Chem. Senses 24: 281-287,
1999
© Oxford University Press
Perception of Sweetness in Simple and Complex Taste Stimuli by Adults and Children
Children's Food Research and Education Unit, Centre For Advanced Food Research, University of Western Sydney, Bourke Street, Richmond, NSW 2753, Australia
Correspondence to be sent to: D.G. Laing, Children's Food Research Education Unit, Centre For Advanced Food Research, University of Western Sydney, Bourke Street, Richmond, NSW 2753, Australia
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Abstract |
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Currently, there is little information on the ability of children to analyse complex chemosensory stimuli in terms of the presence and magnitude of the components. The present study investigates this question by comparing the ability of 95 adults and 8- to 9-year-olds to estimate the sweetness of several concentrations of sucrose in water and in three foods, namely, orange drink, custard and shortbread biscuits, using a magnitude estimation procedure. The results indicated that similar response functions were produced by adults and children for the sweetness of aqueous solutions of sucrose, custard and biscuits, but not for orange juice, where the functions produced by both female and male children were significantly flatter than those of the adults. Stimulus context may have influenced the ratings of children in the no-sucrose and highest sucrose concentration conditions with two of the foods. The absence of differences between the response functions of the female and male children with all types of stimuli indicated that gender had no influence on their responses. It is concluded that, at mid-childhood, humans are capable of estimating the sweetness of sucrose in foods, but that they have a tendency to limit the range of numbers used in their estimates of sweetness at high concentrations of sucrose in some foods.
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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The sensory analysis of foods by children has been restricted to measurements of their liking or acceptance of a product (e.g. Kroll, 1990
;
Kimmel et
al., 1994; Chen et al.,
1996; Hough et al., 1997).
Currently, therefore,
there is no information that indicates
whether (i) children can estimate the magnitude of a single attribute such as sweetness in a food
or (ii) whether children and adults give similar ratings of magnitude for a food attribute.
Regarding the ability of children to estimate the perceived intensity of a taste, it has been
reported that 5- to 7-year-old children used a five-point category scale to estimate the sweetness of
aqueous sucrose solutions (Anliker et al.,
1991), 10-year-old and
older children
produced a steeper slope than adults using magnitude estimation to assess the intensity of sucrose
solutions (Enns et al., 1979), and a group
of 7- to 21-year-olds
produced flatter slopes
than adults when using a cross-modal procedure to indicate the intensity of sucrose and sodium
choride (Shapera et al., 1986).
However, in each of these
studies, the stimuli consisted of
a single tastant in water. It remains to be seen, therefore, whether children can produce reliable
estimates of the magnitude of single components in complex stimuli, namely, foods. For
example,
children are less able than adults to ignore irrelevant sensory information (Witkin et al.,
1967; Berman and Freidman, 1995)
and may find it difficult
to attend to a quality such as
sweetness in the presence of different aromas, other tastants or variations in the texture of a food.
Possible outcomes are that children may fail to detect the target attribute, or may give lower
estimates of the magnitude of the attribute than adults.
The present study investigated the above questions by comparing the ratings of adults and 8-
to 9-year-old children for the sweetness of sucrose in water, orange drink, custard and shortbread
biscuit. These products provide a range of environments which vary in aroma, taste and texture,
and it was proposed that the results should give a good indication of the capability of children in
midchildhood to assess the magnitude of a common food attribute. A set of aqueous sucrose
solutions was included to provide an environment where the perception of sweetness was not
influenced by other sensory attributes in the stimulus. Eight to nine-year-olds were chosen
because this study is part of a larger programme that is assessing the maturity of the sense of
taste
at mid-childhood, and this age group is capable of undertaking many of the psychophysical tasks
used with adults. The ratings of adults and children were obtained using a magnitude estimation
procedure which produced similar sucrose response functions for these groups in an earlier study
(N. Oram et al., submitted for
publication).
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Subjects
The adults were 29 university students (19 females and 10 males, mean age 20.7 years) who had very little experience with sensory testing. The 66 children were from local public schools (34 females, mean age 9.1 years; 32 males, mean age 8.9 years) and participated with the consent of their parents, school principal and the NSW Department of School Education. Children and students participated voluntarily and were given no monetary reward, only the offer of a confectionary at the end of a session. To determine whether gender affects the maturity of the sense of taste at midchildhood, the children were treated as female and male groups.
Stimuli
The stimuli were orange drink, custard, shortbread biscuit and aqueous solutions of sucrose.
For each type of stimulus there were five test samples. With each stimulus type, one sample had
no sucrose, whilst the sucrose concentrations of the other four samples were set so that the
sweetness level recommended by the manufacturer or the recipe was approximately at the centre
of the range used (Table 1). The concentration
difference between each
level of sucrose was 50%
to accommodate the minimum difference required by 8- to 9-year-old children to discriminate
sucrose solutions (C.E. James et al., submitted for
publication).
All products except
shortbread biscuits were prepared the day before testing and discarded after 24 h. The biscuits
were used within 48 h of baking.
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Sucrose solutions
Sucrose solutions were prepared using food grade sugar (CSR caster sugar, a powdered
sugar), and deionized water from a Milli-Ro-6 Plus System (conductivity 0.9 µS) was
used
as the diluent to produce each of the concentration levels (Table 1). The
solutions were
refrigerated overnight at 4°C and allowed to equilibrate to room temperature
(21–22°C) before serving. During a test trial, 8–10 ml of each solution was
presented in a 30 ml clear plastic cup that was coded with a three-digit number.
Orange drink
The appropriate amount of sucrose (Table 1) and 0.125% w/v of analytical grade citric acid (Ajax Chemicals) was dissolved in deionized water. The water-soluble orange flavour (Quest International-2A 24393) was added in the ratio of 1 part per 1000, and the solution dyed with red (carmoisine and tartrazine) and yellow (tartrazine and brilliant scarlet) commercial food colours (McCormick). The samples were refrigerated (4°C) and presented as described for the sucrose solutions.
Custard
Custard was prepared using sugar-free White Wings custard powder. The appropriate amount of sucrose (Table 1) was dissolved in full cream milk to produce a volume of 1 l. This solution was used to dissolve the custard powder (41.6 g). The mixture was then cooked (8 min 20 s) in a 650 Watt microwave oven on high power, stirred and cooked on high power for a further 3 min 20 s. All custard samples were allowed to cool, and were refrigerated at 4°C overnight. Prior to testing, the custard was brought to room temperature (21–22°C) and 15 ml samples were presented in 30 ml clear plastic cups labelled with three-digit code numbers. A spoon was provided to taste each sample.
Shortbread biscuit
The recipe for the biscuit was adapted from that of Blacker (1987).
The total mass of sugar
used for each stimulus level (Table 1) was
divided equally between caster
sugar and icing sugar
(CSR very finely powdered sugar). Butter (125 g) was melted and cooled, and vanilla essence
(1.25 ml) added. The butter mixture was combined with the appropriate levels of caster sugar,
icing sugar and cornflour (20.8 g), and beaten until thick and creamy. Plain flour (156.3 g) was
added and the whole mixed. The shortbread mixture was pressed into a 27 x 18 cm tin,
marked into 128 pieces with a sharp knife and baked in a conventional oven at
180°C for 30 min. Once removed from the oven, the shortbread was cut into 128 pieces and
allowed to cool in the tin. Edges and excessively brown pieces were discarded, and the remaining
pieces stored in an air-tight container until needed. For adults, one piece of shortbread was
presented in a 30 ml plastic cup labelled with a three-digit code number, whilst for children
samples were taken from bowls with tongs by the interviewer and presented one at a time on a
plastic plate.
Two replicates for each of the stimuli were conducted, and each of the possible presentation orders of the five levels was balanced across subjects and replicates for each stimulus and subject group.
Procedure
The children were tested in a hall at their school over two consecutive mornings. Two
products were assessed each morning with a break of ~1 h between products. Each child was
supervised by one experimenter, and six children were tested at a time. Six tables, one for each
child and supervisor, were arranged to form a circle so that a child faced outwards towards their
supervisor and could not easily make eye contact with other children. The children were trained
in
the use of the magnitude estimation procedure using six lengths of wood (2.8, 5.0, 13.0, 26.0,
52.0 and 132.5 cm long x 1 cm wide x 1 cm thick) (C.E. James et
al.,
submitted for publication). First, the children were asked several questions about
their
knowledge
of large and small numbers, and of long and short lines. Secondly, they were shown the longest
and shortest lengths of wood one at a time in random order, and asked whether they would
describe each length with a large or small number. Finally, they were shown each of the wood
lengths and asked to provide a number which described its length. This procedure was repeated,
if
necessary, until a set of satisfactory numbers was given. That is, they gave numbers of increasing
value with increasing wood lengths that were non-ordinal and approximated the expected
ratios.
Following this, testing with the aqueous sucrose solutions commenced. Before the first solution was given each child was told `Now we are going to do the same thing you have been doing with the pieces of wood, but I want you to use a number to tell me how much sweetness is in a drink'. Their understanding of the word `sweet' was checked by the supervisor who defined `sweet' as being like a `lolly'. This was followed by the presentation of the least and most sweet solutions one at a time to give each child an indication of the sweetness range they would receive shortly. Each child was then presented with five test stimuli, one at a time, with a different random order for each child. A child was asked to provide a number which described the sweetness of the solution. On completion of the first five samples, a second randomly ordered replicate was conducted. Water was sipped between each sample and there was an inter-trial interval of ~30s.
The order of presentation of the other three products was balanced across subjects The test procedure with the orange drink was the same as that for the sucrose solutions. However, with the custard and biscuit, subjects cleansed their mouth with water followed by a piece of bread and a second water sample between test trials. Before a session commenced with a new product, the children were reminded of the procedure, given the least and most sweet samples of the product to taste, and informed that these were the least and most sweet samples they would be given.
The adults were tested at the University Sensory Laboratory. All four products were assessed during one morning with a break of ~30 min between each session. Adults were given the same training procedures as the children. As with the children, the sweetness of sucrose was assessed first, and the test procedures and the order of assessing samples were similar. The only differences in the test procedures were that adults were given a tray with all 10 test samples of a product (two replicates) and they self-administered the test by following instructions given in a questionnaire.
Statistics
In the magnitude estimation procedure, subjects were free to use any numbers. To
standardize
the data across subjects, each rating by a subject was multiplied by a constant to make the sum of
all the ratings equal to 500 (Lawless, 1979). This
had the effect of
bringing the ratings of all
subjects into the same range without disturbing the response ratios between each stimulus level.
A
zero rating was given a value equal to one log step below the subject's lowest estimate
(Enns et al., 1979), including the zero
values given for the
no-sucrose condition. A
mixed model repeated measures analysis of variance (ANOVA) was conducted on the logged
data
with subjects within groups as a random (not fixed) effect and two within-subject variables
(sweetness, five levels; replicates, two levels). Since there were no systematic differences
between
the replicates in any of the analyses, the data were combined by averaging in further analyses. An
overall group mean was calculated as the geometric mean of the group data. Regression analysis
using an adjusted R2 to accommodate the use of only four points on each
function established the best linear fit of the estimates (logs) of sweetness and sucrose
concentration. Systat for Windows Version 5.0 was used for all the analyses.
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Results |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Sucrose
The ANOVA indicated that all subject groups discriminated the different concentrations of sucrose [F(4, 368) = 250.91, P < 0.001]. The absence of a significant interaction between subject group and concentration [F(8, 368) = 0.805, P = 0.599] showed that similar sweetness ratings were given by adults and children at each of the concentrations of sucrose (Table 2), and that there were no differences between the response functions. Regression analysis showed that the data sets of each group provided a good linear fit (Figure 1a) and accounted for a substantial amount of the variance (Table 3).
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Orange drink
All groups discriminated the sucrose concentrations [F(4, 368) = 74.51, P < 0.001] (Table 2). However, there was a significant group x concentration interaction [F(8, 368) = 4.253, P < 0.001], reflecting the finding that children gave lower sweetness ratings for the highest sucrose concentration than adults (Figure 1b). Two-way ANOVAs with concentrations as a within effect and the groups as a between effect indicated that there were significant group x concentration interactions between adults and male [F(4,236) = 4.71, P < 0.001] and female children [F(4,244) = 8.78, P < 0.001], but not between the responses of the two groups of children [F(4,256) = 0.27, P = 0.78]. Regression analyses indicated that the best linear fit of the means accounted for most of the variance for each group (Table 3), and that the slope of the response function of the adults (0.96) was steeper than those of the children (0.56 and 0.58 for the female and males respectively).
Custard
Discrimination of the sweetness of the custard samples was achieved by each group [F(4,352) = 143.45, P < 0.001], but the group x concentration interaction was not significant [F(8,352) = 1.515, P = 0.151] (Figure 1c). Thus, although the children gave slightly higher sweetness ratings for the lowest sucrose condition and lower ratings for the highest concentrations than adults, in contrast to the result with orange drink, there was no significant difference between the three response functions. The best linear fit of the means accounted for most of the variance (Table 3), and the slope of the adult function, although steeper, was not significantly different from those of the female and male children.
Shortbread biscuit
All groups successfully discriminated between the sweetness levels of the shortbread biscuit [F(4, 372) = 138.95, P < 0.001], and there was no significant group x concentration interaction [F(8, 372) = 1.821, P = 0.072] (Figure 1d). Thus, although the regression analyses indicated that there was a significant linear fit of the data of the adults, and the fit of the data for the children was only marginally significant (Table 3), there was no significant difference between the slopes of the response functions of the three groups.
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Discussion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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The two most significant findings of the present study, were that (i) adults and children had similar sweetness response functions for three of the four types of stimuli, differing only in the response to the orange drink; and (ii) at mid-childhood humans can analyse complex foods and indicate the magnitude of a particular sensory attribute.
The finding that very similar sweetness response functions were produced by all three groups
to the aqueous sucrose solutions replicates recent work in this laboratory (C.E. James et al., submitted for publication). The exponents are
also similar to those
reported with adults
(Kroeze, 1976; Moskowitz, 1977;Green et al., 1993). However, the result with children
is in contrast to the reports of Enns et al. (1979), who found the
slope of the sucrose
response function of 10-year-olds to be steeper than that of adults (1.7 versus 1.12), and Shapera
et al. (1986), who reported a low
exponent (0.5) for a
group ranging in age from 7 to 21
years. Since the latter two results are very different to those reported for adults, and are from
older children, it is likely they may be due to methodological problems. For example, Enns
et
al. suggested that the use of `extreme' numbers by the children may have
caused the steeper slope.
The similar results found here for adults and children for the sucrose response function also strengthen the view that the different rating behaviour of the children compared with the adults with the complex stimulus orange drink was context dependent and not due to an underdeveloped sense of taste. It is clear that the flatter slopes of the sweetness functions obtained with orange drink for the children were due to the difficulty they had in giving ratings to the stimulus that had the highest sucrose concentration when other food components were present. Indications of the difficulty were also observed with the highest concentration of sucrose in custard.
Comparison of the slopes of the functions obtained with the four types of stimuli is only
possible for the sucrose solutions and orange drink. Those for custard and shortbread cannot be
used in an across-food comparison because different amounts and ranges of amounts of sucrose
were used in their preparation. Comparison of the responses of adults to the sucrose and orange
solutions (Table 2), however, showed that very
similar responses were
used at each of the five
levels of sucrose for the two types of stimuli. In contrast, both groups of children gave
substantially higher estimates for the sweetness of the orange drink that had no sucrose added
than for water alone, and lower estimates for the highest concentration of sucrose in orange drink
compared with the highest concentration of sucrose presented alone. Thus, the slopes of the
sweetness functions produced by the adults for the two types of stimuli were the same (0.96), in
contrast to the corresponding ones produced by the female (1.07 and 0.56) and male children
(0.85 and 0.58). It is possible that with the no-sucrose orange drink the children were influenced
by the colour of the drink and gave a higher than expected estimate. Such an interpretation is in
keeping with the finding of Oram et al. (1995) that in beverages
colour is a more salient
feature than flavour for children under ~12 years of age. It is also possible that the inherent
sweetness of the orange flavour of the drink, and to a lesser extent the vanilla flavour of custard
and the biscuit, induced the children to give higher estimates than the adults for the no-sucrose
conditions with these foods. The presence of irrelevant or distracting quality components,
therefore, may have affected the judgements of sweetness by the children. Such distractions have
also been reported for children in studies involving other modalities (Witkin et
al., 1967).
Why children appeared to find little difference between the sweetness of the two highest
concentrations of sucrose with orange drink is unknown. It is unlikely that this occurred because
they could not discriminate between the two levels, since 8- to 9-year-olds can easily discriminate
differences in sucrose levels that differ by ~35% (C.E. James
et al.,
submitted
for
publication), compared with the difference of 50% used here. One possibility,
however, is that the
children were influenced by their high familiarity with the three products. Accordingly, they may
have tended to regress their rating of sweetness to that commonly found in each product, which
for this study was at the middle of the concentration range used. Nevertheless, the possibility
remains that the presence of other stimuli in the foods made it more difficult to detect differences
in sweetness.
An unexpected aspect of the rating behaviour exhibited by the children was their avoidance
of
both very low and very high numbers. This was contrary to the finding by Moskowitz
(1985) that
children tend to use the extremes of scales more often than adults. However, in that study
hedonic
ratings were obtained, and it may be that for children hedonic aspects of foods are described by a
love–hate relationship that is absent when estimating different levels of a food
attribute.
An interesting outcome was that there was no difference between the response functions of the two groups of children for any of the foods or sucrose alone. Gender therefore had no influence on the ability of the children to perceive and rate the intensity of sweetness in simple or complex chemosensory stimuli. Since none of the other studies of taste magnitude compared the responses of female and male children, the present study is the first to report that gender has no influence on this measure at mid-childhood.
It can be concluded that by mid-childhood humans can analyse complex chemosensory stimuli and provide estimates of the magnitude of a specific sensory attribute, in this instance, sweetness. The resultant estimates showed that similar sweetness response functions for adults and children exist over a wide range of sucrose concentrations in very different food products. However, the different response functions obtained for the adults and children with orange drink, arising primarily from the children rating the sweetness of the highest concentration of sucrose very differently from adults, suggests that children's responses may be influenced by other food components in some products.
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Acknowledgments |
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The authors extend special thanks to the children and adults who participated, to the teachers for their cooperation, and to G. Rose and A. Jinks for assisting with the statistical analysis. We also wish to thank the anonymous reviewers for their helpful comments and suggestions. C.E.J. was supported by a University of Western Sydney, Hawkesbury Postgraduate Scholarship, and N.O. by a Meat Research Corporation grant to D.G.L.
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Accepted January 4, 1999
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