Changes in Apple Liquid Phase Concentration …ucanr.edu/datastoreFiles/608-810.pdfChanges in Apple Liquid Phase Concentration Throughout Equilibrium in Osmotic ... could be explained

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JFS E: Food Engineering and Physical Properties

Changes in Apple Liquid Phase ConcentrationThroughout Equilibrium in Osmotic DehydrationJ.M. BARAT, C. BARRERA, J.M. FRıAS, AND P. FITO

ABSTRACT: Previous results on apple tissue equilibration during osmotic dehydration showed that, at very long pro-cessing times, the solute concentration of the fruit liquid phase and the osmotic solution were the same. In the presentstudy, changes in apple liquid phase composition throughout equilibrium in osmotic dehydration were analyzed andmodeled. Results showed that, by the time osmosed samples reached the maximum weight and volume loss, soluteconcentration of the fruit liquid phase was higher than that of the osmotic solution. The reported overconcentrationcould be explained in terms of the apple structure shrinkage that occurred during the osmotic dehydration withhighly concentrated osmotic solutions due to the elastic response of the food structure to the loss of water and intakeof solutes. The fruit liquid phase overconcentration rate was observed to depend on the concentration of the osmoticsolution, the processing temperature, the sample size, and shape of the cellular tissue.

Keywords: equilibrium, liquid phase concentration, osmotic dehydration, over-concentration

Introduction

Apple tissue has been widely used as a model food for a bet-ter understanding of the osmotic dehydration process in fruits

and vegetables due to its homogeneous tissue structure and sam-ple preparation (Barat and others 1998, 1999; Fito and others 1998;Salvatori and others 1998, 1999a, 1999b). Among different aspects,osmotic dehydration research has focused on the influence of theprocess conditions on osmotic dehydration kinetics of apple tissueand its evolution to an equilibration stage (Barat and others 1998,2001a, 2001b). Previous work on apple tissue changes in weightand volume throughout its equilibration in osmotic dehydrationat different process conditions showed the existence of a pseudo-equilibrium stage when the concentration of the apple liquid phaseand the osmotic solution were very close (Barat and others 1998).At this stage, structure relaxation was reported to promote a bulkflux of osmotic solution into the fruit tissue. According to this, trueequilibrium would be achieved when no changes either in samplecomposition or weight would occur. At the equilibrium stage bothactivity and pressure gradients disappeared, and the solid cellularmatrix showed a full relaxation. After sufficiently long processingtimes, the solute concentration in the liquid phase of the osmoticallydehydrated samples and that corresponding to the surrounding os-motic solution were also observed to be the same. Nevertheless, littleinformation was reported on compositional changes in apple tissuesubjected to long-term osmotic treatments.

The aim of this work was to study and model the main changesin apple liquid phase composition throughout its evolution to anequilibrium stage in order to corroborate the important role of cellwall viscoelastic properties on cellular structure equilibration.

MS 20060491 Submitted 9/1/2006, Accepted 12/7/2006. Authors Barat,Barrera, and Fito are with Institute of Food Engineering for Development,Dept. of Food Technology, Polytechnic Univ. of Valencia, Camino de Vera, s/n46022 Valencia, Spain. Author Frıas is with Dublin Institute of Technology,School of Food Science and Environmental Health, Cathal Bruha St., Dublin1., Ireland. Direct inquiries to author Barat (E-mail: [email protected]).

Materials and Methods

Preliminary studiesA preliminary study was done to check the equilibrium point in

osmotic dehydration of apple (var. Granny smith) cuboids (30 × 16 Q1

× 3.5 mm). Apples were peeled and tissue samples were cut alongthe stem-base direction. Equilibrium studies were done at 40 and50 ◦C with sucrose osmotic solutions of 5, 15, 25, 35, 45, 55, and65 Brix. Three samples from the same fruit piece were used at eachexperimental condition. Samples were placed in a flask with a coverTwist-off containing 300 g of different nonstirred sucrose solutionsand were immersed for a maximum of 360 h (in the case of lowerconcentrated solutions). The flask was placed in a thermostated bath. Sodium azide (Sigma, U.K., 1000 ppm) was added to the osmotic Q2Q3

solution to prevent microbial growth. Water activity, moisture, andsoluble solids content were measured in triplicate for both the fruitsamples and the osmotic solution at the end of the experiment.

Kinetics of apple tissue osmoticdehydration toward equilibrium

Additional experiments were set up in order to further study thepreliminary results from the previous experiment (see Results andDiscussion).

Apples (var. Granny smith) were peeled and cut into cylindricalshape (2 cm in length × 2 cm in diameter) with the longitudinalaxes in the stem-base direction. Four samples from the same fruitpiece were placed in a flask containing nonstirred sucrose solution(1:25 w(w sample to osmotic solution ratio) (35 and 55 Brix) and sub-jected to long-term osmotic dehydration. Samples were immersedby means of a metallic grid and kept at constant temperature (30,40, and 50 ◦C) by placing the flask in an oven. Potassium sorbate(2000 ppm) was added to the osmotic solution to stabilize samplesmicrobiologically. In order to corroborate the effect of the struc-ture in sample behavior during the osmotic equilibration, not onlyfresh, but also thawed samples were subjected to the osmotic dehy-dration at 50 ◦C with a 55 Brix sucrose solution. Freezing of applecylinders was carried out by storing the enveloped samples at –18 ◦Cfor 24 h. Subsequent thawing was carried out at room temperature.

C© 2007 Institute of Food Technologists Vol. 00, Nr. 0, 2007—JOURNAL OF FOOD SCIENCE E1doi: 10.1111/j.1750-3841.2006.00266.xFurther reproduction without permission is prohibited

E:FoodEngineering&PhysicalProperties

Apple changes throughout equilibrium . . .

Changes in sample weight, volume, moisture, and soluble solidscontent throughout the process were analyzed in triplicate, as wellas changes in the osmotic solution composition.

Analytical determinationsVolume was determined with a pycnometer for liquids using the

osmotic solution as reference liquid. Moisture content of sampleswas determined by holding them in a vacuum oven until constantweight was reached (AOAC 1980). Soluble solids were analyzed bymeasuring the refractive index with a thermostated refractometer(Atago, NAR T3, Japan) at 20 ◦C. Water activity was measured withQ4

a 3-cell Novasina (Novasina AG, Zurich, Switzerland) water activitymeter at 25 ◦C.

Mathematical modelingIn order to study in detail the osmotic dehydration operation and

to be able to describe the different processes and flux kinetics in-volved in the process, a mathematical model describing the transferof solutes and water through the tissue together with an elastic re-sponse of the cellular material against the solute and water transferwas proposed. This model was fitted to the experimental resultsobtained in the kinetic studies toward the equilibrium.

Hypothesis. The hypotheses of the model applied to our studywere:

1. The osmotic dehydration can be characterized by the transferof water and solutes between 3 compartments: (a) the osmotic so-lution, (b) the extracellular space of the apple sample, and (c) theintracellular space of the apple tissue. As a result of the mass transfer,changes in volume occur.

2. The main fluxes involved in the osmotic dehydration processcorrespond to water, sucrose added to the osmotic solution, andapple-native-soluble solids transfer.

3. Gradients inside the compartments lump in the transfer co-efficients, and the driving forces are measured as the differences ofaverage properties between compartments.

4. The physical properties of the tissue remain constant duringthe experiment.

5. The osmotic pressure (π) across a semipermeable membraneas a function of the temperature was approximated using Van’t Hofflaw (Eq. 1):

π = σ ∗C RT (1)

where σ ∗ accumulates the activity coefficient, the reflection coeffi-cient, and the proportionality coefficient between the molar con-centration and Brix degrees for each solute.

6. The net volumetric flux of water across a non-ideal membrane(Jv(t)) can be defined as (Eq. 2):

Jv(t) = AmdVdt

= kf (�p(t) − �π(t)) (2)

where kf is the volumetric rate change constant, �p is the pressuregradient, and �π is the osmotic pressure gradient, considering apurely elastic response from a compartment in the tissue. The hy-draulic permeability Lp is defined as the ratio between kf and Am.

7. For each compartment the pressure change (p(t)) depends onthe volume change (V (t)) (Eq. 3):

p(t) = p0 + Elast(V (t) − V0) (3)

where p0 is the initial pressure of the system (1 atm), (V (t) – V 0) isthe decrease in volume and Elast stands for the elastic response ofthe compartment for a change in volume.

8. The flux of a given solute S between 2 compartments, neglect-ing coupling of transport is (Eq. 4)

dSdt

= −k∗p�S (4)

where k ∗p is the effective permeability of the membrane and S is

the concentration of the solute. Two main groups of solutes wereconsidered (i) the osmotic solution solids (A, mainly sucrose) and(ii) native apple solutes (B, mainly glucose and fructose).

System of ordinary differential equations (ODE). From thesehypothesis the following system of ODEs was built (Eqs. 5 to 13):

dV1

dt= −L∗

p1( p1 − p2 − (πA1 − πA2 + πB1 − πB2 )) (5)

dV2

dt= L∗

p1( p1 − p2 − (πA1 − πA2 + πB1 − πB2 ))

−L∗p2

( p2 − p3 − (πA21 − πA3 + πB2 − πB3 )) (6)

dV3

dt= L∗

p2( p2 − p3 − (πA21 − πA3 + πB2 − πB3 )) (7)

V1dA1

dt= −k∗

A1(A1 − A2) (8)

V2dA2

dt= k∗

A1(A1 − A2) − k∗

A2(A2 − A3) (9)

V3dA3

dt= k∗

A2(A2 − A3) (10)

V1dB1

dt= −k∗

B1(B1 − B2) (11)

V2dB2

dt= k∗

B1(B1 − B2) − k∗

B2(B2 − B3) (12)

V3dB3

dt= k∗

B2(B2 − B3) (13)

The subscripts 1, 2, and 3 denote the osmotic solution, extracellularspace, and intracellular space compartments, respectively, and Aand B species stand for osmotic solution solutes and native apple-soluble solids, respectively.

Auxiliary equations. To calculate osmotic pressure and pres-sure at each compartment Eq. 14 was used:

∀i = 1, 2, 3 πAi = σ ∗ Ai (t)RT ; πBi = σ ∗ Bi (t)RT

pi (t) = p0 + Elast · (Vi (t) − V0i ) (14)

Initial conditions. The initial volume of the osmotic solutionwas 100 mL, which was employed as initial condition for Eq. 5, andthe volume of each cylinder (6.28 cm3) was divided between extra-cellular space and intracellular space considering the porosity of theapple tissue (0.21), so as to provide initial conditions for Eqs. 6 and7. The initial weight of the apple samples in the model was set to5 g.

The Brix degree of the osmotic solution provided the initial con-dition for Eq. 8.

A significant amount of sucrose was present in the extracellularand the intracellular space of the apple (0.82 Brix), which was usedas initial conditions for Eqs. 9 and 10.

The extracellular space and the osmotic solution were consideredto have a negligible content of apple-soluble solids and a zero initialcondition was used for Eqs. 11 and 12.

E2 JOURNAL OF FOOD SCIENCE—Vol. 00, Nr. 0, 2007

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The soluble solids Brix content of the sample was measured toan average of 13.66 and was considered as the initial point for theintracellular space (Eq. 13).

Observable quantities. The predicted values obtained bymeans of the proposed equations were (Eqs. 15 to 19)

Brixsol = A1 + B1 (15)

Brixapple = ((A2 + B2) · V2 + (A3 + B3) · V3)/(V2 + V3) (16)

�V 0t = (V2 + V3 − (V2,0 + V3,0))/(V2,0 + V3,0) (17)

�Mst = ((A2 + B2)/100 · ρ2V2 + (A3 + B3)/100 · ρ3V3.

((A2,0 + B2,0)/100 · ρ2,0 · V2,0 + (A3,0 + B3,0)/

100 · ρ3,0 · V3,0))/M0

(18)

�Mwt = ((A2 + B2)/100 · ρ2 · V2 + (A3 + B3)/100 · ρ3 · V3− · · ·

((A2,0 + B2,0)/100 · ρ2,0 · V2,0 + (A3,0 + B3,0)/

100 · ρ3,0 · V3,0))/M0

(19)

The subscripts 1, 2, and 3 denote the osmotic solution, extracellularspace, and intracellular space, respectively, and ρ is the density ofthe osmotic solution, estimated as (Barat, J, private communication)

ρ = 2 × 10−5 × Brix2 + 0.0038 × Brix + 0.9982 (20)

where ρ is the density of the osmotic solution, extracellular space,or intracellular space and Brix is the accumulated Brix degree of thecompartment, including sucrose and apple-native-soluble solids.

Numerical methods. Model building and individual fitting ofeach of the experiments were performed using JSim v1.602 (Bass-ingthwaighte 2005). Sensitivity analysis was performed by forwardapproximation with a � of 0.01 in each parameter). The fitting of themodel to the whole experimental data was performed using simula-tions employing the subroutine DLSODA from the May 2005 versionof the ODEPACK library (ODEPACK 2001) and the multiresponse

Figure 1 --- Comparison betweentheoretical and real Brix reached byapple parallelepipeds (filledsymbols) and the osmotic solution incontact with them (open symbols) atthe end of the experiment.

Figure 2 --- Differences in aw valuesreached by apple parallelepipeds(filled symbols) and the osmoticsolution in contact with them (opensymbols) at the end of theexperiment.

nonlinear regression subroutine DODRC from the ODRPACK library(ODRPACK 1992; Boggs and others 1992). In order to simplify the re- Q5

gression of the whole experimental data set and given the complexityof the model, the following simplifications were assumed:

9. The extracellular space of the cell was assumed to behave asa plastic body, therefore assuming an elasticity coefficient of 0 forcompartment 2.

10. To avoid the high collinearity between the activity coeffi-cients, the σ ∗

B coefficient was fixed to 1 and σ ∗A was estimated

and forced to be bigger than 1.

Results and Discussion

Preliminary studiesSolutes concentration (Brix) of the osmosed apples and the os-

motic solutions at each sampling time are shown in Figure 1. Inall experiments, the soluble solids content of the liquid phase ofthe apple tissue was significantly higher (P ( 0.05) than that of thecorresponding osmotic solution for all the osmotic solutions em-ployed. The above mentioned differences were found to be biggeras the processing temperature increased. In addition, water activityvalues of the osmotic solutions employed were found to be higherthan those reached by fruit samples that were in contact with them(Figure 2). These differences in water activity values were only sta-tistically significant for the most concentrated solutions (55 and65 Brix) and decreased as the osmotic solution became more di-luted. In previous studies on long-term osmotic dehydration of ap-ple cylinders (Barat and others 1998), the concentration of the fruitliquid phase and the osmotic solution at equilibrium were found tobe same, thus suggesting that contact time between apple samplesand each osmotic solution in the present study (up to 15 d for thelower Brix solutions) was not long enough to reach the equilibriumstage. According to these results, the fruit liquid phase might experi-ence certain overconcentration on its way to the equilibrium. There-fore, studying changes in weight, volume, and composition through-out long-term osmotic treatments were considered of special

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interest in following experiments carried out at 30, 40, and 50 ◦C,when differences in concentration between the fruit liquid phaseand the correspondent osmotic solution were found to be greater.In such experiments, the influence of sample size and shape on itsevolution to the equilibrium stage was evaluated by processing ap-ple cylinders instead of cuboids. As it was reported that the fruitliquid phase overconcentration rate increased with the concentra-tion of the osmotic solution, 35 and 55 Brix sucrose solutions wereemployed as osmotic agents.

Study of samples evolution to the equilibrium stageChanges in weight, volume, and composition throughout long-

term osmotic treatments of apple cylinders in different sucrose so-

Figure 3 --- Changes throughout osmotictreatment in 35 and 55 Brix sucrosesolutions at 50 ◦C.

lutions (35 and 55 Brix) at 50 ◦C, calculated according to Eqs. 1 to 3(Fito and Chiralt 1996), are shown in Figure 3.

�M0t = M0

t − M00

M00

(21)

�Mit = M0

t × xit − M0

0 × xi0

M00

(22)

�V 0t = V 0

t − V 00

V 00

(23)

In the above equations M t0 ( mass of sample at time 0 or t in kg; xi

t

( mass fraction of water (i ( w) or soluble solids (i ( ss) at time 0 or t;and V 0

t ( volume of sample at time 0 or t.


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Figure 4 --- Normalized modelparameters (estimated parameterdivided by the average of all theexperiments) estimated fromindividually fitted experiment (a: k∗

A1,b: k∗

B1, c: k∗A2, d: k∗

B2, e: L∗p1; f: L∗

p2; g:Elast2, h: Elast3, i: σ∗

A, j: σ∗B)

Results corroborated the existence of 2 periods in porous foodequilibration (Barat and others 1998; Figure 3). During the 1st period(<24 h), water loss and soluble solids uptake would be mainly pro-moted by activity gradients resulting in a moisture content decreaseand a soluble solids content increase. As expected, mass fluxes inthe system during the 1st period involved considerable weight andvolume losses, which noticeably increased with the concentrationof the osmotic solution. During the 2nd period, both water and sol-uble solids gain were observed to promote an important recovery ofweight and volume with small changes in samples composition, thussuggesting that mass fluxes in the system were mainly promoted bypressure gradients. As reported by Barat and others (1998), initialcell wall shrinkage and deformation caused by water loss might beassociated with stress accumulation in the solid matrix. Subsequentrelaxation of the structure might result in an uptake of the externalsolution in which the product remained immersed. This could ex-plain the mass and volume gain observed during the 2nd period. Forboth osmotic solution concentrations tested, weight recovery wasshown to be greater than volume recovery and mass values becamehigher than the initial ones. Weight and volume recovery were fasteras the concentration of the osmotic solution decreased.

In terms of water and soluble solids content, equality betweenthe samples liquid phase composition and that of the osmotic solu-tion would be achieved during the 1st period. By the time samplesreached maximum weight and volume losses, the concentration ofthe fruit liquid phase was observed to be higher than that of the su-crose solution in contact with it. Compositional differences between

Table 1 --- Estimated parameters from the regression of theosmotic dehydration data

Parameter Units Estimate SE

k∗A1 h−1 0.32 0.04

k∗B1 h−1 0.19 0.08

k∗A2 h−1 0.023 0.01

k∗B2 h−1 0.016 0.009

L∗p1 Pa−1 cm3 s−1 0.0050 0.0007

L∗p2 Pa−1 cm3 s−1 0.020 0.002

Elast3 Pa cm−3 0.092 0.02σ ∗

A Mol l−1 Brix−1 1.19 0.15Deviance 575.38σ Residual 2.86

the fruit liquid phase and the osmotic solution were observed to bemore noticeable when working with highly concentrated osmoticsolution (55 Brix). Changes occurring during the 2nd period (>24 h)slowly reduced differences in concentration between the fruit liquidphase and the osmotic solution in contact with it. When comparingthe liquid phase composition of apple samples of different shapeon its way to the equilibrium with a 55 Brix sucrose solution at 50◦C, significantly higher soluble solids content (P < 0.05) was ob-served in the case of working with apple cuboids, thus suggestingthe important role of sample size and shape on their evolution to anequilibrium stage.

Overconcentration observed in the fruit liquid phase on its wayto an equilibrium stage could be related to shrinkage observed inapple samples at the end of the 1st period. The pressure gradientsbetween the samples and the external solution and(or the higherdensity of cell membranes (which represents a barrier for the nativesoluble solids outflow) could be the reason for the overconcentrationobserved in the liquid phase.

At the beginning of the osmotic treatment, both pressure and ac-tivity gradients between the samples and the osmotic solution incontact with them would promote water to flow toward the exter-nal solution. Even when compositional equality between the fruitliquid phase and the osmotic solution was reached, weight and vol-ume were still reported to decrease for a short period of time. At thisstage, a gradient of osmotic pressures should appear to balance thestress accumulated in the solid matrix during fruit contraction, thusjustifying the observed overconcentration phenomena. Mass trans-port at this period might be proportional to pressure fall inside theproduct, which was expected to be higher when working at highertemperatures or with higher concentrated solutions. That wouldexplain higher overconcentration rates observed in apple cuboidsprocessed at 50 ◦C or in apple cylinders processed with a 55 Brixsucrose solution. Although neither weight loss nor volume reduc-tion at the 1st step of apple cuboids equilibration with a 55 Brixsucrose solution at 50 ◦C was evaluated, greater overconcentrationrate reported when working with apple cuboids suggested that thesewould be higher than those achieved by apple cylinders.

Once samples reached their maximum weight loss and volumereduction, the structure might relax and lead inner pressure to equi-librium with the external one by means of a bulk flux of osmoticsolution into the fruit tissue (Figure 3). At this step, concentration




gradients might promote water to flow toward the fruit liquid phasetill the equilibrium between the osmotic and volumetric pressuresis reached. As reported by Barat and others (1998), true equilibriumwould be achieved when no changes either in sample compositionor weight would occur. In such a state, differences in both activityand pressure would disappear, and the solid cellular matrix wouldbecome fully relaxed (Figure 3).

Model fitting and sensitivity analysisThe coefficients estimated by individual fitting of each of the per-

formed experiments are shown in Figure 4. Although the standarderrors of the coefficients were high, the fact that estimated coeffi-cients did not differ greatly between experiments lead us to assumethat a single group of parameters could be used to explain all theexperiments together.

The estimated parameters, together with their associated stan-dard errors are presented in Table 1. It can be seen that in general thetransfer coefficients through the cell membrane (k∗

A 2, k∗B 2, L∗

p 2)

Figure 5 --- Experimental data andglobal model prediction of anosmotic drying experiment in 35Brix sucrose solution at 50 ◦C.

are generally smaller than the transfer coefficients through the veg-etable cell wall (k∗

A 1, k∗B1, L∗

p1), except for the hydraulic transportcoefficient L∗

p. It also can be seen that sucrose molecules seem tohave a slightly higher activity coefficient σ ∗

A (1.19 ± 0.15) than fruc-tose (1.0).

Examples of typical fits of the model to the different responses canbe seen in Figure 5 and 6. In general, the model systematically over-predicted the soluble solids gain of the experiment, but predictedreasonably well the patterns of the evolution of Brix degrees of boththe solution and the apple-soluble solids, the volume change of thesample, and the water losses. The model, in general, was able topredict the overconcentration phenomena in the sample, showinghow the shrinkage of the sample and the elastic stress allowed for atemporary overconcentration of the solutes inside the sample. Aftersufficient time to relax the structure of the sample was achieved,this overconcentration phenomenon disappeared and the solutesfinal equilibrium was reached. It is important to note that this phe-nomenon can only be explained by taking into consideration the


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existence of the 3 compartments mentioned before: the extracellu-lar space acts as a buffer so that elastic tensions can be developedand volume changes can be delayed with concentration fluxes andoverconcentration can occur. Further studies considering concen-tration gradients and effective diffusivity would be needed to assessthe effect of dimensions and volume of the sample into this phe-nomenon.

A sensitivity analysis of the model and the estimated parame-ters were performed by approximating the derivatives of the modelprediction over time for an osmotic dehydration with a 35 Brix su-crose at 40 ◦C. The parameters contributing most significantly tothe responses of the model were the hydraulic permeabilities (Lp1

and Lp2), which are shown in Figure 7. It can be seen how the over-concentration phenomena that occurs early in the osmotic dryingis associated with a change in the derivatives associated with thehydraulic transport coefficient in the extracellular space (Lp1). Inthis way any phenomenon that increases the water permeabilitythrough the cell wall (for example, pulse vacuum treatments) or the

Figure 6 --- Experimental data andglobal model prediction of anosmotic drying experiment in 35Brix sucrose solution at 40 ◦C.

vegetable cell membrane (for example, freeze thawing) is foreseento affect most the kinetics of the osmotic dehydration.

The present results confirmed the important role of tissue elas-tic properties on sample behavior during the osmotic dehydration.Therefore, different behavior would be expected in osmotic equili-bration of samples submitted to different structural changes. Masschanges throughout osmotic treatment of frozen-thawed samplesin 55 Brix sucrose solutions at 50 ◦C (Figure 8) corroborated this as-sumption. Results showed that cell membrane differential perme-ability, which was reported to limit solutes transfer and to promotelarge-scale transfer of water during osmotic dehydration (Mauroand others 2002), might be lost when the cellular structure was de-stroyed by prior freezing and thawing. As a result, soluble solidscould penetrate more easily. On the other hand, no significant dif-ferences in composition between sample liquid phase and the ex-ternal solution at the equilibrium stage were found when workingwith frozen-thawed samples. According to what was previously re-ported, structural damage taking part during the freezing-thawing




Figure 7 --- Sensitivity of applesample Brix degree and samplevolume kinetics to hydraulicpermeability coefficients (Lp1 andLp2).

Figure 8 --- Changes throughoutosmotic treatment of frozen-thawedapple cylinders in 55 Brix sucrosesolutions at 50 ◦C.

process might lead to a lower volume contraction and therefore, toa lower overconcentration rate.

Conclusions

An overconcentration of the apple liquid phase was observedwhen compared to the osmotic solution close to the point of

maximum weight and volume during sample equilibration. The ob-served overconcentration seems to be closely related with tissueshrinkage, since this phenomena was higher for the samples pro-cessed with the higher osmotic solution concentration. The pro-posed model fitted to the experimental data reproduces the men-tioned overconcentration related to the accumulated stress in ap-

ple tissue. When apple samples were frozen and thawed before os-motic dehydration, neither shrinkage nor overconcentration wasobserved, reinforcing the above mentioned hypothesis.

ReferencesAOAC. 1980. Assn. of Official Analytical Chemist Official Methods of Analysis. Wash-

ington, D.C.Barat JM, Chiralt A, Fito P. 1998. Equilibrium in cellular food osmotic solution systems

as related to structure. J Food Sci 63(4):836–40.Barat JM, Albors A, Chiralt A, Fito P. 1999. Equilibration of apple tissue in osmotic

dehydration: microstructural changes. Drying Technol 17(7(8):1375–86.Barat JM, Chiralt A, Fito P. 2001a. Effect of osmotic solution concentration temperature

and vacuum impregnation pretreatment on osmotic dehydration kinetics of appleslices. Food Sci Technol Intl 7(5):451–6.


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Barat JM, Chiralt A, Fito P. 2001b. Modelling of simultaneous mass transfer and struc-tural changes in fruit tissue. J Food Eng 49:77–85.

Bassingthwaighte JB. 2005. JSIM 1.6.42 (Java Simulator). The Natl. Simulation Resourcefor Transport, Metabolism and Reaction. Washington, D.C.: Univ. of Washington.Available from: http://www.nsr.bioeng.washington.edu/PLN. Accessed Dec, 2005.

Boggs PT, Richard BH, Rogers JE, Schnabel RB. 1992. User’s reference guide for ODR-PACk version 2.01 software for weighted orthogonal distance regression. NISTIR92-4834. Gaithersburg, MD: Natl. Inst. of Standards and Technology.

Fito P, Chiralt A. 1996. Osmotic dehydration. An approach to the modelling of solidfood-liquid operations. In: Fito P, Ortega-Rodrıguez E, Barbosa-Canovas GV, editors.Food engineering 2000. New York: Chapman and Hall. p 231–52.

Fito P, Chiralt A, Barat J, Salvatori D, Andres A. 1998. Some advances in osmotic dehy-dration of fruits. Food Sci Technol Intl 4(5):329–38.

Hindmarsh AC. 1983. ODEPACK, a systematized collection of ODE solvers. In: Steple-man RS, editor. Scientific computing. Amsterdam: North-Holland. p 55–64. Q6

Mauro MA, Tavares D, Menegalli FC. 2002. Behaviour of plant tissue in osmotic solu-tions. J Food Eng 56:1–15.

Salvatori D, Andres A, Albors A, Chiralt A, Fito P. 1998. Structural and compositionalprofiles in osmotically dehydrated apple. J Food Sci 63(4):606–10.

Salvatori D, Andres A, Chiralt A, Fito P. 1999a. Osmotic dehydration progression inapple tissue I: spatial distribution of solutes and moisture content. J Food Eng42(3):125–32.

Salvatori D, Andres A, Chiralt A, Fito P. 1999b. Osmotic dehydration progression inapple tissue II: generalized equations for concentration prediction. J Food Eng42(3):133–8.



Queries

Q1 Author: Please provide year and origin of ‘var. Granny smith’.

Q2 Author: Please provide manufacturer’s details of ‘thermostated bath’.

Q3 Author: Please provide city where ‘Sigma’ is located.

Q4 Author: Please provide city where ‘Atago’ is located.

Q5 Author: Please check the suggested citing of reference ‘Boggs and others 1992’.

Q6 Author: Reference ‘Hindmarsh 1983’ is not cited. Please check.

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Changes in Apple Liquid Phase Concentration …ucanr.edu/datastoreFiles/608-810.pdfChanges in Apple Liquid Phase Concentration Throughout Equilibrium in Osmotic ... could be explained