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Understanding potato chips crispy texture by simultaneous fracture and acoustic measurements, and sensory analysis

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Understanding potato chips crispy texture by simultaneous fracture and acoustic measurements, and sensory analysis
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  Understanding potato chips crispy texture by simultaneous fractureand acoustic measurements, and sensory analysis A. Salvador, P. Varela, T. Sanz, S.M. Fiszman * Instituto de Agroquı´mica y Tecnologı´a de Alimentos (CSIC), Apartado de Correos 73, 46100 Burjassot, Valencia, Spain a r t i c l e i n f o  Article history: Received 29 April 2008Received in revised form23 September 2008Accepted 24 September 2008 Keywords: Potato chipsTextureAcoustic measurementsSensory a b s t r a c t The fracture and acoustic properties of six commercial potato chips that differ in sensory hardness andsensory crispness were analysed and related in this work. Principal component analysis showeda correlation among the sensory attributes and the instrumental parameters (both mechanical andacoustic). Two components mainly explained the behaviour of the different potato chips. The firstcomponent was positively related to the number of force and sound events, to sound pressure levelmaximum, to the area under the force curve, and to sensory crispness, and negatively related to fatcontent; and the second component was positively related to the gradient (slope of the first part of thecurve), the potato chip thickness, and to sensory hardness and sensory crispness. The behaviour of thedifferent potato chips was explained by either one of the two components or by both components.Results indicate that certain degree of sensory hardness is necessary for higher crispness perception.   2008 Published by Elsevier Ltd on behalf of Swiss Society of Food Science and Technology. 1. Introduction Potato chips, also known as potato crisps, are popular saltysnacks. A potato chip is a thin slice of potato, deep fried or bakeduntil crisp. Potato chips serve as an appetizer, side dish, or snack.Commercial varieties are packaged for sale, usually in multilayeredbags. The simplest chips of this kind are just cooked and salted, butmanufacturers can add a wide variety of seasonings (mostly madeusing herbs, spices, cheese or artificial additives). Potato chips arean important part of the snack food market in many countries.The characteristic crispy texture of potato chips is one of themost important quality indicators of the finished product, apartfrom colour, odour and flavour. Potato chips texture is oftendescribed in terms of crispness, hardness and crunchiness. Thiscrispy/crunchy character is an important sensory characteristic onwhich consumers base their appreciation.Raw potato properties as well as manufacturing conditions areimportant factors determining crispness of potato chips. Segnini,Dejmek, and O¨ ste (1999a) highlighted the significance of potatostarch content, position of the sample within the tuber, and finalmoisture content on the texture of potato chips. Pre-drying afterblanching was found to decrease oil absorption and to significantlyincreased crispness of potato chips (Pedreschi & Moyano, 2005).Also,soakinginNaClat25   Cfor5 minafterblanchingwasfoundtoincrease crispness (Pedreschi, Moyano, Santis, & Pedreschi 2007).Fatcontentandtextureofpotatocrispsarealsoinfluencedbyfryingtemperature and the type of oil used for frying (Kita, Lisinska, &Golubowska, 2007).Texture of potato chips can be evaluated using sensory andinstrumentalmethods(Szcesniak,Brant,&Friedman,1963).Amongthe instrumental tests, the puncture test placing the entire potatochip in a three-point support has been widely employed. Themaximum breaking force was proposed to quantify the texture of the samples (Pedreschi & Moyano 2005; Pedreschi et al.,2007;Segnini, Dejmek, & O¨ ste 1999a, 1999b). This fracture forceseemed to be a good predictor of all the sensory texture attributes(hardness, crunchiness, chewiness, and tenderness) as measuredby a trained panel, while deformation at fracture did not signifi-cantly correlate with any of the sensory attributes Segnini et al.(1999b).Vincent (1998) fractured the potato chips and extracted thenumber of drops in force and the size of the drops from the force–deflection curves. The frequency curves obtained provideda mechanical signature of the crisp food.Kita, Lisinska, and Golubowska (2007) measured the texture of potato chips using a rectangular share blade and determined themaximum shear force necessary to cut one slice of chips.The above mentioned methods evaluated texture of the entirepotato chip. To be able toobtain fundamental parameters, Rojo andVincent (2008) evaluated potato chips crispy texture in homoge-neous specimens carefully obtained from the potato chips. Themechanical strength was found to be related both to the intrinsicmaterialpropertiesandtothetextureofchips.Thecentrallyloaded *  Corresponding author. Tel.:  þ 34 963 90 0022; fax:  þ 34 963 63 6301. E-mail address:  sfiszman@iata.csic.es (S.M. Fiszman). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt 0023-6438/$34.00    2008 Published by Elsevier Ltd on behalf of Swiss Society of Food Science and Technology.doi:10.1016/j.lwt.2008.09.016 LWT - Food Science and Technology 42 (2009) 763–767  plate tests provided a qualitative evaluation of crispness (Rojo &Vincent, 2008).In general, crispness is characterized by a brittle fracture at lowfracture force, and distinguishable fracture events, with theconcomitantemission of sound (Duizer, 2001; Luyten, Plijter, & vanVliet, 2004). Vickers (1987) related sensory crispness with acoustic attributes of potatochips measured withan oscilloscope and foundthat measurements indicating the loudness of the sounds corre-latedmost closelywith crispness. Duizer(2001) reviewedthe mainaspects of acoustic research for studying the sensory perception of crisp, crunchy and crackly textures. Srisawas and Jindal (2003)developed a method for evaluating the sensory crispness of snackfood products based on direct application of frequency domainspectra of acoustic signals and the use of neural network models;this study measured the perception of air-conducted sounds andtheir correspondence with the sensation of crispness; the authorsconcluded that the precise interpretation of acoustic data wasdifficult.A new approach to investigate the acoustic nature of crispnesshas recently emerged; it is based on the simultaneous recording of the sound and fracture/mechanical events produced during theapplication of a force to a crisp product. To do so an AcousticEnvelope Detector (AED) was attached to a Texture Analyser. Littleresearch has been done byapplying this technique. Recently, Chen,Karlsson, and Povey (2005) and Varela, Chen, Fiszman, and Povey(2006) found a very good connection between some recordedsound parameters, the instrumental texture measured, and thesensory assessment of crispness in biscuits and roasted almonds,respectively.The aim of this work was to assess the crispness of six differentcommercial potato chips by using force/displacement measure-ments in combination with the corresponding acoustic emission,and to relate these results with some compositional and sensorycharacteristics associated to crispness. 2. Materials and methods  2.1. Samples Six kinds of commercial potato chips of different characteristicshave been studied: ‘‘Traditional potato chips’’ (‘‘T’’), ‘‘0% salt potatochips’’ (‘‘0%’’), ‘‘Extra-crunchy potato chips’’ (‘‘Extra C’’), ‘‘Wavypotato chips’’ (‘‘W’’), ‘‘Light potato chips’’ (‘‘L’’), and ‘‘Potato-basedsnack’’ (‘‘Snack’’). Their specific composition is shown inTable 1. All the samples came in their srcinal package (PET-met/PE) of 200 gand were kept at room temperature (21   C) until testing. For eachsample a selection of chips with similar shape and size was made.The potato chips were measured immediately after opening thepackage.  2.2. Thickness of potato chips Thickness of potato chips was measured using an electronicdigital calliper (range 0–150  0.01 mm). Twenty potato chips of each kind were measured.  2.3. Moisture and fat content  Moisturewasdeterminedbyvacuumdryingat95   Ctoconstantweight (standard technique, method 950.46, AOAC, 2000). Total fatcontent was determined by direct extraction with ethyl ether for12 h in a Soxhlet extractor (AACC,1967). Four determinations wereperformed for each kind of potato chip.  2.4. Texture and sound emission analysis A TA-XT plus Texture Analyser (Stable Micro Systems, God-alming, UK) was used for force/displacement measurements witha 25 kg load cell, using a spherical probe (P/0.25S) of ¼-inchdiameter; the samples were placed on the HDP/CFS (Crisp FractureSupport Rig and corresponding platform, SMS) (Fig. 1). The testsettings were: test speed 1 mm/s, trigger force 5 g, travel distanceof the probe 3 mm. An AED described in detail elsewhere (Chenet al., 2005; Varela et al., 2006) was used for sound recording, withthe corresponding software (Texture Exponent 32). The gain of theAEDwas setatone.ABrueland Kjaerfree-fieldmicrophone(8-mmdiameter),calibratedusinganAcousticCalibratorType4231(94 dBand 114 dB SPL-1000 Hz) was positioned at 4 cm distance with anangle of 45  to the sample. Ambient acoustic and mechanical noisewasfilteredbytheuseofahighpassfilterof1 kHz.Alowpassfilterset the upper calibrated and measured frequency at 16 kHz. TheAED operates by integrating all the frequencies within the band  Table 1 Characteristics of the commercial potato chips per 100 g, as described by themanufacturer in the package and the nomenclature adopted in the text.Sample Ingredients Protein(g)Carbo-hydrates(g)Fat(g)Fibre(g)Sodium(g)Caloriccontent(Kcal)‘‘T’’ Potato, vegetable oil andsalt6.0 52.0 37.0 ND ND 568‘‘0%’’ Potato and vegetable oil 6.5 48.0 35.0 4.5 0.06 530‘‘ExtraC’’Potato, vegetable oil andsalt6.0 48.0 32.0 5.0 1.20 505‘‘W’’ Potato, vegetable oil andsalt6.6 48.6 36.2 ND ND 547‘‘L’’ Potato, vegetable oil andsalt7.0 60.0 21.0 5.5 0.70 460‘‘Snack’’ Dehydrated potatoes,vegetable oil, and fat,corn flour, wheat starch,maltodextrin, emulsifier:E 471, salt, rice flour anddextrose6.0 51.0 34.0 4.0 0.50 535ND: composition not declared. Fig. 1.  Schematic diagram of the Crisp Fracture Support Rig and correspondingplatform.  A. Salvador et al. / LWT - Food Science and Technology 42 (2009) 763–767  764  pass range generating a voltage proportional to the sound pressurelevel (SPL). The data acquisition rate was 500 points per second forboth force and acoustic signals. All tests were performed ina laboratory with no special soundproof facilities at room temper-ature. Fifteen replications were performed for each kind of potatochip. Force/displacement and SPL/displacement curves weresimultaneously plotted. From the force curve the followingparameters were extracted: area below the force curve, number of forcepeaks (dropinforcehigher than0.049 N), and gradient (slopeof the curve up to the first major peak). From the sound curves, thenumber of sound peaks (drop in sound pressure level higher than10dB) and the sound pressure level (average of the ten higherpeaks, SPLmax 10 ).  2.5. Sensory analysis A panel of 9 assessors with experience in the descriptive eval-uation of crispy products was used to evaluate the six samples of potato chips. Testing was carried out in a sensory laboratoryequipped with individual booths (ISO, 1988). A balanced completeblock experimental designwas carried out to evaluate the samples.The intensities of sensory attributes ‘‘hardness’’ and ‘‘crispness’’were scored on 10 cm unstructured line scales labelled from ‘‘low’’(0) to ‘‘high’’ (10). To evaluate hardness the instruction was to bitethe whole chip with the incisors until fracture and to score thematerial resistance. To score crispness the instruction was toevaluate altogether during mastication, amount and quality of thesound produced, deformability and brittleness. The samples wereserved in random order, each on a separate plastic tray, identifiedwith a three digit random code. Panellists were instructed to rinsetheir mouths with water between sample evaluations.  2.6. Statistical analysis One-way analysis of variance (ANOVA) was performed on theinstrumental and on sensory parameters to evaluate differencesamong the chip samples. Besides, principal component analysis(PCA) was done to correlate sensory and instrumental parameters.In this analysis the rotation method used was Varimax with Kaisernormalisation and correlations were taken into account if higherthan 0.6. Statistical analysis was performed using the SPSS 12package program (SPSS Inc., Chicago). 3. Results and discussion  3.1. Thickness, moisture and fat content of potato chips The different potato chips showed significant differences in thevalues of thickness, moisture and fat contents (Table 2). Potatochips ‘‘W’’ and ‘‘Snack’’ showed significantly the highest thicknessvalues, while potato sample ‘‘T’’ and ‘‘0%’’ showed significantly thelowest. The fat content of potato chips ‘‘T’’ and ‘‘0%’’ was signifi-cantly higherthanall the otherpotato chips.Ascan beexpectedforbeing a ‘‘light’’ product, ‘‘L’’ potato chips had the lowest fat content.No relationship among the moisture and fat content could beestablished, due to the unknown but expected differences in theraw potatoes characteristics and in the manufacturing process of the different potato chips.The influence of the raw potato characteristics and of theproduction conditions on the fat content of potato chips wasstudied by several authors. Kita (2002) studied fat content of chipsmade from potato tubers of five varieties; he found significantdifferences among the samples and related fat content to dry masscontent: higher dry mass content produced chips with lower fatcontent. In another study (Kita et al., 2007), the quantity of fatabsorbed in potato chips was related to the type of oil and fryingtemperature. Lower temperature was associated to higher fatcontent. Pedreschi and Moyano (2005) studied the effect of pre-drying on fat content of potato chips. They found that a pre-dryingprocess increased the crispness of potato chips and reducedsignificantly the oil absorption of blanched potato slices afterfrying. However, the relation between fat and moisture content of potato chips and their crispy texture remains unclear. A possiblerelationship among moisture and fat content of potato chips andtheir crispy texture is analysed further in this article.  3.2. Texture and sound emission analysis A representative profile of the force and the simultaneouslyrecorded sound during the probe displacement in the potato chipsis shown in Fig. 2.The force–displacement curves show a jagged appearance withseveral fracture events, typical of crispy food (Chen et al., 2005;Varela et al., 2006; Vincent,1998).Two well differentiated regions were observed in the curves. Afirst region, starting from the first contact between the probe andthe potato chip until the first major drop in force, was associatedwith a major structural breakdown; in this first region, the probemainly deformed the potato chip and the force increased nearlylinearly with time. During this first region, not much structuralbreakdowntookplaceandtheacousticemissionwasalsoquitelow.The second region started from the first major structural break-down; in this region, higher force and acoustic events wererecorded in comparison to the first region.In order to compare objectively the behaviour of the differentpotatochips,specificparameterswereextractedfromtheforceandsound curves. The parameters evaluated were: 1) the gradient(slope of the first part of the force curve), which is related to the  Table 2 Thickness, moisture and fat contents of the potato chips studied.Sample Thickness (mm) Moisture (%) Fat (%)‘‘T’’ 1.2 a 1.8 a 35.9 a ‘‘0%’’ 1.2 a 1.6 a 36.9 a ‘‘Extra C’’ 1.3 b 2.7 b 29.6 b ‘‘W’’ 1.5 c 1.5 a 30.7 b ‘‘L’’ 1.3 b 2.2 ab 18.7 c ‘‘Snack’’ 1.4 bc 3.0 b 28.7 babc For the same column means without a common letter differ (  p < 0.05) accordingto Tukey’s test. Fig. 2.  Force (grey line) and Sound Pressure Level (SPL, black line) versus probedisplacement. Potato chip ‘‘T’’.  A. Salvador et al. / LWT - Food Science and Technology 42 (2009) 763–767   765  stiffness; 2) the area under the force versus displacement curve,which is related to the total work involved in the test; 3), 4) and 5)the numberof force peaks before and after the first main structuralbreakdown, and the number of total force peaks, which are anindex of the jaggedness of the curve; 6) and 7) the number of acoustic events before and after the first main structural break-down, and the number of total sound peaks, and 8) the soundpressurelevel (average of the ten higher peaks, SPLmax 10 ); this lastparameter was found more representative of the maximum soundpressure level than the value of just the maximum peak, whichcould have a more unpredictable value.The parameters obtained are shown in Table 3 (force/displace-ment plot parameters) and Table 4 (sound/displacement plotparameters).Samples ‘‘Snack’’ and ‘‘0%’’ had a significantly lower area thanany other sample, which showed no significant differences amongthem.Sample ‘‘W’’ presented the highest gradient and was thereforethestiffest.Onthecontrarysample‘‘T’’showedthelowestgradient.Ingeneral,thehighernumberoftotalforcepeakswasassociatedwith higher number of total sound peaks and to SPLmax 10 . Asexpected, in all the potato chips the number of force and acousticpeaks was lower in the first region (before breaking) than in thesecondregion(afterbreaking),whichconfirmsthefactthatthemainstructuralbreakdownoccursinthesecondregion.Samples‘‘L’’,‘‘T’’,and‘‘ExtraC’’showedthehighernumberofforcepeaks,soundpeaksand SPLmax 10 . A high number of force and sound peaks have beenassociatedtoahighsensorycrispness(Chenetal.,2005;Varelaetal.,2006). In potato chips ‘‘Extra C’’, ‘‘L’’, ‘‘Snack’’, and ‘‘0% salt’’ thispositiverelationamongnumberofpeaksandsensorycrispnesswasalso found. However, in samples ‘‘W’’ and ‘‘T’’ this relation was notfound. The discrepancy in the behaviour of these two samples isdiscussed in the next section, where the correlation among thedifferent parameters evaluated will be studied.  3.3. Sensory analysis Values of sensory attributes evaluated are shown in Table 3.Significant differences in the attributes ‘‘hardness’’ and ‘‘crispness’’were found among the different potato chips samples. ‘‘Extra C’’,‘‘W’’ and ‘‘Snack’’ chips were the samples with higher sensoryhardness and ‘‘Extra C’’, ‘‘W’’ and ‘‘L’’ were the samples with highersensory crispness.  3.4. Correlation between sensory and instrumental analysis To evaluate the correlation among the different instrumentalandsensoryparametersaPCAwascarriedout.Therotationmethodused was Varimax with Kaiser Normalisation and rotationconverged in 5 iterations. Three components were extracted thattogether explained 87.7% of the variance. The first two componentsthat explained together 68.9% of the variance are represented inFig. 3. The first component explained 39.5% of the variance andshowed a positive correlation with the instrumental parameters‘‘area’’, ‘‘number of force peaks’’, ‘‘number of sound peaks’’,‘‘SPLmax 10 ‘‘, and sensory crispness, and a negative correlationwiththe fat content.Behaviour of samples ‘‘L’’ and ‘‘Extra C’’ was explained by thepositive part of PC1. As previously stated, these samples are char-acterized by high number of force, sound peaks and SPLmax 10  andwith high sensory crispness. In the opposite situation appearssample ‘‘Snack’’, which behaviour is explained by the negative partof PC1, characterized as a sample with low number of force, soundpeaks, SPLmax 10 , and low sensory crispness.The second component explained 29.4% of the variance andshowed a positive correlation with the thickness, the gradient,sensory hardness and sensory crispness.The positivepartofPC2 explainedthe behaviourof sample‘‘W’’,which was the thicker sample with a high gradient value and alsowith high sensory hardness.The third component explained 18.8% of the variance andshowed a positive correlation with the moisture content andsensory hardness. The positive part of PC3 explained the behaviourof sample ‘‘Snack’’, which was the samplewith the higher moisturecontent and the highest sensory hardness (data not shown).Unlike other samples, sample ‘‘W’’ despitehaving a lownumberof force and sound peaks showed a high sensory crispness; thisdifferential behaviour may be explained due to the way this potatochip fractured during the instrumental texture test, which failed tosimulate the way the trained panel evaluate crispness. Upon con-tactingwiththesphericalprobe,potatochips‘‘W’’brokeveryeasilyinto two parts (following exactly one of the waves of their surface).These two broken parts fell apart and the probe did not continuebreaking them. As a consequence of this fracture pattern, thenumber of fracture and sound events registered was low (see theforce–sound/displacement plot in Fig. 4). The panellists scoredsensory crispness during mastication, which implied that theyalsoevaluatedthecrispnessprovidedbybitingthetwobrokenpiecesof the potato chip, which failed to be registered by the texture ana-lyser. Therefore, potato chips ‘‘W’’ were scored with high sensorycrispness,despitetheirlowinstrumentalcrispnessintermsofforceand acoustic events.Finally, the behaviour of samples ‘‘T’’ and ‘‘0% salt’’ is explainedby both components. Sample ‘‘T’’ was related to the positive part of PC1 (high number of force peaks, sound peaks and SPLmax 10 ) andto the negative part of PC2 (low gradient, low thickness, and lowsensory hardness). The relation of sample ‘‘T’’ with the negativepart of PC2 explained its low sensory crispness, despite its highnumber of force and sound peaks, revealing its very brittle andweak structure, so the crispness perception is very short in themouth. Sample ‘‘0% salt’’ was related to the negative part of both  Table 3 Mean values of the instrumental texture and sensory parameters.ChipSampleInstrumental texture parameters Sensory parameterscoresArea(Ns)Gradient(N/s)Number of force peaksbeforebreakingNumber of force peaksafterbreakingNumberof totalforcepeaksHardness Crispness‘‘T’’ 4.5 a 3.3 a 2.1 ab 6.3 a 8.4 ab 2.7 ab 4.9 ab ‘‘0%’’ 2.1 b 3.9 ab 0.4 b 1.6 b 2.0 c 2.6 a 5.2 ab ‘‘ExtraC’’2.8 ab 4.7 ab 2.1 ab 3.6 ab 5.7 abc 5.9b cd 7.7 bc ‘‘W’’ 3.7 ab 6.5 b 2.8 ab 3.0 ab 5.8 abc 6.1 cd 8.7 c ‘‘L’’ 3.6 ab 4.2 ab 3.8 b 5.3 ab 9.1 a 4.1abc 7.3 bc ‘‘Snack’’ 2.6 b 4.4 ab 1.4 ab 2.2 b 3.7 bc 7.4 d 2.7 aabc Different letters for the same column means there is a significant difference(  p < 0.05) according to Tukey’s test.  Table 4 Mean values of the instrumental parameters extracted from sound/displacementplots.ChipSampleNumber of soundpeaks beforebreakingNumber of soundpeaks afterbreakingNumber of total soundpeaksMax SPL (dB)(average of 10peaks)‘‘T’’ 5.2 a 22.2 a 27.4 ab 85.1 ab ‘‘0%’’ 2.6 a 9.6 b 12.1 ac 82.6 ad ‘‘ExtraC’’8.0 ab 12.8 ab 20.8 abc 86.7 b ‘‘W’’ 2.3 a 7.8 b 10.2 c 84.6 ab ‘‘L’’ 12.4 b 23.4 a 35.8 b 91.8 c ‘‘Snack’’ 1.2 a 8.3 b 9.6 c 80.4 dabc Different letters for the same column means there is a significant difference(  p < 0.05) according to Tukey’s test.  A. Salvador et al. / LWT - Food Science and Technology 42 (2009) 763–767  766  components and it is characterized as a sample with both lowsensory crispness and low sensory hardness. Another reason thatcould explain the low sensory crispness of both ‘‘0% salt’’ and ‘‘T’’ istheir significantly higher fat content (Van Vliet, Visser, & Luyten,2007), as fat content was related to the negative part of PC1 andtherefore negatively related to sensory crispness.Previous work on potato chips texture studied parameters suchas potato variety (Blahovec, Vacek, & Patocka, 1999; Kita, 2002;Lefort, Durance, & Upadhyaya, 2003), starch quantity (Lefort et al.,2003), position of the slice within the tuber (Segnini et al.,1999b), temperatureof thefryingoil(Kitaetal.,2007;Pedreschi&Moyano,2005;Segninietal.,1999b),kindofoil(Kitaetal.,2007),allof them interesting factors influencing potato chip texture. However, thereis little research on the relationship among crispness-relatedsensory attributes and physical properties of the potato chips. Theinstrumental test described in this article was able to evaluate, todiscriminate and to predict quite reasonably sensory crispness. Inaddition, the following specific advantages make it suitable forindustrial application: 1-The samples can be analysed as it, noregular geometry is necessary; 2-industries are familiarized withthe main machinery employed, a texture analyser, as it is aninstrument widelyemployed forqualitycontrol of awide varietyof food items; 3-No soundproof facilities are needed for soundrecording; 4-The analysed parameters can be easily obtained fromthe curves using the instrumental software. 4. Conclusions Information from the force/deformation and simultaneouslysound recording during fracturing of potato chips constitutes aneffective instrumental tool to predict sensory crispness. However,careful interpretation of the results has to be done.In general sensory crispness is positively related to the numberof fracture and acoustic events, to SPLmax 10 , and to the area belowthe force curve. In addition, results indicated that certain degree of sensory hardness is necessary for crispness perception. On theotherhand,a lownumberofforceand acousticeventsnormallyaretaken as an index of low crispness; however, a careful observationand analysis of the fracture pattern is necessary.  Acknowledgements The authors are indebted to the Comisio´n Interministerial deCienciayTecnologı´aforfinancialsupport(ProjectAGL2006-11653-C02-01). References AACC. American Association of Cereal Chemists. (1967).  Cereal laboratory methods .Method 30–20.AOAC. Association of Official Analytical Chemists. (2000).  Official methods of analysis. (17th ed.). Gaithersburg, MD: AOAC.Blahovec, J., Vacek, J., & Patocka, K. (1999). Texture of fried potato tissue as affectedby pre-blanching in some salt solutions.  Journal of Texture Studies, 30 , 493–507.Chen, J., Karlsson, C., & Povey, M. (2005). Acoustic envelope detector for crispnessassessment of biscuits.  Journal of Texture Studies, 36  , 139–156.Duizer, L. (2001). A review of acoustic research for studying the sensory perceptionof crisp, crunchy and crackly textures.  Trends in Food Science and Technology,12 ,17–24.ISO. (1988).  Sensory analysis. General guidance for design of test rooms . Standard no.8589. Geneve, Switzerland.Kita, A. (2002). The influence of potato chemical composition on crisp texture.  FoodChemistry, 76  , 173–179.Kita, A., Lisinska, G., & Golubowska, G. (2007). The effects of oils and fryingtemperatures on the texture and fat content of potato chips.  Food Chemistry,102 , 1–5.Lefort, J. F., Durance, T. D., & Upadhyaya, M. K. (2003). Effects of tuber storage andcultivar on the quality of vacuum microwave-dried potato chips.  Journal of FoodScience, 68 , 690–696.Luyten, H., Plijter, J. J., & van Vliet, T. (2004). Crispy/crunchy crusts of cellular solidfoods: a literature review with discussion.  Journal of Texture Studies, 35 ,445–492.Pedreschi, F., & Moyano, P. (2005). Effect of pre-drying on texture and oil uptake of potato chips.  LWT - Food Science and Technology, 38 , 599–604.Pedreschi, F., Moyano, P., Santis, N., & Pedreschi, R. (2007). Physical properties of pre-treated potato chips.  Journal of Food Engineering, 79 , 1471–1482.Rojo, F. J., & Vincent, J. F. V. (2008). Fracture properties of potato chips.  International Journal of Food Science and Technology, 43 (4), 752–760.Segnini, S., Dejmek, P., & O¨ ste, R. (1999a). Relationship between instrumental andsensory analysis of texture and color of potato chips.  Journal of Texture Studies, 30 , 677–690.Segnini, S., Dejmek, P., & O¨ ste, R. (1999b). Reproducible texture analysis of potatochips.  Journal of Food Science, 64 (1), 309–312.Srisawas, W., & Jindal, V. K. (2003). Acoustic testing of snack food crispness usingneural networks.  Journal of Texture Studies, 34 , 401–420.Szczesniak, A. S., Brandt, M. A., & Friedman, H. H. (1963). Development of standardrating scales for mechanical parameters of texture and correlation between theobjective and the sensory methods of texture evaluation.  Journal of Food Science, 28 , 397–403.Van Vliet, T., Visser, J. E., & Luyten,H. (2007). On the mechanism by which oil uptakedecreases crispy/crunchy behaviour of fried products.  Food Research Interna-tional, 40 , 1122–1128.Varela, P., Chen, J., Fiszman, S. M., & Povey, M. (2006). Crispness assessment of roasted almonds by an integrated approach to texture description: texture,acoustics, sensory and structure.  Journal of Chemometrics, 20 , 311–320.Vickers, Z. M. (1987). Sensory, acoustical and force-determination measurements of potato chips crispness.  Journal of Food Science, 52 , 138–140.Vincent, J. F. V. (1998). The quantification of crispness.  Journal of the Science of Foodand Agriculture, 78 , 162–168. Fig. 3.  PCA. 2D-loading plot of the samples in the two principal componentsexplaining 68.9% of the variance. Fig. 4.  Force (grey line) and Sound Pressure Level (SPL, black line) versus probedisplacement. Potato chip ‘‘W’’.  A. Salvador et al. / LWT - Food Science and Technology 42 (2009) 763–767   767
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