Abstract The influence of the degree of compression, atdeformation rates of 50, 250 and 500 mm min–1, on thetextural parameters in the texture profile analysis (TPA)of cylindrical samples of potato and apple tissues wasexamined. The tests were performed at up to eight differ-ent deformation levels ranging from 10% to 80%. Thevalues of all the parameters measured in the samples ofboth tissues were influenced more by the degree of com-pression than by the deformation rate. Degrees of com-pression greater than 40% and 20% caused the rupture ofpotato and apple specimens, respectively. Regressionmodels were fitted to express the variation of cohesive-ness and chewiness with deformation rate and degree ofcompression. In apple and potato tissues, the degree ofcompression had a quadratic effect on the cohesivenesswhile the effect of the deformation rate was only linear.Cohesiveness was the most appropriate textural parame-ter for detecting effects of deformation rate and degreeof compression in TPA tests of potato and apple tissues.Recoverable instantaneous springiness offers a high po-tential to differentiate the structural natures of differenttissues.

Keywords Cohesiveness · Fruits · Regression · Texture ·Vegetables

Introduction

Compression testing has been widely applied to assessthe mechanical behaviour of potato and apple tissues [1, 2, 3]. This test has also been used to study deforma-tion rate and degree effects on rheological parameters.Shama and Sherman [4] were the first to show that, asdeformation rate increases, the force required to achievea particular compression also increases in differentfoods. However, deformation rate did not exert a signifi-

cant effect on the failure stress of raw potatoes, althoughthe values tended to decrease slightly with increasingrates of standard and lubricated compression [5]. Defor-mation rates much less than those typical of masticationcan be used to characterize the firmness of UF-Fetacheese from compression testing [6].

Texture profile analysis (TPA) was developed about35 years ago and adapted to a universal texturometer,providing a useful means of analysing a series of texturalparameters in a single test by means of a double com-pression of the sample [7, 8, 9]. TPA was performed onapple, carrot, frankfurter, cream cheese and pretzels withthe Instron texturometer, and the effect of the degree ofcompression on TPA parameters measured at a fixed de-formation rate [10]. However, the use of TPA becamewidespread with the appearance of versatile computer-assisted texturometers such as the TA.HD [Stable MicroSystems (SMS), Godalming, UK] or the QTS (Stevens,UK). This type of instrument can be used to perform aTPA test and obtain all the TPA parameters directly bymeans of software.

Nevertheless, TPA is often used without knowledgeof the correct definitions of its parameters, or selectionof suitable experimental conditions. Since TPA parame-ters vary with sample size and shape, ratio of compress-ing probe size versus sample, degree of compression, de-formation rate, number of bites, and replicates per meanvalue [11], all the TPA measurements in reports shouldclearly state what conditions were used. In TPA tests, thechoice of the degree of compression will depend uponthe purpose of the test. For an imitation of the highly de-structive process of mastication in the mouth, deforma-tion values that will fracture the specimen are required.However, some parameters such as springiness or cohe-siveness can become physically meaningless, since thesecond compression cycle does not usually find a weak-ened sample with just the first internal cracks, but por-tions or small pieces of the initial sample [12, 13].

Current instruments such as the TA.HD (SMS) givethe option of selecting a variable time period to elapsebetween bites. The amount of time between bites clearly

M.D. Alvarez (✉ ) · W. Canet · M.E. LópezInstituto del Frío-CSIC, c/ José de Novais n0 10, 28040 Madrid,Spaine-mail: ifrat44@if.csic.es

Eur Food Res Technol (2002) 215:13–20DOI 10.1007/s00217-002-0515-0

O R I G I N A L PA P E R

María Dolores Alvarez · Wenceslao CanetMaría Elvira López

Influence of deformation rate and degree of compression on texturalparameters of potato and apple tissues in texture profile analysis

Received: 3 January 2002 / Published online: 10 April 2002© Springer-Verlag 2002

determines TPA parameters such as springiness, cohe-siveness, gumminess and chewiness, mainly in systemswith a high viscous component [14]. One of the parame-ters which has undergone most modifications is springi-ness, initially called elasticity. Pons and Fiszman [11]measured two different springiness-related parameters inthe same test: “instantaneous recoverable springiness”,derived from the first compression cycle, and “retardedrecoverable springiness”, which corresponds to thespringiness parameter normally measured by instrumen-tal TPA and defined by Bourne [15].

TPA software for some texturometers automaticallygives results for the adhesiveness parameter, although itis not worth measuring adhesiveness in all cases [16].For some kinds of food, the measurement of adhesive-ness by this method is not appropriate [11]. Hoseney andSmewing [13] stated that in order to study adhesiveproperties it is imperative to have a procedure that forcesa clean separation at the probe-material interface. Be-sides, gumminess and chewiness are mutually exclusiveparameters and should not both be reported for the sameproduct [17, 18].

The aim of the present work was to test the validityand reproducibility of the textural parameters calculatedautomatically from the TA-HD Texture Analyser (SMS).This was investigated by measuring texture in potato andapple tissues over a wide range of deformation rates anddegrees of compression in order to address the broadspectrum of experimental conditions in which this testmay be used. Raw potatoes were studied and consideredas a model vegetable for comparisons. Regression mod-els were fitted to express the variation of the most appro-priate textural parameters with deformation rate and de-gree of compression, and correlations between parame-ters were studied in order to find redundant parameters.

Materials and methods

Sample preparation. The produce used in this study were potato tubers (cv. Kennebec) and apple (cv. Golden Delicious). Thesewere purchased locally and stored in the dark in polythene bags at 4 °C prior to testing. All experiments were completed within 4 days of purchase. Potato tubers and apples were conditioned atroom temperature (≈20–22 °C) first (with their skin), and then cutimmediately before testing. Cylindrical specimens were obtainedusing a stainless-steel cork borer, nominally 19.1 mm in diameter.Each cylinder was subsequently trimmed to a length of 10.0 mmusing a mechanically guided razor blade. From the potato tubers,cylindrical specimens were taken from the center part of slices cutperpendicular to the long axis of the tuber, to avoid the large textur-al differences reported to exist between the cortex and pith tissues[19]. Three specimens were taken from each tuber. From appleflesh, cylindrical specimens were taken from the outer cortex ofslices cut perpendicular to the core of the fruit, taking care to avoidthe core. Three specimens were obtained of each piece.

TPA tests. TPA tests were performed with a TA.HD texturometer(SMS) using a 2500 N load cell and the application program pro-vided with the apparatus (Texture Expert for Windows, version2.03). A flat 75-mm diameter aluminum plunger (SMS P/75) wasused in the TPA tests. The texturometer was programmed so thatthe downward movement began at a point 5 mm above the surfaceof the sample. The following experimental conditions were select-

ed for each TPA test: three different deformation rates (50 mmmin–1, 250 mm min–1 and 500 mm min–1), eight compression levels (10, 20, 30, 40, 50, 60, 70 and 80%), and a rest period of 3 sbetween cycles. The position to which the probe returned after thefirst compression cycle cannot be selected: the probe always returned to the trigger point before beginning the second cycle.After the second cycle, the probe returned to its initial position.There were five replicates for each experimental unit.

From the curve generated by such a test, according to the pro-gram User Guide [20] the textural parameters are automaticallycalculated by the software as follows: hardness is given as the firstforce peak if there are only two peaks found, or the second peak ifthere are three peaks found on the TPA curve. Cohesiveness is cal-culated as the ratio of the positive force area during the secondcompression portion to that during the first compression. Springi-ness is calculated as the ratio of the distance or time from the startof the second area up to the second probe reversal over the dis-tance, or time between the start of the first area and the first probereversal. Adhesiveness is the negative area between the point atwhich the first curve reaches a zero force value after the first com-pression and the start of the second curve. Fracturability is theforce value corresponding to the first peak (only when there arethree peaks). Gumminess is calculated as hardness×cohesiveness,and chewiness as hardness×cohesiveness×springiness. The soft-ware also gives the peak force corresponding to the second com-pression cycle, which was designated force peak 2 throughout thisstudy. A broad survey of the evolution and different definitions ofeither the current or the original TPA parameters can be found inthe literature [11].

Preliminary tests of compression to failure for the potato andapple specimens were conducted to assess the value of deforma-tion at rupture, measured as a percentage of the original sampleheight. Potato specimens required a much higher deformation(40–50%) than apple specimens (15–25%) to rupture, confirmingprevious studies [1, 2, 3, 5].

Statistical analysis. The effects of the deformation rate and degree of compression were statistically tested using a two-wayanalysis of variance, and the means were compared by least signif-icant difference (99%). The data were subjected to backward step-wise regression, and the best model for each textural parameterwas chosen by maximizing r2 (determination coefficient), whilemaintaining a significant F-ratio for each independent variable inthe model selected. Statgraphics software version 5.0 (STSC,Rockville, Md., USA) was used in the multiple regression in-volved in the modelling [21]. Three-dimensional plots were drawnto highlight the main effects of deformation rate and degree ofcompression on textural parameters.

Results and discussion

TPA curves

Force/time curves of the double cycle for potato and ap-ple tissues at various deformation rates (50, 250 and500 mm min–1) and degrees of compression (10–80%)were plotted. Figure 1 and Figure 2 show curves for potato and apple tissues respectively, corresponding to50 mm min–1. Curves similar in shape were plotted at theother two deformation rates.

Figure 1 shows that for degrees of compression be-tween 10% and 40% of the initial height of the potatospecimens, i.e. below the rupturing deformation range(40–50%), the TPA curves had only two force peaks, thefirst peak corresponding to hardness and the secondpeak, corresponding to force, designated as force peak 2.As specimens did not fracture under these degrees ofcompression, the resulting hardness value was always

14

lower than the required rupture force of the specimens.However, at deformation levels greater than deformationat failure, i.e. compression between 50% and 80%, thespecimens ruptured and three force peaks were thenfound on TPA curves. The first peak of the first compres-sion cycle corresponds to the rupture force of the speci-mens, the second to hardness, also lower than ruptureforce at such high degrees of compression, and the thirdcorresponds to force peak 2 (Fig. 1).

In apple specimens, which ruptured at lower percent-ages of deformation (15–25% as indicated above), therewere three force peaks on the TPA curves at degrees ofcompression greater than 10% or 20% (Fig. 2). As in thepotato specimens, the first peak corresponds to ruptureforce, the second peak corresponds to hardness, which isagain lower than the rupture force, and the third peakrepresents force peak 2. Given that the height of the firstsignificant break in the TPA curve peak, at 50–80% de-formation levels in potato tissue and at 20–80% defor-mation levels in apple tissue, corresponded exactly to therupture force of each specimen, this value was not con-sidered as the fracturability of the sample. This parame-

ter was originally defined as a change in the inflection ofthe curve whose magnitude would be expected to belower than that of hardness. There are examples in theliterature where fracturability is referred to as the bio-yield point [22]. In fruits and vegetables, the fracturabili-ty value coincides in most cases with the rupturing of theexternal peel of the fruit or vegetable [9].

Figure 1 and Figure 2 also show that at 10% deforma-tion, the curve for the upstroke of the plunger was almostsymmetrical with respect to the downstroke portion. Thisindicates that there was instantaneous recovery of potatoand apple specimens at so low a deformation level. Simi-lar results have been reported in cylindrical samples ofdifferent gels subjected to two successive cycles of com-pression at deformation levels corresponding to 25% oftheir respective degrees of compression at failure [14].As the applied degree of deformation increased, curvesdid not show this symmetry, implying that the deforma-tion was not followed by a rapid recovery. This is due tothe fact that at higher compression levels, but below de-formation at failure, the potential damage to the structureis greater and recovery is less likely, indicating that de-

15

Fig. 1 Texture profile analysis (TPA) curves from the TA.HDtexturometer for potato specimens at 50 mm min–1 at degrees ofcompression varying between 10% and 80% of their initial heights

Fig. 2 TPA curves from the TA.HD texturometer for apple speci-mens at 50 mm min–1 at degrees of compression varying between10% and 80% of their initial heights

formation causes structural weakening, which augmentsthe degree of compression. The weak internal structure isthen incapable of storing the energy received. When theapplied degree of deformation caused rupture of thespecimens, curves showed total asymmetry, with thecurve for the upstroke of the plunger much greater thanthe curve for the downstroke (Fig. 1 and Fig. 2).

Figure 2 shows slight adhesiveness in TPA curvescorresponding to 10% and 20% deformation levels forapple tissue. Since only two samples showed adhesive-ness at 10% and 20% degrees of compression, this parameter was also discarded.

TPA parameters

Of the TPA parameters supplied automatically by thesoftware provided with the TA.HD texturometer, hard-

ness, force peak 2, cohesiveness, springiness and chewi-ness were chosen as the parameters for determining theinfluence of deformation rate and degree of compression.Potato and apple tissues should be considered as solidsamples; therefore, since both gumminess and chewinesscannot be determined in the same food, gumminess wasdiscarded as a parameter [17, 18].

Table 1 shows that both effects and their interactionsinfluenced the values of the textural parameters in bothtissues. From the F-ratio values for both effects, it seemsclear that the degree of compression influenced the parameters measured in the samples of both tissues morethan did the deformation rate. The deformation rate hadno significant effect on the hardness of either potato orapple tissue (Fig. 3 and Fig. 4). However, the degree ofcompression significantly (P≤0.01) affected the hardnessvalues of both tissues. In potato, hardness increased with

16

Fig. 3 Values of four TPA parameters of potato tissue atthe three deformation rates andthe eight degrees of compres-sion studied

Table 1 Effect of deformation rate, degree of compression and interaction between the two effects analysed on textural parameters inpotato and apple tissues. ns Non significant

Mechanical Hardness N Force peak 2 N Cohesiveness Springiness Chewiness Nparameter

Potato Apple Potato Apple Potato Apple Potato Apple Potato Apple

Main effects A: Deformation rateF-ratio 3.97 (ns) 2.12 (ns) 7.09a 33.10a 111.64a 142.32a 5.03a 18.16a 51.74a 29.25a

B: Degree of compressionF-ratio 257.12a 33.14a 43.88a 38.78a 521.57a 879.82a 73.98a 124.00a 162.79a 139.45a

Interactions ABF-ratio 2.97a 4.29a 1.48 (ns) 14.52a 14.04a 21.45a 1.12 (ns) 3.32a 7.09a 4.80a

a Significant difference at the level of P<0.01

the degree of compression up to 40% (Fig. 3) and de-creased when the deformation level passed the deforma-tion at failure. When sample-breaking degrees of com-pression (>40%) were applied, there were no significantdifferences in the hardness values of the potato speci-mens. Only for 80% deformation was hardness signifi-cantly greater than at 70%. This could be due to compac-tion of the remnants of the collapsed structure at high de-grees of compression [23]. In apple tissue, hardness in-creased up to 20% (Fig. 4) and decreased when the de-formation level surpassed the level of deformation forfailure. There were no significant differences in the hard-ness values of apple specimens at 30–60% deformation.For deformation levels of 70% and 80%, hardness in-creased significantly with respect to the values obtainedat 60%, again possibly due to increasing compaction ofthe collapsed structure.

Both the deformation rate and the degree of compres-sion significantly affected force peak 2 (P≤0.01) in pota-to and apple tissues. In potato, force peak 2 decreasedwhen the deformation rate increased, although the onlysignificant differences were between the slowest and thefastest rates. In potato, the interaction between the twoeffects did not affect this parameter. In apple, force peak2 increased when the deformation rate increased, withsignificant differences between the slowest rate and thetwo fastest. This parameter behaved similarly to hard-ness when the level of deformation changed. For thisreason, plots of force peak 2 are not included in Fig. 3and Fig. 4. However, the deformation level in potato in-fluenced this parameter (F-ratio) much less than hard-ness. This may be because at deformation levels that rup-

ture the sample in the first compression cycle, the secondcompression cycle finds portions or small pieces of theinitial sample, so that the reliability of this parameter atbreaking deformation levels is questionable. Comparisonof means by two-sample analysis showed that hardnessand force peak 2 in apple were significantly lower thanin potato at the various combinations of the studied factors.

Of the textural parameters, cohesiveness was the onemost significantly influenced (P≤0.01) by deformationrate and deformation degree in potato and apple tissues.The interaction between these effects was also signifi-cant. Moreover, there were no significant differences inthe cohesiveness values of either tissue as calculated directly by the software. In both potato and apple, thefaster the deformation, the higher the cohesiveness. Co-hesiveness values in potato and apple tissues were higherat 500 mm min–1 than at slower rates up to the degrees ofdeformation at which either specimen broke (Fig. 3 andFig. 4). Potato and apple tissues are known to be visco-elastic [24], and one of their prominent characteristics isthat the stress they develop in compression is a functionnot only of the deformation level, but also of the rate atwhich the compression is applied. The exact nature ofthe rate dependency is a characteristic of each material.It has been stated that at high rates, the response of a vis-coelastic material converges to what is equivalent to thebehaviour of an elastic material [25]. The more solid orelastic it is, the less is the rate effect in compressive andtensile tests [23]. The deformation rate affected cohe-siveness more in apple than in potato (Table 1), which isconsistent with those findings. Potato tissue is in fact a

17

Fig. 4 Values of four TPA parameters of apple tissue atthe three deformation rates andthe eight degrees of compres-sion studied

more solid material than apple tissue due partly to itshigher dry matter content. Cohesiveness decreased whenthe deformation level increased, with significant differ-ences between 10% and 40% compression in both sam-ples (Fig. 3 and Fig. 4). There were no significant differ-ences between deformation levels of 60%, 70% and80%; nor were there significant differences between de-formation levels of 50% and 60% in potato tissue or 50%and 80% in apple tissue.

Again, there were no significant differences in thespringiness values of potato and apple, and both factorssignificantly affected springiness in both samples(P≤0.01). Springiness also increased with increasing de-formation rate, although the effect in potato tissue wasminor. The deformation rate effect on springiness wasmore significant in apples than in potatoes (F-ratios). Theeffect of degree of compression was also more significantin apple tissue, with values decreasing with increasingdeformation level. Springiness was close to 1 at 10% de-formation (Fig. 3 and Fig. 4). This was to be expectedsince the curve for the plunger upstroke was almost sym-metrical with respect to the downstroke part at such a lowdeformation level. For k-carrageenan/locust bean gum(LBG) and gellan gels the values of recoverable instanta-neous springiness and recoverable retarded springinesswere quite different, indicating that recovery of their ini-tial heights was retarded [14]. Recoverable instantaneousspringiness was derived from the first compression cycle,and retarded recoverable springiness corresponds to thespringiness parameter normally measured for instrumen-tal TPA and considered throughout this study. By consid-ering these two springiness parameters separately, a vis-cous component can be detected which causes recoveryof the initial height of the sample to be delayed. In thisway, if the calculation is made only from the curve for thefirst cycle, the viscous element does not intervene andwhat is considered is principally the elastic element [11].These parameters seem to be a good index of the relativemagnitude of elastic and viscous components of foods.Recoverable instantaneous springiness is not calculatedautomatically from SMS software and has to be derivedmanually from each TPA curve. Since it is not directlyreadable, instantaneous springiness was not considered asa TPA parameter. However, in order to ascertain the rela-tive magnitude of elastic and viscous components in thesetissues, the values of recoverable instantaneous springi-ness at 250 mm min–1 were derived from the correspond-ing double-compression curves. The instantaneous andretarded recoveries of the initial heights of the samples

were compared, and the effect on these of the degree ofcompression was analysed (Table 2). Proposed parame-ters should be measured and compared over a deforma-tion range without fracture of the sample [11, 14]. Thevalues of the two parameters were significantly differentin both potato and apple. The value of retarded springi-ness was always greater than instantaneous springinessfor a specific percentage of compression, since the valueof retarded springiness included instantaneous springi-ness plus the recovery achieved by the sample during thewaiting time. The effect of the percentage of compressionwas even more significant on instantaneous springiness(F-ratio, Table 2) than on retarded springiness in potato.As the degree of compression increased, significantlylower values (P≤0.01) were recorded for the two springi-ness parameters of both tissues. There were similar dif-ferences between the values of the two parameters in thedeformation range for no fracture of the sample. The dif-ferences between the values of the two parameters weregreater in potato tissue, indicating a more perceptible vis-cous component in this tissue. The degree of compressiondid not influence the viscous component of potato tissue,reflecting the presence of a considerable viscous compo-nent in this tissue as found for k-carrageenan/LBG andgellan systems [14]. On the other hand, the degree ofcompression did influence the viscous component of apple tissue, which was higher at 20% than at 10% defor-mation. At both these compression levels, the values forthe different tissues can be compared since there was nofracture of the samples. The difference between springi-ness parameters was greater in potato than in apple at thelowest compression level; the potato samples presented a higher initial rate of relaxation and more pronouncedviscous characteristics, as has been found in previousrheological studies [2, 24]. It must be emphasized that themeasurement of the retarded springiness normally calcu-lated in TPA, did not indicate differences in the elastic re-sponse of the two tissues. This means that the proposedparameter differentiates products more than does the tra-ditional retarded springiness parameter.

Deformation rate, compression degree and the inter-action between the two effects significantly affectedchewiness (Table 1). Chewiness increased with the de-formation rate; there were significant differences be-tween the three deformation rates used in potato tissueand between 50 mm min–1 and the two fastest rates in ap-ple tissue. In potato, chewiness increased with deforma-tion level up to 30%. Chewiness decreased for higher de-formation levels, and there were no significant differ-

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Table 2 Effect of the degree ofcompression on instantaneousrecoverable springiness and re-tarded recoverable springinessin potato and apple tissues at250 mm min–1

Degree of Retarded Instantaneous Retarded Instantaneous compression springiness Springiness Springiness Springiness

Potato tissue Potato tissue Apple tissue Apple tissue

10 (%) 0.866a 0.628a 0.885a 0.739a

20 (%) 0.706b 0.464b 0.750b 0.514b

30 (%) 0.622b 0.400b – –40 (%) 0.625b 0.382b – –F-ratio 10.03 16.58 22.28 14.77

a, b Different letters in the samecolumn indicate significant dif-ferences at 1%

ences in the 50–80% deformation range. In apple, chewi-ness decreased with an increasing degree of compressionin all cases, although the differences were not significantbetween 40% and 80% (Fig. 3 and Fig. 4).

Regression models

Table 3 shows models fitted to express the variation ofcohesiveness and chewiness with deformation rate anddegree of compression. Polynomial models did not use-fully express the variation of hardness, force peak 2 andspringiness under both effects. Figure 5a, b highlights theeffect of the deformation rate and the degree of compres-sion on cohesiveness of potato and apple tissues. In bothtissues, the degree of compression had a quadratic effecton cohesiveness, while the deformation rate had only alinear effect on this parameter. Interaction between the ef-fects was significant for cohesiveness in both tissues asevidenced previously in Table 1. Models fitted for cohe-siveness presented high percentages of explained vari-ability (r2) and could be considered sufficiently accurateto make predictions in the ranges of deformation rate anddegree of compression studied. Both effects had a linear

influence on chewiness in potato tissue. Although themodel fitted was significant, the r2 found was lower than0.75, so that this model should only be used to analysetrends, not to predict [26]. Plots for chewiness are not in-cluded. However, the model fitted for chewiness of appletissue was similar to the model fitted for cohesiveness ofthe same tissue. It offered a high percentage of explainedvariability and may be suitable for making predictions.The similarity of the last models mentioned was to be expected since these parameters are highly correlated. Table 4 shows correlation coefficients between texturalparameters of both tissues. Hardness and force peak 2 aresignificantly and positively correlated, especially in appletissue, suggesting that there could be redundancy betweenthe two parameters. Cohesiveness shows a negative butsignificant correlation with hardness in potato tissue. Co-hesiveness, springiness and chewiness are significantlyand positively correlated in both potato and apple, thehighest correlations being found between cohesivenessand chewiness in apple tissue. These findings could bedue to the definition of the parameters, since chewiness iscalculated as hardness×cohesiveness×springiness. Thecorrelations found weaken the relevance of calculation ofall the parameters given automatically by the software.

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Fig. 5 a Three dimensional plot of cohesiveness, deformation rate (mm min–1) and degree of compression (%) in potato tissue. b Threedimensional plot of cohesiveness, deformation rate (mm min–1) and degree of compression (%) in apple tissue

Table 3 Regression coeffi-cients and analysis of varianceof the polynomials. In thesemodels X1=deformation rate,X2=degree of compression, b0 is a constant, b1 and b2 areparameter estimates for linearterms; b11 and b22 are parameterestimates for quadratic terms;and b12 is parameter estimatefor interaction terms

Coefficients Cohesiveness Chewiness

Potato Apple Potato Apple

b0 0.712** 0.765** 34.227** 12.342**b1 0.000687** 0.000628** 0.0218* 0.012**b2 –0.0212** –0.02843** –0.496** –0.473**b11 – – – –b22 0.000166** 0.000257** – 0.004272**b12 –9.133×10–6** –8.536×10–6* – 0.000166**r2 0.967 0.920 0.665 0.930F-ratio 138.675 54.437 20.832 77.781

*Significant at 5%; **significant at 1%

The results of this study show that in TPA tests on po-tato and apple tissues, the cohesiveness parameter wasmost affected by deformation rate and deformation de-gree. Significant polynomial models can be used to pre-dict cohesiveness at deformation rates ranging from 50to 500 mm min–1 and degrees of compression rangingfrom 10% to 80%. As calculated automatically from thesoftware, cohesiveness seemed to be the most suitabletextural parameter for detecting deformation rate and de-gree of compression effects in potato and apple tissues.Springiness can also offer some more relevant informa-tion, although the proposed recoverable instantaneousspringiness has a higher potential to differentiate thestructural natures of different tissues. In contrast, the cal-culation of highly correlated parameters, such as hard-ness and peak force 2 seems to be unnecessary. In addi-tion, results show that a 50% compression in potato and30% in apple are enough to fracture specimens and sig-nificantly reduce the duration of tests with respect to theapplication of higher compression percentages. This timesaving is worth considering in application to quality con-trol of these and other fruit and vegetable tissues.

Acknowledgements The authors wish to thank to the CICyT forfinancial support (ALI98–1055).

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Table 4 Correlation matrix be-tween textural parameters ofpotato and apple tissues. Valuesin first rows are for potato tissue; values in second rowsare for apple tissue

Hardness Force peak 2 Cohesiveness Springiness Chewiness

Hardness 11

Force peak 2 0.4412** 10.8433**a 1

Cohesiveness –0.7630**a –0.0843 1-0.1514 0.0911 1

Springiness –0.6096** –0.2088* 0.7994**a 1–0.2801** –0.0711 0.7476**a 1

Chewiness –0.2517** 0.4454** 0.7438**a 0.6167** 1–0.0365 0.1714 0.9510**a 0.7669**a 1

**Significant at 1%; *signifi-cant at 5%a The highest correlations