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Journal of Food Engineering 78 (2007) 1439–1445

Deacidification of clarified tropical fruit juices by electrodialysis.Part II. Characteristics of the deacidified juices

Edwin Vera a, Jacqueline Sandeaux b,*, Francoise Persin c, Gerald Pourcelly b,Manuel Dornier d, Georges Piombo d, Jenny Ruales a

a Department of Food Science and Biotechnology, Escuela Politecnica Nacional, P.O. Box 17012759, Quito, Ecuadorb Institut Europeen des Membranes, Universite de Montpellier II, UMR 5635-CC047, Place Eugene Bataillon 34095, Montpellier Cedex 5, France

c UMR 016, Universite de Montpellier II, CC 005, Place Eugene Bataillon 34095, Montpellier Cedex 5, Franced CIRAD/ENSIA-SIARC, UR24 Tropiqual, Avenue Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France

Received 22 August 2005; accepted 7 January 2006Available online 9 March 2006

Abstract

The electrodialysis (ED) process was investigated to reduce the acidity of four tropical fruit juices, passion fruit, castilla mulberry,najanrilla and araza. In this part of the study, the results of physico-chemical and sensory analyses of juices treated were collectedand compared to fresh juices. Low differences (<10%) were observed whatever the ED configurations (conventional or bipolar ED)and operating conditions used. At a final pH of 4, the titrable acidity and organic anion concentration decreased of about 70% and50–60%, respectively, for all the juices. Inorganic anions were almost eliminated, between 70% and 95%, while the sugar and cation con-centration remained unchanged, except for the sodium concentration in conventional ED. Slight changes of colour were observed, exceptfor the mulberry juice, because of the presence of anthocyanidins which varied in colour vs. pH. The sensory characteristics of juices werepreserved, but a decrease in the intensity of odour was detected. Different nectars with the same sugar–acid ratio were prepared by mixingfresh and deacidified juices. Except for passion fruit, the increase in the juice content of the nectars did not improve significantly theiraromatic quality.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Tropical fruit juices; Deacidification; Electrodialysis; Sensorial quality; Composition

1. Introduction

Tropical fruit juices are appraised for their intensearoma and flavour, but the high acidity of some of themlimits their use as an ingredient in the formulation of var-ious preparations such as beverages, ice creams, marma-lades, cocktails or pies.

Since years ago, membrane technology is successfullyused in the food industry. Electrodialysis (ED), based on

0260-8774/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jfoodeng.2006.01.015

* Corresponding author. Tel.: +33 04 67 14 91 17; fax: +33 04 67 14 9119.

E-mail address: jacqueline.sandeaux@iemm.univ-montp2.fr (J. San-deaux).

the electromigration of ionic species through ion-exchangemembranes is nowadays well-known for its applicationsin food processings such as demineralization of wheyand sugar-juices and tartaric stabilization of wine (Scott,1995).

In a previous study, it has been demonstrated that EDwas an interesting alternative method for deacidificationof passion fruit juice compared to calcium salt precipitationwhich implies addition of chemical reagents and ion-exchange resins which strongly modify the aroma profileof the product and provide effluents during the regenera-tion step (Vera et al., 2003a, 2003b).

The results of the part I of this study have shown the EDefficiency for deacidification of tropical fruit juices such aspassion fruit, castilla mulberry, naranjilla and araza. Two

1440 E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445

ED configurations, using homopolar or bipolar mem-branes, were investigated for raising pH from 3 until 7.9with satisfactory performances. As described in part I, theeffect of the deacidification process is the extraction of cit-rate and malate anions from the juice and their replacementby hydroxyl ions provided either by a soda solution circu-lating in an adjacent compartment of juice (ED3C configu-ration), or by a bipolar membrane in contact with the juice(EDBM2C configuration). The membrane fouling was themain limit of the process; nevertheless it could be reducedunder some operating conditions of current density andflow rate, specific for each juice.

It is important, now, to better evaluate the impact of theED process on the chemical composition and sensorialquality of the treated juices. This is the aim of this partII of the study where the results of physico-chemical andsensory analyses were collected.

2. Materials and methods

2.1. Fruit juices

The juices were obtained from fresh fruits gathered inEcuador and treated as follows: washing, elimination ofshell, pulp extraction, centrifugation, pasteurization andfreezing. After an enzymatic treatment (Pomaliq, Gist-Brocades, Seclin, France), they were clarified by usingcrossflow micro-filtration with a ceramic membrane of0.2 lm average pore diameter. A special treatment of wash-ing with boiling water during 10 min. was carried out forthe naranjilla fruits to inhibit the enzymatic browning ofthe juice.

Table 1Main characteristics of the clarified fruit juices

Passion fruit Cast

pH 2.95 ± 0.05 2.96Density (kgm�3) 1050 ± 1 1042Viscosity (mPas) 1.36 ± 0.13 1.07Conductivity (25 �C, mScm�1) 8.05 4.85Total soluble solids (gkg�1) 135 ± 3 80 ±Total sugars (gkg�1) 71.7 ± 1.8 48.0

Fructose (gkg�1) 26.0 ± 1.8 29.6Glucose (gkg�1) 28.4 ± 1.2 18.3Sucrose (gkg�1) 17.3 ± 1.0 0.0

Titrable acidity (meqdm�3) 700 ± 13 334Citric acid (gkg�1) 40.9 ± 1.6 28.6Malic acid (gkg�1) 1.6 ± 0.2 7.5 ±Tartaric acid (gkg�1) 0.13 ± 0.08 0.10Ascorbic acid (gkg�1) 0.15 ± 0.06 0.05

Total minerals (gkg�1) 6.7 4.5 ±Phosphate (mgkg�1) 306 ± 24 183Sulphate (mgkg�1) 118 ± 21 135Chloride (mgkg�1) 52 ± 15 100Potassium (mgkg�1) 3030 ± 144 1350Magnesium (mgkg�1) 142.6 ± 11 154.Calcium (mgkg�1) 42.4 ± 16 86.3Sodium (mgkg�1) 87.6 ± 5 46.7

The characteristics of the clarified juices are given inTable 1. The araza juice showed a marked difference incomparison with the other juices studied: lower pH, con-ductivity, total soluble solids, total sugars, total mineralsand malic acid as major organic anion.

For passion fruit, mulberry and naranjilla, the juices hadlow viscosity.The initial pH was close to three. These pHvalues were not correlated to the titrable acidity. Indeed,for the passion fruit juice, the organic acid content was twicehigher than those of the other juices. That can be due to dif-ferent buffer effects in the juices. The solute contents weregenerally higher for the passion fruit juice except for thetotal minerals which were higher in the naranjilla juice.

As shown in Table 2, the acidity was mainly due to citricand malic acids and the total amount of inorganic anionswas only 62%. Potassium was the most abundant cation(65–82%), but its amount was low compared to all protonsable to be neutralized (6–20%).

2.2. Electrodialysis equipment

Electrodialysis experiments were performed at labora-tory and pre-industrial scale with two stack designs asdepicted in the part I. The main differences between thepilots used were in the membrane area, ten times greaterand compartment spacing, thirteen times lower, with thepre-industrial pilot.

The principle of deacidification consisted in a partialtransfer of organic anions through an anion exchange mem-brane and partial neutralization of protons by hydroxylions provided either by a NaOH solution (ED3C configura-tion) or by a bipolar membrane (EDBM2C configuration).

illa mulberry Naranjilla Araza

± 0.05 3.13 ± 0.05 2.62 ± 0.05± 1 1032 ± 2 –± 0.10 1.04 ± 0.10

6.06 3.002 70 ± 2 40 ± 2± 1.5 32.8 ± 1.7 18.9 ± 3.2± 1.5 9.0 ± 1.0 5.1 ± 1.6± 1.4 16.2 ± 1.7 3.8 ± 1.4

7.6 ± 1.7 9.9 ± 3.2± 78 320 ± 11 321 ± 14± 3.0 35.8 ± 2.1 1.6 ± 0.7

0.8 2.6 ± 0.5 29.9 ± 2.80.03 0.050.20 0.16

0.7 9.0 1.0219 12998 87107 91950 560

5 104.8 4054.4 4610.9 6

Table 2Proportion of main ions in the clarified fruit juicesa

Fruit juice Citrate/total anions (%) Malate/total anions (%) Inorganic anions/total anions (%) Potassium/cations (%) Cations/protonsb (%)

Passion fruit 94.1 3.5 2.0 81.4 13.6Mulberry 78.1 19.6 2.0 64.4 16.0Naranjilla 91.4 6.3 2.0 80.9 19.3Araza 5.2 93.2 1.3 70.8 6.3

a Calculated in equivalents.b Total amount of protons able to be neutralized.

Table 3Composition of nectars

Juice Passion fruit Mulberry Naranjilla

Sample E1 E2 E3 E4 E1 E2 E3 E4 E1 E2 E3 E4Total amount of juice (%) 15.1 30.0 50.0 89.4 32.7 45.0 60.0 98.1 34.0 45.0 70.0 96.6Initial juice (%) 15.1 13.1 10.5 5.4 32.7 31.4 29.2 25.7 34.0 31.9 27.0 21.2Deacidified juice (%) 0.0 16.9 39.5 84.0 0.0 13.6 30.1 72.3 0.0 13.1 43.0 75.4Sucrose (%) 7.8 6.2 4.1 0.0 6.2 5.4 4.4 1.9 6.7 6.1 4.9 3.4Water (%) 77.1 63.8 45.9 10.6 61.2 49.6 35.6 0.0 59.3 48.9 25.1 0.0Titrable acidity (gkg�1) 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.8 6.8 6.8 6.8Total soluble solid (gkg�1) 102 102 102 102 92 92 92 90 94 94 95 95pH 3.15 3.49 3.85 4.29 3.13 3.28 3.42 3.76 3.31 3.45 3.78 3.96

E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445 1441

2.3. Analytical procedures

Acidity was assayed by titration with 0.1 mol dm�3

NaOH and expressed as g of the main organic acid (citricor malic) per 1 kg of juice (AOAC, 2000, chap. 7). Totalsoluble solids were determined by refractometry with anAtago hand refractometer. Colour was measured with aMinolta CR-A70 colorimeter in the Lab space. Colour var-iation was calculated according to Eq. (1) using theuntreated sample as reference solution.

DE ¼ ðDL2 þ Da2 þ Db2Þ1=2 ð1ÞThe cation concentrations were measured by ICP.

Anions and sugars were determined by HPLC, with a Dio-nex AS11 column and a conductivity detector and an AstecNH2 Purospher column and a RI detector, respectively.

Sensorial analyses were done by 13–18 semi-trained pan-ellists in a cabin under white or red light. Difference testswere carried out to compare the odour of the fresh juiceswith the deacidified juices (triangular tests). Ranking testswere performed with various nectars in order to class thesamples by aroma, sweetness and bitterness/astringency.The nectars were prepared by blending untreated juice,deacidified juice at pH 4.5, water and sucrose, in order toobtain constant titrable acidity and total soluble solids,but an increase in the total amount of juice (Table 3).

3. Results

After each ED treatment, physico-chemical analysessuch as titrable acidity, total soluble solids, colour, organicand inorganic anions, cations and sugars were achieved.Various kinds of sensorial tests were also performed.Low differences (<10%) occurred for all the parameters

measured between the two ED processes involving homo-polar or bipolar membranes and the two pilots used.Low differences were also observed whatever the operatingconditions of current density, flow rate and temperature.The only parameter, which has influence on the character-istics of juices, was the final pH of deacidification. There-fore, the results given in the following tables and figuresare average values of several experiments.

3.1. Physico-chemical analysis

3.1.1. Titrable acidity and total soluble solidsTable 4 shows the decline in the titrable acidity and total

soluble solids as a function of the final pH of deacidifica-tion. At pH 4, the titrable acidity decreased of about 70%for all the juices. Fig. 1(a) exhibits the linear relationbetween the total soluble solids and titrable acidity varia-tion. This means that the amount of total soluble solidswas not only depending on the sugar concentration, butalso organic acid concentration. Experiments performedwith synthetic solutions of citric acid showed a similar var-iation (Fig. 1(b)). The identical value of the slope of thecurves, 0.78 and 0.75 for Fig. 1(a) and (b), respectively, cor-roborates the relation between these two parameters.

3.1.2. Colour

The colour variation was depicted by Fig. 2. It increasedwhen the pH increases, nevertheless at pH 4, it was verylow. Colour variations can be visually detected only atpH 7.9 for the passion fruit and naranjilla juices. The majorcoloured compounds of these two fruits are carotenoids,whose absorption spectra is not depending on pH. Forthe mulberry juice that contains anthocyanidins, changesin colour were perceptible from pH 4. This result is

Table 4Titrable acidity and total soluble solids of the deacidified juices at variouspH

Fruit pH Titrableacidity (gkg�1)

Total solublesolids (g kg�1)

Passion fruit 2.96 42.6 ± 1.6 131 ± 24.00 12.4 ± 1.3 111 ± 34.50 6.7 ± 1.0 108 ± 27.90 0 105 ± 2

Mulberry 2.99 20.0 ± 1.1 78 ± 24.00 5.6 ± 1.0 68 ± 24.50 2.1 ± 0.3 65 ± 2

Naranjilla 3.17 19.1 ± 1.4 66 ± 34.00 6.6 ± 0.8 57 ± 34.50 3.3 ± 0.3 56 ± 27.90 0 51 ± 3

Araza 2.62 21.5 ± 1.0 40 ± 23.30 4.6 ± 0.6 27 ± 2

0.0

0.2

0.4

4.0 4.5 7.9

pH

Col

our

varia

tion

(ΔE

)

Passion Mulberry Naranjilla

Fig. 2. Colour variation for various final pH of deacidification.

1442 E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445

correlated to the variation of the chemical structure ofanthocyanidins with the pH, leading to a decrease ofextinction coefficients in the visible spectra when the pHincreases (Belitz & Grosch, 1987; Mayer, 1973). Therefore,the Lab method used, which did not detect significant mod-ifications, seems to be not adequate to measure the colourin the mulberry juice.

3.1.3. Ion concentration

The ion analysis was performed in the deacidified juicesuntil pH 4. Fig. 3 shows the concentration of the majororganic anion (citrate for the passion fruit, mulberry andnaranjilla juices; malate for the araza) before and afterED treatment. A similar decrease between 50–60% wasobtained whatever the juice treated. The other mainorganic anion (malate for the passion fruit, mulberry andnaranjilla juices; citrate for the araza) was also removedwith similar ratios. The inorganic anions which had a lowconcentration were almost eliminated, by 70–95%.

Fruit juice

10

14

18

22

26

10 15 20 25 30 35

ΔTitrable acidity (g.kg-¹)

Passion Mulberry Naranjilla Araza

(a)

ΔSol

uble

sol

ids

(g.k

g-¹)

Fig. 1. Variation of the total soluble solid

The analyses of cations showed that there was no changein the concentration of potassium, magnesium and calciumions. This result was expected because the juice circulatedbetween two anion exchange membranes in the ED3C con-figuration and between an anion exchange membrane and abipolar membrane in the EDBM2C. Consequently, in thetwo ED configurations used, cations cannot enter or leavethe juice compartment.

However, an increase in the sodium concentrationoccurred in the juices treated with ED3C (Fig. 4). Thisincrement was probably due to NaOH (0.2 moldm�3 inthe C2 compartment) and NaCl (0.1 mol dm�3 in the C1compartment) dialysis arising from the adjacent compart-ments to that of juice. Indeed, it is well known that a con-centration gradient between ion-exchange membranesinduces a dialysis phenomenon. Nevertheless, the contribu-tion of the sodium ion to the current efficiency, as definedin part I, was very low (<2%), that pointed out the low lossof permselectivity of the membrane. Moreover, the sodiumconcentration remained low compared to the total cationconcentration: it varied from 3% to 7% in the passion fruitand mulberry juices and from 0.5% to 3% in the naranjillajuice.

H3Cit

0

10

20

30

40

0 20 40

Titrable acidity (g.kg-¹)

Sol

uble

sol

ids

(g.k

g - ¹)

60(b)

s as a function of the titrable acidity.

0

10

20

30

40

50

Passion Mulberry Naranjilla Araza

Fruit juice

Con

cent

ratio

n (g

.kg - ¹)

initial deacidified up to pH 4

Fig. 3. Concentration variation of the major organic anion (citrate forpassion fruit, mulberry and naranjilla juice, malate for araza).

0

50

100

150

200

250

300

350

Passion Mulberry Naranjilla

Fruit juice

Con

cent

ratio

n (m

g.kg

- ¹)

initial deacidified up to pH 4

Fig. 4. Sodium concentration variation in ED3C.

NaranjillaMulberry

Passion

5

7

9

11

13

14 15 16 17 18 19Number of tests

Num

ber o

f cor

rect

resu

lts

Difference

No difference

Fig. 5. Triangular test of odour comparing the initial and deacidified juiceup to pH 4.5.

E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445 1443

3.1.4. Sugar concentrationAs expected, no change was measured in the fructose,

glucose and sucrose concentration (p < 0.05) whatever thejuice treated, the ED configuration used and the operatingconditions. These compounds, which have a relatively highsize and no electrical charge, are not transferred throughion-exchange membranes, neither by dialysis nor electro-diffusion. Identical comments were made for electrodialysisof apple juice (Quoc, Lamarche, & Makhlouf, 2000).

These results confirm the observations concerning Table4 and Fig. 1; the decline in the total soluble solids was dueto the variation of the organic acid and not sugarconcentration.

3.2. Sensorial analysis

The following results are related to the juices deacidifieduntil pH 4.5.

3.2.1. Triangular tests

Fig. 5 shows the results of triangular tests of odour per-formed between the fresh and deacidified juices. A signifi-

cant difference, corresponding to a decrease in the odourintensity was observed for the mulberry and naranjillajuices. The loss of aroma can be due to: (i) volatilizationof these compounds during the ED process, (ii) modifica-tion of the liquid/vapour equilibrium related to the varia-tion of the chemical composition of the juice and (iii)adsorption onto the membranes and spacers made in poly-propylene. Indeed, various studies have shown the aromaaffinity for hydrophobic polymers such as polypropylene(Ali, Dornier, Duquenoy, & Reynes, 2003).

The intense aroma of the passion fruit can explain thatno change of odour was detected for this fruit juice.

3.2.2. Ranking tests

The aim of these tests performed with various nectarswas to investigate an application of deacidified juices. Asshown in Table 3, from each fruit, four nectars at the samesugar–acid ratio, were prepared by mixing fresh and deaci-dified juice at pH 4.5, water and sucrose. The total amountof juice used in the beverage was increased in order to tryto increase the aromatic strength of the nectar.

The results of rank sums were presented in Fig. 6. Thesamples that present a rank within the range delimited bythe two horizontal lines, are not significantly different at5% level (Jellinek, 1985).

The following comments can be made about the resultsof Fig. 6: when the total juice concentration increased, itwas detected (i) a significant increase in aroma for the pas-sion fruit nectars, the values remaining not significantly dif-ferent for the two other fruit juices, (ii) a decrease insweetness and (iii) an increase in bitterness/astringencyfor all juices.

The results obtained for aroma corroborate those of thetriangular tests on the odour. Indeed, the increase of thejuice concentration in the nectar is related to an increasein the deacidified juice concentration and a decrease inthe fresh juice concentration. Consequently, the loss ofaroma observed in the deacidified juices of mulberry andnaranjilla (Fig. 5) was counterbalanced by an increase in

Mulberry

010203040506070

32.7 45.0 60.0 100.0Juice concentration (%) Juice concentration (%)Juice concentration (%)

Naranjilla

010203040506070

34.0 45.0 70.0 100.0

Ran

k

Ran

k

Ran

k

Passion fruit

0

10

20

30

40

50

60

15.1 30.0 50.0 89.4

Flavour Sweetness Bitter/astringency

Fig. 6. Ranking test for nectars of fruit juices.

1444 E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445

the concentration. For the passion fruit, the aromaticintensity increased with the juice concentration becauseED process did not lead to significant loss of aroma asproved during triangular tests (Fig. 5).

A decrease in sweetness was measured even though thesugar concentration and the sugar–acid balance were notmodified. This result shows that the sweetness perceptionis not only affected by the sugar and acid contents andproves that the sugar–acid ratio is not a good indicatorto characterize the taste of these beverages. The bitter-ness/astringency was markedly increased in the mulberryand naranjilla juices. These properties being naturally pres-ent in the juices, an increase of the juice concentration inthe nectars leads to an increase in their perception. Fur-thermore, the decrease of sweetness probably enhancesthe perception of these taste descriptors.

To resume, except for the passion fruit, the sensorialquality of the nectars was not significantly improved byusing higher concentrations of fruit juice. The fact thatthe quantity of the sucrose to be added in the nectarsdecreases when the juice concentration increases, is inter-esting for the health of consumers.

4. Conclusion

The results of this study showed that electrodialysis is anefficient process to deacidify fruit juices without addedreagents.

Regarding the quality of the product, the physico-chem-ical and sensory analysis showed that the final productproperties were similar whatever the ED configurationand the operating conditions of current density and flowrate. The properties were only affected by the final pH ofdeacidification.

The reduction of the acidity led to a decrease in theamount of total soluble solids and partial elimination oforganic and inorganic anions, the sugar and cation concen-tration remaining unchanged, except for the sodium ion inthe ED3C configuration. Nevertheless, despite the increasein the latter cation concentration, its proportion remainedlow in all juices.

Slight changes of colour were observed for the passionfruit and naranjilla juices, but for the mulberry juice the

decrease in the intensity of the colour was perceptible evenat visual observation. This phenomenon is related to thedeacidification of the product and not to the method used,because the colour of anthocyanes, main colouring of thered fruits, is pH dependent. The presence of these com-pounds in some fruit juices, is a limiting factor for theED process, because their precipitation at basic pH induc-ing a membrane fouling.

Among the sensory tests performed, one can be noticeda loss of flavour only for the mulberry and naranjilla juices.Nectars with various juice concentrations were prepared inorder to test possible applications of deacidified juices, butthe results of sensorial analyses showed that the incrementof juice concentration did not improve the aromatic qualityof nectars.

However, the deacidification would facilitate the use ofacid fruit juices in some food preparations, particularly inthe milky ones, because of precipitation of casein at acidicpH. Furthermore, the deacidification of fruit juices couldalso be employed as a method for the normalisation ofacidity, in order to maintain a constant quality in industrialproductions.

Acknowledgement

This research was supported by the IFS, Stockholm andthe OPCW, The Hague, through the grant E3328-1.

References

Ali, F., Dornier, M., Duquenoy, A., & Reynes, M. (2003). Evaluatingtransfers of aroma compounds during the concentration of sucrosesolutions by osmotic distillation in a batch-type pilot plant. Journal of

Food Engineering, 60, 1–8.AOAC (2000). Fruits and fruit products. In Helrich K. (Ed.), Official

methods of analysis of association of official analytical chemists (Vol. 2,17th ed.), (pp. 37–38). Arlington: USA.

Belitz, H. D., & Grosch, W. (1987). Fruits and fruit products. In Food

Chemistry (pp. 578–621). Berlin: Springer Verlag.Jellinek, G. (1985). Sensory evaluation of food. Theory and practice.

Chichester, England: Ellis Horwood Ltd (pp. 184–288).Mayer, F. (1973). La quımica de las materias naturales colorants. Aguilar

Ediciones: Madrid (pp. 237).Quoc, A. L., Lamarche, F., & Makhlouf, J. (2000). Acceleration of pH

variation in cloudy apple juice using electrodialysis with bipolar

E. Vera et al. / Journal of Food Engineering 78 (2007) 1439–1445 1445

membranes. Journal of Agricultural and Food Chemistry, 48,2160–2166.

Scott, K. (1995). Handbook of industrial membranes. Amsterdam: ElsevierAdvance Technology (pp. 760–770).

Vera, E., Ruales, J., Dornier, M., Sandeaux, J., Sandeaux, R., &Pourcelly, G. (2003a). Deacidification of the clarified passion fruit

juice using different configurations of electrodialysis. Journal of

Chemical Technology and Biotechnology, 78, 918–925.Vera, E., Ruales, J., Dornier, M., Sandeaux, J., Persin, F., Pourcelly, G.,

et al. (2003b). Comparison of different methods for deacidificationof clarified passion fruit juice. Journal of Food Engineering, 59,361–367.