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When producing filled chocolates, the selection of the ingredients and production process are both crucial for the sensory characteristics of the pralines. Sensory ...
Artikel - Article Sara De Pelsmaeker, Xavier Gellynck, Claudia Delbaere, Nathalie Declercq, Renata Januszewska, Adrienn Hegyi, Tünde Küti, Frédéric Depypere and Koen Dewettinck*

FOOD SCIENCE &LAW 2013/2

The influence of different storage conditions and fat bloom on sensory characteristics of pralines Abstract

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hen producing filled chocolates, the selection of the ingredients and production process are both crucial for the sensory characteristics of the pralines. Sensory attributes such as hardness, chocolate flavour, gloss, etc. are closely related to both the selected ingredients and the parameters used in production. During storage, these characteristics can change due to alterations in the microstructure of the filled chocolates. The aim of this study is to measure the sensory characteristics at the moment fat bloom occurs on the surface of the filled chocolates. This study identifies which characteristics deteriorate when stored for three months and therefore gives an indication on which characteristics technologists and researchers need to focus on when improving the quality of filled chocolates by trying to find solutions to fat bloom.

Samenvatting

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ijdens de productie van pralines zijn de selectie van de ingrediënten en het productieproces van cruciaal belang voor de sensorische kenmerken van de pralines. Sensorische eigenschappen zoals hardheid, chocoladearoma, glans enz. staan in nauw verband met zowel de geselecteerde ingrediënten als de parameters die in het productieproces worden gebruikt. Tijdens de bewaring kunnen wijzigingen in de microstructuur van de pralines deze eigenschappen doen veranderen. Het doel van deze studie is om de sensorische eigenschappen te meten op het moment dat vetbloem aan de oppervlakte van de pralines verschijnt. Deze studie stelt vast welke eigenschappen verslechteren wanneer ze drie maanden bewaard worden. Op deze manier krijgen technologen en de onderzoekers een indicatie van op welke eigenschapen ze zich moeten focussen wanneer ze de kwaliteit van pralines verbeteren door oplossingen te zoeken voor vetbloem.

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Sara De Pelsmaeker, Xavier Gellynck, Claudia Delbaere, Nathalie Declercq and Renata Januszewska: Ghent University, Department of Agricultural Economics; Adrienne Hegyi and Tünde Küti: Campden, BRI Magyarország Nonprofit Kft.; Frédéric Depypere and Koen Dewettinck: Ghent University, Department of Food Safety and Food Quality; Contactadres: [email protected], tel.: +32 9 264 59 30, fax: +32 9 264 62 46.

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Résumé

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ors de la production de chocolats fourrés, la sélection des ingrédients et le processus de production sont cruciaux pour maîtriser les qualités sensorielles des produits. Les caractéristiques sensorielles, par exemple la dureté, le goût chocolaté, la brillance, etc., sont étroitement liées aux ingrédients ainsi qu’aux paramètres de production sélectionnés. Lors de la conservation, ces caractéristiques peuvent évoluer suite à des altérations au niveau de la microstructure des chocolats fourrés. Le but de cette étude est de mesurer les caractéristiques sensorielles lorsque du blanchiment gras ou ‘fat bloom’ apparaît à la surface des chocolats fourrés. Cette étude identifie les caractéristiques qui se détériorent après trois mois de conservation. Elle offre donc une indication aux technologistes et chercheurs quant aux caractéristiques sur lesquelles ils doivent se concentrer afin d’améliorer la qualité des chocolats fourrés en tentant de les prémunir du blanchiment gras ou ‘fat bloom’.

I. Introduction

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hen defining the quality of chocolate, the sensory properties of chocolate are considered to be the most important parameters (Popov-Raljic & Lalicic-Petronijevic, 2009). The liking of chocolate by consumers is mostly depending on the sensory acceptance. Dark chocolate is a complex suspension of solid particles such as cocoa mass and sugar in a continuous fat matrix of cocoa butter (Jaeger, Jørgensen, Aaslyng & Bredie, 2008). Milk chocolate also contains milk powder or other raw materials. Plain chocolate has a shelf life of 12 to 24 months (Tuorila, 1996) although it depends on different parameters such as storage temperature, humidity, accessibility of oxygen and ingredients (Mexis, Badeka, Riganakos & Kontominas). Those parameters are even more important in the case of filled chocolates, which are chocolate confections filled with a lipid substance such as nut paste or an alcohol filling (Ali, Selamat, Che Man & Suria, 2001; Choi, McCarthy & McCarthy, 2005). During storage, oil migration occurs depending on the different chemical and physical properties. This oil migration causes unwanted texture changes such as hardening of the filling and softening of the couverture chocolate. Additionally, a recrystallisation of the oil occurs, which may eventually lead to fat bloom on the surface of the filled chocolate (Lonchampt & Hartel, 2004). Fat bloom can be described as a gradual change in colour and loss of gloss giving a grayish appearance to the surface of chocolate (Briones & Aguilera, 2004) (Figure 1). Thus, this oil migration results in texture, colour but also in flavour changes (Ali et al., 2001; Andrae-Nightingale, Lee & Engeseth, 2009).

Figure 1. Example of fat bloom on the used pralines

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everal authors studied the effect of storage temperature on the appearance of fat bloom. Ali et al. (2001) stated that fat migration can occur at a considerable rate at room temperature (17 °C-23 °C) and increases as the temperature increases. Moreover, it is proven that next to a high storage temperature, fluctuating temperature also causes and even accelerates fat bloom. The changing temperature causes the melting and the recrystallisation of low melting point crystals. The process has an impact on the microstructure, visual appearance and textural properties (Afoakwa, Paterson, Fowler & Vieira, 2009; Nöbel, Böhme, Schneider & Rohm, 2009). Several studies have indicated that fat bloom causes changes in the sensory characteristics of chocolate or pralines. A recent study indicated that fat bloom causes chocolate to be harder, less cohesive, less chewy and have a longer melting time. Next

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to that, the chocolate has a less intense sweet taste and lower cream flavour (Andrae-Nightingale et al., 2009; Tuorila, 1996). When focusing on filled chocolates, Depypere (2009) stated that quality defects may arise by oil migration. Several defects that may occur are softening of the chocolate layer, hardening of the filling and deterioration in the sensorial aspect of the chocolate (appearance, colour or taste). Thus, previous studies have focused on the microstructural influences and causes of fat bloom but little on the sensory quality of filled chocolate and the changes during storage. Therefore, this study aims to identify influence of storage temperature and fat bloom on the sensory quality of filled chocolates. Colour measurements were conducted on the different variants to identify fat bloom. Further, a trained sensory panel evaluated the filled chocolate immediately after production and after three months of storage using quantitative descriptive analysis.

Variant V1 V2 V3 V4 V5 V6

Couverture Dark chocolate (32 % fat) Dark chocolate (32 % fat) Milk chocolate (33 % fat) Milk chocolate (33 % fat) Dark chocolate (32 % fat) Dark chocolate (32 % fat)

II. Materials and methods A. Materials

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his research was done in the framework of FP7-project ProPraline. Six different formulations of filled chocolates, composed of milk or dark chocolate and hazelnut or alcoholic fillings, were prepared differing in couverture and/or filling as shown in Table 1. The pralines were produced at the UGent Cacaolab. A standard tempering procedure was used for dark and milk chocolate. The chocolate was filled in the mold to form the chocolate shell. The hazelnut fillings were tempered on a marble table while the alcoholic fillings were heated to 28 °C. Both fillings were sprayed in the chocolate shells with a piping bag. The pralines were closed by a chocolate layer and were subsequently coded. Finally, they were cooled for 30 minutes on 20 °C, followed by storage at 15 °C for ± 12 hours.

Filling Low-level hazelnut oil (26 % cocoa butter, 43 % fat) High-level hazelnut oil (30 % cocoa butter, 43 % fat) Low-level hazelnut oil (26 % cocoa butter, 43 % fat) High-level hazelnut oil (30 % cocoa butter, 43 % fat) Low-level strawberry alcoholic (8.9 % alcohol) High-level strawberry alcohol (12.9 % alcohol)

Table 1. Overview of the six variants

B. Storage

C. Sensory analysis

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he pralines were divided in three batches, of which one was immediately evaluated and the two other batches were stored at a different temperature. The fresh pralines were used as reference for comparison of the pralines stored at 20 °C and 23 °C. The second batch was stored at 20 °C, which is a control temperature at which oil migration is slow but significant. The third batch is exposed to a fluctuating room temperature with a mean of 23 °C in an office at the university with an upper and lower range of 1.5 °C. This is the closest to how consumers keep their filled chocolates stored at their homes. The intention of the study was to mimic as close as possible the consumer’s environment.

trained panel was used to create the sensory profile of the produced filled chocolates. The use of sensory analysis techniques with trained assessors provides an objective measurement of the sensory characteristics of the pralines; thus descriptive methods are adopted which show differences between samples. The panellists were trained over a period of 10-15 hours to perform quantitative descriptive analysis (Murray, Delahunty & Baxter, 2001). Each panelist received a blind coded sample in two replicates. The samples were randomised in order to minimise the carry-over and order effects. For every attribute, the assessors scored the product on a 0-9 category scale, anchored with the ‘none’ and ‘high’. The evaluation was carried out in a sensory laboratory.

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D. Colour measurement

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he chocolate colour was measured on a Minolta Model CM-2500D spectrophotometer (Konica Minolta Sensing Inc., Osaka, Japan). The Minolta measurements were expressed in L* value for lightness, a* value for redness and b* for yellowness. The Whiteness Index (WI) is used as indicator of white colour development due to fat bloom formation and made it possible to compare different samples (Altimiras, Pyle & Bouchon, 2007). The WI is based on the Euclidian distance between a particular CIE-Lab coordinate and the white point at L*/a*/b* = 100/0/0 (Anonymous, 2007). WI data are normally calculated with the following equation: WI = 100 – [(100-L*)² + a*² + b*²]1/2 For every variant, 8 filled chocolates were randomly selected for measurements. The colour of the bottom of the chocolates was measured at three different locations for each sample.

E. Data analysis

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irst, analysis of variance is carried out to test if there are significant differences between the means of samples (products) for the measured parameters of instrumental analysis (Cartier et al., 2006). Moreover, a two-way ANOVA was

  Fresh 20 °C 23 °C

done to identify the significant differences between the sensory attributes. The Neuman Keuls (NK) multiple comparison test is therefore applied to determine whether the samples are significantly different for each attribute at a specified level of significance (5 %).

III. Results A. Colour measurement

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he colour was measured after 3 months of storage at 20 °C and 23 °C using the CIEE L*, a*, b*, coordinates. Based on these measurements, the whiteness index was calculated for all the different variants (Table 2). The effect of storage is explained by comparing the three temperatures for the six variants. For V1 and V2, the results indicate that the whiteness index increases after storage and as function of temperature for V2 although there are no significant differences detected for V1. For V3, no significant differences were measured. It is possible that fat bloom did occur although it was not visible due to the lighter colour of the milk chocolate. For V4, significant differences were found. V5 chocolates show an increase of WI with higher temperature. For V6, the WI for samples stored at 20 °C is significantly different from the fresh pralines. Although the WI for the samples stored at 23 °C is also higher, this is not a significant difference.

V1 a

V2 a

V3 a

V4 a

V5 a

V6 a

27.76 ± 0.38 a

27.26 ± 0.12 a

33.31 ± 0.28 a

33.06 ± 0.33 a, b

26.00 ± 1.09 a

27.13 ± 0.26 a

31.54 ± 3.83 a

31.25 ± 1.67 b

33.70 ± 0.50 a

33.65 ± 0.57 b

34.75 ± 3.79 b

31.29 ± 1.63 b

31.61 ± 4.16 a

35.71 ± 2.33 c

33.88 ± 1.99 a

32.50 ± 1.31 a

40.46 ± 4.16 c

28.27 ± 0.79 a

Mean ± standard deviation. Means within the same column with different letter are significantly different. Table 2. Whiteness index for all six variants a

B. Sensory analysis

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li (2001) studied the effect of storage on the sensory characteristics of chocolates but limited his study to colour, texture, flavour and overall acceptability. This study deepens the knowledge on sensory changes after storage on different sensory attributes and thus gives a more complete overview of the influence of storage and ingredients. Moreover, these results help to intercept the possible defects that a chocolate producer needs to understand before changing a recipe, altering

storage conditions or even when implementing actions to reduce fat bloom. Fresh pralines: influence of ingredient

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n order to identify the sensory differences caused by the ingredients, the fresh filled chocolates were compared within the same group thus V1 with V2, V3 with V4 and V5 with V6. Immediately after production, V1 and V2 are only significantly different for hardness (p = 0.001) and melting in mouth (p = 0.045). V1 is harder and melts slower than V2, which is due to

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the lower percentage of hazelnut oil in the filling. The trained panel did not detect any significant differences between V3 and V4 after production. The chocolates filled with an alcohol filling had a different gloss (p = 0.019) and a different amount of air bubbles (p = 0.003). As the gloss was higher and the air bubbles lower for V6, it might be suggested that this is due to production of V5. Next to that V5 was perceived as harder (p = 0.018) and slower melting (p = 0.004) than V6, which can be related to the higher alcohol level in V6, which is in line with the texture measurements. Comparison of fresh and stored pralines: influence of storage

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ased on the visible bloom recorded by the researchers and the colour measurements, only three variants were chosen to perform sensory analysis on for storage at 20 °C as well 23 °C namely V1, V4 and V5. This was a precaution as not to overload the trained panel. Although the detected differences caused by storage are rather small, fat bloom is anyhow altering the characteristics of these types of pralines as well. Figure 2 shows the results for the attributes that are significantly different for V1. The sensory analysis shows little difference in gloss. However, the panel indicated that the intensity of the colour is significantly lower after storage at 23 °C, which is linked to the higher amount of fat bloom. The filled chocolates stored at 20 °C and 23 °C have a less distinct aroma profile

such as lower chocolate, bitter and specific (= hazelnut) aroma. These results suggest that aromas tend to fade due to storage or fat bloom. The texture attributes hardness and homogeneity decrease significantly after storage. Finally, the fresh filled chocolate has a moderate bitter flavour which decreases slightly for storage at 20 °C and significantly for storage at 23 °C. For V4, the gloss of the filled chocolate is rated as significantly higher due to storage (Figure 3). This can be explained as fat bloom on milk chocolates is more difficult to detect visually than when it appears on dark chocolate. The texture attributes snap and hardness decrease during storage. Further, the sweet flavour fades to a lower intensity during storage. These results indicate that fat bloom also affects the sensory characteristics, particullarly texture and sweet flavour, of pralines with a milk chocolate couverture.

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he trained panel identified few changes on the dark chocolates with alcohol filling due to storage and fat bloom (Figure 4). The gloss of stored filled chocolates is evaluated as significantly higher than on fresh samples. This indicates that the process of fat bloom formation is difficult to assess. Further, the density of the filling increases, suggesting that an unknown process is altering the texture of the alcohol filling. Finally, the specific alcohol flavour decreases during storage. Although the detected differences caused by storage are rather small, fat bloom is anyhow altering the characteristics of these types of pralines as well.

Figure 2. Differences between the V1 samples fresh, stored at 20 °C and 23 °C

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Figure 3. Differences between the V4 samples fresh, stored at 20 °C and 23 °C

Figure 4. Differences between the V5 samples fresh, stored at 20 °C and 23 °C

IV. Conclusions

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his study confirms previous studies that indicate that fat bloom alters the sensory characteristics of chocolate and filled chocolate. Colour measurements showed significant changes to the surface colour, especially for the pralines with dark chocolate couverture. This was confirmed by the evaluation of the trained panel. Previous literature indicated that fat bloom changes texture of chocolate and filled chocolates. This study confirms these results as sensory analysis shows that hardness decreases for the hazelnut filled pralines due to the softening of the couverture. Moreover, the results indicating that the aroma and flavour is altering during storage is interesting. For V1 and V2, the aromas that define these samples (chocolate, bitter and specific hazelnut) are changing from high intensity to moderate. All

samples have one flavour, bitter for V1-V2 and specific filling flavour for V3-V4 (hazelnut) and V5-V6 (alcohol) that significantly decreases during storage. It would be interesting if these changes can be picked up in further studies with instrumental analysis through GC-MS aroma component detection and find the correlations between sensory and instrumental analysis.

V. Acknowledgments

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his study has been carried out with the financial support of the European Commission in the frame of the FP 7 project ProPraline. The authors want to thank and acknowledge the input from Bühler, Guylian and UGent Cacaolab for the production of the different samples.

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VI. References Afoakwa, E.O., Paterson, A., Fowler, M. & Vieira, J.,. ‘Fat bloom development and structure-appearance relationships during storage of under-tempered dark chocolates’, (2009) Journal of Food Engineering, 91(4), 571-581.

Murray, J.M., Delahunty, C.M. & Baxter, I.A., ‘Descriptive sensory analysis: past, present and future’, (2001) Food Research International, 34(6), 461-471. Nöbel, S., Böhme, B., Schneider, Y. & Rohm, H., ‘Technofunctional barrier layers for preventing fat bloom in triple-shot pralines’, (2009) Food Research International, 42(1), 69-75.

Ali, A., Selamat, J., Che Man, Y.B. & Suria, A.M., ‘Effect of storage temperature on texture, polymorphic structure, bloom formation and sensory attributes of filled dark chocolate’, (2001) Food Chemistry, 72(4), 491-497.

Popov-Raljic, J.V. & Lalicic-Petronijevic, J.G., ‘Sensory Properties and Color Measurements of Dietary Chocolates with Different Compositions During Storage for Up to 360 Days’, (2009) Sensors, 9(3), 1996-2016.

Altimiras, P., Pyle, L. & Bouchon, P., ‘Structure-fat migration relationships during storage of cocoa butter model bars: Bloom development and possible mechanisms’, (2007) Journal of Food Engineering, 80(2), 600-610.

Tuorila, H., ‘Hedonic responses to flavor and their implications for food acceptance’, (1996) Trends in Food Science & Technology, 7(12), 453-456.

Andrae-Nightingale, L.M., Lee, S.Y. & Engeseth, N.J., ‘Textural changes in chocolate characterized by intstrumental and sensory techniques’, (2009) Journal of Texture Studies, 40(4), 427444. Briones, V. & Aguilera, J.M., ‘Image analysis of changes in surface color of chocolate’, (2004) Food Research International, 38, 87-94. Cartier, R., Rytz, A., Lecomte, A., Poblete, F., Krystlik, J., Belin, E. et al., ‘Sorting procedure as an alternative to quantitative descriptive analysis to obtain a product sensory map’, (2006) Food Quality and Preference, 17(7-8), 562-571. Choi, Y.J., McCarthy, K.L. & McCarthy, M.J., ‘Oil migration in a chocolate confectionery system evaluated by magnetic resonance imaging’, (2005) Journal of Food Science, 70(5), E312E317. Depypere, F., de Clercq, N., Segers, M., Lewille, B. & Dewettinck, K., ‘Triacylglycerol migration and bloom in filled chocolates: Effects of low-temperature storage’, (2009) European Journal of Lipid Science and Technology, 111(3), 280-289. Jaeger, S.R., Jørgensen, A.S., Aaslyng, M.D. & Bredie, W.L.P., ‘Best-worst scaling: An introduction and initial comparison with monadic rating for preference elicitation with food products’, (2008) Food Quality and Preference, 19(6), 579-588. Lonchampt, P. & Hartel, R.W., ‘Fat bloom in chocolate and compound coatings’, (2004) European Journal of Lipid Science and Technology, 106(4), 241-274. Mexis, S.F., Badeka, A.V., Riganakos, K.A. & Kontominas, M.G., ‘Effect of active and modified atmosphere packaging on quality retention of dark chocolate with hazelnuts’, (2010) Innovative Food Science & Emerging Technologies, 11(1), 177186.

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