Original article

The quality of orange juice processed by coupling

crossflow microfiltration and osmotic evaporation

Mady Cisse1,2, Fabrice Vaillant1,3, Ana Perez3, Manuel Dornier1,2* & Max Reynes1

1 Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement (CIRAD), Tropical Fruits Dept.

(FLHOR), av. Agropolis, TA 50/PS4, 34398 Montpellier Cedex 5, France

2 Ecole Nationale Superieure des Industries Alimentaires (ENSIA), Tropical Food Dept. (SIARC), 1101 av. Agropolis, CS

24501, 34093 Montpellier Cedex 5, France

3 Centro Nacional de Ciencia y Tecnologıa de Alimentos (CITA), Universidad de Costa Rica, Codigo Postal 2060, San Jose,

Costa Rica

(Received 28 November 2003; Accepted in revised form 15 June 2004)

Summary Crossflow microfiltration (CFM) and osmotic evaporation (OE) were implemented on a

semi-industrial pilot scale to obtain clarified orange juice concentrates at 450 and

620 g kg)1 of total soluble solids. The characteristics of the juice were then assessed and

compared with fresh juice and commercial concentrates. With CFM, most aroma

compounds and vitamin C remained in the permeate while the more apolar compounds

such as terpenic hydrocarbons and carotenoids were strongly retained by the membrane.

With OE, significant losses of vitamin C and aroma compounds occurred at first, with

losses progressively decreasing during treatment. Pre-conditioning the membrane and cold

regeneration of the brine reduced losses drastically, with the aroma composition tending

towards that of the initial juice. The quality of pulp, a blend of the CFM retentate and OE

concentrate, was high and much closer to that of the initial fresh juice than to the

commercial thermal concentrate.

Keywords Clarification, concentration, integrated membrane process, juice quality, stabilization.

Introduction

The ability to concentrate is a primary requisite for

the fruit juice industry, principally for economic

reasons such as reduced transport and storage costs.

Nowadays, multi-stage vacuum evaporation (VE)

is the classical technology used in the industry.

However, this process always reduces the quality of

the juice. Temperatures higher than 50 �C degrade

sensorial characteristics, leading to a partial loss of

the fresh juice flavour, even when the evaporator is

equipped with an aroma recovery system.

In order to limit thermal damage, other proces-

ses that concentrate juices at low temperatures,

such as freeze concentration and membrane pro-

cesses have been developed (Ramteke et al., 1993;

Jariel et al., 1996), including those involving

osmotic evaporation (OE). Also called osmotic

distillation, OE is creating considerable interest

(Hogan et al., 1998; Girard & Fukumoto, 2000) in

that it concentrates juices by as much as

650 g kg)1 of total soluble solids (TSS) at ambient

temperatures. Because of the high viscosity of

pulpy juices, removing pulp before concentration

often significantly improves performance. The

potential of OE, particularly when coupled with

crossflow microfiltration (CFM) is thus very

attractive and should permit the preparation of

better-quality concentrates, both clarified and

pulpy, than those obtained by classical methods.

This integrated membrane process has already

been suggested for treating different pulpy juices

(Shaw et al., 2001; Vaillant et al., 2001 a; Rodri-

gues et al., 2004). Nevertheless, the literature has

little information on the product’s overall quality*Correspondent: Fax +33/4-67614433;

e-mail: dornier@cirad.fr

International Journal of Food Science and Technology 2005, 40, 105–116 105

doi:10.1111/j.1365-2621.2004.00914.x

� 2005 Institute of Food Science and Technology Trust Fund

during processing on a semi-industrial scale. This

study aimed to characterize the effect of a coupled

membrane process on the quality of orange juice,

including its chemical composition, vitamin C

content, aroma compounds, and on its sensorial

characteristics. The intermediate products obtained

in the pilot plant after clarification by CFM and

concentration by OEwere also analysed. The pulpy

juice obtained from the membrane concentrate was

compared with a standard single-strength juice and

a vacuum-evaporated concentrate.

Material and methods

Raw materials

Frozen, single-strength, pasteurized, orange juice

(F) and frozen, vacuum-evaporated (VE), orange-

juice concentrate (CVE650) were provided by Ticofrut

S.A. (San Carlos, Costa Rica). Both were obtained

from oranges of the Valencia variety. The CVE650 was

a typical commercial frozen orange juice (FCOJ)

that had been concentrated to 650 g kg)1 TSS on

an industrial scale by a TASTE evaporator (Gulf

Machinery Co., Winter Haven, FL, USA), which

featured seven effects (the temperature of the first

effect was 80 �C) and an aroma recovery unit.

Clarification by CFM

Single-strength orange juice (F) was clarified,

using a CFM unit that featured a ceramic mem-

brane Membralox IP19–40 (Pall-Exekia, Bazet,

France) with an average pore diameter of 0.2 lmand a filtration area of 0.22 m2. All filtration trials

were conducted with the juice without prior

enzymatic treatment.

A continuous �feed and bleed� microfiltration

method was followed, as described elsewhere

(Vaillant et al., 2001b). When the set volumetric

reduction ratio (VRR) reached 3.5, the retentate

was removed continuously at a specific flowrate

that allowed the VRR to remain constant, while

fresh juice F was fed into the unit and permeate

(P) was collected. Crossflow velocity, transmem-

brane pressure and temperature were 7 m s)1,

400 kPa and 20 ± 2 �C, respectively. The perme-

ate (P), i.e. the clarified juice, was then stored

(<1 day) at 0 �C until its process by OE.

Concentrating the clarified juice by OE

The OE unit (Fig. 1) and the concentration

procedure were similar to those described by

Vaillant et al. (2001a) except that a brine evapo-

rator was not used. The pilot plant featured a

hydrophobic polypropylene hollow fibres mem-

brane with a total area of 10.2 m2 and an average

pore diameter of 0.2 lm. The juice to be concen-

trated circulated inside the hollow fibres at

0.2 m s)1. The juice loop had a hold-up volume

of 7.5 L. It was continuously fed with the clarified

juice and the concentrate was also extracted

continuously once the set TSS was reached.

Clarified juice

F

PT

P

T

Brine

Concentrated juice

Valve

Juice pump Brine pump

Mem

bran

a m

odul

e

Flow metre

Pre-filter

Support

CaCl2

Figure 1 Schematic of the pilot plant of osmotic evaporation used for concentration of orange juice.

Improving orange juice quality M. Cisse et al.106

International Journal of Food Science and Technology 2005, 40, 105–116 � 2005 Institute of Food Science and Technology Trust Fund

Calcium chloride solution circulated concur-

rently on the other side of the membrane at about

0.02 m s)1. Juice conductivity was always monit-

ored during concentration to ensure membrane

integrity and hydrophobicity, and to detect poss-

ible salt leakage through the membrane. During

the trials, CaCl2 crystals were added to maintain

the brine solution near saturation (at

5.5 mol L)1). The brine temperature was main-

tained between 30 and 33 �C.Pressure and temperature values at the inlet and

outlet of the membrane were registered with

pressure (±2%) and temperature gauges

(±1 �C). The feed flowrate was recorded with a

Krohne electromagnetic flow meter (Krohne

Messtechnik GmbH, Duisburg, Germany) to give

the average evaporation flux (Jw). At the end of

the trials, the dilute brine was recovered and

concentrated by heating until the salts crystallized.

The crystals were kept for reuse in further trials.

As previously suggested, to improve perform-

ance (Vaillant et al., 2001a), the concentration of

the clarified orange juice was carried out in two

stages: from initial TSS to 450 g kg)1 TSS,

obtaining the concentrate COE450 and then to

620 g kg)1 TSS, obtaining the final concentrate

COE620. The concentration loop was continuously fed

with the clarified juice (P) during the first stage

and with COE450 during the second stage. The

temperature of this loop was maintained at

26 ± 2 �C by feeding the unit with juice or

concentrate (450 g kg)1 TSS) at 6 ± 1 �C. The

cleaning procedure described in Vaillant et al.

(2001a) was followed, except that, after the alka-

line cleaning, an acidic step was implemented,

using a citric acid solution at 10 g kg)1. The

general processing set-up used in this study is

presented in Fig. 2.

Evaluating juice quality

We used standard methods to measure TSS

content, titratable acidity and density (AOAC,

1990), and suspended insoluble solids (SIS)

Single strength

orange juice F

Permeate P

Osmotic evaporation (OE)

(First stage, 450 g TSS kg–1)

Concentrate C450OE

Concentrate C620OE

Osmotic evaporation (OE)

(Second stage, 620 g TSS kg–1)

Blending

Thermal

pasteurization

Retentate (R)Crossflow microfiltration (CFM)

R + C620OE

Figure 2 General processing flow chart.

Improving orange juice quality M. Cisse et al. 107

� 2005 Institute of Food Science and Technology Trust Fund International Journal of Food Science and Technology 2005, 40, 105–116

(Vaillant et al., 2001a). Carotenoids were deter-

mined by spectrophotometry at 453 nm after

solvent extraction according to Taungbodhitham

et al. (1998). High-performance liquid chromatog-

raphy (HPLC) was used to determine vitamin C

level by adopting the methodology developed by

Kacem et al. (1986) and Brause et al. (2003).

Sucrose, glucose and fructose were also analysed

by HPLC according to the method of Englyst &

Cummings (1984). Results were expressed accord-

ing to TSS to make comparisons easier between

juices. Colour was analysed using a HunterLab

DP 9000 colorimeter (Hunter Associates Labora-

tory Inc., Reston, VA, USA) and data were

expressed as luminosity (L�), Hue angle (H�) andcolor purity (C�) calculated from the tristimulus

parameter L*, a*, b* as L� ¼ L*, H� ¼ tan)1 (b*/

a*) and C� ¼ (a*2 + b*2)1/2, respectively.

Viscosity was measured with an Oswald glass

capillary viscosimeter, and water activity with an

Aw-Meter AquaLab CS-2 (Decagon Devices Inc.,

Pullman, WA, USA).

We used gas chromatography to analyse aroma

compounds after carrying out quantitative liquid–

liquid extraction with dichloromethane on an

aliquot of 50 mL of juice (v/v, replicated three

times). Before extraction, 200 lg of two internal

standards were added to the juice. The extract was

dried using anhydrous sodium sulphate and even-

tually concentrated by VE at 25 �C to a volume of

0.5 mL before injection (1 lL). We used a Hewlett

Packard 5890 chromatograph (Hewlett Packard

Co., Palo Alto, CA, USA), with an HP-5 (cross-

linked 5% phenyl methyl siloxane) fused-silica

capillary column (30 m · 0.25 mm ·0.25 lm) and a mass spectrometer as the detector.

Helium was the carrier gas, flowing at

1 mL min)1.

Injector and detector temperatures were 250 and

280 �C, respectively. The oven’s initial tempera-

ture was 40 �C. It was raised to 220 �C at

6 �C min)1, then to 250 �C at 15 �C min)1 and

was maintained at 250 �C for 4 min. Injection was

splitless. Aroma compounds were identified on the

basis of linear retention index, Chemical Abstracts

Service (CAS) index number, and mass spectra.

Hexanol and ethyl benzoate GC grade (Aldrich,

Saint Quentin Fallavier, France) were chosen as

internal standards for compounds with retention

times below and above 18 min, respectively.

Response factors were taken as 1.0 for all

compounds with respect to the internal standards.

Sensorial tests used the triangular test method

with a panel of 25 highly trained orange-juice

tasters from Ticofrut S.A. Four descriptors were

chosen: aroma, taste, acidity and colour. First,

to evaluate the effect of the OE process on

sensorial quality, the clarified juice obtained

after microfiltration (P) was compared with

COE620 concentrate after dilution with distilled

water to the same TSS (115 g kg)1). Secondly,

to evaluate the effect of the overall integrated

process (CFM + OE) on sensory quality, single-

strength orange juice (F) was compared with the

clarified juice concentrate (COE620) reconstituted

with water and the microfiltration retentate (R)

previously pasteurized at 72 �C for 30 min.

Finally, this last reconstituted juice (R + COE620)

was compared with CVE650. Both concentrates were

evaluated at the same pulp content (SIS ¼80 g kg)1) and TSS (118 g kg)1).

Results and discussion

Clarification by CFM

For the operating conditions chosen, the VRR, set

at 3.5, was reached after 2.5 h (Fig. 3). This VRR,

corresponding to a permeate production yield of

71.4% (w/w), was found to be the optimum for

orange juice because flux density decreased dras-

tically above this value. After reaching the set

VRR, permeate flux was maintained at about

62 L h)1 m)2 for more than 10 h by removing the

retentate to keep VRR constant. As previously

reported by Vaillant et al. (2001b), membrane

fouling appeared to reach an almost steady state

when the viscosity of the retentate was kept

constant.

The main physico-chemical and nutritional

properties of initial single-strength juice (F), per-

meate (P) and retentate (R) at a VRR of 3.5 are

reported in Table 1. The permeate was totally

clarified (SIS ¼ 0 g kg)1) and the retentate was

enriched with pulp (SIS ¼ 90 g kg)1). The latter

value remained surprisingly very close to that of

the initial juice. As previously stated by Vaillant

et al. (2001b), we assumed that the strong shear

stress being exerted on pulp fibres during constant

recirculation could affect their swelling capacity,

Improving orange juice quality M. Cisse et al.108

International Journal of Food Science and Technology 2005, 40, 105–116 � 2005 Institute of Food Science and Technology Trust Fund

thus skewing pulp measurements by the centri-

fugation method.

The TSS content was found to be higher in the

retentate than in the recovered permeate, being

about 15 g kg)1. Similar results have already been

reported in the literature as a measurement arte-

fact (Todisco et al., 1996; Vaillant et al., 1999).

The refractive index was affected by the presence

of high pulp content in the retentate, as confirmed

by the values for sugars and organic acids not

being significantly different from those in fresh

juice, retentate and permeate. The membrane did

not reject these solutes and the clarification did not

affect the sugar/acid balance of the permeate (P).

The vitamin C contents of the single-strengh

juice (F), the retentate (R) and the permeate (P)

Table 1 Composition and main characteristics of the different juices

F R P COE450 COE

620 R + COE620 CVE

650

pH (20 �C) 3.62 (0.05) 3.45 (0.07) 3.58 (0.05) 3.59 (0.06) 3.52 (0.05) 3.49 (0.05) 4.12 (0.07)

Water activity (25 �C) 0.98 (0.02) 0.97 (0.02) 0.99 (0.02) 0.90 (0.02) 0.77 (0.02) 0.95 (0.02) 0.75 (0.02)

Viscosity (25 �C, mPa s) 1.1 (0.4) 1.7 (0.4) 1.2 (0.3) 7.5 (0.4) 28.2 (0.7) 1.6 (0.3) 37.3 (0.4)

Density (kg m)3) 1032 (2) 1045 (2) 1028 (2) 1187 (2) 1290 (2) 1280 (2) 1383 (2)

Total soluble solids (g kg)1) 118 (2) 130 (2) 115 (2) 450 (2) 620 (2) 118 (2) 655 (2)

Suspended insoluble solids (g kg)1) 80 (3) 90 (4) 0 0 0 80 (2) 80c (2)

Titrable acidity (g citric acid kg)1 TSS) 68 (1) 62 (2) 61 (1) 59 (1) 62 (1) 63 (1) 44 (1)

Glucose (g kg)1 TSS) 186 (1) 188 (2) 185 (2) 183 (2) 187 (2) 185 (2) 114 (1)

Fructose (g kg)1 TSS) 220 (2) 221 (2) 220 (2) 219 (2) 221 (2) 219 (2) 136 (1)

Sucrose (g kg)1 TSS) 491 (2) 494 (2) 489 (2) 490 (2) 491 (2) 48 (2) 291 (2)

Carotenoids (g kg)1 TSS) 0.38 (0.04) 0.34 (0.05) <0.02 <0.02 <0.02 0.35 (0.05) 0.24 (0.05)

Vitamin C (g kg)1 TSS) 3.7 (0.3) 3.3 (0.2) 3.6a.3.5b (0.3) 2.9 (0.3) 3.3 (0.3) 3.2 (0.3) 2.2 (0.2)

Colour (L) 52 62 62 49; 61d 25; 61d 53 20; 28c

Hue angle (H�) 88 82.3 88.3 82.4; 88.3d 38.7; 88.3d 88 63.4; 86.4d

Colour purity (C�) 30 37.3 17 30.3; 17d 25.6; 17d 29 31; 15d

Results are mean ± SD of six analyses.aAfter CFM.bBefore OE.cAfter dilution to 118 g kg)1 TSS.dAfter dilution to 115 g kg)1 TSS.

00 2 4 6 8 10 12

20

40

60

80

100

Time (h)

J (l

h–1

m–2

)

0

1

2

3

4

VR

R

Jp Jr VRR

Figure 3 Permeate flux (Jp), removal flux of retentate (Jr) and volumetric reduction ratio (VRR) during CFM of orange juice

(TmP ¼ 400 kPa, U ¼ 7 m s)1, T ¼ 20 �C).

Improving orange juice quality M. Cisse et al. 109

� 2005 Institute of Food Science and Technology Trust Fund International Journal of Food Science and Technology 2005, 40, 105–116

were not significantly different. Neither retention

by the membrane nor oxidative damage (because

of low temperature) affected this compound. No

carotenoids were noticed in the permeate. As these

compounds are insoluble in water and are mainly

associated with cell-wall fragments, they are

retained by the CFM membrane along with the

pulp. As a consequence, the clarified juice was

almost colourless (low colour purity C�), whereasthe retentate (R) was more intensely yellow than

the initial juice (F) (Table 1).

In the initial single-strength juice (F), the

identification of aroma compounds showed the

typical aromatic profile of Valencia orange juice

(Coleman & Shaw, 1971; Radford et al., 1974;

Johnson et al., 1996; Shaw et al., 2001), although

the product was particularly rich in a-pinene, c-terpinene, myrcene, decanal, octanal, hexanal and

poor in limonene (Table 2). The same orange

variety grown in humid tropical area may have a

different aromatic profile than oranges grown in

more Mediterranean climate.

The oxygenated compounds (alcohols, esters,

aldehydes and terpenols) were mainly found in the

permeate, whereas the terpenic hydrocarbons were

largely retained by the CFM membrane. More

than 60% of the ethanol, hexanal, decanal, benz-

aldehyde, linalool and terpineol from the fresh

juice were recovered in the permeate, whereas

more than 75% of the limonene, terpinolene and

valencene were found in the retentate. The selec-

tivity of the membrane according to aroma

compound is clearly demonstrated with these

results corroborating those of Hernandez et al.

(1992) and Johnson et al. (1996).

As terpenic hydrocarbons are highly apolar

compounds, an important portion of these com-

pounds could be adsorbed into the pulp, which

contains hydrophobic sites (Radford et al., 1974;

Hernandez et al., 1992) and subsequently rejected

Table 2 Concentration (in mg kg)1 TSS) of the principal aroma compounds in the different juices obtained

Compound of aromas F R P COE450* COE

620* R + COE620 COE

650

Ethanol 2356 (141) 377 (30) 2106 (147) 1558 (120) 1784 (125) 1885 (130) 1649 (115)

Octanol 29 (2) 15 (2) 20 (2) 12 (1) 13 (2) 46 (3) tr

Decanol 20 (2) 5 (1) 15 (1) 9 (1) 11 (1) 15 (2) tr

Total alcohols 2405 397 2141 1579 1808 1946 1649

a-Pinene 21 (2) 6 (1) 20 (2) 1 (1) 1 (1) 5 (1) tr

Myrcene 163 (12) 260 (25) 62 (5) 39 (4) 46 (3) 120 (20) 163 (15)

Limonene 2186 (196) 1708 (165) 1382 (134) 984 (101) 1155 (132) 1498 (155) 1432 (140)

c-Terpinene 15 (1) 9 (2) 12 (1) 6 (1) 6 (1) 8 (2) tr

Valencene 130 (11) 92 (8) 38 (2) 38 (6) 52 (6) 98 (9) 156 (12)

Terpinolene 336 (60) 501 (50) 108 (15) 108 (10) 116 (11) 378 (36) tr

Total terpenic hydrocarbons 2851 2576 1717 1176 1376 2107 1751

Decanal 15 (2) 7 (2) 12 (1) 8 (1) 9 (2) 12 (1) 13 (1)

Octanal 11 (1) 5 (1) 10 (1) 7 (1) 8 (1) 9 (1) 8 (1)

Hexanal 5 (1) 3 (1) 4 (1) 3 (1) 3 (1) 4 (1) 4 (1)

Benzaldehyde 81 (9) 28 (2) 76 (6) 53 (5) 61 (5) 68 (8) 21 (2)

Total aldehydes 112 43 102 71 81 93 46

Ethyl hexanoate 865 (80) 84 (10) 828 (78) 552 (48) 553 (50) 510 (52) tr

Butyl butyrate 625 (70) 62 (6) 665 (62) 402 (39) 452 (43) 470 (55) 338 (40)

Linalyl propanoate 320 (40) 145 (12) 302 (28) 182 (15) 211 (20) 383 (32) 206 (22)

Total esters 1810 291 1795 1136 1216 1363 544

Linalol 16 (2) 11 (1) 15 (1) 5 (1) 10 (1) 9 (1) 7 (1)

a-Terpineol 8 (1) 2 (1) 9 (2) 7 (1) 7 (1) 7 (1) tr

4-Terpineol 6 (1) 3 (1) 5 (1) 4 (1) 4 (1) 5 (1) tr

Geraniol 92 (12) 51 (4) 91 (8) 75 (6) 85 (7) 80 (12) 58 (7)

Carveol 44 (52) 85 (7) 15 (1) 11 (1) 13 (1) 36 (5) 37 (4)

Total terpenols 166 152 135 102 119 137 102

Results are mean ± SD of six analyses.

tr, traces; *Analysis on all OE concentrate recovered until collecting two hold-up volumes and obtained after pre-conditioning

the membrane.

Improving orange juice quality M. Cisse et al.110

International Journal of Food Science and Technology 2005, 40, 105–116 � 2005 Institute of Food Science and Technology Trust Fund

by the CFM membrane. The content of aroma

compounds in the juice (F) was significantly

modified by clarification. These changes should

alter the aroma characteristics of the product.

However, for orange juice, high terpenic hydro-

carbon content is not generally considered essen-

tial to orange flavour. Indeed, a high content of

terpenic hydrocarbons is often detrimental to the

stability of the juice during storage because these

unsaturated compounds are very susceptible to

oxidation.

Concentrating the clarified juice by OE

Figure 4 shows that, during OE, when TSS

increased, the evaporation flux (Jw) decreased

from 0.7 L h)1 m)2 at low TSS to

0.67 L h)1 m)2 when TSS reached 450 g kg)1,

and to 0.59 L h)1 m)2 when TSS reached

620 g kg)1. Nonetheless, the decrease in evapor-

ation flux was relatively low (only 17% difference

between initial TSS and 620 g kg)1) when com-

pared with other �cold� concentration processes.

Because evaporation flux was mainly correlated to

the TSS and did not depend on time, we can

assume that no significant membrane fouling

occurred during the long-term trial. The low

decrease of evaporation flux with respect to TSS,

and the absence of fouling, allowed working at

different concentration stages, following a con-

tinuous �feed and bleed� procedure. These results

confirmed those obtained with passionfruit juice

(Vaillant et al., 2001a).

Main characteristics of the concentrates

Table 1 gives the main physico-chemical charac-

teristics of both concentrates (COE450 and COE

620)

obtained by OE and the initial clarified juice (P)

(i.e. the microfiltration permeate).

For the main solutes, a direct comparison of

results expressed in gram per kilogram of TSS

showed that no significant differences existed in

sugar and organic acid content between clarified

juice (P) and OE concentrates (COE450 and COE

620).

The vitamin C content appeared to be lower in

the OE concentrates COE450 (by 17%) and COE

620 (by

6%) with regard to the initial clarified juice before

concentration (P). Vitamin C losses were mainly

observed during the first 3 h of concentration,

after which the vitamin C content (expressed in

gram per kilogram TSS) started to increase and

tended progressively to reach the levels of the

initial juice (Fig. 5). We assume that this pheno-

menon is mainly due to ascorbic acid oxidation by

the residual oxygen entrapped within the pores of

the membrane. This oxidation was most important

for the juice that penetrated into the concentration

loop at the beginning of the concentration. As

residual oxygen contained in the circuit is con-

sumed, vitamin C losses decrease during process-

ing and finally tend towards zero. For long-term

trials with continuous �feed and bleed� operations,the concentrate COE

620, obtained after recovering

two hold-up volumes of concentrate, showed no

significant differences with respect to the initial

juice (P) (differences below 5%).

Second stage OE

0

100

200

300

400

500

600

700

1086420 12 14 16 18

Time (h)

TSS

(g

kg–1

)

0.0

0.2

0.4

0.6

0.8

J (k

g h–1

m–2

)

First stage OE

0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14Time (h)

TSS

(g

kg–1

)

0.0

0.2

0.4

0.6

0.8

J (k

g h–1

m–2

)

TSS Jw Jc

Figure 4 Concentration in total soluble solids (TSS), water flux (Jw) and concentrate removal flux (Jc) during OE

(26 �C < Tc < 28 �C, 30 �C < Tb < 33 �C, Uc ¼ 0.2 m s)1).

Improving orange juice quality M. Cisse et al. 111

� 2005 Institute of Food Science and Technology Trust Fund International Journal of Food Science and Technology 2005, 40, 105–116

Even if the colour of the concentrate became

darker when the TSS increased because of pigment

concentration, after dilution to the same initial

TSS, no significant difference in colour was

noticed for either OE concentrate (COE450 or COE

620),

when compared with the initial clarified juice (P).

Table 1 shows that the low temperatures achieved

during OE (<28 �C) preserved the colour of the

juice when comparing L-value, Hue angle (H�)and colour purity (C�) of both concentrates with

respect to the initial juice P. Thus the Maillard

reactions in particular were avoided.

Aromatic qualities of the concentrates

On comparing the composition of the initial

clarified juice (P) with both concentrates collected

after 10 h of continuous extraction, loss of aroma

compounds was seen to occur during the two

concentration stages (Table 2). The losses evalu-

ated for all aroma compounds were higher in the

first stage ()31%) than in the second stage

()22%). This trend was confirmed for all aroma

compounds, whether considered individually or as

chemical class. The decrease in aroma concentra-

tion was always more prominent in the concen-

trate at 450 g kg)1 TSS (COE450) than in the

concentrate at 620 g kg)1 TSS (COE620).

Within each class of compounds, not all the

volatiles were affected at the same intensity. For

each compound the transfer flux was different.

During OE, mass transfer depends on (a) the

initial concentration of the compound in the juice,

(b) its relative volatility, (c) its diffusivity in liquid

phases and, finally, (d) its diffusivity in air

entrapped within the membrane pores (Courel

et al., 2000).

Nevertheless, using sensorial analysis, no signi-

ficant difference (at 95% confidence level) was

noticed between the initial clarified juice (P) and

the clarified concentrate at 620 g kg)1 TSS (COE620).

The effect of OE on the aromatic quality of the

juice was not significant, at least from the sensorial

viewpoint.

Nonetheless, to better characterize losses of the

volatiles, the transfer kinetics of the aroma com-

pounds were assessed during the OE process

(Fig. 6). The concentration of all groups of aroma

compounds decreased as TSS levels increased

during the first 3 h of concentration, and then

increased slightly for both concentration stages.

These results can be explained by both the

reduction of the driving force versus time and

the adsorption phenomena on the membrane.

During OE, water transfers were always accom-

panied by the weak transfer of some aroma

compounds through the membrane (Ali et al.,

2003). Because the brine was not regenerated by

evaporation but maintained saturated by adding

CaCl2 crystals, the concentration of the aroma

compounds in the brine progressively increased.

The driving force for the transfer of aroma

First OE stage (115 to 450 g TSS kg–1)

3

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

4

1050 15

Time (h)

Vit.

C (

g kg

–1 T

SS)

0

50

100

150

200

250

300

350

400

450

500

TSS

(g

kg–1

)

Vitamin C TSS

Figure 5 Evolution of the content

of vitamin C during the first stage

of OE concentration

(26 �C < Tc < 28 �C,30 �C < Tb < 33 �C,Uc ¼ 0.2 m s)1).

Improving orange juice quality M. Cisse et al.112

International Journal of Food Science and Technology 2005, 40, 105–116 � 2005 Institute of Food Science and Technology Trust Fund

compounds through the membrane thus de-

creased, continuously reducing the transmem-

brane flux. The large membrane area used

(10.2 m2) and the strong affinity that these com-

pounds have for hydrophobic polymers like poly-

propylene are also highly favourable for

adsorption phenomena to take place, as already

described by Ali et al. (2003). This adsorption may

also contribute to aroma compound losses at the

beginning of the processing.

Complementary trials were carried out to dis-

cover how to limit the loss of aroma compounds

to adsorption on the membrane during the initial

phase of OE. Clarified juice was first circulated

inside the membrane for 3 h, then discarded and a

new concentration trial was carried out immedi-

ately after draining without rinsing and using

brine that had been thermally regenerated before-

hand.

Table 3 shows that pre-conditioning the mem-

brane slows down the loss of aroma compounds.

Losses were strongly reduced for all aromatic

classes excepted for aldehydes. For concentrate

collected after 3 h of the second OE stage, losses

were reduced respectively for alcohols and esters,

from 35 to 13% and 55 to 25% (Table 3). As the

brine was not regenerated by evaporation during

the trial, membrane adsorption alone must have

been responsible for 63 and 54% of the losses of

alcohols and esters, respectively, during the first

3 h of OE concentration. Losses of aroma com-

pounds can thus be drastically reduced by imple-

menting a stage of pre-conditioning the membrane

to limit adsorption phenomena on the hydropho-

bic membrane. The other losses, caused by the

driving force for aroma transfers to the brine,

decrease with time during the trial as the brine is

not thermally regenerated. Analysis of concentra-

tion of aroma compounds done on the concentrate

COE620 collected at the end of the trial (after having

collected two hold-up volumes of the concentrate),

showed that the concentrate present insignificant

losses of the aroma compounds with respect to the

initial juice P (Table 3).

Second stage OE

60

80

100

120

0 2 4 6 8 10 12 14 16

Ca

(mg

kg–1

TSS

)

400

500

600

700

TSS

(g

kg–1

)

Aldehydes Terpenols TSS

First stage OE

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14

Time (h) Time (h)

Ca

(mg

kg–1

TSS

)

0

100

200

300

400

500

TSS

(g

kg–1

)

Alcohols Esters TSS

Figure 6 Example of the concentration kinetic of some classes of aroma compounds (Ca) during OE concentration of orange

juice (26 �C < Tc < 28 �C, 30 �C < Tb < 33 �C, Uc ¼ 0.2 m s)1).

Table 3 Comparison of the aroma

concentration (mg kg)1 TSS) in

orange juice collected after 3 h (a)

or at the end of the trial (b) during

OE concentration with and

without pre-conditioning of the

membrane

P

(a) COE620 without

pre-conditioning

(%)

(a) COE620 with

pre-conditioning

(%)

(b) COE620 with

pre-conditioning

(%)*

Alcohols 2141 1379 1857 2097

Aldehydes 102 86 80.5 97

Esters 1795 824 1341 1556

Terpenics

hydrocarbons

1717 1047 1408 1579

Terpenols 135 96 103 112

*Samples collected after recovering two hold-up volumes of the concentrate.

Improving orange juice quality M. Cisse et al. 113

� 2005 Institute of Food Science and Technology Trust Fund International Journal of Food Science and Technology 2005, 40, 105–116

Comparing the processed pulpy juices

To evaluate the benefit of coupling CFM and OE,

OE concentrate (COE620) was collected at the end of

the trial (after collecting at least two hold-up

volumes of concentrate) and reconstituted with the

microfiltration retentate (R) previously pasteur-

ized to give a pulpy juice (R + COE620). The

chemical composition of the mix (R + COE620) was

compared with the single-strength juice (F) and

commercial concentrate FCOJ (CVE650) (Table 1).

The composition of R + COE620 was very close to

that of the single-strength juice (F). No significant

difference was found for carbohydrates and acid-

ity. Only 14% of vitamin C was lost. The colour of

R + COE620 was not significantly affected by the

processing as can be seen in Table 1. Thus the

integrated process minimizes heat-induced chem-

ical reactions, particularly the Maillard reactions.

We noticed important modifications in the

composition of the commercial concentrate

obtained by VE (CVE650). Significant differences with

respect to sugar content and acidity were found,

probably as a result of thermal damage. Indeed,

vitamin C content is 41% lower in the concentrate

(CVE650) than in fresh juice (F). The strong decrease

in colour purity (C�), and luminosity L (colour

measurement after dilution) indicated an import-

ant browning of the commercial FCOJ (CVE650). The

chemical composition and nutritional quality of

the fresh juice were thus clearly less affected by the

membrane processes than by thermal evaporation.

The contents of all classes of aroma compounds

in the pulpy juices CVE650 and R + COE

620 were lower

than those in fresh juice (Table 2). Nevertheless,

important differences were found between the two

processed products, with the losses of aroma

compounds being much higher in the vacuum-

evaporated juice. Depending on chemical class,

losses between 31 and 70% was recorded for CVE650,

whereas losses between 17 and 25% were obtained

for R + COE620. Furthermore, some volatiles (octa-

nol, decanol, terpinolene, c-terpinene, ethyl hex-anoate, a-terpineol and 4-terpineol) were totally

removed in CVE650.

Even if the aromatic profile of the raw juice was

slightly modified, the aroma quality of the integ-

rated-membrane-processed juice remained closer

to that of the fresh juice than that of the thermally

treated juice.

According to the sensorial tests, no significant

differences (at 95% confidence level) could be

noticed between single-strength orange juice (F)

and concentrated clarified juice previously recon-

stituted with pasteurized retentate and water

(R + COE620). The process used had no significant

effect on the sensorial quality of the juices. On the

contrary, the juice reconstituted from CVE650 and the

R + COE620 juice were significantly recognized as

different (twenty right answers out of twenty-five

panellists) according to aroma (40%), taste (30%),

acidity (20%) and colour (10%). All the tasters

agreed that the juice reconstituted from OE

concentrate presented a better �fresh orange juice�aroma profile.

Conclusions

Orange juice can be microfiltred reasonably easily

through a 0.2 lm ceramic membrane at an average

flow rate of about 62 L h)1 m)2 at a VRR of 3.5.

The permeate would contain solutes at a level very

close to that of fresh pulpy juice. The modifications

of chemical composition observed were not signi-

ficant, except for the carotenoids, which were

completely retained by the membrane, and some

aroma compounds, mainly terpenic hydrocarbons,

which were partially rejected by the membrane

because of their apolar properties and association

with the insoluble solids found in the retentate. The

clarified orange juice (permeate) could then be

concentrated at low temperatures byOE to asmuch

as 620 g kg)1 TSS in two stages, with an average

evaporation rate of about 0.6 L h)1 m)2.

The quality of the concentrate obtained was

very similar to the initial clarified juice. The OE

process did not modify sugar and acid contents.

Small losses of vitamin C were noticed at the

beginning of the concentration process, probably

because of oxidation phenomena. Nevertheless,

the vitamin C content of the concentrate progres-

sively increased towards the levels found in the

initial juice. The colour of the product was

unchanged.

Some losses of aroma compounds occurred

mainly during the initial hours of concentration.

These losses could be drastically limited by pre-

conditioning the membrane with the clarified juice

from CFM and by avoiding thermal regeneration

of brine during concentration. OE then allowed

Improving orange juice quality M. Cisse et al.114

International Journal of Food Science and Technology 2005, 40, 105–116 � 2005 Institute of Food Science and Technology Trust Fund

the juice to be concentrated without significantly

affecting the aroma quality.

Sensorial tests did not show significant differ-

ences between the initial single-strength juice and

the OE concentrate reconstituted with pasteurized

retentate. The resulting pulpy juice was very

similar to fresh pulpy juice and much richer in

�fresh orange juice� aroma than typical commercial

juice (FCOJ) obtained by reconsituting the con-

centrate from VE. The integrated process, i.e.

CFM and OE, represents an attractive technical

alternative to thermal technologies because it

preserves the juice’s original quality better. Nev-

ertheless, for any industrial application, a deep-

ened economic study is needed in order to evaluate

the impact of these new technologies on the cost of

the final product.

Nomenclatures

Symbols

C Concentrate

CFM Crossflow microfiltration

F Pulpy fresh juice

J Flux density (kg h)1 m)2)

OE Osmotic evaporation

P Microfiltration permeate

R Microfiltration retentate

SIS Suspended insoluble solids (g kg)1)

T Temperature (�C)TmP Transmembrane pressure (kPa)

TSS total soluble solids (g kg)1)

U Crossflow velocity (m s)1)

VE Vacuum evaporation

VRR Volumetric reduction ratio (microfiltration)

Subscripts

a aroma compound

b brine

c concentrate

j juice

p permeate

r retentate

w water

Acknowledgments

Authors wish to thank the French agency AIRE

Developpement for funding this project, Grant No.

01-8-CR-27-1, as well as EARTH University

(Guapiles, Costa Rica) and TICOFRUT S.A.

(San Carlos, Costa Rica) for their valuable tech-

nical support.

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