Journal of Food Engineering 121 (2014) 9–14 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier .com/ locate / j foodeng Texture profile and correlation between sensory and instrumental analyses on extruded snacks 0260-8774/$ - see front matter � 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.08.007 ⇑ Corresponding author. Tel.: +55 17 32212548; fax: +55 17 32212299. E-mail addresses: mandinha_depaula@yahoo.com.br (A.M. Paula), contisil@ ibilce.unesp.br (A.C. Conti-Silva). Amanda Maldo Paula, Ana Carolina Conti-Silva ⇑ Departamento de Engenharia e Tecnologia de Alimentos, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista ‘‘Júlio de Mesquita Filho’’, Rua Cristóvão Colombo, 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil a r t i c l e i n f o a b s t r a c t Article history: Received 27 March 2013 Received in revised form 26 July 2013 Accepted 5 August 2013 Available online 12 August 2013 Keywords: Snack food Texture Instrumental analysis Descriptive analysis Instrumental texture analysis on extruded snacks is widely applied, however there is no scientific con- sensus about the test and probe types that can be correlated with the sensory texture of snacks. Eleven commercial extruded snacks of different shapes were evaluated instrumentally using different probes and sensorially through descriptive analysis. The snack texture was described using the attributes of hardness, crispness, adhesiveness, fracturability and chewiness. Cylindrical snacks were described through crispness and fracturability, pelleted and shell-shaped snacks by chewiness and ring-shaped snacks by adhesiveness and hardness. Hardness and adhesiveness were correlated with a Warner–Brat- zler test using a ‘‘V’’ shape probe (r = 0.718 and r = 0.763, respectively), while fracturability and chewiness were correlated with a Warner–Bratzler test using a guillotine (r = 0.776 and r = 0.662, respectively). The fairly strong good correlations enable application of these instrumental tests as an indication of the sen- sory texture of extruded snacks. � 2013 Elsevier Ltd. All rights reserved. 1. Introduction Texture, defined as the sensory manifestation of food structure and the way in which this structure reacts to the forces applied, represents the junction of all the mechanical, geometric and super- ficial attributes of a product, sensed through mechanical, tactile, vi- sual and hearing receptors (Szczesniak, 1963a). Moreover, texture can be related to the deformation, disintegration and flow of the food when a force is applied (Bourne, 2002). Texture can be measured by means of objective (instrumental) and intrinsic subjective (sensory) tests. Among the instrumental test devices, texturometers imitate mastication conditions and present excellent correlations with sensory evaluations of texture (Szczesniak, 1963b). For this reason, they have been widely used to measure the texture of different kinds of foods. With regard to sensory analysis in the mouth, the characteristics perceived in- clude mechanical attributes (relating to reaction to the applied force), geometrical attributes (relating to the shape, size and parti- cle orientation inside the food) and attributes relating to percep- tion of moisture or fat content (Szczesniak, 2002). Correlations between sensory and instrumental measurements of texture result in: (1) finding instruments to measure quality control of food in industries; (2) predicting consumer response, as the degree of liking and the overall acceptance of a new product; (3) understanding what is being sensed and perceived in the mouth during the sensory assessment of texture; (4) improving or optimizing instrumental methods to complementary the sen- sory evaluation (Szczesniak, 1987). Texture is a critical sensory attribute that can dominate the quality of a product, as in snacks obtained through thermoplastic extrusion. In extruded snacks, expansion is desired and puffed products are expected, and this is why texture plays an important role regarding the acceptability of snacks among consumers (Anton and Luciano, 2007). Many studies have measured the texture of snack products using instrumental analysis, but different tests and probes have been used. The tests most often applied have been texture profile analysis (Liu et al., 2000; Veronica et al., 2006), cut or shear tests (Conti-Silva et al., 2012; Saeleaw et al., 2012 and Yuliani et al., 2006), compression tests (Nath et al., 2012) and puncture tests (Ding et al., 2006; Pamies et al., 2000 and Nascimento et al., 2012). Besides the diversity of tests and probes applied, different sensory terms have been used to describe the texture diagnosed through the instrumental test, even when the same test and probe have been used. In other words, there is no consensus regarding which terms should be used to describe textures diagnosed through instrumental tests, or whether these terms can be corre- lated with sensory texture, although the terms most used are hard- ness, brittleness, firmness and crispness (Ding et al., 2006; Mazumder et al., 2007; Nascimento et al., 2012; Nath et al., 2012; Veronica et al., 2006; Yuliani et al., 2006). http://crossmark.crossref.org/dialog/?doi=10.1016/j.jfoodeng.2013.08.007&domain=pdf http://dx.doi.org/10.1016/j.jfoodeng.2013.08.007 mailto:mandinha_depaula@yahoo.com.br mailto:contisil@ibilce.unesp.br mailto:contisil@ibilce.unesp.br http://dx.doi.org/10.1016/j.jfoodeng.2013.08.007 http://www.sciencedirect.com/science/journal/02608774 http://www.elsevier.com/locate/jfoodeng 10 A.M. Paula, A.C. Conti-Silva / Journal of Food Engineering 121 (2014) 9–14 Instrumental and sensory evaluations on snack textures have been widely performed, but it is important to establish which tests and probes are more appropriate for describing the sensory attri- butes of texture, thereby ascertaining which objective test corre- lates best with the sensory perception of texture. Therefore, the aim of this study was to evaluate the texture profile of extruded snacks and determine the most appropriate instrumental test for correlations with sensory analyses on snack texture. 2. Material and methods 2.1. Material Four different shapes of extruded snacks were purchased in a lo- cal supermarket. The shapes were selected based on the most com- mon types of snacks available on the market, which are cylindrical (Fig. 1A), pelleted (Fig. 1B), ring-shaped (Fig. 1C) and shell-shaped (Fig. 1D). Out of the eleven snack products purchased, three were cylindrical, three pelleted, two ring-shaped and three shell-shaped. All cylindrical, ring-shaped and shell shaped snacks are made with corn flour, while pelleted snacks are made with wheat flour. Different raw materials to produce the snacks and different shapes were chosen precisely to involve a major variety of extruded snacks in this study. 2.2. Descriptive analysis of texture Panelists were recruited from among the students, staff and professors of the Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista ‘‘Júlio de Mesquita Filho’’ (IBILCE). Descriptive analysis of texture was performed in accordance with Stone and Sidel (1993). Twelve panelists out of the twenty recruited were preselected using a difference-from-control test relating to crispness. The three cylindrical snacks, among which one of them was standardized as a control sample based on the instrumental analysis, were subjected Fig. 1. Shapes of the extruded snacks. Legend: A (cylindric to the difference-from-control test. The panelists were preselected according to their discriminative capacity (Fsample 6 0.50) and reproducibility capacity (Frepetition P 0.05) (ASTM, 1981). The sensory attributes were generated by the twelve panelists, using the Kelly Repertory Grid method (Moskowitz, 1983) to de- scribe the texture of the same three cylindrical snacks. After dis- cussions to reach a consensus, the descriptive terms that were most important for characterizing the snack texture were selected. The sensory panel also defined the attributes, the references for each of these and the product evaluation form. During this stage, which took three sessions of 1 h each one, four panelists dropped out of the analysis, and thus, eight remained. After the training stage with the same three cylindrical snacks, which took four sessions of 1 h each one, the panelists were se- lected according to their discriminative capacity (Fsample 6 0.50), reproducibility capacity (Frepetition P 0.05) and capacity for consen- sus with the panel for each attribute (ASTM, 1981; Damásio and Costell, 1991). Thus, six of the eight trained panelist were selected to conduct analyses on the sensory texture profile of the snacks. The sensory analysis was performed in individual booths, under red light and at a temperature of 22 �C. The eleven snacks were presented in plastic cups coded with three-digit random numbers and were evaluated in triplicate by the six panelists. The sample presentation was balanced with complete sets (performed in two sessions), that were randomized and monadic, and an unstructured linear intensity scale of 90 mm in length was used for each descriptor. The ethical issues of the sensory analysis were approved by the Research Ethics Committee of the IBILCE. 2.3. Instrumental analyses of texture The extruded snacks were analyzed by means of the TAXT2i texturometer (Stable Micro Systems, Godalming, UK), using a load cell of 5.0 kg and the following tests and probes: al), B (pelleted), C (ring-shaped) and D (shell-shaped). A.M. Paula, A.C. Conti-Silva / Journal of Food Engineering 121 (2014) 9–14 11 – Compression test: an aluminum cylinder probe (Fig. 2A) was used, with diameter 25 mm, test speed of 1 mm/s and compres- sion of 50% of the sample height. The necessary force to com- press 50% of the sample height, in newtons, was taken to be the result from the test. – Cut test: a Warner–Bratzler shear blade with guillotine probe (Fig. 2B) was used, with test speed of 1 mm/s. The cut was per- formed perpendicularly to the main axis of the snack until com- pletely breaking it. The peak force obtained, in newtons, was taken to be the result from the test. – Cut test: a Warner–Bratzler shear blade with a ‘‘V’’ shape probe (Fig. 2C) was used, with test speed of 1 mm/s. The cut was per- formed perpendicularly to the main axis of the snack until com- pletely breaking it. The peak force obtained, in newtons, was taken to be the result from the test. – Puncture test: a needle probe (Fig. 2D) was used, with test speed of 1 mm/s and perforation of 50 % of the sample thickness. The peak force obtained, in newtons, was taken to be the result from the test. – Shear test: a Kramer shear cell five-blade probe (Fig. 2E) was used, with test speed of 1 mm/s. Sufficient quantity of snack was used to cover the bottom of the cell, without overlapping Fig. 2. Texturometer probes. Legend: A (aluminum cylinder probe with diameter of 25 m blade with ‘‘V’’ shape probe), D (needle probe) and E (Kramer shear cell five-blade prob of the pieces, and shearing was performed until the probe had completed its travel. The peak force obtained, in newtons, was taken to be the result from the test. Before the analyses, the snacks were carefully cut to achieve standardization regarding the shape for the instrumental test: – Compression test: all snacks were cut into squares of side length 1.5 cm (smaller than the probe); – Cut test with guillotine, cut test with ‘‘V’’ shape probe and puncture test: the cylindrical and ring-shaped snacks were standardized with lengths of 3 cm; the pellet snacks were cut into rectangles of length 2 cm and width 1.5 cm; the shell-shaped snacks were cut to have a diameter of 1.5 cm. – Shear test: the original shape of all the snacks was preserved. All analyses were performed at ten replicates. 2.4. Statistical analysis The means of the sensory attributes were compared using var- iance analysis followed by the Tukey test (significant difference m), B (Warner–Bratzler shear blade with guillotine probe), C (Warner–Bratzler shear e). 12 A.M. Paula, A.C. Conti-Silva / Journal of Food Engineering 121 (2014) 9–14 when p 6 0.05), using the PASW Statistics 18 software (SPSS Inc.), since all of the data follow a Gaussian distribution. The results were also standardized and subjected to cluster analysis followed by multidimensional scaling analysis, using the Statistica 7.0 soft- ware (StatSoft, Inc.). The texture means obtained by instrumental tests were com- pared using variance analysis followed by the Tukey test (signifi- cant difference when p 6 0.05), using the PASW Statistics 18 software (SPSS Inc.), since all of the data follow a Gaussian distribution. Pearson correlation analysis was performed between the eleven means of the five sensory attributes of texture and of the five instrumental tests, using the PASW Statistics 18 software (SPSS Inc.), because the means follow a Gaussian distribution. In addi- tion, the same means from the sensory and instrumental analyses were subjected to Principal Component Analysis (PCA), using the Statistica 7.0 software (StatSoft, Inc.). For PCA analysis, the sensory attributes and instrumental tests were fixed in columns (variables) and the snacks in lines (cases), and the data were standardized be- fore analysis. The PCA analysis was performed with correlation ma- trix and without factor rotation. 3. Results and discussion 3.1. Descriptive analysis on texture The texture of the snacks was described using the attributes of hardness, crispness, adhesiveness, fracturability and chewiness (Table 1). These are the most used descriptors in studies evaluating the texture of extruded snacks (Ding et al., 2006; Liu et al., 2000; Nascimento et al., 2012; Nath et al., 2012; Veronica et al., 2006; Yuliani et al., 2006). Furthermore, while hardness relates to the ‘‘force applied by the molar teeth to compress the food’’, fractura- bility relates to the ‘‘ability to break food into pieces when it is bit- ten using the incisors’’. Thus, different forces applied by the teeth were evaluated. A similar investigation was conducted by Varela et al. (2009) to evaluate the crispness of extruded snacks. The hardness, crispness, adhesiveness and fracturability of the snacks were discriminated by the panelists, while only chewiness was not different for all the samples (Table 2). In general, cylindri- cal snacks presented higher degrees of hardness, adhesiveness and fracturability than shown by other shapes. Cluster analysis showed three groups of sensory attributes (Fig. 3A): one group for hardness and adhesiveness and another group for the attributes of crispness and fracturability, while chew- iness was kept in a separate group. Groups are formed based on Euclidean distances, which means that values of hardness and adhesiveness and of crispness and fracturability are proximal be- tween them, while values to chewiness is more distant from the others attributes. Multidimensional scaling (Fig. 3B) was used to present the spa- tial dispersion of the snacks in relation to the sensory attributes of Table 1 Definitions and references for sensory attributes of the extruded snacks. Sensory attribute Definition Hardness Force applied by the molar teeth to compress the food Crispness Noise of food during mastication Adhesiveness Ability of food to adhere to the teeth when chewed Fracturability Ability to break food into pieces when it is bitten using Chewiness Number of chews necessary for food to be swallowed texture. This could be evaluated using the stress value, which indi- cated the goodness-of-fit of the model. Stress values below 0.01 indicate that the data conform to the model, i.e. the model fits well (Johnson and Wichern, 1992; Kruskal and Wish, 1978). The stress value, in this case, was 0.0000. Cylindrical snacks were described in terms of crispness and fracturability, while ring-shaped snacks were described by adhe- siveness and hardness. Although chewiness was not discriminated by panelists (Table 2), the multidimensional scaling showed that shell-shaped and pelleted snacks were described by the chewiness. 3.2. Instrumental texture The different probes and tests applied resulted in different mean forces and, as in the sensory analysis, the snacks were dis- criminated according to the type of instrumental test (Table 3). In general, cylindrical snacks showed higher forces when the cut tests were applied, while shell-shaped snacks presented higher forces when the puncture test was used. The values found in the present study were lower than what was found for different kinds of extruded snacks in the literature, comparing similar tests and probes (Conti-Silva et al., 2012; Ding et al., 2006; Veronica et al., 2006), although some studies have shown similar results (Nath et al., 2012; Pamies et al., 2000) or lower values compared to the present study (Liu et al., 2000; Saeleaw et al., 2012). 3.3. Correlation between sensory and instrumental texture The instrumental forces derived from the cut tests were corre- lated with the sensory attributes of texture (Table 4). Hardness cor- related positively with both cut tests, although the correlation coefficient for the cut test with a ‘‘V’’ shape probe (r = 0.718) was higher than for the cut test with a guillotine (r = 0.687). The adhe- siveness of the snacks correlated positively with the cut test using a ‘‘V’’ shape probe (r = 0.763) and chewiness correlated positively with the cut test with a guillotine, although the correlation coeffi- cient was only 0.662. Similarly to hardness, fracturability corre- lated positively with both cut tests, although the correlation coefficient was higher for the cut test with a guillotine (0.776). Cor- relation coefficient about of 0.70 indicates fairly strong correlation according to Rayner (1969) cited by Leighton et al. (2010). No sig- nificant correlation was found with crispness. Varela et al. (2009) evaluated the crispness of two types of ex- truded snacks (wheat crusts and cheese balls) by means of com- pression and puncture tests and by using a sensory panel, who bit the snacks with the incisor teeth and chewed them with the back molars. These authors reported that the ratings from the bit- ing and chewing tests were very similar and that the results ob- tained from the sensory evaluation were similar to the instrumental results, although no correlation analysis was performed. References Low: Finger-sized soft bread rolls (Pullman) High: Hard candy (Halls) Low: Finger-sized soft bread rolls (Pullman) High: Breakfast cereal (Crunch) Low: Sliced carrot with thickness 2 mm High: Toffee candy with caramelized milk sweet (Arcor) the incisors Low: Sliced carrot with thickness 2 mm High: Commercial toast (Pullman) – – Table 2 Intensity of the sensory attributes for the extruded snacks (mean data ± SD, n = 18). Snacks Hardness Crispness Adhesiveness Fracturability Chewiness Cylindrical 1 4.2 (2.2)b 6.6 (1.8)b 4.6 (2.2)abc 6.7 (1.0)d 11.3 (4.9)a Cylindrical 2 3.2 (2.2)ab 6.1 (1.5)b 4.7 (2.2)bc 6.0 (1.5)cd 10.9 (5.1)a Cylindrical 3 3.2 (2.2)ab 6.0 (1.5)ab 4.9 (1.7)c 5.7 (1.3)bcd 10.3 (4.3)a Pelleted 1 3.4 (1.9)ab 4.8 (2.1)ab 2.9 (1.6)ab 4.5 (1.8)ab 10.7 (5.2)a Pelleted 2 2.3 (1.4)ab 5.7 (2.3)ab 2.7 (1.8)ab 4.1 (1.5)a 9.5 (4.2)a Pelleted 3 1.8 (0.9)a 6.0 (2.3)ab 2.6 (1.5)a 4.2 (1.5)ab 8.6 (3.5)a Ring 1 2.8 (1.6)ab 6.3 (1.6)b 3.8 (1.9)abc 5.2 (1.7)abcd 11.2 (5.4)a Ring 2 3.0 (1.6)ab 6.6 (1.5)b 3.5 (1.7)abc 6.2 (1.1)cd 12.2 (6.9)a Shell 1 3.1 (1.8)ab 6.3 (1.5)b 3.7 (2.1)abc 5.7 (1.4)bcd 8.7 (3.8)a Shell 2 2.3 (1.1)ab 4.1 (2.0)a 3.5 (1.9)abc 3.7 (1.3)a 8.8 (4.0)a Shell 3 2.6 (1.4)ab 5.3 (1.7)ab 3.9 (1.9)abc 5.1 (1.3)abc 9.3 (4.4)a Different letters in the same column indicate different means (p 6 0.05). A B Fig. 3. Euclidean distances diagram (A) and multidimensional scaling (B) on sensory texture of the extruded snacks. Table 3 Instrumental texture measurementsa for the extruded snacks (mean data ± SD, n = 10). Snacks Compression force Peak of cut-guillotine Peak of cut-‘‘V’’ shape Peak of puncture Peak of shear Cylindrical 1 33.4 (5.8)bcd 19.9 (3.1)d 26.2 (2.6)f 5.2 (0.6)ab 185 (24.4)bc Cylindrical 2 34.2 (5.1)bcd 18.4 (2.4)cd 21.2 (2.1)e 5.4 (0.8)ab 250 (23.4)d Cylindrical 3 21.6 (4.1)ab 12.6 (0.8)abc 16.3 (1.9)cd 3.7 (0.5)a 188 (19.9)bc Pelleted 1 22.3 (4.7)ab 13.3 (5.3)abc 12.3 (2.5)bc 7.3 (1.9)bc 186 (17.8)bc Pelleted 2 26.3 (9.6)abc 13.2 (6.8)abc 12.3 (3.1)bc 7.6 (3.0)bc 164 (22.0)b Pelleted 3 13.0 (3.0)a 11.3 (1.6)a 6.8 (0.8)a 5.3 (0.7)ab 100 (10.8)a Ring 1 13.8 (2.0)a 12.4 (6.1)ab 12.7 (3.4)bc 6.7 (1.4)ab 178 (24.4)bc Ring 2 37.6 (8.5)cd 18.1 (4.6)bcd 13.7 (1.6)bc 8.0 (2.1)bc 113 (22.3)a Shell 1 28.8 (11.9)bc 13.5 (2.9)abc 11.7 (3.8)b 10.2 (2.3)cd 295 (30.7)e Shell 2 45.7 (22.9)d 12.6 (2.6)abc 14.9 (2.9)bcd 12.8 (5.4)d 301 (17.8)e Shell 3 25.4 (10.9)abc 14.0 (3.7)abcd 18.5 (6.0)de 10.1 (1.6)cd 214 (48.8)cd Different letters in the same column indicate different means (p 6 0.05). a All results are expressed in newtons (N). Table 4 Coefficients of correlation between sensory and instrumental texture measurements for the extruded snacks. Hardness Crispness Adhesiveness Fracturability Chewiness Compression 0.223 �0.237 0.243 0.138 0.111 Cut-guillotine 0.687* 0.478 0.484 0.776** 0.662* Cut-‘‘V’’ shape 0.718* 0.172 0.763** 0.640* 0.427 Puncture �0.332 �0.574 �0.318 �0.442 �0.437 Shear 0.143 �0.406 0.365 �0.06 �0.369 * p 6 0.05. ** p 6 0.01. A.M. Paula, A.C. Conti-Silva / Journal of Food Engineering 121 (2014) 9–14 13 Fig. 4. Principal component analysis on sensory and instrumental texture of the extruded snacks. 14 A.M. Paula, A.C. Conti-Silva / Journal of Food Engineering 121 (2014) 9–14 Principal component analysis on the sensory and instrumental data (Fig. 4) showed that the first and second principal components explained, respectively, 48.5% and 25.9% of the observed variation (74.4% in total). The significance level of Bartlett’s test of sphericity was 0.000, which indicates that the correlation matrix is not an identity matrix and that principal component analysis can be ap- plied to the data (Hair et al., 1998). All sensory attributes (hardness, crispness, adhesiveness, fracturability and chewiness) and the instrumental forces with a guillotine and with a ‘‘V’’ shape contributed to explain the variance of principal component 1, while compression, puncture and shear tests explained the variance of principal component 2. These re- sults show that instrumental forces derived from the cut tests present stronger correlation with sensory attributes, as seen in Table 4. Also notice that puncture test, as seen in Table 4, is negatively correlated with sensory attributes, because it is positioned in the quadrant opposite to them. 4. Conclusions Cylindrical snacks are described by crispness and fracturability, while ring-shaped snacks are described by adhesiveness and hard- ness, and chewiness is important to describe shell-shaped and pel- leted snacks. The instrumental forces derived from the cut tests correlate strongly with sensory attributes, and that hardness and adhesiveness present correlations with the Warner–Bratzler test using a ‘‘V’’ shape probe, while fracturability and chewiness corre- late with the Warner–Bratzler test using a guillotine. The fairly strong good correlations enable application of these instrumental tests as an indicator of the sensory texture of extruded snacks, which facilitates comparisons among scientific works and allows to industries produce extruded snacks with desirable sensory tex- ture characteristics. Acknowledgement The authors are grateful for financial support from FAPESP (Fun- dação de Amparo à Pesquisa do Estado de São Paulo) (Grant 2011/ 08492-4). 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