Expression of Multidisciplinary Flavour Science
CO2 PERCEPTION AND ITS INFLUENCE ON FLAVOUR
B. LE CALVÉ, H. Goichon, and I. Cayeux
Firmenich SA, Route des Jeunes 1, P.O. Box 239, CH-1211 Geneva 8
Abstract
The oral perception of CO2 dissolved alone in water and in a model beverage was
studied. The dose-response curve showed that a slight increase of CO2 resulted in a
significant increase in the perception of sparkling intensity (selected attribute to
describe CO2 perception). The average detection threshold of dissolved CO2 in water
was measured at 0.26 g/L. The sensation perceived by panellists at threshold level
was not only sparklingness, but also saltiness. Neither sensitisation nor
desensitisation was observed with carbon dioxide under adaptative experiments.
Taste-taste interactions as well as taste-smell interactions were observed with
carbonated beverages. The sparkling intensity was influenced by a congruent taste
such as sourness. Trigeminal-trigeminal interactions also occur between temperature
and sparkling intensity.
Introduction
Drinking a glass of still champagne certainly reveals how important CO2 is in certain
beverages perception. Carbonated drinks simultaneously stimulate the olfactory,
gustatory and somesthetic senses. Although interactions between taste and smell
are well documented (1-3) less information is available on the influence of trigeminal
stimuli on flavour perception (4). The aim of this study was to better understand (a)
CO2 perception when dissolved alone in water and (b) how it interacts with other
sensory modalities in carbonated beverages.
Experimental
Tap water was carbonated using a carbonator (Loop Aqua device, IMI Cornelius).
Different concentrations of CO2 were obtained by mixing different volumes of
carbonated and still water. Samples were prepared the day before the sensory and
carbonation measurements were made and stored at 6°C.
Flavoured samples were prepared as follows: a base of 200 mL containing
sucrose syrup, citric acid and a lemon flavour dissolved in still water added with 800
mL of water (100% still water, 50% still water mixed with 50% carbonated water or
100% carbonated water). Two liters of each sample were prepared; one for sensory
test and the other for carbonation measurement. CO2 gas concentration was
measured by thermal conductivity (Orbisphere 3658 device, HachUltra). Each CO2
gas value was registered with its corresponding temperature.
For sensory tests, samples (30 mL) were served at a temperature between 9°C
and 12°C in three digit random coded cups. Special care was taken to serve samples
in order to minimize the loss of CO2: pouring was done by series of 6 samples; cups
were closed and stored at 6°C for no longer than 15 minutes prior to service.
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Expression of Multidisciplinary Flavour Science
30 subjects participated to each test, except for the threshold determination which
was done with 42 subjects. Panellists were all Firmenich employees and were
familiar with the use of linear scale to rate their perceptions. Subjects were asked to
sip the sample, keep it for 5 seconds in their mouth and then swallow it. They rinsed
their mouth with room temperature water between each sample.
Dose response curve. Five concentrations of CO2 and a replicate were tested
(6.3, 3.7, 3.1 (repeated), 1.5 and 0 g/L corresponding to 100%, 75%, 50%, 25% and
0% of carbonated water in still water). Sparkling intensity was evaluated on linear
scale from “not at all” (= 0) to “very intense” (= 10). At the beginning of the study
subjects tasted the most carbonated sample to best estimate the highest possible
level.
Threshold measurement. The standard ASTM method of the best estimate
threshold was applied (ASTM-E679). Six three-alternative forced choice (3AFC) tests
were performed with the ascending range of CO2 concentrations (0.05, 0.09, 0.19,
0.37, 0.74, 1.49 g/L). For each test, subjects had to determine the odd sample
among three, two samples containing still water and one containing carbonated
water. They were also asked to indicate the attributes of the different sample from the
list: sour, bitter, sparkling, temperature, salty or “by chance”.
Adaptation test. Seven identical samples (6.3 g/L of CO2) were served (30 mL).
Subjects were asked to sip and swallow samples. The seven samples were tested
following the same protocol with ten seconds between each and without any mouth
rinsing. Sparkling intensity was rated on a linear scale. A warm up sample was
presented one minute before the test.
Study of interactions between taste, smell and trigeminal perceptions. Five
parameters with different levels were chosen: sucrose concentration (100 g/L, 40 g/L
or 0 g/L), CO2 gas concentration (4.5 g/L, 3 g/L or 0 g/L), citric acid (1.5 g/L or 0 g/L),
lemon flavour concentration (1.3 mL/L or 0 mL/L) and temperature (8.5°C or 11.5°C).
The 72 samples of the factorial experimental plan were split into 12 sessions of 6
samples. The sample containing 3 g/L CO2, 4 g/L sucrose, 1.5 g/L citric acid and 1.3
mL/L lemon flavour was rated in each session in order to control the repeatability of
the panel. Subjects were asked to evaluate sparkling, sweetness, sourness and
lemon flavour intensities on a linear scale.
Results & Discussion
Dose-response curve. Below 3.7 g/L, the dose response plot appears rather steep,
which means that a slight increase of CO2 concentration (2 g/L) results in a
significant increase of perceived sparkling intensity (Figure 1). This shape of dose
response curve fits with published data on CO2 nasal perception (5). According to
ANOVA and means comparison test (Duncan’s test), each level of CO2 concentration
tested corresponded to a specific level of sparkling intensity.
Detection threshold. The individual detection threshold was calculated as soon as
the subject found the odd sample for at least the two highest concentrations. The
average detection threshold was the geometric mean of all the individual values
(ASTM-E679). The detection threshold of dissolved CO2 in water was measured at
0.26 g/L. This value is comparable to values measured in pasteurized milk (6) and in
yogurt (7).
Around threshold, the subjects rated the odd sample not only as sparkling. Most
subjects who found the odd sample at 0.19 g/L and 0.37 g/L described it as being
salty (Figure 2). Subjects who failed the test mostly answered “by chance”.
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Expression of Multidisciplinary Flavour Science
10
100%
carbonated
water
9
75%
carbonated
water
8
Perceived intensity
7
50%
carbonated
water
6
5
4
25%
carbonated
water
3
0%
carbonated
water
2
1
0
0
1
2
3
4
5
6
7
CO2 Concentration (g/L)
Figure 1.
Dose response curve of CO2 in water.
42 cor. ans.
67 sel. att.
100
Frequency of citations of each attribute
90
80
39 cor. ans.
61 sel. att.
70
Sparkling
Sour
Bitter
60
50
25 cor. ans.
27 sel. att.
22 cor. ans.
25 sel. att.
28 cor. ans.
36 sel. att.
32 cor. ans.
37 sel. att.
Temperature
Salty
By chance
40
Other
30
20
10
0
0.05g/l
0.09g/L
0.19g/L
0.37g/L
0.74g/L
1.49g/L
CO2 concentration
Figure 2. Frequency of citations of each attribute selected by subjects who find the
odd sample. For each concentration, number of correct answers (cor.
ans.) and total number of selected attributes (sel. att.) are indicated.
Adaptation test. Inter-individual differences were observed in terms of the use of
the scale. But, for 26 subjects among 30 the successive tasting of 7 carbonated
samples demonstrated neither an increase nor a decrease of the sparkling intensity.
Study of interactions between taste, smell and trigeminal perceptions. For each
sensory response ANOVA was done with each physical parameter as factor. All
significant effects of each factor on sensory response are summarized in Table 1.
Results obtained for the sample repeated in each session were not significantly
different according to ANOVA (for sparkling intensity: F= 1.27, p= 0.24, for
sweetness: F= 0.35, p= 0.97, for sourness: F= 0.48, p= 0.91 and for flavour intensity:
F= 1.32, p= 0.21).
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Expression of Multidisciplinary Flavour Science
Table 1. Significant effect of an increase of each main factor on each sensory
response.
Factors
Perception
CO2
Quantity
Sucrose
Citric acid
Lemon
Flavour
Temperature
Sparkling intensity
Sweetness
Sourness
Lemon Flavour
As expected, each sensory response was impacted by its corresponding physical
parameter. Sparkling intensity increased with CO2 quantity (F= 850.4; p ≤ 0.0001), in
presence of citric acid (F= 73.6, p≤ 0.0001) and for colder samples (F= 35.5, p≤
0.0001). Sweetness decreased when the quantity of CO2 increased (F= 24.5, p<
0.0001) or citric acid was added (F= 143.9, p< 0.0001). It increased with the sucrose
concentration (F= 4890.8, p< 0.0001) as expected but also when lemon flavour was
added (F= 18.6, p< 0.0001). Sourness increased with CO2 quantity (F= 80.44; p <
0.0001), citric acid (F= 1354.61, p< 0.0001) and lemon flavour addition (F= 12.86, p=
0.001) but decreased when sucrose concentration increased (F= 158.31; p< 0.0001).
Lemon flavour intensity increased with sucrose (F= 27.07, p< 0.0001), citric acid (F=
155.94, p< 0.0001) and lemon flavour concentration (F= 924.14, p< 0.0001).
Conclusion
Taste-taste and taste-smell interactions already demonstrated in non carbonated
samples occur also in carbonated. In the context of carbonated soft drinks lemon
flavour, citric acid and sucrose are congruent. This congruence seems to enhance
these interactions (8). The reduction of sweetness and sourness observed with
increasing CO2 could be explained by a physical effect: the pH of the solutions
decreases when CO2 quantity increases. Conversely, samples with or without citric
acid, at low or high temperature contain the same quantity of CO2. Sparkling intensity
increases observed for colder samples or with citric acid demonstrate that trigeminaltrigeminal and taste-trigeminal interactions do occur in carbonated beverages.
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