896 (Kiesow, 1896) and much of the literature since then has been contradictory, at least
in parts. There are several types of contradictory statements made in the literature.
6.1
Individual variation
Taste perception varies between people (Delwiche et al., 2001; Yokomukai,
Cowart & Beauchamp, 1993), one person may find a 50ppm iso-α acid solution
extremely bitter, while a second person barely notices the bitterness. Thus, differences in
24
sample populations between experiments may affect results. Even within an individual
the perceived intensity of a compound may vary according to the time of day or choice of
food or beverage prior to testing (Faurion, 1987).
6.2
Experimental protocol
The experimental design has a direct influence over the results. The method of
stimulus delivery has an impact: flowing tastants over the anterior tongue or exposing the
whole mouth to the taste compounds will alter the psychophysical function (Bartoshuk et
al., 1977). The psychophysical function of compounds may be altered depending on the
method used. For example, delivering a concentration series in ascending order versus
random order can alter the shape of the concentration-intensity function. Also the
number and training of subjects can influence final results. Kamen et al. (1961)
employed close to 1,000 subject in a simple half replicate design with single sample
methodology, while Beebe-Center et al. (1959) had only 2 subjects, but utilized more
powerful paired comparison and direct matching protocol.
6.2.1
Experimental protocol for assessing synergy or suppression
One approach to assess mixture interactions over a range of concentrations is to
construct psychophysical function for the compound of interest (Figure 7, compound A).
To assess interactions between two compounds, a weak concentration of a second
compound (Figure 7, B’) is added at different concentrations along the function of the
primary compound. In order to make a direct comparison of intensity, a weak intensity
(matching the weak intensity of the B’) of the primary compound (A’) is added to itself;
in essence, the psychophysical curve is shifted left and the baseline moves up to weak
(Figure 7, [A]+A’). The additive curve of the primary compound ([A]+A’) is compared
25
to the mixture curve of the primary compound mixed with the secondary compound
([A]+B’). In Figure 7, we see the [A]+B’ curve is left of [A]+A’ curve demonstrating an
enhancement of taste intensity.
A second, less intensive method would be to match two compounds (X and Y)
for intensity. The difference between adding compound X to itself (X+X) or compound
Y to X (Y+X) can be synergistic (X+Y greater than the intensity of X+X), strictly
additive (X+Y the same as X+X), or suppressive (X+Y less than the intensity of X+X).
The importance of the experimental protocol and method of calculation were evident
when Schiffman et al. (1995) demonstrated synergy for a mixture using one method of
analysis and no synergy using the second method of analysis for the same data. In
addition, one could have reported that the greatest suppression of sweetness was observed
with the sodium saccharin + sodium saccharin self mixture, which is obviously not
suppression but a normal function of sodium saccharin’s non-linear psychophysical curve
(Schiffman et al., 1995).
6.3
Choice of sapid compound
The choice of sapid compound can cause large variation in experimental outcome.
Both urea and quinine are perceived as bitter but presumably activate different taste
transduction pathways (Keast et al., 2002a; Lawless, 1979b; McBurney, Smith & Shick,
1972; Yokomukai et al., 1993). The observation that compound X affects the bitter taste
of quinine, does not predict that X will affect the bitter taste elicited by urea (Breslin et
al., 1995). Further to this, concentrations of compounds required to elicit isointense taste
vary; at 0.4mM, quinine can elicit a strong bitterness, but 0.4mM urea is usually tasteless.
26
Thus, the impact of osmolarity in solution should not be overlooked (Keast et al., 2002a;
Lyall, Heck, De & Feldman, 1999) (see 6.4 below).
6.4
Psychophysical function of a compound
Different experimenters use different single concentrations of a given compound,
and as previously stated, the position of this concentration along the expansive, linear or
compressive phase of its psychophysical function will influence results.
6.5
Method of rating
There are three main scaling techniques used to measure the intensity of taste
samples: visual-analog scales, magnitude estimation (Meilgaard, Civille & Carr, 1991),
and the labeled magnitude scale (Green et al., 1996; Green, Shaffer & Gilmore, 1993).
Depending on the method utilized, the scale may expand or compress different portions
of the psychophysical curve. In addition, the experimental context and number of scales
and qualities simultaneously used can have an impact on final data (Frank et al., 1993;
Schifferstein, 1994a; Schifferstein, 1994b; Schifferstein & Frijters, 1992; Stillman, 1993).
7.0
Summary of current level of understanding and future directions
We have reviewed studies of taste-taste interaction as well as selected taste
psychophysical theories. In general, the literature supports the idea that three phases of a
psychophysical function may be used to predict how taste stimuli will behave when
mixed; low intensity/concentration mixtures tend to result in enhancement, medium
intensity/concentration tend to result in additivity, high intensity/concentration tend to
27
result in suppression. In making these conclusions, however, we recognize that there
exist several caveats. First, there is the possibility of chemical interactions occurring in
the matrix before contacting taste receptor cells. Second, there also exists the potential
for oral peripheral physiological interactions that occur at the taste receptor cell level that
will alter transduction such as occurs with the synergy of MSG and ribonucleotides and
the blocking of quinine’s bitterness by NaCl. Third, we recognize that the interactions
among qualities will be highly specific to the individual compounds involved.
Future psychophysical research on taste-taste interactions should focus on the
peripheral mechanisms that may alter taste. Also, as Table 1 shows, there are many gaps
in our knowledge of taste interactions. The discovery of putative receptors involved in
sweet ( Bachmanov et al., 2001; Kitagawa, Kusakabe, Miura, Ninomiya & Hino, 2001;
Li et al., 2001; Max et al., 2001; Montmayeur, Liberles, Matsunami & Buck, 2001;
Nelson et al., 2001; Sainz, Korley, Battey & Sullivan, 2001), umami/savory (Li et al.,
2002; Nelson et al., 2002), and bitter taste transduction (Adler et al., 2000;
Chandrashekar et al., 2000), has furthered interest in peripheral mechanisms of taste.
Potentially some of the most interesting taste interactions, such as synergies and
suppression, occur at the peripheral level. Psychophysical investigation of bitterness
suppression, salt and sweet taste enhancement and ‘flavor’ enhancement using MSG all
have the potential to elucidate mechanisms involved in taste transduction, and are
economically advantageous for the food, beverage or pharmaceutical industries. In
addition, more complex trinary or quaternary interactions will eventually need to be
studied for all the same reasons as given above.
28
References
Adler, E., Hoon, M., Mueller, K., Chandrashekar, J., Ryba, N., & Zuker, C. (2000). A
novel family of mammalian taste receptors. Cell, 100, 693-702.
Anderson, R. J. (1950). Taste thresholds in stimulus mixtures. Microfilm Abstracts, 10,
287-288.
Arabie, P., & Moskowitz, H. (1971). The effects of viscosity upon perceived sweetness.
Perception and Psychophysics, 9, 410-412.
Ayya, N., & Lawless, H. (1992). Quantitative and qualitative evaluation of high-intensity
sweeteners and sweetener mixtures. Chemical Senses, 17, 245-259.
Bachmanov, A., Li, X., Reed, D., Ohmen, J., Li, S., Chen, Z., Tordoff, M., de Jong, P.,
Wu, C., West, D., Chatterjee, A., Ross, D., & Beauchamp, G. (2001). Positional
cloning of the mouse saccharin preference (Sac) locus. Chemical Senses, 26: 925933.
Bartoshuk, L. M. (1975). Taste mixtures: Is mixture suppression related to compression?
Physiology and Behavior, 14, 643-649.
Bartoshuk, L. M., & Cleveland, C. T. (1977). Mixtures of substances with similar tastes.
A test of a psychophysical model of taste mixture interactions. Sensory
Proceedings, 1, 177-186.
Bartoshuk, L. M., Rennert, K., Rodin, J., & Stevens, J. C. (1982). Effects of temperature
on perceived sweetness of sucrose. Physiology and Behavior, 28, 905-910.
Beebe-Center, J. G., Rogers, M. S., Atkinson, W. H., & O'Connell, D. W. (1959).
Sweetness and saltiness of compound solutions of sucrose and NaCl as a function
of concentration of solutes. Journal of Experimental Psychology, 57, 231-234.
Bournazel, M. M. E., Keast, R. S. J., & Breslin, P. A. S. (2002). Taste interactions among
binary mixtures of bitter compounds. Paper presented at the Association of
Chemosensory Scientists Meeting, Sarasota.
Breslin, P. A., & Beauchamp, G. K. (1995). Suppression of bitterness by sodium:
variation among bitter taste stimuli. Chemical Senses, 20, 609-623.
Breslin, P. A., & Beauchamp, G. K. (1997). Salt enhances flavour by suppressing
bitterness. Nature, 387, 563.
Breslin, P. A. S. (1996). Interactions among salty, sour and bitter compounds. Trends in
Food Science and Technology, 7, 390-398.
Calvino, A., Garcia-Medina, M., Cometto-Muniz, J., & Rodriguez, M. (1993). Perception
of sweetness and bitterness in different vehicles. Perception and Psychophysics,
54, 751-758.
Calvino, A. M., Garcia-Medina, M. R., & Cometto-Muniz, J. E. (1990). Interactions in
caffeine-sucrose and coffee-sucrose mixtures: evidence of taste and flavor
suppression. Chemical Senses, 15, 505-519.
Calvino, A. M., & Garrido, D. (1991). Spatial and temporal behavior of bitter sweet
mixtures. Perception and Motor Skills, 73, 1216.
Cameron, A. T. (1947). The taste sense and the relative sweetness of sugars and other
sweet substances. Sci Rept, Sugar Research Foundation, NY, series 9.
29
Chandrashekar, J., Mueller, K., Hoon, M., Adler, E., Feng, L., Guo, W., Zuker, C., &
Ryba, N. (2000). T2Rs function as bitter taste receptors. Cell, 100, 703-711.
Christensen, C. M. (1980). Effects of solution viscosity on perceived saltiness and
sweetness. Perception and Psychophysics, 28, 347-353.
Cragg, L. H. (1937). The sour taste: threshold values and accuracy, the effects of saltiness
and sweetness. Trans R Soc Can, 31, 131-140.
Curtis, D. W., Stevens, D. A., & Lawless, H. T. (1984). Perceived intensity of the taste of
sugar mixtures and acid mixtures. Chemical Senses, 9, 107-120.
De Graaf, C., & Frijters, J. E. (1987). Sweetness intensity of a binary sugar mixture lies
between the intensities of its components, when each is tasted alone and at the
same total molarity as the mixture. Chemical Senses, 12, 113-129.
De Graaf, C., & Frijters, J. E. (1989). Interrelationships among sweetness, saltiness and
total taste intensity of sucrose, NaCl and sucrose/NaCl mixtures. Chemical
Senses, 14, 81-102.
Delwiche, J. F., Buletic, Z., & Breslin, P. A. S. (2001). Covariation in individuals'
sensitivities to bitter compounds: Evidence supporting multiple mechanisms.
Perception and Psychophysics, 63, 761-776.
Fabian, F. W., & Blum, H. B. (1943). Relative taste potency of some basic food
constituents and their competitive and compensatory action. Food Research, 8,
179-193.
Faurion, A. (1987). MSG as one of the sensitivities within a continuous taste space:
electrophysiological and psychophysical studies. In Y. Kawamura, & M. R. Kare,
Umami: a basic taste. New York: Marcel Dekker.
Feller, R. P., Sharon, I. M., Chauncey, H. H., & Shannon, I. L. (1965). Gustatory
perception of sour, sweet and salt mixtures using parotid gland flow rate. Journal
of Applied Physiology, 20, 1341-1344.
Frank, R. A., Mize, S. J. S., & Carter, R. (1989). An assessment of binary mixture
interactions for nine sweeteners. Chemical Senses, 14, 621-632.
Frank, R. A., van der Klaauw, N. J., & Schifferstein, H. (1993). Both perceptual and
conceptual factors influence taste-odor and taste-taste interactions. Perception
and Psychophysics, 54, 343-354.
Frijters, J. E., & Schifferstein, H. N. (1994). Perceptual interactions in mixtures
containing bitter tasting substances. Physiology and Behavior, 56, 1243-1249.
Fuke, S., & Konosu, S. (1991). Taste active components in some foods: a review of
Japanese research. Physiology and Behavior, 49, 863-868.
Gillan, D. J. (1982). Mixture suppression: The effect of spatial separation between
sucrose and NaCl. Perception and Psychophysics, 32, 504-510.
Gillan, D. J. (1983). Taste-taste, odor-odor, and taste-odor mixtures: greater suppression
within than between modalities. Perception and Psychophysics, 33, 183-185.
Gillette, M. (1985). Flavor effects of sodium chloride. Food Technology, 39, 47-56.
Glendinning, J. (1994). Is the bitter rejection response always adaptive? Physiology and
Behavior, 56, 1217-1227.
Green, B., Dalton, P., Cowart, B., Shaffer, G., Rankin, K., & Higgins, J. (1996).
Evaluating the 'Labeled Magnitude Scale' for measuring sensations of taste and
smell. Chemical Senses, 21, 323-334.
30
Green, B. G., Shaffer, G. S., & Gilmore, M. M. (1993). Derivation and evaluation of a
semantic scale of oral sensation magnitude with apparent ratio properties.
Chemical Senses, 18, 683-702.
Gregson, R. A. M., & McCowen, P. F. (1963). The relative perception of weak sucrosecitric acid mixtures. Journal of Food Science, 28, 371-378.
Hellemann, U. (1992). Perceived taste of NaCl and acid mixtures in water and bread.
International Journal of Food Science Technology, 27, 201-211.
Hopkins, J. W. (1953). Laboratory flavor scoring: two experiments in incomplete blocks.
Biometrics, 9, 1-21.
Indow, T. (1969). An application of the t scale of taste: interaction among the four
qualities of taste. Perception and Psychophysics, 5, 347-351.
Kamen, J. M. (1959). Interaction of sucrose and calcium cyclamate on perceived intensity
of sweetness. Food Research, 245, 279-282.
Kamen, J. M., Pilgrim, F. J., Gutman, N. J., & Kroll, B. J. (1961). Interactions of
suprathreshold taste stimuli. Journal of Experimental Psychology, 62, 348-356.
Keast, R. S. J., & Breslin, P. A. S. (2002a). Cross adaptation and bitter inhibition of Ltryptophan, L-phenylalanine and urea: Further support for shared peripheral
physiology. Chemical Senses, 27, 123-131.
Keast, R. S. J., Bournazel, M.M. E., & Breslin, P. A. S. (2002b). Bitterness Inhibition
Using the Bitter Compound Urea. Paper presented at the Association of
Chemosensory Scientists Meeting, Sarasota.
Keast, R. S. J., & Breslin, P. A. S. (2002c). Modifying the bitterness of selected oral
pharmaceuticals with cation and anion series of salts. Pharmaceutical Research,
19, 1019-1026.
Keast, R. S. J., Breslin, P. A. S., & Beauchamp, G. K. (2001). Suppression of bitterness
using sodium salts. Chimia, 55, 441-447.
Kemp, S. E., & Beauchamp, G. K. (1994). Flavor modification by sodium chloride and
monosodium glutamate. Journal of Food Science, 59, 682-686.
Kiesow, F. (1896). Philosoph Studien, 12, 255-278.
Kitagawa, M., Kusakabe, Y., Miura, H., Ninomiya, Y., & Hino, A. (2001). Molecular
genetic identification of a candidate receptor gene for sweet taste. Biochemical
and Biophysical Research Communications, 283, 236-242.
Kokini, J. L., Bistany, K., Poole, M., & Stier, E. F. (1982). Use of mass transfer theory to
predict viscosity-sweetness interactions of fructose and sucrose solutions
containing tomato solids. Journal of Text Study, 13, 187-200.
Kremer, J. H. (1917). Influence de sensations de gout sur d'autres specifiquement
differentes. Arch Neerl Physiol de l'Homme Animaux, 1, 625-634.
Kroeze, J. H. (1979). Masking and adaptation of sugar sweetness intensity. Physiology
and Behavior, 22, 347-351.
Kroeze, J. H. (1982). The influence of relative frequencies of pure and mixed stimuli on
mixture suppression in taste. Perception and Psychophysics, 31, 276-278.
Kroeze, J. H. (1990). The perception of complex taste stimuli. In R. L. McBride, & H. J.
H. MacFie, Psychological basis of sensory evaluation (pp. 41-68). London:
Elsevier.
Kroeze, J. H., & Bartoshuk, L. M. (1985). Bitterness suppression as revealed by splittongue taste stimulation in humans. Physiology and Behavior, 35, 779-783.
31
Lawless, H. T. (1979a). Evidence for neural inhibition in bitterness taste mixtures.
Journal of Comparative Physiology and Psychology, 93, 538-547.
Lawless, H. T. (1979b). The taste of creatine and creatinine. Chemical Senses and
Flavor, 4, 249-258.
Lawless, H. T. (1982). Adapting efficiency of salt-sucrose mixtures. Perception and
Psychophysics, 32, 419-422.
Li, X., Inoue, M., Reed, D., Huque, T., Puchalski, R., Tordoff, M., Ninomiya, Y.,
Beauchamp, G., & Bachmanov, A. (2001). High-resolution genetic mapping of
the saccharin preference locus (Sac) and the putative sweet taste receptor (T1R1)
gene (Gpr70) to mouse distal Chromosome 4. Mammalian Genome, 12, 13-16.
Li, X., Staszewski, L., Xu, H., Durick, K., Zoller, M., & Adler, E. (2002). Human
receptors for sweet and umami taste. Annals of the New York Academy of Science,
99, 4692-4696.
Lindemann, B. (2001). Receptors and transduction in taste. Nature, 413, 219-225.
Lyall, V., Heck, G., De, S. J., & Feldman, G. (1999). Effects of osmolarity on taste
receptor cell size and function. American Journal of Physiology, 277, C800-813.
Max, M., Shanker, Y., Huang, L., Rong, M., Liu, Z., Campagne, F., Weinstein, H.,
Damak, S., & Margolskee, R. (2001). Tas1r3, encoding a new candidate taste
receptor, is allelic to the sweet responsiveness locus Sac. Nature Genetics, 28, 5863
McBride, R. L. (1976). Temporal properties of the human taste system. Sensory
Proceedings, 1, 150-162.
McBride, R. L. (1986). The sweetness of binary mixtures of sucrose, fructose, and
glucose. Journal of Experimental Psychology, 12, 584-592.
McBride, R. L. (1988). Taste reception of binary sugar mixtures: psychophysical
comparison of two models. Perception and Psychophysics, 44, 167-171.
McBride, R. L. (1989). Three models for taste mixtures. In D. G. Laing, Perception of
complex smells and tastes (pp. 265-282). Australia: Academic Press.
McBride, R. L., & Finlay, D. (1990). Perceptual integration of tertiary taste mixtures.
Perception and Psychophysics, 48, 326-330.
McBurney, D. H., Smith, D. V., & Shick, T. R. (1972). Gustatory cross adaptation:
Sourness and bitterness. Perception and Psychophysics, 11, 228-232.
Meilgaard, M., Civille, G. V., & Carr, B. T. (1991). Sensory evaluation techniques. Boca
Raton: CRC Press.
Montmayeur, J., Liberles, S., Matsunami, H., & Buck, L. (2001). A candidate taste
receptor gene near a sweet taste locus. Nature Neuroscience, 4, 492-498.
Moskowitz, H. R. (1973). Models of sweetness additivity. Journal of Experimental
Psychology, 99, 88-98.
Moskowitz, H. R. (1974). Sourness of acid mixtures. Journal of Experimental
Psychology, 4, 640-647.
Nelson, G., Chandrashekar, J., Hoon, M., Feng, L., Zhao, G., Ryba, N., & Zuker, C.
(2002). An amino acid taste receptor. Nature, Advanced online publication,(24
February 2002).
Nelson, G., Hoon, M., Chandrashekar, J., Zhang, Y., Ryba, N., & Zuker, C. (2001).
Mammalian sweet taste receptors. Cell, 106, 381-390.
32
Oram, N., Laing, D., Freeman, M., & Hutchinson, I. (2001). Analysis of taste mixtures by
adults and children. Developmental Psychobiology, 38, 67-77.
Pangborn, R. M. (1960a). Influence of color on the discrimination of sweetness.
American Journal of Psychology, 73, 229-238.
Pangborn, R. M. (1960b). Taste interrelationships. Food Research, 25, 245-256.
Pangborn, R. M. (1961). Taste interrelationships II: Suprathreshold solutions of sucrose
and citric acid. Journal of Food Science, 26, 648-655.
Pangborn, R. M. (1962). Taste interrelationships III: Suprathreshold solutions of sucrose
and sodium chloride. Journal of Food Science, 27, 494-500.
Pangborn, R. M. (1965). Taste interrelationships of organic acids and selected sugars. In
J. M. Leitch, Proceedings of the first international congress of food science and
technology (pp. 291-305). New York: Gordon and Breach.
Pangborn, R. M. (1987). Selected factors influencing sensory perception of sweetness. In
J. Dobbing, Sweetness. London: Springer-Verlag.
Pangborn, R. M., Berg, H. W., & Hansen, B. (1963). The influence of color on
discrimination of sweetness in dry table wine. American Journal of Psychology,
76, 492-495.
Pangborn, R. M., & Chrisp, R. B. (1964a). Taste interrelationships VI: Sucrose, sodium
chloride, and citric acid in canned tomato juice. Journal of Food Science, 29, 490498.
Pangborn, R. M., Gibbs, Z. M., & Tassan, C. (1978). Effect of hydrocolloids on apparent
viscosity and sensory properties of selected beverages. Journal of Texture Studies,
9, 415-436.
Pangborn, R. M., & Hansen, B. (1963). The influence of color on discrimination of
sweetness and sourness in pear-nectar. American Journal of Psychology, 76, 315317.
Pangborn, R. M., Ough, C. S., & Chrisp, R. B. (1964b). Taste interrelationships of
sucrose, tartaric acid, and caffeine in white table wine. Journal of the American
Society of Enology and Viticulture, 15, 154-161.
Pangborn, R. M., & Trabue, I. M. (1964c). Taste interrelationships V: Sucrose, sodium
chloride, and citric acid in lima bean puree. Journal of Food Science, 29, 233-240.
Pangborn, R. M., & Trabue, I. M. (1967). Detection and apparent taste intensity of saltacid mixtures in two media. Perception and Psychophysics, 2, 503-509.
Pangborn, R. M., Trabue, I. M., & Szczesniak, A. S. (1973). Effect of hydrocolloids on
oral viscosity and basic taste intensities. Journal of Texture Studies, 4, 224-241.
Prescott, J., Ripandelli, N., & Wakeling, I. (2001). Binary taste mixture interactions in
PROP non-tasters, medium-tasters and super-tasters. Chemical Senses, 26, 9931004.
Rifkin, B., & Bartoshuk, L. (1980). Taste synergism between monosodium glutamate and
disodium 5'-guanylate. Physiology and Behavior, 24, 1169-1172.
Sainz, E., Korley, J., Battey, J., & Sullivan, S. (2001). Identification of a novel member
of the T1R family of putative taste receptors. Journal of Neurochemistry, 77, 896903
Schifferstein, H. (1994a). Contextual effects in the perception of quinine HCl / NaCl
mixtures. Chemical Senses, 19, 113-123.
33
Schifferstein, H. N. (1994b). Sweetness suppression in fructose/citric acid mixtures: A
study of contextual effects. Perception and Psychophysics, 56, 227-237.
Schifferstein, H. N. (1995). Prediction of sweetness intensity for equiratio
aspartame/sucrose mixtures. Chemical Senses, 20, 211-219.
Schifferstein, H. N. (1996). An equiratio model for non-additive components: a case
study for aspartame/acesulfame-K mixtures. Chemical Senses, 21, 1-11.
Schifferstein, H. N. (1997). Perceptual and imaginary mixtures in chemosensation.
Journal of Experimental Psychology, 23, 278-288.
Schifferstein, H. N., & Frijters, J. E. (1990). Sensory integration in citric acid/sucrose
mixtures. Chemical Senses, 15, 87-109.
Schifferstein, H. N., & Frijters, J. E. (1992). Contextual and sequential effects on
judgements of sweetness intensity. Perception and Psychophysics, 54, 343-354.
Schifferstein, H. N., & Frijters, J. E. R. (1993). Perceptual integration in heterogeneous
taste percepts. Journal of Experimental Psychology, 19, 661-675.
Schifferstein, H. N., & Kleykers, R. W. G. (1996). An empirical test of Olsson's
interaction model using mixture tastants. Chemical Senses, 21, 283-291.
Schiffman, S., Gill, J., & Diaz, C. (1985). Methyl xanthines enhance taste: evidence for
modulation of taste by adenosine receptor. Pharmacology Biochemistry and
Behavior, 22, 195-203.
Schiffman, S. S., Booth, B. J., Carr, B. T., Losee, M. L., Sattely-Miller, E. A., & Graham,
B. G. (1995). Investigation of synergism in binary mixtures of sweeteners. Brain
Research Bulletin, 38, 105-120.
Schiffman, S. S., Frey, A. E., Luboski, J. A., Foster, M. A., & Erickson, R. P. (1991).
Taste of glutamate salts in young and elderly subjects: role of inosine 5'monophosphate and ions. Physiology and Behavior, 49, 843-854.
Schiffman, S. S., & Gatlin, C. A. (1993). Sweeteners: State of the knowledge review.
Neuroscience and Biobehavioral Reviews, 17, 313-345.
Schiffman, S. S., Gatlin, L. A., Sattely-Miller, E. A., Graham, B. G., Heiman, S. A.,
Stagner, W. C., & Erickson, R. P. (1994). The effect of sweeteners on bitter taste
in young and elderly subjects. Brain Research Bulletin, 35, 189-204.
Schiffman, S. S., Sattely-Miller, E. A., Graham, B. G., Bennett, J. L., Booth, B. J., Desai,
N., & Bishay, I. (2000). Effect of temperature, pH, and ions on sweet taste.
Physiology and Behavior, 68, 469-481.
Shallenberger, R. S. (1993). Taste chemistry principles. In R. S. Shallenberger, Taste
Chemistry. Cambridge: Chapman and Hall.
Sjostrom, L. B., & Cairncross, S. E. (1953). Role of sweeteners in food flavor. Advances
in Chemistry Series, 108-113.
Stevens, J. (1995). Detection of heteroquality taste mixtures. Perception and
Psychophysics, 57, 18-26.
Stevens, J. (1997). Detection of very complex taste mixtures: generous integration across
constituent compounds. Physiology and Behavior, 62, 1137-1143.
Stevens, J., & Traverzo, A. (1997). Detection of a target taste in a complex masker.
Chemical Senses, 22, 529-534.
Stevens, S. S. (1969). Sensory scales of taste intensity. Perception and Psychophysics, 6,
302-308.
34
Stillman, J. (1993). Context effects in judging taste intensity: A comparison of variable
line and category rating methods. Perception and Psychophysics, 54, 477-484.
Stone, H., & Oliver, S. (1966). Effect of viscosity on the detection of relative sweetness
intensity of sucrose solutions. Journal of Food Science, 31, 129-134.
Stone, H., & Oliver, S. M. (1969). Measurement of relative sweetness of selected
sweeteners on their sweetener mixtures. Journal of Food Science, 34, 215-222.
Stryer, L. (1988). Introduction to enzymes. In L. Stryer, Biochemistry (pp. 187-195). New
York: W.H. Freeman.
von Skramlik, E. (1962). Uber die erscheinungen der positiven und negativen
unterdruckung beim geschmackssinne. Z Biology, 113, 266-292.
Woskow, M. H. (1969). Selectivity in flavor modification by 5'-ribonucleotides. Food
Technology, 23, 32-37.
Yamaguchi, S. (1967). The synergistic taste effect of MSG and disodium 5'-inosinate.
Journal of Food Science, 32, 473-478.
Yamaguchi, S. (1987). Fundamental properties of umami in human taste sensation. In Y.
Kawamura, & M. R. Kare, Umami: a basic taste (41-73). New York: Marcel
Dekker.
Yamaguchi, S. (1991). Basic properties of umami and effects on humans. Physiology and
Behavior, 49, 833-841.
Yamaguchi, S., Yoshikawa, T., Ikeda, S., & Ninomiya, T. (1970). Studies on some sweet
substances. II. Interrelationships among them. Agricultural and Biological
Chemistry, 34, 187-197.
Yokomukai, Y., Cowart, B. J., & Beauchamp, G. (1993). Individual differences in
sensitivity to bitter tasting substances. Chemical Senses, 18, 669-681.
Zuntz, N. (1892). Beitrag zur physiologie des geschmacks. Archives Anatomy and
Physiology, Physiology Abstracts, 556.
35
Table
Table 1
Subjective numerical scale (0 to 9) representing current knowledge of
specific binary taste interactions
Sour
Bitter
Salty
Sweet
Sour
0.5
Bitter
2
0.5
Salty
1
3
0.5
Sweet
4
4
4
6
Savory
0.5
1
3
2
Savory
4
Numerical scale 0-9
0
No relevant literature on binary interaction
9
Comprehensive literature on binary interaction
36
List of Figures
Figure 1
Three examples of psychophysical curves. Curve A is a theoretical
psychophysical curve from the auditory system. Curves B and C are theoretical
psychophysical curves from the taste system. The auditory function exponentially
increases with increasing dB. The taste functions show an asymptote at maximum taste
intensity. The y axis represents perceived intensity and the x-axis represents physical
intensity.
Figure 2
Theoretical psychophysical concentration-intensity function for sapid
compound. Concentration of the taste compound is plotted along the X axis, and
perceived taste intensity is plotted along the Y axis. As the physical concentration of a
compound increases, the perceived intensity elicited by that compound also increases but
at varying rates. The curve can take on a sigmoidal shape; at very low concentrations of
sapid compound the taste intensity can grow in exponential fashion, at medium
concentration the perceived intensity can increase in linear fashion, at higher
concentrations the perceived intensity may plateau. Three specific regions of a typical
psychophysical concentration intensity function. Stevens power law (Stevens, 1969) can
be applied to taste:
I=kCn
where I is the perceived intensity, k is a constant related to the tastant, C is the
concentration of the taste compound, and n is the exponential variable associated with the
37
shape of the curve. The three regions correspond to expansive (1), linear (2), and
compressive (3) (Bartoshuk, 1975). The expansive region should result in hyperaddivity
of intensity when low concentrations of compounds are added together. The linear (2)
region is in the middle of the psychophysical function and should result in intensity
additivity when two concentrations within this range are added together. The
compressive (3) region is found in the upper portion of the psychophysical function,
when two concentrations from this region are added together we expect to see
suppression of the expected intensity. When co-ordinates are plotted in log-log, the
exponent n from Stevens’s power law represents the shape of the line for each phase. For
the expansive phase the exponent is greater than 1, for the linear phase the exponent is
equal to 1, and for the compressive phase the exponent is less than 1.
Figure 3
Graphic example of two hyperbolic psychophysical functions (Compound
A and Compound B) transformed to a sigmoid on mixing (Compound A:B, 50:50 ratio).
Figure 4
Effect of taste mixtures on psychophysical curve. Changes in slope or
maximum height of psychophysical curves show inhibition or synergy. Curve E
represents the concentration response of a sapid compound plot against increasing
concentrations of the compound. To the left of curve E, curve D shows an increase in
slope with an additive. This suggests synergy is occurring between the sapid compound
and the additive. Curve D’ shows the maximum intensity is elevated above what the
sapid compound can stimulate alone. To the right of curve E, curve F shows a decrease
38
of slope when mixed with an additive. This suggests that masking or inhibition is
occurring. Curve F’ shows suppression of maximum achievable intensity.
Figure 5
Non-monotonic and asymmetrical interactions between compounds with different
primary tastes. Compound J is a sweet compound and its theoretical psychophysical
function for sweetness is shown in the upper panel (bold black line). The lower panel is
the theoretical salt intensity psychophysical function for salty compound L. The upper
shows the psychophysical function for sweetness when the two compounds are mixed
(dashed black line). The arrowhead points to the new sweetness intensity of the binary
mixture of J and L; the blunt end of the arrow indicates the concentration and salt
intensity of added compound L. At low concentration of compound J and L there is
enhancement of sweetness, at moderate concentration there is no effect on sweetness and
at high concentrations of J and L there is suppression of sweetness. The lower panel
shows mixing compound J and L at low concentration causes suppression of saltiness, at
moderate concentration a slight enhancement of saltiness, and no effect on saltiness at
high concentration. These theoretical data illustrate that one may not always be able to
use the form of the function to predict the outcome of mixture, as in the bottom panel.
Figure 6a,b,c
Schematic review of binary taste interactions. A represents a review of interactions of
taste qualities from the expansive portion of the curve, B represents the linear phase and
C the compressive phase.
Research investigating taste-taste interactions is variable for a
39
number of reasons (see text) and the schematic reviews are merely indications of what
happens to taste qualities when 2 are mixed together (Anderson, 1950; Bartoshuk, 1975;
Beebe-Center et al., 1959; Breslin et al., 1995; Breslin, 1996; Calvino et al., 1990;
Calvino et al., 1991; Cameron, 1947; Cragg, 1937; De Graaf et al., 1989; Fabian & Blum,
1943; Feller, Sharon, Chauncey & Shannon, 1965; Frank et al., 1993; Frijters et al., 1994;
Gillan, 1983; Gillette, 1985; Gregson & McCowen, 1963; Hellemann, 1992; Hopkins,
1953; Indow, 1969; Kamen et al., 1961; Keast et al., 2002b, c; Kremer, 1917; Kroeze,
1982; Kroeze et al., 1985; Lawless, 1979a; McBride & Finlay, 1990; Pangborn, 1960b,
1961, 1962, 1965; Prescott et al., 2001; Schifferstein et al., 1990; Schifferstein et al.,
1993; Schiffman et al., 1985; Schiffman et al., 1994; Schiffman et al., 2000; Sjostrom &
Cairncross, 1953; Stevens, 1995; von Skramlik, 1962; Yokomukai et al., 1993; Zuntz,
1892).
Figure 7
Graphic example of assessing potential synergy between two compounds
A & B. A psychophysical function for Compound A was plotted. To assess interactions
between the two compounds, a set concentration of B’ corresponding to a weak intensity
was added along the function of the compound A and the intensity plotted ([A]+B’). In
order to make a fair comparison, a set concentration corresponding to a weak intensity of
compound A (A’, the concentration corresponding to weak intensity is shown by arrow)
is added to itself and plotted ([A]+A’) (the psychophysical curve is shifted left and up).
The [A]+B’ curve is compared to the [A]+A’ self-addition curve. The shift of the
[A]+B’curve to the left of [A]+A’ curve demonstrates an enhancement of taste intensity.
40
30
Perceived Intensity
25
20
15
10
Curve A, exponential
Curve B, sigmoidal
Curve C, hyperbolic
5
0
Physical Intensity
41
Compressive
3
Linear
2
Expansive
1
Concentration
Y=kX>1
Y=kX1
Y=kX<1
42
25
20
Intensity
15
10
Compound A
Compound B
Compounds A:B 50:50 mix
5
0
Concentration
43
D’
Synergy
F’
D
E
F
Suppression
Concentration
D
E
F
Changes in slope of linear phase
D1
E
F1
Left and right shift of linear phase
44
Concentration [J]
Concentration [L]
45
Low intensity/concentration
Sweet
nil effect
variable
variable
enhanced
enhanced
Salty
Sour
suppressed
enhanced
enhanced
variable
Bitter
46
Medium intensity/concentration
suppressed
Sweet
suppressed
suppr essed
variable
variable
enhanced
Salty
suppressed
Sour
suppressed
enhanced
nil effect
Bitter
47
High intensity/concentration
nil effect
Sweet
suppressed
Suppressed
nil effect
Suppr essed
Suppressed
nil effect
Salty
Sour
suppressed
variable
nil effect
suppressed
Bitter
48
20
Intensity
15
10
Compound A
mix [A]+A'
mix [A]+B'
5
0
0
5
10
15
20
A’
25
B’ 30
Concentration [A]
49