Effect of sensory education on food preferences in children

Food Quality and Preference 21 (2010) 794–804

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Food Quality and Preference journal homepage: www.elsevier.com/locate/foodqual

Effect of sensory education on food preferences in children C. Reverdy a,*, P. Schlich b, E.P. Köster c, E. Ginon b, C. Lange b,** a

Pancosma, Le Grand Saconnex, Switzerland Centre des Sciences du Goût et de l’Alimentation, UMR6265 CNRS, UMR1324 INRA, Université de Bourgogne, Agrosup Dijon, F-21000 Dijon, France c Centre of Innovative Consumer Studies (CICS), Wageningen, The Netherlands b

a r t i c l e

i n f o

Article history: Received 14 August 2009 Received in revised form 8 December 2009 Accepted 15 March 2010 Available online 23 March 2010 Keywords: Sensory education Children Food preferences Complexity Intensity

a b s t r a c t During an evaluation of the effects of a French sensory education program for 8–10 years old school children, an experiment was carried out to investigate the influence of the program on the development of children’s preferences for stimuli differing in arousal potential (higher complexity and/or intensity). An experimental group (n = 101) who participated in the education program and a control group (n = 102) who did not, rated liking for five stimuli differing in arousal potential in each of three product categories (mashed potatoes, fruit yoghurts and compotes) at three moments: just before (T0) and after (T1) the education program and 10 months later (T2). Although initially both groups showed the same increase in liking for more arousing stimuli in two foods, indicating that exposure to more arousing stimuli alone sufficed, whereas the effect of the education program was only shown in the further extension of this change at T2 in the experimental group. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction In humans, as in all other omnivores, food choice is a predominantly learned behaviour. Apart from an aversion for bitter and an attraction to sweet substances that seem to be inborn (Ganchrow & Menella, 2003; Steiner, 1974) all other taste preferences are learned. Odour preferences are also acquired by learning that starts in some cases even before birth (Schaal, Soussignan, & Marlier, 2002). Furthermore, it has been shown that preferences formed in infancy and early childhood may have long-lasting effects on later food choice behaviour (Garcia, Simon, Beauchamp, & Menella, 2001; Haller, Rummel, Henneberg, Pollmer, & Köster, 1999; Nicklaus, Boggio, Chabanet, & Issanchou, 2005). Very diverse learning mechanisms such as flavour–flavour and flavour–nutrient conditioning (Mobini, Chambers, & Yeomans, 2007), imitation of parents and peers and parental education practices (Birch, 1998) are involved in the acquisition of food preferences. The influence of ‘‘mere exposure” (Zajonc, 1968) on the appreciation of novel food by children was investigated by Pliner (1982). She came to the conclusion that the effect was mainly due to the dissipation of food neophobia (reluctance to taste new foods). The efficacy of an exposure-based approach to overcome

* Correspondence to: C. Reverdy, PANCOSMA, 6 voie-des-Traz, CH-1218 Le Grand Saconnex, Switzerland. Tel.: +41 22 929 84 33; fax: +41 22 929 84 95. ** Correspondence to: C. Lange, CESG, 15 rue Hugues Picardet, F-21000 Dijon, France. Tel.: +33 380 68 16 12; fax: +33 380 68 16 32. E-mail addresses: [email protected] (C. Reverdy), christine.lange@dijon. inra.fr (C. Lange). 0950-3293/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodqual.2010.03.008

eating resistances has been supported in experimental studies with schoolchildren (Loewen & Pliner, 1999; Pliner & Stallberg-White, 2000). In a study carried out in primary schools, 10 daily exposures to the taste of an unfamiliar vegetable (raw red pepper) significantly increased children’s liking and consumption of the vegetable (Wardle, Herrera, Cooke & Gibson, 2003). However, with repeated exposure, children can either learn to prefer and consume, or dislike and reject foods depending on the social contexts in which the foods are eaten and the physiological consequences of their consumption (Birch, 1998). There are also good arguments to consider mere exposure theory as a special case of more general motivational theories (Köster & Mojet, 2007). In this connection, attention has also been given to the possible role of stimulus complexity and ‘‘motivational learning” in the development of food preferences. Based on motivational theories (Berlyne, 1960; Dember, 1964; Dember & Earl, 1957; Walker, 1980) experiments were carried out that confirmed the role of arousal and perceived complexity as one of the factors in the development of food preferences during repeated exposure (Köster, Couronne, Léon, Lévy, & Marcelino, 2002; Lévy & Köster, 1999; Lévy, MacRae, & Köster, 2006; Porcherot & Issanchou, 1998). As predicted, stimuli that were originally less liked because they were more complex than the level of stimulus complexity the subjects liked most, became more appreciated with repeated exposure, whereas stimuli that were less complex than the optimally preferred one became less appreciated with exposure. Nevertheless, other authors (Sulmont-Rossé, Chabanet, Issanchou, & Köster, 2008; Zandstra, de Graaf, & van Trijp, 2000; Zandstra, Weegels, Van Spronsen, & Klerk, 2004) demonstrated the fragility of these effects that may

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stimuli. The perception of the developed variants in terms of their stimulus arousal potential was validated with a separate group of subjects. In line with Berlyne (1960) who stated that the arousal potential of a stimulus depends on the degree of novelty, the degree of complexity and the intensity of the stimulus, measurements of familiarity, complexity, and intensity were used to characterize the arousal potential of the variants. A first hypothesis, stating that the arousal potential will increase with both the added intensity and complexity of the stimuli, was tested in this preliminary experiment. Three other hypotheses were tested in the main experiment. According to the second hypothesis it is to be expected that the subjects will initially show a preference for the least complex and intense variants as predicted by the theory of Berlyne on specific exploratory behaviour. The third hypothesis predicts that the sensory education of the ‘‘Classes du goût” will lead to an increase in appreciation for the more complex variants and thus will corroborate the theory of Dember and Earl that predicts a positive shift in the optimal complexity level of the participants under the influence of exposure to more complex stimuli. Finally, a fourth hypothesis predicts that the effect of sensory education on preference will be long lasting (still present 10 months after the end of the sensory education period).

2. Materials and method 2.1. Products A range of stimuli with increasing arousal potential in each of three different food categories (mashed potatoes, drinkable yoghurts, and compotes) was established for use in the main experiment by varying both complexity and intensity and was tested in the preliminary experiment. The selection criteria of the product categories were based on the following characteristics: (1) together the products had to compose the equivalent of a complete meal, (2) the products had to be easily modifiable by the experimenter and (3) they had to be appreciated by most children. Apart from the products already mentioned, that were supposed to vary in arousal potential by complexity and intensity, tomato sauces that only varied in familiarity (three levels) were also tested, but the results are not included in the present paper because the arousal potential of these products was not based on the same principles.

I+C-

Taste intensity (I)

easily be affected by other differences between the stimuli than perceived complexity alone, such as differences in caloric content (Zandstra et al., 2000) or sweetness of the food products (Sulmont-Rossé et al., 2008). Although the learning mechanisms described are indeed very diverse in nature, they all have in common that they are forms of implicit non-intentional learning and that they result in largely implicit and unconscious food preferences and habits. This may be one of the reasons why such habits are highly resistant to efforts to change them by interventions that are based on conscious and rational argumentation. Obviously, explicit knowledge alone has little effect on behaviour that is driven by implicit habits and desires. In France, a different approach has been developed in the form of a school program (Classes du goût) for 9–10 years old children ( Puisais, Mac Leod, & Politzer, 2002; Puisais & Pierre, 1987), providing a combination of explicit learning about sensory perception and implicit learning through actual sensory experience with food (both novel and traditional). This education program for school children has been used in several European countries, e.g., in Sweden (Hagman & Algoston, 2000). It is the aim of the program to teach young children to become well-informed consumers with awareness of the quality and differentiation of foods with regard to smells, textures and tastes. Children’s awareness is developed by awakening their interest and curiosity in foods by exercising their senses. Ton Nu (1996) reported that, after the program, children’s interest in food quality was higher and their ability to describe sensory properties of food was better than that of a control group, but since no measurements were conducted to establish a baseline level, group differences could not be excluded as an explanation for this result. Sune, Lacroix, and de Kermanec (2002) compared children who attended the Classes du goût program with their nontrained peers and with adults on the sensory characterization of chocolate and found that despite the education, children described the chocolate in their own way and so did adults. In Finland, Mustonen, Rantanen, and Tuorila (2009) studied the effects of the Classes du goût with children aged from 7 to 11 years old. They showed an improvement in the identification of tastes and odors, and in characterizing foods, while there was no difference in the performance of the control group. In Dijon, France, a 15 months follow-up study was started with school children to track the influence of the program on the development of food preferences, neophobia, food description and odour categorization. Half of children received 12 lessons (Classes du goût) and the other half only performed the same baseline- and follow-up measurements as the first group. The effects of the sensory education were studied with sensory tests conducted in the laboratory. The effects of the program on food neophobia have been reported elsewhere. It was shown that neophobia was temporarily reduced by it, but that this effect was lost after 10 months (Reverdy, Chesnel, Schlich, Köster, & Lange, 2008). The present paper reports the results of the evaluation study with special attention to the relative roles of two arousing properties (intensity and complexity) of the stimuli in the development of preferences. Although during life the liking for intensity usually decreases, whereas that for complexity increases, both these factors play a role in the arousal raised by stimuli at a given moment in the life cycle. To this end, five variants differing in level of arousal potential were formulated for each of three product ranges. Three of these varied in stimulus complexity and three varied in intensity, while one stimulus occupied the middle position in both series. The participants were asked to rate the hedonic value of the variants at three stages, an initial pre-rating (T0) before the sensory education period, a post-rating (T1) just after the sensory education period and a final rating (T2) 10 months later. A preliminary experiment was devoted to the measurement of the arousal potential of the

I+C +

IC

I-C+

I-C-

Flavour complexity (C) Fig. 1. Schematic representation of the rules of formulation of the five products.

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Table 1 Composition of the products. I Mashed potatoes Flavours Basic taste Drinkable yoghurts Flavours Basic taste Compotes Flavours Basic taste

C

I+ C

IC

I

Potatoes

Potatoes

Potatoes Celery

Not very salty

Relatively salty

Moderately salty

Potatoes Celery Nutmeg Not very salty

Potatoes Celery Nutmeg Relatively salty

Grape fruit

Grape fruit

Grape fruit Orange

Not very bitter Relatively sweet

Relatively bitter Not very sweet

Moderately bitter Moderately sweet

Grape fruit Orange Peach Not very bitter Relatively sweet

Grape fruit Orange Peach Relatively bitter Not very sweet

Apple

Apple

Apple Mango

Not very sweet

Relatively sweet

Moderately sweet

Apple Mango Ginger Not very sweet

Apple Mango Ginger Relatively sweet

To this end, five variants differing in level of arousal potential were formulated for each of three product ranges. Three of these were varied in stimulus complexity and three varied in intensity (see diagonals in Fig. 1), while one stimulus occupied the middle position in both series. Starting from a base product (mashed potatoes, grapefruit yoghurt and apple compote), five such variations were prepared for each product by adding basic tastes and different flavours that were more or less surprising to French people (see Table 1). 2.2. Subjects A total of 203 school children aged from 8 to 11 years were divided into two groups each consisting of four primary school classes: an experimental group (101), that took part in the sensory education and in a pre- and a post-tests, and a control group (102) that only took part in the pre- and post-tests. A Student’s t-test revealed no significant difference between the two groups for the variable age (t = 0.58; p = 0.4454), and a Chi square test revealed no significant difference for gender (v2 = 0.1297; p = 0.7188). A total of 92 experimental subjects and 95 control subjects were present at the first and the second test stages and only 83 experimental subjects and 83 control subjects were present at all three test stages (T0, T1 and T2) due to different personal circumstances. Moreover, some of the subjects did not participate in the hedonic evaluation of the yoghurts or compotes due to potential food allergy problems. Six extra classes of almost 25 children with same age and gender distribution as in the main study were recruited to take part in the preliminary experiment. Permission to execute the experiments with the full cooperation of the teachers was obtained from the responsible authorities and the parents of all participating children gave their written consent. 2.3. Experimental design All sessions took place at the Centre des Sciences du Goût in a room with separate booths that were equipped with a computer screen and children responded using the mouse. All questionnaires were prepared with FIZZ software (Biosystèmes, Couternon, France). 2.3.1. Preliminary experiment Since classical descriptive analysis is not well adapted for children we chose a paired comparison test in order to assess the children’s perception of the level of the arousal potential of each

C+

I+ C+

variant, taking the dimensions familiarity, intensity and complexity into account. Each range of products was evaluated by two different classes twice. During the first session, the children were asked to answer three questions: which sample do you know best? (familiarity); which sample is the most intense? (overall intensity); which sample contains the highest number of tastes? (complexity). During the second session, children were first trained to recognise the basic taste of the products they had to evaluate later with the help of basic taste solutions (saltiness for mashed potatoes, bitterness and sweetness for the drinkable yoghurts and sourness and sweetness for the compotes). After this training, the children received the pairs of products and were asked to answer the questions: which sample is the most surprising? (complexity); which sample is the sweetest/saltiest/most bitter or most sour one? (taste intensity). They were instructed to taste the two samples of each pair again before answering each question. The presentation order of the 10 pairs followed a Williams’ Latin square balanced for order effect (MacFie, Bratchell, Greenhoff, & Vallis, 1989).

2.3.2. Main experiment 2.3.2.1. Description of the hedonic measurement. Both groups performed sensory tests before (T0) and after (T1) the sensory education period. In addition, in order to assess the effect of the education over time, these tests were repeated after a 10 months interval (T2). The comparison of the measurements at T0 and T1 or T2 makes it possible to evaluate the persistence and/or further development of the effects of the sensory education over time. If the education programme is effective, the changes should be larger for the educated group than for the control group. Over three sessions, the sensory tests measured the level of the children’s food neophobia, their ability to categorise and to describe the sensations perceived while eating food and the preferences and choices for several ranges of products varying in sensory and complexity aspects. In this paper, only the procedure and results concerning the evaluation of the preference for the products described above will be presented. It should be noted that liking was always the first question the children were asked to respond to at each stage of the experiment (T0, T1 and T2). Six sessions were organised during the three stages (T0, T1 and T2) in order to evaluate children preference and choice. They were held at lunchtime and the children were invited to take part in a meal together with their classmates (maximum 32 children). After a macedoine served as a starter, and three different tomato sauces served with three meatballs, the five samples of mashed potatoes, the five samples of drinkable yoghurts and then the five samples of compotes were served sequentially one at a time. For each product

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category, the presentation of the samples followed Williams Latin squares balanced over children for order and first-order carry-over effects. Care was taken to maintain for each child the same presentation order of the variants at each experimental stage (T0/T1/T2) in order to be able to compare them and measure changes without contamination by possible order effects. The children were asked to rate their liking on a seven point structured hedonic scale, labelled ‘‘very bad” (left) ‘‘bad” ‘‘relatively bad” ‘‘I don’t know” ‘‘relatively good” ‘‘good”, ‘‘very good” (right). 2.3.2.2. Description of the education program. The education programme for the experimental group consisted of 12 lessons in the classroom of one and a half hour each, spread over a period of 4 months between the two measurements at T0 and T1 (6 months). These lessons were adapted from ‘‘Les classes du goût” (Puisais et al., 2002)1. Appendix 1 gives an overview of the main characteristics of these lessons.

797

on the level of arousal potential for this range of products and that increasing the intensity only adds some subsidiary arousal to the complexity of the stimuli. On the contrary, the order of drinkable yoghurt variants on the first axis is quite different (Fig. 2b) and reveals a greater impact of taste intensity than of flavour complexity on the level of arousal potential. In fact, the bitterness (basic taste intensity) of the grapefruit juice added to all variants was probably strongly perceived by the children. Thus for the mashed potatoes and the compotes, the results of the preliminary experiment demonstrate a relatively good consistency between the perception as predicted by the formulation of the products and the real perception evaluated by the children, but the results also show that a taste like bitterness for which an inborn aversion exists, may outweigh the influence of the flavour complexity in the determination of the arousal potential. 3.2. The initial level of liking for the variants (T0)

2.4. Data treatment For the preliminary experiment, a Friedman analysis (Meilgaard, Civille, & Carr, 1991) was performed on the scores of the paired comparison. Then, a non-normalised principal component analysis was performed on the rank sums of the Friedman scores taking the familiarity-, complexity- and overall-intensity dimensions into account. With regard to the percentage of the variance ratio of the first axis (higher than 84% whatever the product), we consider the arousal potential of each variant to correspond to the coordinates on the first axis. For the main study, the children’s marks on the structured scale were converted into values from 1 to 7. In order to compare the initial (T0) hedonic scores and their development at the different stages (T1 and T2) between the educated and the control groups, analyses of variance were performed with the following model: hedonic scores (T0 or T1–T0 or T2–T1) = group + subject(group) + variant + group  variant + error. If significant effects were revealed, a comparison of the mean test (Fisher’s LSD) was performed. 3. Results 3.1. The children’s perception of the variants It was the aim of the preliminary experiment to assess the children’s perception of the variants of mashed potatoes, drinkable yoghurts and compotes in terms of arousal potential. Our first hypothesis was that, in accordance with the objective for the formulation of the variants, the level of the arousal potential would follow the order I C < I+ C = I C = I C+ < I+ C+ for all three products. Our expectation that no difference would be found between the variants I+ C , I C and I C+ level was based on the hypothesis that the increase in flavour complexity might compensate the decrease in taste intensity and would thus maintain the same level of the arousal potential. The first axis of the PCA based on the rank sums of the Friedman tests represents the arousal potential taking into account the familiarity, the perceived complexity (two questions) and the overall intensity dimensions. The projection of the variants shows that the first hypothesis is partially confirmed for mashed potatoes and compotes (see Fig. 2), except that the expected iso-intensity of the arousal potential for the variants I+ C , I C and I C+ was not obtained. Inspection of the Fig. 2a and c shows that complexity has a greater impact (large spread over the x-axis) than taste intensity 1

This programme is available in the form of a compact disc-read only memory

In accordance with results from previous studies, we expected that children without sensory education would like the simpler variants (the ones with the lower arousal potential) more than the more complex variants (with the higher arousal potential). The ANOVA carried out on the whole panel revealed a strong variant effect on the initial liking scores (F4,187 = 86,97 ; p < 0.0001). Fig. 3 gives the mean liking scores for each variant ranked according to their increasing level of arousal potential as well as the results of the comparison of the means (lsd test). For mashed potatoes (Fig. 3a), it shows four different groups of variants. In more detail, for a same level of flavour complexity, the saltier variants were significantly more preferred than the less salty variants, and for a same level of saltiness, the more aromatically complex variants were significantly less liked than the aromatically simpler ones. For the drinkable yoghurts and compotes, Fig. 3b and c shows only two separate groups of variants that are directly linked to the level of the arousal potential and reveal a preference for the simpler or less intense variants. Note that, contrary to our expectation, the children did not prefer the sweetest variants in the compotes when they were presented at a same level of flavour complexity, and that at a same level of bitterness in drinkable yoghurts, they did not significantly prefer simpler flavour variants over complex ones. This latter observation is probably due to the children’s dislike of bitterness as demonstrated elsewhere (Menella, Pepino, & Beauchamp, 2003). Thus, the earlier mentioned hypothesis according to which children without sensory education will prefer the least arousing variants is partially confirmed and the results are in accordance with Berlyne’s theory (1967) on specific exploratory behaviour, which predicts a slight preference for simpler stimuli. Furthermore, the fact that neither a group effect nor a group  variant interaction was observed (see Table 2), confirmed that there was no significant difference in initial liking scores between the groups and thus allowed us to compare the changes occurring in the results of these groups at T1 after the experimental group had followed the sensory education program. 3.3. Change in liking scores under the immediate influence of sensory education (T1–T0) It was hypothesised that sensory education would lead to changes in the liking of the educated children only, revealing an increase of hedonic scores for the more complex and a decrease for the simpler variants as expected by the Dember and Earl theory (1957). Results of the ANOVA carried out to test this hypothesis are shown in Table 3 and the results of the comparison of the means are presented in Fig. 4.

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120

Unfamiliarity

80

Complexity (surprise)

DIM2 13.43 %

40

I- C-

b

I- C+

0

I+ C+

I+ C-

- 40

Complexity (number of taste)

40

IC

% .4 3 1 2 IM D

60

DIM2 11.11 %

a

Intensity

Unfamiliarity

20 I- C+

IC

Intensity I+ C+

0

- 80

I- C-

--120

-120

I+ C-

Complexity (number of taste)

-80

-40 0 40 DIM1 84.34 %

c

Complexity (surprise)

- 20

80

120

-40

100

-20

0 DIM1 88.66 %

20

40

60

Complexity (number of taste)

80

DIM2 3.11 %

60

.1 3 2 IM D

40

20

I+ C-

IC

Intensity

0

I+ C+

I- C+

- 20

I- C-

Unfamiliarity Complexity (surprise)

- 40 -60

-40

-20 0 20 DIM1 96.03 %

40

60

Fig. 2. Principal component analysis of the familiarity, complexity and intensity dimensions for, respectively, mashed potatoes (2a), drinkable yoghurts (2b) and compotes (2c).

Just after sensory education, an increase in liking scores for complex mashed potatoes I C and I+ C+ was observed and a decrease in liking for the simplest variant I C in both the educated and the control group, while the liking score of I C+ increased in the control group only (Fig. 4a). For compotes, the more the variant was arousing, the more the liking scores increased at T1 compared to T0 for both the experimental and the control groups. As for mashed potatoes, an ANOVA revealed no significant difference between the experimental and the control groups (Table 3). Nevertheless, for the compotes, we did not observe any decrease for the least complex variants (Fig. 4c), indicating perhaps that even the least complex product was perceived as more complex than their optimum by the children. These results indicate that only a few exposures to more complex stimuli (as in the case of the control group) were sufficient to improve the liking for complex foods

and at the same time reduce liking for simpler variants. Since the groups did not differ, these effects could be explained by exposure according to Dember and Earl’s theory (1957), but, contrary to expectation, not by the effects of sensory education. The results of the drinkable yoghurts did not point in the same direction. In fact, in both groups the increase in liking was always higher for the less bitter variants. This observation is probably due to the bitterness provided by the grapefruit juice which seems to disturb all children whether educated or not. 3.4. Change in liking scores under the delayed influence of sensory education (T2–T1) In order to study the long term effects on the development of the preferences of sensorily educated children, the sensory tests

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a

Table 3 Effects of variants and groups on the mean changes of hedonic scores, over the period between before (T0) just after (T1) the sensory education (T1–T0).

7

Hedonic scores

6

Effect (df)

5 4 3

b

c

a

2 1

I- C-

I+ C-

IC

I- C+

I+ C+

b7

a

Drinkable yoghurts (N = 92/90a)

Compotes (N = 91/92a)

Variants (4.4.4)

F p Value

10.53 <.0001

2.76 0.0267

3.78 0 .0048

Group (1.1.1)

F p Value

0.19 0.6606

0.03 0.8682

0.53 0.4664

Group  variants (4.4.4)

F

1.78

0.34

1.04

p Value

0.1306

0.8532

0.3881

c

d

Mashed potatoes (N = 95/92a)

N = N control group/N educated group.

Hedonic scores

6 5 4 3

a

a

b

b

b

I- C-

I- C+

IC

I+ C-

I+ C+

a

a

b

b

b

I- C-

I+ C-

IC

I- C+

I+ C+

2 1

c

7

Hedonic scores

6 5 4 3 2 1

Fig. 3. Means and 95% confidence intervals of the initial (T0) hedonic scores of the whole panel for the product variants arranged according to their level of arousal potential. Results for, respectively, mashed potatoes (3a, N = 187), drinkable yoghurts (3b, N = 182) and compotes (3c, N = 183).

Table 2 Effects of the variants and groups on the mean initial hedonic scores of mashed potatoes, drinkable yogurts and compotes. Effect (df)

a

Mashed potatoes (N = 95/92a)

Drinkable yoghurts (N = 92/90a)

Compotes (N = 91/92a)

Variants (4.4.4)

F p Value

86.97 <.0001

4.83 0.0007

8.79 <.0001

Group (1.1.1)

F p Value

0.05 0.8212

2.06 0.1533

0.27 0.6013

Group  variants (4.4.4)

F

1.61

0.39

0.13

p Value

0.1703

0.8149

0.9723

N = N control group/N educated group.

were repeated 10 months after the end of the last lesson. The change in the hedonic scores between steps T1 and T2 was estimated using an ANOVA performed with regard to the effect of variant, group and the interaction group  variant. For the results see Table 4 and the comparison of the means are presented in Fig. 5. Ten months after sensory education, children’s liking scores for complex mashed potatoes continued to increase except for the

Fig. 4. Means and 95% confidence levels of the changes (T1–T0) in the hedonic scores for the product variants arranged according to their level of arousal potential over the period between before (T0) and just after (T1) the education period. Results for, respectively, mashed potatoes (4a), drinkable yoghurts (4b) and compotes (4c).

most complex variant I+ C+ (Fig. 5a). Interestingly, this increase was only observed in the educated group, suggesting that an effect of sensory education appeared 10 months after the end of the program. Indeed, Table 4 shows a significant group effect and a

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Table 4 Effects of variants and groups on the mean changes (T2–T1) in hedonic scores over the period from just after the sensory education (T1) till 10 months later (T2). Effect (df)

a

Mashed potatoes (N = 83/83a)

Drinkable yoghurts (N = 78/83a)

Compotes (N = 79/83a)

Variants (4.4.4)

F p Value

3.23 0.0122

1.73 0.1423

0.13 0.9696

Group (1.1.1)

F p Value

3.99 0.0475

0.81 0.3709

0.63 0.4290

Group  variants (4.4.4)

F

3.19

0.23

2.53

p Value

0.0131

0.9236

0.0394

N = N control group/N educated group.

Fig. 5. Means and 95% confidence levels of the changes (T2–T1) in the hedonic scores for the product variants arranged according to their level of arousal potential over the period between just after the education period (T1) and 10 months later (T2). Results for, respectively, mashed potatoes (5a), drinkable yoghurts (5b) and compotes (5c).

significant group  variant interaction. To a lesser extent, a similar increase was observed for compotes and there the group  variant interaction is also significant (Fig. 5c). This result confirms our hypothesis according to which a sensory education could increase the liking for complex products, even if this effect is not immediate. However, for drinkable yoghurt variants no development was significant, which we attribute to the disturbing impact of

the bitter grapefruit taste (Fig. 5b). Furthermore, the variant I+ C+ of mashed potatoes is probably too arousing for children whose preference remained stable even after sensory education, as might be the case with strongly complex stimuli according to the Dember and Earl theory (1957).

4. Discussion Perhaps the most striking result of this study is the fact that just after the sensory education period both groups (and not just the educated experimental group) increase their liking for the mashed potatoes and the compotes with a higher arousal potential and in the case of the mashed potatoes reduce their liking for the stimuli with a lower arousal potential. It is clear that three exposures to the products (preference measures at T0 and T1, plus a choice measure at T0) suffice to invoke a remarkable change in the preferences at T1 of the control group and that the sensory education of the experimental group does not seem to provide an extra contribution to this immediate change, but on the contrary seems to dampen the effect (see I C+ in Fig. 4a and the differences between the groups in the increase of liking at the lower end of the range of compotes Fig. 4c). On the other hand, it seems that the effect of the sensory education appears 10 months later (T2) in the form of a consolidation and further extension of the positive exposure effects on some of the stimuli that are not found in the control group (see the positive changes in Fig. 5a and c). This latter difference between the two groups not only shows that the sensory education may have positive effects on the further preference development of the children, but can also serve as an argument in the discussion about the nature and origin of the observed change between T0 and T1. It reduces the likelihood that all effects found in that period are merely the result of the age related development of the children. If this had been the case, the same similarity in the preference development of the two groups would have been found in the even longer period between T1 and T2. The fact that with the three different products different changes have been observed over this period is a further argument against such a ‘‘mere ageing” hypothesis. The fact that children can shift their liking towards more complex flavour stimuli after relatively little exposure and independent of their ageing, has also been established by Léon (Köster et al., 2002; Léon, Couronne, Marcuz, & Köster, 1999) who showed that children shifted their liking from simple to complex strawberry jam taste over just a few exposures within a period of 3 weeks. The ‘‘optimal arousal shift” theory of Dember and Earl (1957), on which most of the hypotheses forwarded here were based and Berlyne’s views on exploratory behaviour seem to offer the best explanations for most, but not all of the results found. Thus, it is clear that the results obtained with the mashed potatoes and with the compotes are fully in line with what one might expect on the basis of the Dember and Earl theory if one assumes that the arousal potentials of the mashed potatoes samples ranged from at or just below to higher than the optimal level and that the ones for the compotes were all considerably higher than the optimum. At the same time it is clear that in the case of the yoghurts the arousal effects are disturbed by the rather strong aversive effects of the bitterness which seems to dominate the preference. This latter finding is in line with the results of Sulmont-Rossé et al., 2008 and of Zandstra et al. (2004) who did find that the effects of arousal raised by stimulus complexity could easily be disturbed by, respectively, strong sweetness or caloric content differences in their stimuli. Nevertheless, the results obtained with the mashed potatoes and the compotes seem to lend support to the idea that the composition of the set of stimuli combining complexity and intensity

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as the two factors that determine the arousal potential of the stimuli has been successful. The preliminary experiment with the extra-group of children had already checked that the expected order of arousal level of the stimuli seemed to correspond with the real order. The results of the main experiment seem to confirm that different levels of arousal potential could indeed be obtained by the formulation of the range of product differing in basic taste intensity and flavour complexity. The lowest arousal level was closest to the children’s individual optimal arousal level. That means that the less aromatic and less intense stimuli were initially preferred as one might expect on the basis of both Dember and Earl’s theory and Berlyne’s ideas about specific exploratory behaviour and the initial unpleasantness caused by uncertainty in the confrontation with novel and more complex stimuli. In the preliminary experiment, it has further been shown that paired comparison is a well-adapted method for the measurement of complexity with children. Moreover, the evaluation of complexity based on a reduced number of questions seemed to be sufficient for this type of study. Jellinek and Köster (1979, 1983) measuring perceived complexity in odorants with adult subjects used also paired comparison with success. Their subjects simply had to decide which of each pair of stimuli contained most odour notes according to their opinion. 4.1. The effects of the sensory education program: mere exposure versus cognitive education The fact that the development of the preference for more complex foods just after the sensory education period was the same for both groups indicates that it is based on mere exposure rather than on the cognitive education provided in the program. Moreover, the fact that in the control group the newly acquired preferences hardly changed over the following 10 months (see Fig. 5) may indicate that the exposure has probably caused a permanent shift in the optimal arousal level of the children as is expected by the arousal theory of Dember and Earl. According to their view the optimal arousal level can only be influenced by exposure to pacers (stimuli that are more complex and arousing than the optimum) and not by stimuli of a lower arousal level. This is the way in which one learns to appreciate more complex things in life. That mere exposure may play an important role in food preference development has been shown by a number of authors (Birch & Marlin, 1982; Pliner, 1982; Sullivan & Birch, 1990). It should be remembered however, that there are also cases in which it has no or even an adverse effect and that the occurrence of these opposing effects seems to depend on the arousal potential of the stimuli relative to the optimal arousal level of the subjects (Köster & Mojet, 2007). Birch and Marlin (1982) exposed children either to new cheeses or to new fruits and showed that preference increased with exposure frequency. Pliner (1982) also showed the influence of mere exposure on the acceptance of novel foods and interpreted it in terms of the dissipation of neophobia. Whether this latter interpretation applies in the present case is not certain, because although the educated children showed a clear decrease of neophobia immediately after the education program, the control group children did not (Reverdy et al., 2008) and showed nevertheless the same preference shifts. Furthermore, the preference shifts stayed at least stable in both groups over time after the program and became even more pronounced at T2 in a number of cases for the educated group, although the earlier found decrease in neophobia for this latter group disappeared again over this same period (see T2–T1 in Reverdy et al. (2008)). If the sensory education program had no immediate effect on the development of the preferences, why did it have an effect on

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the later developments as shown tentatively for the compotes and clearly for at least the middle range of the mashed potato samples? In these cases the educated group clearly distinguishes itself from the control group at T2. Several possible explanations for this education effect present themselves. One possibility might be that the sensory education has instigated the educated group to try more new foods in the period immediately following the program in which they showed a decreased food neophobia. If among these new foods there were a number of more complex or otherwise arousing foods they would develop a higher optimal level of arousal than the control group that remained neophobic throughout this period. That complexity is a strong factor in the change of the arousal level has been shown in a number of studies (Lévy & Köster, 1999; Lévy, MacRae & Köster, 2006; Reverdy, Lange, & Schlich, 2004). In the latter of these studies a faster effect of sensory education was obtained with young adults and teas differing in perceived complexity. Another explanation of the delayed effect of the sensory education in the present experiment might be that the cognitive aspects of the education provided the educated group with a better vocabulary to talk about food and made them indeed more consciously interested in the complexity of the sensory interactions in foods. Thus, they might discuss foods more often in their peer group. This raised interested might than in turn result in more frequent experiences with new and interesting food. Other tests in the program have indeed shown that the educated group developed a better ability to describe and categorise sensory experiences in a more objective way (Lange et al., in preparation, personal communication; Reverdy, 2008). Mustonen et al. (2009) showed the effect of sensory education on activation of children’s odour and taste perception and an improvement in their ability to describe the sensory properties of the food. Nevertheless, these effects were not consistent over the 2 years period of their study. Still another explanation of the difference at T2 between the groups may be found in the fact that both groups continue to be with their teacher who was involved (education group) or not involved (control group) in giving the lessons in the program. Teacher modelling can be effective if it is enthusiastic rather than silent (Mmm! I love mangos!) and as long as it does not compete with peer modelling (Hendy & Raudenbush, 2000). As the first of these authors explains Hendy (2002): ‘‘Social Cognitive Theory (Bandura, 1997), peer models would be expected to be one of the most powerful agents to encourage food acceptance during preschool lunch, with same-gender peers expected to be especially effective”. Thus, the effect of the teacher supported by the fact that the whole class took part in the sensory education program, may have been a powerful stimulation for the further exploration of new foods. It is not possible to decide which of these mutually non-exclusive explanations of the delayed success of the sensory education should prevail, but the fact that the education shows these late results seems to be a very hopeful sign for the influence of the program on the further development of a more varied food pattern in children.

Acknowledgments We would like to thank the Academy of Dijon, including Corinne David, Elodie Lecki, Pascale Petitjean and Alain Lamboley for including the ‘‘Classes du goût” in their teaching programme. We gratefully acknowledge the children and their parents for their willingness to participate in this study. Warm thanks to Nathalie Politzer who adviced for the sensory education program. We also

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thank Catherine Pédron, Aurélie Dagain and Renaud Garret for their assistance in the measurement sessions. This project was sponsored by the French National Agency for Research (ANR) and

the National Institute for Agronomical Research (INRA); it was also labellised by the ‘‘Taste-Nutrition-Health” competitive cluster Vitagora.

Appendix 1. Description of the sensory education program Title and aim of the session

Organization of the session

Conclusion and/or contribution of the session

Lesson 1

«The five senses» This session evokes the pupils’ understanding of the way in which one makes contact with foods

The teacher proposes a tasting procedure in three steps (before, during and after) that uses the five senses to describe a food. This session allows children to enrich their vocabulary on what they feel sensorially and emotionally

– All five senses are necessary to establish contact with the world of foods – This contact always comes about in three phases (before, during and after the tasting)

Lesson 2

«Taste» This session lets the pupils discover the basic tastes (sweet, salty, sour, bitter and umami) and other mouth sensations (prickling, burning, astringency)

The teacher proposes varied tastings to the pupils to let them discover their own taste perception and let them find out that they give answers that are both similar to those of others, but still very personal

– Foods offer a wide variety of tastes and chemical sensations in the mouth – Knowing how to express different tastes and sensations – Showing the diversity between individuals in gustative perception

Lesson 3

«Vision» This session lets the pupils understand how vision creates expectations that allow them to anticipate food taste

Tastings making use of colorants can show how visual perception creates expectations capable of modifying other perceptions

– Colours have an impact on other sensory perceptions – Establishment of precise vocabulary for visual perception

Lesson 4

«Olfaction» This session shows the pupils how difficult it is to recognise odours

Odour bottles (more or less familiar odours, fruity odours. . .) are presented to evoke the pupils’ memories and lead to identification

– Show the relationship between an odour and the evocation of its source as well as of associated memories – Identify some familiar odours

Lesson 5

«Touch and hearing» This session aims at enrichment of the vocabulary for touch and to show how touch and hearing complement each other

Samples of different materials (silk, wool, velvet . . .) are presented to the pupils. Foods of different hardness, crispness and crumbliness are tasted

– Different sensations are linked to touch during tasting: tactile, auditory and thermal perception – Enrich vocabulary on touch and hearing – Link food texture, consistence and temperature with each other

Lesson 6

«Aroma» This session shows how aromas in the mouth are perceived by retro-nasal olfaction and how a food when eaten cold or warm gives off different aromas

Different very aromatic foods are tasted and the teacher explains how one can get rid of the aromatic sensations by using the ortho or retro-nasal way

– Distinction between direct (odours) and indirect (aromas) olfaction – The temperature of foods modifies the sensations

Lesson 7

«Flavour» This session provides the possibility to study the sensations of sessions 2, 4 and 6 simultaneously

The pupils learn to identify these different sensations when they are simultaneously present in complex foods, as well as to identify their development over time

– Definition of flavour – Forms of interactions between the senses involved – Synthesis of all themes evoked hitherto (important information and vocabulary)

Lesson 8

«Preparation of a dish» In this session, with the help of a professional, the pupils prepared a recipe for food

This cooking workshop takes place with a professional

– Experiencing the pleasure of working out a dish – Understanding the variety of possible ways to eat a given food – Discussion on eating habits

Lesson 9

«Food preferences»

Tasting unfamiliar food: each group is

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Appendix A1 (continued) Title and aim of the session

Organization of the session

The pupils are asked to justify their preferences and to stimulate their curiosity for new foods

required to search for taste information about one fruit and then to encourage other children to taste it

– Individual food preferences differ a lot – To talk about your preferences and to justify them – To accept the taste of new foods

Lesson 10

«Regional specialities» The pupils note differences in local and international specialities and how cultural history may explain them

The teacher and pupils offer different local specialities for tasting

– Present regional culinary specialties brought along by the pupils and think about their origin – Enlarge their knowledge by tasting specialties from other regions and cultures

Lesson 11

«Recapitulation» In this session, the pupils have to remember the knowledge built up during these lessons

They participate in a quiz that synthesizes the acquired knowledge

– To remember the acquired knowledge that can be of help when evaluating food

Lesson 12

«The festive meal» This last session presents the pupils with an occasion to transfer the things they have learned during the foregoing lessons by evaluating a meal prepared for them

The pupils eat a meal at the restaurant

– Re-use the acquired knowledge – Take part in a relaxing experience: the pleasure of eating together – Develop skills linked to table manners and ‘‘savoir-vivre” – Evaluate the effect of preserving on the taste of food

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