Chemical Senses Vol. 29 No. 8 © Oxford University Press
2004; all rights reserved
Sour Taste Preferences of Children Relate to Preference for Novel and Intense Stimuli
Division of Human Nutrition, Wageningen Taste & Smell Centre, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands
Correspondence to be sent to: Djin Gie Liem, Division of Human Nutrition, Wageningen Taste & Smell Centre, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands. e-mail: djin-gie.liem{at}wur.nl
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Previous research has suggested that some children have a preference for sour tastes. The origin of this preference remains unclear. We investigated whether preference for sour tastes is related to a difference in rated sour intensity due to physiological properties of saliva, or to an overall preference for intense and new stimuli. Eighty-nine children 7–12 years old carried out a rank-order procedure for preference and category scale for perceived intensity for four gelatins (i.e. 0.0 M, 0.02 M, 0.08 M, 0.25 M added citric acid) and four yellow cards that differed in brightness. In addition, we measured their willingness to try a novel candy and their flow and buffering capacity of their saliva. Fifty-eight percent of the children tested preferred one of the two most sour gelatins. These children had a higher preference for the brightest color (P < 0.05) and were more likely to try the candy with the unknown flavor (P < 0.001) than children who did not prefer the most sour gelatins. Preference for sour taste was not related with differences in rated sour intensity, however those who preferred sour taste had a higher salivary flow (P < 0.05). These findings show that a substantial proportion of young children have a preference for extreme sour taste. This appears to be related to the willingness to try unknown foods and preference for intense visual stimuli. Further research is needed to investigate how these findings can be implemented in the promotion of sour-tasting food such as fruit.
Key words: citric acid, color, hedonics, intensity, saliva, sensation seeking
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionAcknowledgementsReferences |
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The food choices of children in industrialized countries are an important determinant of the development of obesity during childhood (Ricketts, 1997
;
Ludwig et al., 2001).
Children’s food choices are for the most part determined by their taste preferences
(Olson and Gemmill, 1981;
Pangborn and Giovanni, 1984;
Michela and Contento, 1986;
Liem and Mennella, 2002, 2003;
Perez-Rodrigo et al.,
2003).
Since the late 1960s researchers have been trying to understand the sensory-taste
world of young children (Cowart,
1981). In the past four decades the investigations were mainly focused on
sweet, salt and, more recently, bitter taste (for a review, see
Birch, 1999). However, little research
has focused on preference for sour taste.
Darwin (1877) noted that his children
had a preference for this taste quality. A systematic scientific investigation of sour
taste preferences of children, however, has not been carried out until recently. To our
knowledge,
Liem and Mennella (2003) were the
first to show that a substantial proportion of children (5–9 years old) they tested
had a preference for high concentrations of citric acid in gelatin, which were perceived
as extremely sour by their parents.
The basis of these sour taste preferences remains unknown. One hypothesis is that
children who have a preference for high concentrations of citric acid in foods, rate this
as less sour compared to those who do not prefer these concentrations of citric acid. In
order to achieve a similar sensation, those who rate a lower intensity need more
stimulation of sour taste. In adults it has been suggested that a high salivary flow
(Spielman, 1990), high buffering
capacity of saliva (Christensen et al.,
1987) and low salivary pH (Norris
et al., 1984) are related to a lowrated intensity of sour-tasting
foods.
An alternative, but not mutually exclusive, hypothesis is that preference for sour
taste is secondary to their desire for adventures, thrills and excesses (Frauenfelder, 1999;
Urbick, 2000). In this view,
preference for sour taste might be related to preference for unfamiliar foods and intense
stimuli perceived by other senses such as vision (e.g. bright colors). More generally,
preference for sour taste might be related to an overall thrill-seeking behavior.
Research suggests that this behavior is reflected by the rise in cortisol after
encountering a challenging or stressful situation. That is, the increase in cortisol
concentration in saliva, shortly after encountering a challenging or stressful situation,
is larger for thrill-seekers compared with non-thrill-seekers (Gunnar et al., 1997;
Davis et al., 1999;
Donzella et al., 2000).
The present study had two main objectives. First, we investigated whether children who preferred sour taste rated sourness as less intense. This might be due to a high salivary flow, a high buffering capacity of saliva and/or a low salivary pH. Secondly, we investigated whether children who preferred sour taste are more likely to prefer intense colors, to try new foods and/or are more thrill-seeking in general, than those who do not prefer this taste.
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Materials and methods |
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Subjects
Parents of 116 children were invited to participate in the study. They received a brochure with information that explained the procedures of the research. Parents of 92 children signed the informed consent. All children attended one of the two primary schools where the study was carried out. Exclusion criteria for participation were diabetes, sugar restriction in the diet, presumed allergies for one of the test stimuli and color blindness. In addition, subjects with non-removable braces (n = 3) were excluded from participation, because of the use of chewing gum during the test procedure. The final sample of subjects who participated in the study consisted of 89 children (40 females and 49 males) ranging in age from 7 to 12 years (mean = 10.3 ± 1.0 years; see Table 1). The study protocol was approved by the Medical Ethical Committee of Human Nutrition of Wageningen University.
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General overview
The present study involved a training session and 2 days of testing. During the training session, children were trained in recognizing sweet, sour, salt and bitter tastes. During the 2 days of testing, separated from the training session by 2 days, the children carried out a variety of sensory tests. These tests were conducted at the children’s primary school in a room that was familiar to them. This room conisted of 10 low tables, each separated by a screen that prevented the children from seeing each other during testing. Children had personal guidance from a trained adult who sat in front of them.
The first day of testing aimed to determine children’s preference (±5 min) and rated sourness (±5 min) for four gelatins that varied in the amount of added citric acid. After a 5 min break, during which we measured children’s weight and height, we determined children’s willingness to try a novel food. We subsequently took a salivary sample, in order to determine the pH and cortisol concentrations of children’s saliva.
The second day of testing started with a second salivary sample. After this we tested children’s preference and perceived brightness for four yellow-colored squares that varied in brightness. Furthermore, we measured the buffering capacity and flow rate of the children’s saliva. The order of testing (i.e. preference–intensity versus intensity–preference) was balanced across subjects.
Stimuli
Gelatins
The gelatins were sweet lemon flavored (Rowntrees Wobbly Fruity Fun; Nestlé,
UK) with different amounts of added citric acid (0.00, 0.02, 0.08 and 0.25 M; Sigma
Chemical Co., St Louis, MO). Similar stimuli were previously used by
Liem and Mennella (2003). Twenty
milliliters of each gelatin were poured into a 30 ml clear medicine cup and refrigerated
at 4°C for at least 4 h to obtain firmness. They were transported in boxes at a
constant temperature of 4°C. Several minutes before the actual test began, the
gelatins were removed from the boxes and presented to the subjects.
Colors
The four colors were printed on small (5 x 5 cm) squares and were placed on
larger (7 x 7 cm) white colored squares. The squares were of different intensities
of the color yellow (soft yellow (SOY), lemon yellow (LY), canary yellow (CY) and sulphur
yellow (SY) (Modo van Gelderen, Amsterdam, The Netherlands) and were used to measure
children’s preference and perceived brightness of colors. The colors were all
different in brightness according the judgements of six adults (30 ± 8.2 years,
three female and three males). From least intense to most intense, all adults but one
placed the colors in the following order: SOY, LY, CY, SY.
Training session
In order to ensure that children were able to recognize sweet, sour, salt and bitter tastes, they were presented with 10 ml of a sweet solution (20% w/v sucrose in water), a sour solution (30% w/v natural lemon juice in water), a salt solution (20% w/v NaCl in water) and a bitter solution (tonic water; Schweppes International Ltd, Amstelveen, The Netherlands). After tasting each solution, the researcher asked the children whether it was sweet, sour, salty or bitter. The majority of the children were able to correctly identify the different solutions.
Preference test
Preferences for the different gelatins and colors were measured with a
rank-by-elimination procedure (Birch,
1999). Subjects tasted the four gelatins in a random order, after which the
researcher asked: ‘Which one do you like most?’ The children could either
tell or point at the gelatin that was most preferred. This was then removed and after
this subjects were asked to taste the remaining three gelatins again. Subsequently, the
researcher asked: ‘Which one of these three do you like most?’ This procedure
continued until a rank-order of preference was established. In order to determine
reliability, children were asked to rank the four gelatins again according to their
preference. After tasting each gelatin, subjects drank a sip of water. The same procedure
was followed for the four different colors, with the difference that subjects did not
drink a sip of water after each stimulus.
The results of the rank-order test gave insight into how the different gelatins were preferred relative to each other. In order to have a direct measurement of preference, subjects were presented with two pictures, a smiley face and sad face. The researcher told the children the following: ‘I am going to give you one gelatin. If you like the taste I want you to give it to ‘smiley face’. If you do not like the taste, I want you to give it to ‘sad face’. Subsequently, the researcher gave the children the gelatin with no added citric acid. After tasting each gelatin, the subjects drank a sip of water
Rated sourness/brightness test
During a child-friendly game, children were presented with each of the four gelatins in a random order. Children rated each gelatin on perceived sourness using a five-point-category scale. The five categories were labeled ‘not sour at all’, ‘a little bit sour’, ‘sour’, ‘very sour’ and ‘extremely sour’. Before the actual test began, the researcher explained the game by explaining each category of the five-point scale. After subjects rated the four gelatins on perceived sourness, the gelatin with 0.08 M added citric acid was presented again in order to determine consistency of the test. A similar procedure was followed for the four different colors, in which the five-point category scale was labeled, ‘not bright at all’, ‘a little bit bright’, ‘bright’, ‘very bright’ and ‘extremely bright’. In order to test consistency, the color CY was presented twice.
Willingness to try a novel food
In order to test children’s willingness to try a novel food, children were
presented with three identical white opaque cups in a randomized order. The cups were
labeled with ‘z’, ‘y’ and ‘x’ and placed up-side
down. The researcher explained the test by saying: ‘Under each cup a candy is
hidden. Each candy had its own taste. Under cup ‘z’ a candy with a strawberry
flavor is hidden, under cup ‘y’ a candy with a raspberry flavor is hidden and
under cup ‘x’ a candy with a mysterious flavor is hidden.’ The subjects
could not see the actual candies that were hidden inside the different cups. After the
researcher clarified the content of each cup, the subjects were told that they were
allowed to pick one candy to try. They could either point to the cup or tell the research
which one they wanted to try. A similar procedure was used by
Raudenbush et al.
(1998).
Collection of saliva
Salivary production was stimulated by having the child chew on sugarless gum (Freedent
Menthol without sugar; Wrigley, France). Before the collection started, children were
asked to rinse their mouth with water and to swallow the saliva left in their mouth.
Subsequently, children were instructed to chew for 30 s on a piece of sugarless gum,
without swallowing any saliva. After these 30 s, they expectorated their saliva directly
in plastic tubes (Schwartz et al.,
1998). This procedure continued until at least 4 ml saliva was collected. If
after 5 min the collected saliva did not reach a total of at least 4 ml, the collection
was terminated. A similar procedure was previously used by
Schwartz et al. (1998).
Saliva was stored on dry ice and transported to the laboratory for the measurement of pH
and cortisol concentration.
pH was measured by using non-bleeding pH indicator strips (pH 6.5–10.0; Merck, Darmstadt, Germany). Salivary cortisol concentrations were measured by the LDN Cortisol saliva test (DSL Diagnostic Laboratory Systems, Houston, TX)
Overall thrill-seeking behavior
In order to measure general thrill-seeking behavior in children, salivary cortisol was measured in a stress situation (hereafter referred to as stress-cortisol) and a non-stress situation (hereafter referred to as baseline-cortisol). We expected the children to be in a stress/challenge situation during the first day of testing due to the novelty of the sensory tests. The baseline-cortisol was measured at the beginning of the second day of testing. We expected the cortisol in saliva to be at baseline, because the measurement took place at the start of the stressor/challenge (sensory tests).
Salivary flow and buffering capacity
Before the measurement of salivary flow and buffering capacity, children were asked to
rinse their mouth with water and to swallow the saliva left in their mouth. Salivary flow
and buffering capacity was determined by having children rinse their mouth for 30 s with
10 ml citric acid solution (0.03 M citric acid, pH 2.5; Sigma Chemical Co., St Louis,
MO), after which they expectorated the citric acid solution into a plastic cup.
Subsequently, we measured the pH (Piccolo II; Hanna Instruments, Bedfordshire, UK) and
weight (Sartorius GmbH, Göttingen, Germany) of the expectorated solution. A similar
procedure was previously used by
Dawes et al. (2000). The
buffering capacity of saliva was defined as:
(pH after rinsing – pH before rinsing)/(volume of solution after rinsing – volume of solution beforre rinsing).
Statistical procedure
Sour taste preference and rated intensity
Subjects were divided into two groups based on their sour preferences. Subjects who
classified at least one of the two most sour gelatins as their most-preferred or
second-most-preferred were grouped in the High-sour group. The remaining subjects were
grouped in the Low-sour group. Reliability of the preference test for gelatins was
defined as the percentage of subjects that were grouped in the High- or Low-sour group
based on the first and the second preference ranking. Chi-square tests were conducted to
determine differences between the two groups in terms of the distribution of boys and
girls and differences in preference during the direct measurement of preference.
Student’s t-tests were used to determine differences in age, height,
weight and body mass index (BMI). Wilcoxon analyses (Z) were conducted to
determine differences between the first and the second intensity ratings for sour taste.
Separate Friedman two-way analyses of ranks were performed to determine differences
between the High- and Low-sour groups in intensity rank-order. When significant, multiple
comparisons were carried out to determine which differences were significant (Siegel and Castellan, 1988). Student’s
t-tests determined differences in salivary pH, salivary flow rate and buffering
capacity of saliva.
Sour taste preference, color preferences and thrill-seeking behavior
Reliability for the preference test for colors was defined as the percentage who
preferred the brightest color during both the first and the second rankings. Wilcoxon
analyses (Z) were conducted to determine differences between the first and the
second intensity ratings for color. Mann–Whithney U-tests were performed
to determine differences in preference for the four colors, between the High-and Low-sour
groups. Chi-square tests were conducted to determine differences in children’s
willingness to try a novel food. Log transformations were applied to the cortisol
concentrations in order to normalize the data. Student’s t-tests were
carried out to determine differences in cortisol concentrations. All summary statistics
are expressed as means ± SD.
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Results |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionAcknowledgementsReferences |
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Sour taste preferences and subject characteristics
Fifty-two children (58%) preferred one of the two most sour gelatins as either
their most- or second-most-preferred gelatin (the High-sour group). The consistency
between the first and the second rank-order was 91%. Subjects in the High-sour
group showed an inverse U-shaped curve for preference with an increasing concentration of
added citric acid. The most-preferred stimulus was the gelatin with 0.08 M added
citric acid. Subjects in the Low-sour group showed a decrease in preference with an
increase in concentration of added citric acid (see Figure
1, panel a). Ninety-five percent of
the children in the Low-sour group and 65% of the children in the High-sour group
gave the gelatin with no added citric acid to ‘happy face’. This was
significantly different [ 
2(1 df) = 10.6, P <
0.01]. Children in the High- and Low-sour groups were not significantly different in
age [t(84 df) = 1.3, P = 0.18], BMI
[t(87 df) = 1.0, P = 0.30] or proportion of
boys to girls [ 2(1 df) = 1.1, P = 0.31; see
Table
1].
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Rated sour intensity
Children did not rate the perceived sourness of the gelatin with 0.08 M added citric acid significantly differently during the two times this gelatin was presented (Z = –3.0, P = 0.76). No differences between the High- and Low-sour groups were observed in the rated sourness of any of the gelatins (no added citric acid, U = 868.0, P = 0.32; 0.02 M added citric acid, U = 960.0, P = 0.99; 0.08 M added citric acid, U = 899.0, P = 0.59; 0.25M added citric acid, U = 918.5, P = 0.80; see Figure 1, panel b). Children in both groups recognized differences in sourness across the four gelatins (Low-sour, Fr = 128.0, P < 0.001; High-sour: Fr = 181.8, P < 0.001). Post hoc analyses revealed that the gelatins with 0.08 M and 0.25 M added citric acid were rated as the most intense gelatins by children in the Low-sour group and High-sour groups (P-values < 0.05; see Figure 1, panel b).
Salivary flow, pH and buffering capacity
Children in the High-sour group produced significantly more saliva after stimulation
with water with added citric acid than children in the Low-sour group [High-sour,
1.8 ± 1.0 g; Low-sour, 2.3 ± 0.8 g; t(79 df) = –2.4,
P < 0.05]. No differences, between the Low-and High-sour groups were
observed between the salivary pH [High-sour, 7.2 ± 0.12; Low-sour, 7.2
± 0.12; t(85 df) = 0.01, P = 0.99] and the pH
of the sour solution after subjects rinsed their mouth with this solution
[t(79 df) = –1.23, P = 0.22]. Children in
the High-sour group, however, had a significantly lower buffer capacity of their saliva
than children in the Low-sour group [High-sour, 0.18 ± 0.07 (
pH/ml
produced saliva); Low-sour, 0.33 ± 0.44 (pH/ml produced saliva);
t(79 df) = 2.3, P < 0.05].
Color preferences and rated brightness
Children in the High-sour group were more likely to judge the SY color as their most
favorite than children in the Low-sour group [High-sour, 75%; Low-sour,
51%, 2(1 df) = 5.1, P < 0.05; see Figure
2, panel a]. Children in both the
Low-and High-sour groups recognized differences in brightness across the four colors
(Low-sour, Fr = 103.1, P < 0.001; High-sour,
Fr = 56.8, P < 0.001). Post hoc analyses
revealed that the CY and SY colors were rated as the most intense by children in the
Low-sour group and High-sour group (P-values < 0.05; see Figure
2, panel b). A significant difference
was found between the first (3.1 ± 0.9) and the second time (3.4 ± 1.1)
children rated the CY color on perceived brightness (Z = 2.8, P
< 0.01).
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Willingness to try a novel food and overall thrill-seeking behavior
The candy with the unknown flavor was chosen significantly more often by children in
the High-sour group (67%) than by children in the Low-sour group [36%
(2(1 df) = 7.6, P < 0.001].
Children aged 7–10 years did not show a significant difference between their stress-cortisol and baseline-cortisol concentrations [Low-sour, t(27 df) = –0.80, P = 0.43; High-sour, t(39 df) = –1.4, P = 0.16]. Children aged 11–12 years, however, did show a significant lower baseline-cortisol concentration than stress-cortisol concentration [Low-sour, baseline 0.52 ± 0.04 ng/ml, stress 0.73 ± 0.06 ng/ml, t(13 df) = 3.2, P < 0.01; High-sour, baseline 0.67 ± 0.06 ng/ml, stress 0.94 ± 0.09 ng/ml, t(22 df) = 2.9, P < 0.01].
Children in the Low- and High-sour groups were not statistically different with respect to baseline-cortisol [0.69 ± 0.38 ng/ml versus 0.74 ± 0.46 ng/ml; t(85 df) = -1.5, P = 0.60] or stress-cortisol [0.69 ± 0.35 ng/ml versus 0.81 ± 0.39 ng/ml; t(87 df) = -1.5, P = 0.14]. The difference between baseline-cortisol and stress-cortisol concentration was also not different between the Low-sour group and the High-sour group [t(35 df) = 0.15, P = 0.88].
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Discussion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionAcknowledgementsReferences |
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The results of the present study suggest that young children’s preference for sour taste is more likely to be related to behavioral determinants than differences in rated sourness as measured with a five-point category scale. Salivary flow may play a role in the preference for sour taste, but a high salivary flow is not related to large differences in rated sourness in children who prefer this taste.
In the present study preferences for sour taste were measured by a
rank-by-elimination procedure. Previous research showed that this is a reliable method to
measure taste preferences of young children (Guinard, 2001;
Liem et al., 2004).
Moreover, children in the present study showed a high consistency between the two times
they rank-ordered the gelatins according to their preference. The finding that a
substantial part of the children tested (58%) had a preference for high
concentrations of citric acid in gelatin, is in line with a previous study (Liem and Mennella, 2003). In the present study
sour taste was defined as gelatins with added citric acid concentrations of 0.08 or 0.25
M. In general children rated these gelatins between sour and extremely sour. It is likely
that those who preferred sour taste during our sensory tests also preferred this taste
outside the testing environment, as suggested by previous research (Moskowitz et al., 1975;
Liem and Mennella, 2003). This could
be beneficial for the consumption of citrus fruit, which are in general high in vitamin C
content. In the present study children, who preferred sourness in gelatins, appeared not
to prefer the gelatins with no added citric acid. Supposedly, these gelatins were too
bland in taste for those who preferred sour taste.
As shown in the present study, preference for sour taste was not related to a difference in rated sour intensity as measured with a five-point category scale. The consistency between the first and second time subjects rated the gelatin with 0.08 M added citric acid on perceived sourness, suggests the consistency of the testing procedure. Moreover, in general children rated the gelatins as more sour as citric acid content increased. We hypothesize that children in the High- and Low-sour groups not only rated the sour intensity similarly, but also perceived the sour intensity similarly. This is supported by the similarity of the pH of children’s expectorated sour solutions. However, due to the methodology used in the present study to measure sour intensity such hypothesis can not be confirmed. We can not be sure that the adjectives used in our five-point scale meant the same to all the children. Children in the High-sour group (preference for extreme sour taste) may judge a stimulus as extremely sour at lower perceived intensities than children in the Low-sour group. Children in the High-sour group may have been limited in their responses by the scale and anchors that were used. Differences might have occurred when we used the label magnitude estimation scale with the anchors ‘not sour at all’ and ‘most extreme sour ever tasted’, but it needs to be determined whether such a procedure is reliable when testing young children. Future research is needed to determine whether children who prefer sour taste perceived it as less intense compared with children who do not prefer this taste.
Despite the similarity in rated sourness, as measured with a five-point category
scale, children in the High-sour group had a higher salivary flow than children in the
Low-sour group. Initially, we hypothesized that high salivary flow would be related to a
lower rated sourness, due to the dilution of the citric acid and the large amount of
buffering agents (Spielman, 1990).
However, as shown by the present study, the high salivary flow of children who preferred
sour taste was not related to large differences in rated sourness. Previous
investigations on the relationship between salivary flow rate and perceived taste
intensity gave conflicting results. Some suggest that high salivary flow rates are
related to a lower perceived intensity (Spielman,
1990), whereas
Norris et al. (1984)
suggested the opposite. Others, however, did not observe any relationship (Christensen et al., 1983, 1987;
Bonnans and Noble, 1995;
Sowalsky and Noble, 1998).
Hypothetically, the saliva of children in the High-sour group had a lower buffering
capacity per milliliter of saliva compared with saliva of children in the Low-sour group.
This could explain why no differences were found in the rated sourness between the High-
and Low-sour groups, despite the differences in salivary flow. This hypothesis can,
however, not be fully confirmed by the present study, because buffering capacity was not
measured by means of titration.
It is more likely that preference for sour taste is related to children’s
general preference for intense and new stimuli. In the present study, children who
preferred sour taste were more willing to try a novel food than children who did not
prefer this taste. A previous study suggests that parents of children who preferred sour
taste were less likely to report that their child was afraid to try new foods (Liem and Mennella, 2003).
Pliner and Hobden (1992) showed that
children who were willing to try a novel food were less shy and emotional compared with
those who were reluctant to try a novel food.
Children in the High-sour group were also more likely to prefer a bright color as
shown in the present study. Previous studies demonstrated that bright colors are more
preferred by people with an extrovert temperament than by people with an introvert
temperament (Birren, 1973). It needs
to be noted that a significant difference was observed between the first time and the
second time children rated the CY color on perceived brightness. It is unlikely that
children were not able to carry out the test. Recall that children rated the colors in
the same order of intensity as adults did. The difference between the first and the
second rating of the color CY, could be a result of an order effect. The duplo was always
presented last.
We suggest that children in the High-sour group were more likely to be sensation
seekers than children in the Low-sour group. But children in the High-sour group and the
Low-sour group did not differ in overall sensation-seeking behavior as measured by
salivary cortisol. Studies by Gunnar and colleagues suggest that surgent temperament
(e.g. extrovert, sensation seeking) in children was related to a high reactivity of
cortisol in reaction to a stressor (Gunnar et
al., 1997;
Davis et al., 1999;
Donzella et al., 2000). The
lack of difference between the High- and Low-sour groups in the reactivity of cortisol in
the present study can be explained by at least three hypotheses.
First, especially in young children, stress may have been experienced at the baseline
measurement. Children were aware when testing was supposed to take place and this could
have resulted in a stress response even before the actual testing began. This could
explain why no differences in the reactivity of cortisol were measured in the young
children. However, previous research indicated that baseline salivary cortisol
concentrations of young children are most likely between 0.7 and 3.7 ng/ml (Gunnar et al., 1997;
de Haan et al., 1998;
Davis et al., 1999;
Donzella et al., 2000). In
the present study, salivary cortisol concentrations in response to our
‘stress’ situation were on average between 0.73 ng/ml and 0.9 ng/ml. A second
hypothesis is therefore that the ‘stress’ situation in our study did not
initiate real stress. In order for the ‘cortisol’ system to respond, the
situation must be perceived as potentially threatening (Gunnar et al., 1997). A third hypothesis is that
the cortisol concentration was not correctly measured. Cortisol, as well as other
hormones in the body, follow a circadian rhythm. In general, cortisol levels peak during
the early morning and decreases during the afternoon (Schmidt, 1998;
Davis et al., 1999). In the
present study, stress-cortisol was measured during the late afternoon, whereas
baseline-cortisol was measured during the early afternoon. The circadian rhythm of
cortisol concentration could potentially have diminished the difference between stress-
and baseline-cortisol levels.
Although the results of the present study are in favor of the behavioral determinants
in the development of sour taste preferences, it cannot be excluded that the biological
development of the sense of taste may also play a role. Previous research has suggested
that the development of preferences for sweet-and salt taste are influenced by biological
determinants such as energy requirement (sweet taste;
Beauchamp and Cowart, 1987) and
postnatal maturation of central and/or peripheral mechanisms (salt taste;
Mistretta, 1981). It remains unknown
whether similar mechanisms are important in the development of preference for sour
taste.
It has been suggested that children who prefer sour taste have experienced the tastes
of a large variety of fruit (Liem and Mennella,
2003). Preference for sour taste could therefore play an important role in
the consumption of sour-tasting fruits. Increasing preference for sour taste in children
who initially do not like sour taste is most likely to succeed if the sour food is not
presented as novel and exciting. Children who do not prefer sour taste should carefully
be introduced to this taste quality. Subsequent repeated exposure could then slowly
increase the preference for sour taste and, hypothetically, increase the consumption of
sour fruits. This, however, needs to be investigated.
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Acknowledgements |
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We acknowledge the expert advice of Drs Lina Engelen, Rene de Wijk and Jon Prinz and the assistance of the teachers and students of the Jena Jozef and Johan Friso schools in Wageningen.
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Accepted August 17, 2004
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