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Effect of structure in the sensory characterization of the crispness of toasted rusk roll
Food Research International 41 (2008) 480–486
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Effect of structure in the sensory characterization of the crispness of toasted rusk roll C. Primo-Martin a,*, E.M. Castro-Prada a,b, M.B.J. Meinders a,c, P.F.G. Vereijken a,d, T. van Vliet a,b a
TI Food and Nutrition (WCFS), Bornsesteeg 59, 6700 AA Wageningen, The Netherlands Wageningen University, Bomenweg 2, 6700 EW Wageningen, The Netherlands c Agrotechnology and Food Sciences Group, Bornsesteeg 59, 6700 AA Wageningen, The Netherlands d Biometris, Wageningen University, P.O. Box 100, 6700 AC Wageningen, The Netherlands b
a r t i c l e
i n f o
Article history: Received 22 October 2007 Accepted 24 February 2008
Keywords: Cellular solids Crispness Structure Toasted rusk roll Water content Water activity Relative humidity Sound Sensory
a b s t r a c t Crispness is a salient textural attribute of toasted foods strongly related to their preference. Crispness is affected by water content, mechanical properties and morphology of the food. Sound emission and force characteristics during food crushing play a key role in crispness. The aim was to assess the effect of product morphology on sensory crispness grading of toasted rusk roll, a cellular solid food. Products with coarse and fine structures were studied. Additionally, the effect of water on crispness was studied by using samples with water activities from 0.30 to 0.8. The sensory test showed that upon absorption of water the product became tough and soft and lost its crispness. The morphology of the product had a significant effect on crispness intensity. Coarse products were rated crispier than those with a fine crumb grain. Deterioration of crispness (Aw10%) started at 0.46 and 0.50 water activity (6.2% and 7.1% H2O) for the fine and coarse structure product, respectively. The critical water activity (Awc) at which the products lost 50% of the crispness was 0.57 and 0.59 (9.1% and 9.7% H2O), respectively for the fine and coarse structure product. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction A salient textural attribute for toasted foods is crispness, which has been shown to determine food preference (Katz & Labuza, 1981). The architecture of a crispy product can mostly be characterized as an open cellular structure that, in physical terms, is stiff, brittle and fractures and disintegrates abruptly and completely during biting and chewing with accompanying sound emission (Dijksterhuis, Luyten, De Wijk, & Mojet, 2007). Sound produced during crushing plays a key role in the perception of crispness and together with the flavor in the mouth and the oral tactile sensations produced during chewing determines the pleasant perception of food (Drake, 1963; Vickers, 1981; Vickers & Bourne, 1976). Crispness is negatively affected by increasing water content or water activity. The effect of water on the texture of crispy products has been widely studied before (Dacremont, 1995; Duizer, Campanella, & Barnes, 1998; Harris & Peleg, 1996; Katz & Labuza, 1981; Marzec, Lewicki, & Ranachowski, 2007; Roudaut, Dacremont, & Le Meste, 1998; Sauvageot & Blond, 1991; Tesch, Normand, & Peleg, 1996; Valles Pamies, Roudaut, Dacremont, Le Meste, & Mitchell, * Corresponding author. Tel.: +31 317 475120; fax: +31 317 475347. E-mail address: [email protected] (C. Primo-Martin). 0963-9969/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2008.02.004
2000). These studies showed that upon adsorption of water a crispy product becomes pliable, ductile and soft and loses its crispness and consequently its acceptability by the consumer. Despite these studies, the relative importance of water activity over water content or viceversa has yet not been clarified and it is currently under study (Van Nieuwenhuijzen et al., submitted for publication). Other factors affecting crispness are the properties of the material (composition, physical properties of the components) and the structure of the product (Luyten, Plijter, & van Vliet, 2004). Several authors suggested that crispness of food is affected by the size of the air cells and the thickness of the cell walls (Coppock & Carnford, 1960; Luyten & van Vliet, 2006; Mallikarjunan, 2004; Matz, 1962) but not clear guidelines for the industry have been produced. Barret, Cardello, Lesher, and Taub (1994) found a relation between mechanical properties (plateau stress) and structural properties (cell size and density of the material). Gao and Tan (1996) could predict mechanical properties from the analysis of the surface and cross-section images of a crispy product. Theoretical models like that of Gibson and Ashby (1997) have been applied to brittle foams to relate mechanical properties, sensory properties and cellular structure (Agbisit, Alavi, Cheng, Herald, & Trater, 2007). Dogan and Kokini (2006) recently showed a relation between crispness and the average number of peaks during
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fracture which varied with structural parameters and with phase change in the extrudates. However, the underlying mechanism relating morphology to the sensory properties of crispy foods is not yet clearly understood. The aim of this work was to assess the effect of the morphology of the product on the crispness perception. Thereto we studied the sensory perception of two toasted rusk rolls that differ significantly from each other regarding to morphology, one had a much coarser morphology than the other one. Conditioning of samples at different water activities was used as a tool to study the effect of the morphology. A mathematical model (Peleg, 1994) was applied to calculate the onset of the loss of crispness as a function of the structure of the product.
shaped mould (3.5 cm diameter). These middle parts were used for sensory analysis.
2. Material and methods
2.2.4. Water activity Water activity (Aw) of crust samples was measured as the relative humidity of the air in equilibrium with the samples in the sealed measuring chamber using a chilled-mirror dewpoint technique at 22 °C (Aqua Lab Series 3, Decagon devices, Pullman, USA).
2.1. Materials Toasted rusk rolls with a fine and a coarse structure were used. The toasted rusk roll with fine structure was kindly supplied by Bolletje (echte beschuit, Bolletje, Almelo, The Netherlands). The toasted rusk roll with a coarse structure was prepared at TNO baking laboratory (TNO Quality of Life, Zeist, The Netherlands) with the formulation supplied by Bolletje. Except with respect to some additives the formulations were the same. 2.2. Methods 2.2.1. Bread making Toasted rusk rolls with a coarse structure were prepared at the TNO baking laboratory (TNO Quality of life, Zeist, The Netherlands). Wheat flour (Dutch Top Rusk flour Meneba 2000 g), water (900 ml), dry yeast (133 g), salt (16 g), sugar (100 g), sugar syrup (200 g), egg (100 g), rusk jelly (240 g) and a mixture of improvers (20 g, provided by Bolletje) were mixed in a mixer (Kemper SP 15, Kemper, The Netherlands). First, all ingredients (at 10 °C) were blended for 1 min at low speed (140 rpm). Next, the water, egg, sugar syrup and rusk jelly (at 20 °C) was added and mixed at low speed for 2 min. Then, the dough was kneaded at high speed (280 rpm) until a final dough temperature of 28 °C was reached. After mixing the dough was scaled and rounded and allowed to rest for 30 min. Next a second and a third cycle of resting and rounding was done for 15 and 20 min. The dough was divided into smaller portions of 36.6 g and given a fourth resting of 10 min. Next, the dough pieces were flattened and put in a rusk tin. A final proofing was done at 30 °C and 80% RH until a fixed volume of gas was produced (900 ml) (in a piece of 186 g dough, SJA Fermentograph, Franken, Goes, The Netherlands). The dough was baked at 215 °C for 13 min in a Rototherm RE oven (Haton, The Netherlands). Afterwards the rusk rolls were cut (15 mm height) and pre-toasted (with the cut side to the top) at 230 °C for 7 min. Final toasting was done at 150 °C for a duration of 12 min. The toasted rusk rolls were allowed to cool at room temperature for 30 min before packaging in a double plastic bag. Top and bottom pieces had different gas cell distribution. The top piece was selected for our experiments because the difference in structure was larger compared with the fine structure of the commercial toasted rusk roll. 2.2.2. Rusk roll preparation for sensory analysis The bottom edge (1–2 mm) of the toasted rusk roll was harder than the rest of the product therefore it was removed using a food slicer. The side edges had the same problem and they were separated from the middle part by cutting this out with a cylindrical
2.2.3. Conditioning at constant relative humidity Samples were conditioned at eight relative humidities (RH) by placing the samples in climatic cabinets (Weiss SB 11300, Weiss technik Ltd., Buckinghamshire, UK) set at 22 °C and RH varying from 30% to 80%. The time needed to reach steady state was about 2 days for the samples at 80% RH, 3 days for the samples equilibrated in the range from 50% to 70% RH, respectively, and 4 days for the samples equilibrated at 30% and 40% RH. Samples were considered to be in steady state with the storage RH when they reached a constant weight in time (+0.001 g).
2.2.5. Water content The water content of the toasted rusk roll was determined by placing the samples in an oven at 105 °C for 24 h. The water content was calculated from the weight determined before and after oven drying. 2.2.6. Image acquisition and analysis Images of the cross sections of the toasted rusks rolls where taken from the top side of the toasted rusk rolls using a Hewlett Packard flatbed scanner (HP Scanjet C7716, Hewlett Packard, USA). Images were scanned fullscale using a resolution of 47.2 pixels/mm. The obtained images were analyzed using computerized image analysis with the free software ImageJ (http://rsb.info.nih.gov/ij/). RGB colour segmentation was performed and the red colour was selected for further analysis of the images. Unevenness and shadows were filtered using the ImageJ settings: bandpass filter of 100 and 5, for large and small structures, respectively. The number of cells, cell area and mean cell area were analyzed with Matlab (Matworks 7.0.4). 2.2.7. Density Toasted rusk roll volume (v) (sample equilibrated at 30% RH) was determined in duplicate using rape seed displacement. Density (q) was calculated as q ¼ mm where m is the mass of the toasted rusk roll. 2.2.8. Sensory analysis A trained panel of 8 Dutch panelists, 3 male and 5 female, aged between 20 and 62 years was used for the sensory tests. Table 1 describes the first bite and multiple bite attributes that were used in this study. They were selected from the attributes described by Dijksterhuis et al. (2007). Multiple bite attributes are used to study the effect of changes happening during food mastication (eg. saliva hydration) that affected the perception of crispness. Sensory attributes were scored by the panelist on line-scales (from 0 to 1000) using the Fizz computer program for automated sensory analysis (Biosystemes, 1998, FIZZ software, v1.20 K, Couternon, France). Prior to testing three training sessions were held to familiarize the participants with the products and with the attributes. Fine and coarse toasted rusk rolls equilibrated at eight different water activities were presented. Two duplicates were performed in two days. Within each day 16 samples were offered to the panelists in random order in one hour session including a 10 min break. For each sample, first bite attributes were rated directly after the first bite. Multiple bite ratings were rated while chewing the sample.
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a coarse structure had more large gas cells than the one with a fine structure which in turn had relatively more small gas cells. Density of the toasted rusk rolls was: 0.11 ± 0.01 and 0.12 ± 0.02 g/ml, respectively, for the coarse and fine structure products.
Table 1 Atributes at first and multiple bite in English and Dutch and English definition Attributes
English
Dutch
Definition
First bite
Amount of sound Snapping Pitch
geluid
Amount and loudness of sound
krakend knisperend
Crackling Crispy Brittle Bite force
knapperig krokant bros bijtkracht
Hard
hard
Tough Crumbly Splinters
taai kruimelig scherfjes
Loud, sharp, short sound High pitched sound, light sound, longer sounding It breaks in pieces Cracks, more airy than crackly Airy, not hard, but giving resistance Resistance, force you have to exert to bite, not necessarily hard Resistance, with sound, snaps. Bite force needed Requires pulling to tear off Small pieces in the mouth Sharp pieces in the mouth
Amount of sound Type of sound Snapping Pitch
geluid
Amount and loudness of sound
type geluid
From low to high pitch (musical scale)
krakend knisperend
Crackling Crispy Brittle Hard
knapperig krokant bros hard
Loud, sharp, short sound High pitched sound, light sound, longer sounding It breaks in pieces Cracks, more airy than crackly Airy, not hard, but giving resistance Resistance, with sound, snaps. Bite force needed
Airy Drying Tough Crumbly Splinters Gooey
luchtig droog taai kruimelig scherfjes klef
Melting
smeltend
Multiple bite
Requires pulling to tear off Small pieces in the mouth Sharp pieces in the mouth By chewing becomes a soft masse in your mouth, sticky Melts in the mouth
C 1 þ expðB ðX X c ÞÞ
Table 2 shows the measured water activity and the water content of the samples after equilibration at the different RH. The differences between water activity as well as the water content of the toasted rusk rolls with different structure are marginal, with the exception of the coarse structure equilibrated at 30% RH. The latter had a lower water content (3.6% H2O) than the one with the fine structure (4.8% H2O). 3.3. Sensory analysis
2.2.9. Statistical analysis Pairwise comparison between sensory attributes, averaged over duplicates and panel members, at each water activity was carried out using a two-sided t-test (P < 0.05) with GenStat software v 8 (VSN international Ltd., Herts, UK). The relationship between water activity, morphology and attributes were studied using principal component analysis (PCA) (Unscrambler, Camo, Inc.) performed on averaged sensory data over panelists and replicates. The sigmoid relationship between the sensory attributes, averaged over panelists and replicates, and the water activity or the water content was described using the logistic curve: S ¼ Smin þ
3.2. Water activity and water content of toasted rusk rolls
ð1Þ
where S is the expected value of the sensory score averaged over panelists, Smin the lower asymptote, C the attribute range (Smax Smin), X the water activity or water content (Aw or [H2O]), B the slope at the transition region or steepness, and Xc the water activity water content at which the sensory attribute dropped by 50% (Awc or [H2O]c). Non linear regression analysis (using GenStat software v 8 (VSN international Ltd., Herts, UK)) was used to fit the curves. 3. Results and discussion 3.1. Morphology of toasted rusk rolls Fig. 1 shows the size distribution of the gas cells of the coarse and fine toasted rusk rolls. The average gas cell size was 0.17 ± 0.02 and 0.10 ± 0.01 mm2, for the toasted rusk roll with coarse and fine structure, respectively. The toasted rusk roll with
Panelists were asked to score samples with different morphology and different water activity on first bite and multiple bite attributes. ANOVA showed that the structure of the product and the water activity had a significant effect (P < 0.05) on first as well as multiple bite attributes. 3.3.1. First bite attributes A principal component bi-plot (Fig. 2) based on all first bite attributes of the averaged sensory scores of the sensory panel shows the different products in the space delimited by the first two principal components (explaining 92% and 5% of the total variance, respectively). The first component separated toughness from all other attributes. The second component separated crispy, crackling, sound, snapping, splinters, bite force and hard from pitch, brittle and crumbly and was associated with samples with low water activity/content. PCA separated in the first dimension the samples as function of the water activity/content, samples on the right side had a lower water activity than the samples on the left side. With increasing water activities the crispy perception started to diminish or finally disappeared completely. The second dimension separated based on morphology samples that had perceptible crispness. The morphology of the samples resulted in a different perception of the sound and the texture during biting of the products. The coarse grain structure was perceived as producing more and louder sound as well as sharper and shorter sound events (snapping). The texture of the fine grain structure was perceived as more brittle and crumblier, breaking into smaller pieces after biting. In contrast, the coarse one was characterized as crispier, crackling, harder and breaking into sharp pieces, splinters, when fractured by the teeth. This is in line with previous work (Vincent, 2004) on potato crisps that showed that more and smaller cells result in a less crisp. Fig. 3 shows the averaged scores for the first bite attributes, sound, snapping, pitch, crispy, hard and splinters, as a function of the water activity for both coarse and fine structure products. Significant differences (shown by arrows) due to product morphology were found specially at low water activities for sound, snapping, crispy, hard and splinters. Pitch was not significantly different between coarse and fine toasted rusk rolls. Crispy related attributes are usually characterized by a sigmoid relationship between the attributes and moisture, water activity or temperature and can be fitted using Eq. (1). The estimated parameters from the fitted logistic curves, describing the relationship between sensory attribute and water activity, are shown in Table 3A. Table 3B shows estimated parameters for the relationship between sensory attribute and water activity. Fitted curves are shown in Fig. 3. R2 of the fitted curves were between 0.97 and 0.99. This sig-
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Fig. 1. Example of images of toasted rusk roll with different gas cell structure: (A) coarse morphology and (B) fine morphology. Gas cell size distribution of toasted rusk roll (C).
Table 2 Water activity and water content of samples conditioned to relative humidities (RH) ranging from 30% to 80% RH storage
30 40 50 55 60 65 70 80
Water activity
Water content
Fine structure
Coarse structure
Fine structure
Coarse structure
Average SD
Average SD
Average SD
Average SD
0.29 ± 0.01 0.37 ± 0.01 0.48 ± 0.01 0.53 ± 0.01 0.59 ± 0.00 0.62 ± 0.00 0.66 ± 0.01 0.77 ± 0.00
0.29 ± 0.02 0.38 ± 0.02 0.48 ± 0.00 0.53 ± 0.00 0.59 ± 0.00 0.61 ± 0.01 0.66 ± 0.01 0.78 ± 0.01
4.8 ± 0.6 5.0 ± 0.1 7.1 ± 0.2 8.2 ± 0.4 9.5 ± 0.1 10.6 ± 0.3 11.6 ± 0.1 15.2 ± 0.2
3.6 ± 0.3 5.1 ± 0.1 7.0 ± 0.1 8.1 ± 0.1 9.6 ± 0.1 10.3 ± 0.2 11.7 ± 0.0 15.6 ± 0.5
moid relationship is characterized by three parts (Peleg, 1994). The first part of the sigmoid curves shows a constant or a slight decrease of the attribute, the second part shows a rapid decrease of the averaged score for the attribute and the third part corresponds to the disappearance of the sensory sensation. The logistic curve can be characterize by the water activity at which the sensory perception is dropped by 50%. Peleg called this the critical water activity (Awc) (Peleg, 1994). However, also of interest is the water activity/content at which the sensory perception starts to decrease due to increasing hydration, that is, the starting point of the rapid decrease of the attribute. We define this point at the drop of the score by 10% (Aw10%, and H2O10%, Table 3A and 3B, respectively).
The onset of crispness decrease was 0.46 and 0.50 water activity (or 6.2% and 7.1% water content) for the fine and course structure product, respectively. And the critical water activity for crispness (Awc) corresponded with values of 0.57 and 0.59 (or 9.1% and 9.7% water content). When taking in consideration all attributes Aw10% was found between 0.43 and 0.51 (4.6% and 7.4% water content) for the products with a fine morphology and 0.47 and 0.54 (6.0% and 8.3% water content) for the products with a coarse morphology, although significant differences were not found between morphologies. For the attribute splinters the relation attributewater activity did not follow a sigmoid relationship (Fig. 3) for the coarse morphology therefore the values of Awc and Aw10% are undefined in this case. From the estimated parameters only the maximum value C was found to be significant for the different morphologies. 3.3.2. Multiple bite attributes Principal component analysis of the multiple bite attributes (Fig. 4) showed the same pattern of distribution of attributes and sample morphology over the first two principal components (explaining 90% and 6% of the total variance, respectively) as observed for the first bite attributes. Additionally, the fine product was perceived as melting and drying more during mastication. Further taste differences that were found between the products are that the coarse product was perceived as more salty and less sweet than the fine product. Fig. 5 shows a comparison of attributes scored at first and at multiple bites for the product with a coarse morphology. Crispness,
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Fig. 2. First two dimensions of PCA for first bite attributes. Letters indicate product morphology: C: coarse, F: fine. Numbers indicate water activity of the product.
Fig. 3. Effect of water activity on attributes: amount of sound, snapping, pitch, crispy, hard and splinters for coarse and fine structure. Open and close squares are experimental data. Solid lines are fittings of Eq. (1). Arrows show statistically significant differences (P < 0.05) between products with the same water activity.
hardness, sound and pitch were scored higher at first bite than on multiple bites. Same results were found for the product with a fine morphology (results not shown). The judgment of higher crispness at first bite corresponds well with previous work (Vickers, 1985) in which the authors compared crispness as perceived from bite sounds and chew sounds, although this author found no difference when crunchiness was judged from bite or chew sounds. Duizer (2001) also described crispness as a maximum during the first bite with a decline as mastication progresses due to breakdown of the cell wall fragments by the teeth and to the hydration by saliva.
4. Conclusions This work shows the importance of morphology for crispness perception and retention besides the known dependence of crispness on the water activity and water content. The onset of decrease of the sensory attributes, defined as Aw10%, was for crispness 0.46 and 0.50 water activity (or 6.2% and 7.1% water content) for the fine and coarse structure product, respectively. The effect of the structure on the onset of crispness decrease, although not significant, has not been described before and it may have important
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C. Primo-Martin et al. / Food Research International 41 (2008) 480–486 Table 3A Estimated parameters from fitted logistic curves Eq. (1), relating first bite sensory attributes averaged over panelists and water activity Morphology
Parameter
Amount of sound
Snapping
Pitch of sound
Crispness
Splinters
Hardness
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Fine
B Awc C Smin Aw10%
18.4 0.61 561 62 0.49
2.3 0.01 32 26 0.02
28.8 0.58 306 74 0.51
13.5 0.02 51 39 0.03
19.4 0.59 714 42 0.48
4.6 0.01 74 57 0.02
19.8 0.57 463 54 0.46
4.3 0.01 44 33 0.03
15.0 0.57 255 46 0.43
5.5 0.02 46 33 0.06
12.3 0.63 288 80 0.45
9.5 0.07 143 119 0.1
Coarse
B Awc C Smin Aw10%
19.6 0.61 666 77 0.50
2.1 0.01 30 24 0.01
16.6 0.60 563 35 0.47
5.2 0.02 85 67 0.04
29.2 0.62 568 78 0.54
8.7 0.01 59 49 0.02
22.9 0.59 595 63 0.50
3.9 0.01 41 32 0.01
23.6 0.61 414 98 0.52
7.5 0.01 51 41 0.02
s.e. = standard error.
Table 3B Estimated parameters from fitted logistic curves Eq. (1), relating first bite sensory attributes averaged over panelists and water content Morphology
Parameter
Amount of sound
Snapping
Pitch of sound
Crispness
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
Splinters s.e.
Estimate
s.e.
0.65 9.1 248 57 5.7
0.29 0.7 54 30 1.9
0.38 10.4 313 82 4.6
0.48 2.0 256 154 7.1
0.83 10.2 416 102 7.5
0.28 0.4 57 43 0.9
Fine
B [H2O]c C Smin [H2O]10%
0.66 10.0 568 71 6.7
0.12 0.3 47 32 0.8
1.11 9.4 304 79 7.4
0.59 0.6 58 42 0.9
0.72 9.6 724 54 6.5
0.20 0.4 90 59 0.6
0.74 9.1 474 60 6.2
0.20 0.4 58 35 1.1
Coarse
B [H2O]c C Smin [H2O]10%
0.71 10.1 671 88 7.0
0.10 0.2 43 30 0.4
0.58 9.8 580 46 6.0
0.23 0.6 114 69 1.9
1.01 10.5 570 77 8.3
0.32 0.3 67 53 0.9
0.85 9.7 598 71 7.1
0.17 0.3 48 34 1.2
Hardness
s.e. = standard error.
Fig. 4. First two dimensions of PCA for multiple bite attributes. Letters indicate product morphology: C: coarse, F: fine. Numbers indicate water activity of the product.
consequences for product storage. This onset value will limit conditions at which these products can be stored in order to keep their crispy sensations. In literature the critical water activity for (Awc)
has been used up to now. Awc for crispness corresponded with values between 0.57 and 0.59 (or 9.1–9.7% water content). which is in reasonable agreement with the results of Roudaut et al. (1998)
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Fig. 5. Comparison of first and multiple bite scores for attributes crispy, brittle, pitch and sound in function of water activity for toasted rusk roll with coarse morphology. Arrows show statistically significant differences (P < 0.05) between products with the same water activity.
who found a decrease of crispness at 10.1% H2O for dried white bread. In this study, the samples with fine structure were considered to be more brittle and crumblier and the samples with a coarse structure were considered to be crispier, with more sound emission. This result may help the industry to design products with an optimal crispness and with a longer crispness retention. Acknowledgements The authors would like to thank Ben Uitdewilligen (Bolletje, Almelo, The Netherlands) for providing us with the recipe and ingredients to prepare the toasted rusk roll with the coarse structure. We also thank Rene de Wijk and Hanneke Elzerman for performing the sensory test. References Agbisit, R., Alavi, S., Cheng, E., Herald, T., & Trater, A. (2007). Relationship between microstructure and mechanical properties of cellular cornstarch extrudates. Journal of Texture Studies, 38, 199–219. Barret, A. H., Cardello, A. V., Lesher, L. L., & Taub, I. A. (1994). Cellularity, mechanical failure and textural perception of corn meal extrudates. Journal of Texture Studies, 25, 77–95. Coppock, J. B. M., & Carnford, S. J. (1960). Texture in Foods. SCI Monograph(7), 64. Dacremont, C. (1995). Spectral composition of eating sounds generated by crispy, crunchy and crackly foods. Journal of Texture Studies, 26, 27–43. Dijksterhuis, G., Luyten, H., De Wijk, R., & Mojet, J. (2007). A new sensory vocabulary for crisp and crunchy dry model foods. Food Quality and Preference, 18, 37–50. Dogan, H., & Kokini, J. L. (2006). Psychophysical markers for crispness and influence of phase behavior and structure. Journal of Texture Studies, 38, 324–354. Drake, B. (1963). Food crushing sounds: An introductory study. Journal of Food Science, 28, 233–241. Duizer, L. (2001). A review of acoustic research for studying the sensory perception of crisp, crunchy and crackly textures. Trends Food Science and Technology, 12, 17–24. Duizer, L. M., Campanella, O. H., & Barnes, G. R. G. (1998). Sensory, instrumental and acoustic characteristics of extruded snacks products. Journal of Texture Studies, 29, 397–411. Gao, X., & Tan, J. (1996). Analysis of expanded-food texture by image processing. Part II: Mechanical properties. Journal of Food Processing Engineering, 19, 445–456.
Gibson, L. G., & Ashby, M. F. (1997). Cellular solids: Structure and properties. Cambridge, UK: Cambridge University Press. Harris, M., & Peleg, M. (1996). Patterns of textural changes in brittle cellular foods caused by moisture sorption. Cereal Chemistry, 73, 225–231. Katz, E. E., & Labuza, T. P. (1981). Effect of water activity on the sensory crispness and mechanical deformation of snack food products. Journal of Food Science, 46, 403–409. Luyten, H., Plijter, J. J., & van Vliet, T. (2004). Crispy/crunchy crusts of cellular solid foods: A literature review with discussion. Journal of Texture Studies, 35, 445–492. Luyten, H., & van Vliet, T. (2006). Acoustic emission, fracture behaviour and morphology of dry crispy foods, a discussion paper. Journal of Texture Studies, 37, 221–240. Mallikarjunan, P. (2004). Understanding and measuring consumer perceptions of crispness. In D. Kilkast (Ed.). Texture in food (Vol. 2, pp. 2–105). Cambridge: Woodhead Publishing Limited. Marzec, A., Lewicki, P. P., & Ranachowski, Z. (2007). Influence of water activity on acoustic emission of flat extruded bread. Journal of Food Engineering, 79, 410–422. Matz, A. (1962). Food texture. Westport, CT: AVI Publishing Co. Inc. (From texture in food). Peleg, M. (1994). A mathematical model of crunchiness/crispness loss in breakfast cereals. Journal of Texture Studies, 25, 403–410. Roudaut, G., Dacremont, C., & Le Meste, M. (1998). Influence of water on the crispness of cereal-based foods: Acoustic, mechanical and sensory studies. Journal of Texture Studies, 29, 199–213. Sauvageot, F., & Blond, G. (1991). Effect of water activity on crispness and mechanical deformation of snack food products. Journal of Texture Studies, 22, 423–442. Tesch, R., Normand, M. D., & Peleg, M. (1996). Comparison of the acoustic and mechanical signatures of two cellular crunchy cereal Foods at various water activity levels. Journal of the Science of Food and Agriculture, 70, 347–354. Valles Pamies, B., Roudaut, G., Dacremont, C., Le Meste, M., & Mitchell, J. R. (2000). Understanding the texture of low moisture cereal products: Mechanical and sensory measurements of crispness. Journal of the Science of Food and Agriculture, 80, 1679–1685. Van Nieuwenhuijzen, N. H., Primo-Martín, C., Tromp, R. H., Meinders, B. J. M., Hamer, R. J., & Van Vliet, T. Water content or water activity which one rules? Journal of Agriculture and Food Chemistry, submited for publication. Vickers, Z. (1981). Relationships of chewing sounds to judgments of crispness, crunchiness and hardness. Journal of Food Science, 47, 121–124. Vickers, Z. (1985). The relationships of pitch, loudness and eating technique to judgments of the crispness and crunchiness of food sounds. Journal of Texture Studies, 16, 85–95. Vickers, Z., & Bourne, M. C. (1976). A psychoacoustic theory of crispness. Journal of Food Science, 41, 1158–1164. Vincent, J. F. V. (2004). Application of fracture mechanics to the texture of food. Engineering Failure Analysis, 11, 695–704.
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Food Research International journal homepage: www.elsevier.com/locate/foodres
Effect of structure in the sensory characterization of the crispness of toasted rusk roll C. Primo-Martin a,*, E.M. Castro-Prada a,b, M.B.J. Meinders a,c, P.F.G. Vereijken a,d, T. van Vliet a,b a
TI Food and Nutrition (WCFS), Bornsesteeg 59, 6700 AA Wageningen, The Netherlands Wageningen University, Bomenweg 2, 6700 EW Wageningen, The Netherlands c Agrotechnology and Food Sciences Group, Bornsesteeg 59, 6700 AA Wageningen, The Netherlands d Biometris, Wageningen University, P.O. Box 100, 6700 AC Wageningen, The Netherlands b
a r t i c l e
i n f o
Article history: Received 22 October 2007 Accepted 24 February 2008
Keywords: Cellular solids Crispness Structure Toasted rusk roll Water content Water activity Relative humidity Sound Sensory
a b s t r a c t Crispness is a salient textural attribute of toasted foods strongly related to their preference. Crispness is affected by water content, mechanical properties and morphology of the food. Sound emission and force characteristics during food crushing play a key role in crispness. The aim was to assess the effect of product morphology on sensory crispness grading of toasted rusk roll, a cellular solid food. Products with coarse and fine structures were studied. Additionally, the effect of water on crispness was studied by using samples with water activities from 0.30 to 0.8. The sensory test showed that upon absorption of water the product became tough and soft and lost its crispness. The morphology of the product had a significant effect on crispness intensity. Coarse products were rated crispier than those with a fine crumb grain. Deterioration of crispness (Aw10%) started at 0.46 and 0.50 water activity (6.2% and 7.1% H2O) for the fine and coarse structure product, respectively. The critical water activity (Awc) at which the products lost 50% of the crispness was 0.57 and 0.59 (9.1% and 9.7% H2O), respectively for the fine and coarse structure product. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction A salient textural attribute for toasted foods is crispness, which has been shown to determine food preference (Katz & Labuza, 1981). The architecture of a crispy product can mostly be characterized as an open cellular structure that, in physical terms, is stiff, brittle and fractures and disintegrates abruptly and completely during biting and chewing with accompanying sound emission (Dijksterhuis, Luyten, De Wijk, & Mojet, 2007). Sound produced during crushing plays a key role in the perception of crispness and together with the flavor in the mouth and the oral tactile sensations produced during chewing determines the pleasant perception of food (Drake, 1963; Vickers, 1981; Vickers & Bourne, 1976). Crispness is negatively affected by increasing water content or water activity. The effect of water on the texture of crispy products has been widely studied before (Dacremont, 1995; Duizer, Campanella, & Barnes, 1998; Harris & Peleg, 1996; Katz & Labuza, 1981; Marzec, Lewicki, & Ranachowski, 2007; Roudaut, Dacremont, & Le Meste, 1998; Sauvageot & Blond, 1991; Tesch, Normand, & Peleg, 1996; Valles Pamies, Roudaut, Dacremont, Le Meste, & Mitchell, * Corresponding author. Tel.: +31 317 475120; fax: +31 317 475347. E-mail address: [email protected] (C. Primo-Martin). 0963-9969/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2008.02.004
2000). These studies showed that upon adsorption of water a crispy product becomes pliable, ductile and soft and loses its crispness and consequently its acceptability by the consumer. Despite these studies, the relative importance of water activity over water content or viceversa has yet not been clarified and it is currently under study (Van Nieuwenhuijzen et al., submitted for publication). Other factors affecting crispness are the properties of the material (composition, physical properties of the components) and the structure of the product (Luyten, Plijter, & van Vliet, 2004). Several authors suggested that crispness of food is affected by the size of the air cells and the thickness of the cell walls (Coppock & Carnford, 1960; Luyten & van Vliet, 2006; Mallikarjunan, 2004; Matz, 1962) but not clear guidelines for the industry have been produced. Barret, Cardello, Lesher, and Taub (1994) found a relation between mechanical properties (plateau stress) and structural properties (cell size and density of the material). Gao and Tan (1996) could predict mechanical properties from the analysis of the surface and cross-section images of a crispy product. Theoretical models like that of Gibson and Ashby (1997) have been applied to brittle foams to relate mechanical properties, sensory properties and cellular structure (Agbisit, Alavi, Cheng, Herald, & Trater, 2007). Dogan and Kokini (2006) recently showed a relation between crispness and the average number of peaks during
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fracture which varied with structural parameters and with phase change in the extrudates. However, the underlying mechanism relating morphology to the sensory properties of crispy foods is not yet clearly understood. The aim of this work was to assess the effect of the morphology of the product on the crispness perception. Thereto we studied the sensory perception of two toasted rusk rolls that differ significantly from each other regarding to morphology, one had a much coarser morphology than the other one. Conditioning of samples at different water activities was used as a tool to study the effect of the morphology. A mathematical model (Peleg, 1994) was applied to calculate the onset of the loss of crispness as a function of the structure of the product.
shaped mould (3.5 cm diameter). These middle parts were used for sensory analysis.
2. Material and methods
2.2.4. Water activity Water activity (Aw) of crust samples was measured as the relative humidity of the air in equilibrium with the samples in the sealed measuring chamber using a chilled-mirror dewpoint technique at 22 °C (Aqua Lab Series 3, Decagon devices, Pullman, USA).
2.1. Materials Toasted rusk rolls with a fine and a coarse structure were used. The toasted rusk roll with fine structure was kindly supplied by Bolletje (echte beschuit, Bolletje, Almelo, The Netherlands). The toasted rusk roll with a coarse structure was prepared at TNO baking laboratory (TNO Quality of Life, Zeist, The Netherlands) with the formulation supplied by Bolletje. Except with respect to some additives the formulations were the same. 2.2. Methods 2.2.1. Bread making Toasted rusk rolls with a coarse structure were prepared at the TNO baking laboratory (TNO Quality of life, Zeist, The Netherlands). Wheat flour (Dutch Top Rusk flour Meneba 2000 g), water (900 ml), dry yeast (133 g), salt (16 g), sugar (100 g), sugar syrup (200 g), egg (100 g), rusk jelly (240 g) and a mixture of improvers (20 g, provided by Bolletje) were mixed in a mixer (Kemper SP 15, Kemper, The Netherlands). First, all ingredients (at 10 °C) were blended for 1 min at low speed (140 rpm). Next, the water, egg, sugar syrup and rusk jelly (at 20 °C) was added and mixed at low speed for 2 min. Then, the dough was kneaded at high speed (280 rpm) until a final dough temperature of 28 °C was reached. After mixing the dough was scaled and rounded and allowed to rest for 30 min. Next a second and a third cycle of resting and rounding was done for 15 and 20 min. The dough was divided into smaller portions of 36.6 g and given a fourth resting of 10 min. Next, the dough pieces were flattened and put in a rusk tin. A final proofing was done at 30 °C and 80% RH until a fixed volume of gas was produced (900 ml) (in a piece of 186 g dough, SJA Fermentograph, Franken, Goes, The Netherlands). The dough was baked at 215 °C for 13 min in a Rototherm RE oven (Haton, The Netherlands). Afterwards the rusk rolls were cut (15 mm height) and pre-toasted (with the cut side to the top) at 230 °C for 7 min. Final toasting was done at 150 °C for a duration of 12 min. The toasted rusk rolls were allowed to cool at room temperature for 30 min before packaging in a double plastic bag. Top and bottom pieces had different gas cell distribution. The top piece was selected for our experiments because the difference in structure was larger compared with the fine structure of the commercial toasted rusk roll. 2.2.2. Rusk roll preparation for sensory analysis The bottom edge (1–2 mm) of the toasted rusk roll was harder than the rest of the product therefore it was removed using a food slicer. The side edges had the same problem and they were separated from the middle part by cutting this out with a cylindrical
2.2.3. Conditioning at constant relative humidity Samples were conditioned at eight relative humidities (RH) by placing the samples in climatic cabinets (Weiss SB 11300, Weiss technik Ltd., Buckinghamshire, UK) set at 22 °C and RH varying from 30% to 80%. The time needed to reach steady state was about 2 days for the samples at 80% RH, 3 days for the samples equilibrated in the range from 50% to 70% RH, respectively, and 4 days for the samples equilibrated at 30% and 40% RH. Samples were considered to be in steady state with the storage RH when they reached a constant weight in time (+0.001 g).
2.2.5. Water content The water content of the toasted rusk roll was determined by placing the samples in an oven at 105 °C for 24 h. The water content was calculated from the weight determined before and after oven drying. 2.2.6. Image acquisition and analysis Images of the cross sections of the toasted rusks rolls where taken from the top side of the toasted rusk rolls using a Hewlett Packard flatbed scanner (HP Scanjet C7716, Hewlett Packard, USA). Images were scanned fullscale using a resolution of 47.2 pixels/mm. The obtained images were analyzed using computerized image analysis with the free software ImageJ (http://rsb.info.nih.gov/ij/). RGB colour segmentation was performed and the red colour was selected for further analysis of the images. Unevenness and shadows were filtered using the ImageJ settings: bandpass filter of 100 and 5, for large and small structures, respectively. The number of cells, cell area and mean cell area were analyzed with Matlab (Matworks 7.0.4). 2.2.7. Density Toasted rusk roll volume (v) (sample equilibrated at 30% RH) was determined in duplicate using rape seed displacement. Density (q) was calculated as q ¼ mm where m is the mass of the toasted rusk roll. 2.2.8. Sensory analysis A trained panel of 8 Dutch panelists, 3 male and 5 female, aged between 20 and 62 years was used for the sensory tests. Table 1 describes the first bite and multiple bite attributes that were used in this study. They were selected from the attributes described by Dijksterhuis et al. (2007). Multiple bite attributes are used to study the effect of changes happening during food mastication (eg. saliva hydration) that affected the perception of crispness. Sensory attributes were scored by the panelist on line-scales (from 0 to 1000) using the Fizz computer program for automated sensory analysis (Biosystemes, 1998, FIZZ software, v1.20 K, Couternon, France). Prior to testing three training sessions were held to familiarize the participants with the products and with the attributes. Fine and coarse toasted rusk rolls equilibrated at eight different water activities were presented. Two duplicates were performed in two days. Within each day 16 samples were offered to the panelists in random order in one hour session including a 10 min break. For each sample, first bite attributes were rated directly after the first bite. Multiple bite ratings were rated while chewing the sample.
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a coarse structure had more large gas cells than the one with a fine structure which in turn had relatively more small gas cells. Density of the toasted rusk rolls was: 0.11 ± 0.01 and 0.12 ± 0.02 g/ml, respectively, for the coarse and fine structure products.
Table 1 Atributes at first and multiple bite in English and Dutch and English definition Attributes
English
Dutch
Definition
First bite
Amount of sound Snapping Pitch
geluid
Amount and loudness of sound
krakend knisperend
Crackling Crispy Brittle Bite force
knapperig krokant bros bijtkracht
Hard
hard
Tough Crumbly Splinters
taai kruimelig scherfjes
Loud, sharp, short sound High pitched sound, light sound, longer sounding It breaks in pieces Cracks, more airy than crackly Airy, not hard, but giving resistance Resistance, force you have to exert to bite, not necessarily hard Resistance, with sound, snaps. Bite force needed Requires pulling to tear off Small pieces in the mouth Sharp pieces in the mouth
Amount of sound Type of sound Snapping Pitch
geluid
Amount and loudness of sound
type geluid
From low to high pitch (musical scale)
krakend knisperend
Crackling Crispy Brittle Hard
knapperig krokant bros hard
Loud, sharp, short sound High pitched sound, light sound, longer sounding It breaks in pieces Cracks, more airy than crackly Airy, not hard, but giving resistance Resistance, with sound, snaps. Bite force needed
Airy Drying Tough Crumbly Splinters Gooey
luchtig droog taai kruimelig scherfjes klef
Melting
smeltend
Multiple bite
Requires pulling to tear off Small pieces in the mouth Sharp pieces in the mouth By chewing becomes a soft masse in your mouth, sticky Melts in the mouth
C 1 þ expðB ðX X c ÞÞ
Table 2 shows the measured water activity and the water content of the samples after equilibration at the different RH. The differences between water activity as well as the water content of the toasted rusk rolls with different structure are marginal, with the exception of the coarse structure equilibrated at 30% RH. The latter had a lower water content (3.6% H2O) than the one with the fine structure (4.8% H2O). 3.3. Sensory analysis
2.2.9. Statistical analysis Pairwise comparison between sensory attributes, averaged over duplicates and panel members, at each water activity was carried out using a two-sided t-test (P < 0.05) with GenStat software v 8 (VSN international Ltd., Herts, UK). The relationship between water activity, morphology and attributes were studied using principal component analysis (PCA) (Unscrambler, Camo, Inc.) performed on averaged sensory data over panelists and replicates. The sigmoid relationship between the sensory attributes, averaged over panelists and replicates, and the water activity or the water content was described using the logistic curve: S ¼ Smin þ
3.2. Water activity and water content of toasted rusk rolls
ð1Þ
where S is the expected value of the sensory score averaged over panelists, Smin the lower asymptote, C the attribute range (Smax Smin), X the water activity or water content (Aw or [H2O]), B the slope at the transition region or steepness, and Xc the water activity water content at which the sensory attribute dropped by 50% (Awc or [H2O]c). Non linear regression analysis (using GenStat software v 8 (VSN international Ltd., Herts, UK)) was used to fit the curves. 3. Results and discussion 3.1. Morphology of toasted rusk rolls Fig. 1 shows the size distribution of the gas cells of the coarse and fine toasted rusk rolls. The average gas cell size was 0.17 ± 0.02 and 0.10 ± 0.01 mm2, for the toasted rusk roll with coarse and fine structure, respectively. The toasted rusk roll with
Panelists were asked to score samples with different morphology and different water activity on first bite and multiple bite attributes. ANOVA showed that the structure of the product and the water activity had a significant effect (P < 0.05) on first as well as multiple bite attributes. 3.3.1. First bite attributes A principal component bi-plot (Fig. 2) based on all first bite attributes of the averaged sensory scores of the sensory panel shows the different products in the space delimited by the first two principal components (explaining 92% and 5% of the total variance, respectively). The first component separated toughness from all other attributes. The second component separated crispy, crackling, sound, snapping, splinters, bite force and hard from pitch, brittle and crumbly and was associated with samples with low water activity/content. PCA separated in the first dimension the samples as function of the water activity/content, samples on the right side had a lower water activity than the samples on the left side. With increasing water activities the crispy perception started to diminish or finally disappeared completely. The second dimension separated based on morphology samples that had perceptible crispness. The morphology of the samples resulted in a different perception of the sound and the texture during biting of the products. The coarse grain structure was perceived as producing more and louder sound as well as sharper and shorter sound events (snapping). The texture of the fine grain structure was perceived as more brittle and crumblier, breaking into smaller pieces after biting. In contrast, the coarse one was characterized as crispier, crackling, harder and breaking into sharp pieces, splinters, when fractured by the teeth. This is in line with previous work (Vincent, 2004) on potato crisps that showed that more and smaller cells result in a less crisp. Fig. 3 shows the averaged scores for the first bite attributes, sound, snapping, pitch, crispy, hard and splinters, as a function of the water activity for both coarse and fine structure products. Significant differences (shown by arrows) due to product morphology were found specially at low water activities for sound, snapping, crispy, hard and splinters. Pitch was not significantly different between coarse and fine toasted rusk rolls. Crispy related attributes are usually characterized by a sigmoid relationship between the attributes and moisture, water activity or temperature and can be fitted using Eq. (1). The estimated parameters from the fitted logistic curves, describing the relationship between sensory attribute and water activity, are shown in Table 3A. Table 3B shows estimated parameters for the relationship between sensory attribute and water activity. Fitted curves are shown in Fig. 3. R2 of the fitted curves were between 0.97 and 0.99. This sig-
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Fig. 1. Example of images of toasted rusk roll with different gas cell structure: (A) coarse morphology and (B) fine morphology. Gas cell size distribution of toasted rusk roll (C).
Table 2 Water activity and water content of samples conditioned to relative humidities (RH) ranging from 30% to 80% RH storage
30 40 50 55 60 65 70 80
Water activity
Water content
Fine structure
Coarse structure
Fine structure
Coarse structure
Average SD
Average SD
Average SD
Average SD
0.29 ± 0.01 0.37 ± 0.01 0.48 ± 0.01 0.53 ± 0.01 0.59 ± 0.00 0.62 ± 0.00 0.66 ± 0.01 0.77 ± 0.00
0.29 ± 0.02 0.38 ± 0.02 0.48 ± 0.00 0.53 ± 0.00 0.59 ± 0.00 0.61 ± 0.01 0.66 ± 0.01 0.78 ± 0.01
4.8 ± 0.6 5.0 ± 0.1 7.1 ± 0.2 8.2 ± 0.4 9.5 ± 0.1 10.6 ± 0.3 11.6 ± 0.1 15.2 ± 0.2
3.6 ± 0.3 5.1 ± 0.1 7.0 ± 0.1 8.1 ± 0.1 9.6 ± 0.1 10.3 ± 0.2 11.7 ± 0.0 15.6 ± 0.5
moid relationship is characterized by three parts (Peleg, 1994). The first part of the sigmoid curves shows a constant or a slight decrease of the attribute, the second part shows a rapid decrease of the averaged score for the attribute and the third part corresponds to the disappearance of the sensory sensation. The logistic curve can be characterize by the water activity at which the sensory perception is dropped by 50%. Peleg called this the critical water activity (Awc) (Peleg, 1994). However, also of interest is the water activity/content at which the sensory perception starts to decrease due to increasing hydration, that is, the starting point of the rapid decrease of the attribute. We define this point at the drop of the score by 10% (Aw10%, and H2O10%, Table 3A and 3B, respectively).
The onset of crispness decrease was 0.46 and 0.50 water activity (or 6.2% and 7.1% water content) for the fine and course structure product, respectively. And the critical water activity for crispness (Awc) corresponded with values of 0.57 and 0.59 (or 9.1% and 9.7% water content). When taking in consideration all attributes Aw10% was found between 0.43 and 0.51 (4.6% and 7.4% water content) for the products with a fine morphology and 0.47 and 0.54 (6.0% and 8.3% water content) for the products with a coarse morphology, although significant differences were not found between morphologies. For the attribute splinters the relation attributewater activity did not follow a sigmoid relationship (Fig. 3) for the coarse morphology therefore the values of Awc and Aw10% are undefined in this case. From the estimated parameters only the maximum value C was found to be significant for the different morphologies. 3.3.2. Multiple bite attributes Principal component analysis of the multiple bite attributes (Fig. 4) showed the same pattern of distribution of attributes and sample morphology over the first two principal components (explaining 90% and 6% of the total variance, respectively) as observed for the first bite attributes. Additionally, the fine product was perceived as melting and drying more during mastication. Further taste differences that were found between the products are that the coarse product was perceived as more salty and less sweet than the fine product. Fig. 5 shows a comparison of attributes scored at first and at multiple bites for the product with a coarse morphology. Crispness,
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Fig. 2. First two dimensions of PCA for first bite attributes. Letters indicate product morphology: C: coarse, F: fine. Numbers indicate water activity of the product.
Fig. 3. Effect of water activity on attributes: amount of sound, snapping, pitch, crispy, hard and splinters for coarse and fine structure. Open and close squares are experimental data. Solid lines are fittings of Eq. (1). Arrows show statistically significant differences (P < 0.05) between products with the same water activity.
hardness, sound and pitch were scored higher at first bite than on multiple bites. Same results were found for the product with a fine morphology (results not shown). The judgment of higher crispness at first bite corresponds well with previous work (Vickers, 1985) in which the authors compared crispness as perceived from bite sounds and chew sounds, although this author found no difference when crunchiness was judged from bite or chew sounds. Duizer (2001) also described crispness as a maximum during the first bite with a decline as mastication progresses due to breakdown of the cell wall fragments by the teeth and to the hydration by saliva.
4. Conclusions This work shows the importance of morphology for crispness perception and retention besides the known dependence of crispness on the water activity and water content. The onset of decrease of the sensory attributes, defined as Aw10%, was for crispness 0.46 and 0.50 water activity (or 6.2% and 7.1% water content) for the fine and coarse structure product, respectively. The effect of the structure on the onset of crispness decrease, although not significant, has not been described before and it may have important
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C. Primo-Martin et al. / Food Research International 41 (2008) 480–486 Table 3A Estimated parameters from fitted logistic curves Eq. (1), relating first bite sensory attributes averaged over panelists and water activity Morphology
Parameter
Amount of sound
Snapping
Pitch of sound
Crispness
Splinters
Hardness
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Fine
B Awc C Smin Aw10%
18.4 0.61 561 62 0.49
2.3 0.01 32 26 0.02
28.8 0.58 306 74 0.51
13.5 0.02 51 39 0.03
19.4 0.59 714 42 0.48
4.6 0.01 74 57 0.02
19.8 0.57 463 54 0.46
4.3 0.01 44 33 0.03
15.0 0.57 255 46 0.43
5.5 0.02 46 33 0.06
12.3 0.63 288 80 0.45
9.5 0.07 143 119 0.1
Coarse
B Awc C Smin Aw10%
19.6 0.61 666 77 0.50
2.1 0.01 30 24 0.01
16.6 0.60 563 35 0.47
5.2 0.02 85 67 0.04
29.2 0.62 568 78 0.54
8.7 0.01 59 49 0.02
22.9 0.59 595 63 0.50
3.9 0.01 41 32 0.01
23.6 0.61 414 98 0.52
7.5 0.01 51 41 0.02
s.e. = standard error.
Table 3B Estimated parameters from fitted logistic curves Eq. (1), relating first bite sensory attributes averaged over panelists and water content Morphology
Parameter
Amount of sound
Snapping
Pitch of sound
Crispness
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
s.e.
Estimate
Splinters s.e.
Estimate
s.e.
0.65 9.1 248 57 5.7
0.29 0.7 54 30 1.9
0.38 10.4 313 82 4.6
0.48 2.0 256 154 7.1
0.83 10.2 416 102 7.5
0.28 0.4 57 43 0.9
Fine
B [H2O]c C Smin [H2O]10%
0.66 10.0 568 71 6.7
0.12 0.3 47 32 0.8
1.11 9.4 304 79 7.4
0.59 0.6 58 42 0.9
0.72 9.6 724 54 6.5
0.20 0.4 90 59 0.6
0.74 9.1 474 60 6.2
0.20 0.4 58 35 1.1
Coarse
B [H2O]c C Smin [H2O]10%
0.71 10.1 671 88 7.0
0.10 0.2 43 30 0.4
0.58 9.8 580 46 6.0
0.23 0.6 114 69 1.9
1.01 10.5 570 77 8.3
0.32 0.3 67 53 0.9
0.85 9.7 598 71 7.1
0.17 0.3 48 34 1.2
Hardness
s.e. = standard error.
Fig. 4. First two dimensions of PCA for multiple bite attributes. Letters indicate product morphology: C: coarse, F: fine. Numbers indicate water activity of the product.
consequences for product storage. This onset value will limit conditions at which these products can be stored in order to keep their crispy sensations. In literature the critical water activity for (Awc)
has been used up to now. Awc for crispness corresponded with values between 0.57 and 0.59 (or 9.1–9.7% water content). which is in reasonable agreement with the results of Roudaut et al. (1998)
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Fig. 5. Comparison of first and multiple bite scores for attributes crispy, brittle, pitch and sound in function of water activity for toasted rusk roll with coarse morphology. Arrows show statistically significant differences (P < 0.05) between products with the same water activity.
who found a decrease of crispness at 10.1% H2O for dried white bread. In this study, the samples with fine structure were considered to be more brittle and crumblier and the samples with a coarse structure were considered to be crispier, with more sound emission. This result may help the industry to design products with an optimal crispness and with a longer crispness retention. Acknowledgements The authors would like to thank Ben Uitdewilligen (Bolletje, Almelo, The Netherlands) for providing us with the recipe and ingredients to prepare the toasted rusk roll with the coarse structure. We also thank Rene de Wijk and Hanneke Elzerman for performing the sensory test. References Agbisit, R., Alavi, S., Cheng, E., Herald, T., & Trater, A. (2007). Relationship between microstructure and mechanical properties of cellular cornstarch extrudates. Journal of Texture Studies, 38, 199–219. Barret, A. H., Cardello, A. V., Lesher, L. L., & Taub, I. A. (1994). Cellularity, mechanical failure and textural perception of corn meal extrudates. Journal of Texture Studies, 25, 77–95. Coppock, J. B. M., & Carnford, S. J. (1960). Texture in Foods. SCI Monograph(7), 64. Dacremont, C. (1995). Spectral composition of eating sounds generated by crispy, crunchy and crackly foods. Journal of Texture Studies, 26, 27–43. Dijksterhuis, G., Luyten, H., De Wijk, R., & Mojet, J. (2007). A new sensory vocabulary for crisp and crunchy dry model foods. Food Quality and Preference, 18, 37–50. Dogan, H., & Kokini, J. L. (2006). Psychophysical markers for crispness and influence of phase behavior and structure. Journal of Texture Studies, 38, 324–354. Drake, B. (1963). Food crushing sounds: An introductory study. Journal of Food Science, 28, 233–241. Duizer, L. (2001). A review of acoustic research for studying the sensory perception of crisp, crunchy and crackly textures. Trends Food Science and Technology, 12, 17–24. Duizer, L. M., Campanella, O. H., & Barnes, G. R. G. (1998). Sensory, instrumental and acoustic characteristics of extruded snacks products. Journal of Texture Studies, 29, 397–411. Gao, X., & Tan, J. (1996). Analysis of expanded-food texture by image processing. Part II: Mechanical properties. Journal of Food Processing Engineering, 19, 445–456.
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