Apple Juice Conc Using RO

www.elsevier.com/locate/jfoodeng

Journal of Food Engineering 76 (2006) 387–395

Concentration of aqua solutions of organic componentsby reverse osmosis. I: Influence of trans-membrane pressure

and membrane type on concentration of different esterand aldehyde solutions by reverse osmosis

A. Pozderovic *, T. Moslavac, A. Pichler

Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, Department of Food Technology, F. Kuhaca 18,

P.O. Box 709, HR-31001 Osijek, Croatia

Accepted 19 May 2005Available online 22 July 2005

Abstract

Volatile aroma components of fruit juices are lost with vapour during concentration by evaporation. However, these componentsare mostly retained in fruit juice by membrane processes concentration. Application of reverse osmosis for concentration of esterand aldehyde solutions, being components of apple juice aroma, was investigated. Influence of process pressure, percentages of dif-ferent esters and aldehydes (0.01% v/v, 0.05% v/v and 0.1% v/v), influence of molecule structure, molecular mass and membranetype on concentration of model solutions of esters and aldehydes by reverse osmosis were studied. Effects of activity and activitycoefficient of esters and aldehydes on concentration were investigated too. Research was carried out with model solutions of esters(ethyl acetate, butyl acetate, hexyl acetate, amyl acetate, iso-amyl acetate, iso-amyl propionate, ethyl butyrate, ethyl 2-methyl buty-rate) and aldehydes (hexanal, trans-2-hexenal). Reverse osmosis concentration was carried out on laboratory equipment with platesand frames using two types of composite membranes (aromatic polyamide membrane HR 95 PP of 95% NaCl rejection and HR 98PP of 97.5% NaCl rejection). Aroma components (esters and aldehydes) of the retentate and permeate were determined by gas chro-matography with a mass detector (GC/MS) and a ‘‘head space’’ technique. Results of this research showed that ester and aldehydewater solutions of different molecular mass and structure could be concentrated successfully by reverse osmosis. These results alsogive a better insight into mechanisms of aroma compounds retention (esters, aldehydes) in the retentate, during concentration ofwater solutions by reverse osmosis. On the membrane HR 98 PP was greater retention of esters: ethyl acetate, butyl acetate, ethylbutyrate and ethyl 2-methyl butyrate than the membrane HR 95 PP. On the membrane HR 95 PP was greater retention of esters:hexyl acetate, amyl acetate, iso-amyl acetate, iso-amyl propionate and aldehydes: hexanal and trans-2-hexenal than the membraneHR 98 PP. Concentration factor was higher in the retentate and OCP (organic components passage) was lower in the permeate whenester and aldehyde portions in the feed solution and molecular mass were greater. Ester concentration of n-structural form showed agreater concentration factor in the retentate and lower OCP (organic components passage) in the permeate. The greater retention inthe retentates was realised by aldehyde concentration with a double bond in the molecule. Membrane selectivity and retention ofesters and aldehydes was greater in the retentate than in the permeate with application of higher process pressure.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Concentration; Aroma; Membrane processes; Reverse osmosis; Esters; Aldehydes; Gas chromatography (GC/MS)

0260-8774/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.jfoodeng.2005.05.038

* Corresponding author. Tel.: +385 31 224313; fax: +385 31 115207.E-mail address: [email protected] (A. Pozderovic).

1. Introduction

Many authors reported that the profile aroma changedwith fruit juice concentration by evaporation (Konja,

mailto:[email protected]

Nomenclature

Vo feed volume (L)Vr retentate volume (L)Ap peak area in permeateAf peak area of feed solutionCFi concentration factor of component in reten-

tate (%)Ar peak area in retentateOCP organic components passage (%)� osmotic pressure (Pa)M molar concentration (mol m�3)

R universal gas constant (Pa m�3 mol�1 K�1)T absolute temperature (K)c activity coefficienta activitycC combinatorial contributioncR residual contributionri, qi volume and surface area parameters (molecu-

lar parameters)Rk, Qk group volume and surface area parameters

388 A. Pozderovic et al. / Journal of Food Engineering 76 (2006) 387–395

Pozderovic, & Lovric, 1988). There is a 90% loss of vola-tile aroma compounds by evaporation. That deficiency ispartially compensated by aroma recovery unit with a rec-tification column (Karlsson, 1995; Sancho & Rao, 1993;Zhang, 1995). Application of other processing solutionsfor aroma recovery with fruit juice concentration by evap-oration was examined in various studies like extractiontechnique (Gomez & Martinez, 1992; Simon, Cully, &Vollbrecht, 1992), adsorption recovery (Cesare, Polesello,& Nani, 1988; Polesello, Cesare, & Naric, 1989) and per-vaporation (Borjesson, Karlsson, & Tragardh, 1996; Ols-son & Tragardh, 1999). New technology was developed inAustralia that gave better results in aroma concentration,based on column application with a rotary cone (SpinningCone Column (SCC)) (Schofild, 1994; Schofield & Riley,1998). High aroma concentration of small volume wasrealized in this process. The promising alternative is fruitjuice concentration by reverse osmosis (RO) and nanofil-tration (NF) (Alvarez, Alvarez, & Riera, 1997; Braddock,Sadler, & Chen, 1991; Hayakawa, Igami, & Nakajima,2000; Medina & Garcia, 1998; Singh & Eipeson, 2000).Greater retention of volatile aroma compounds, bettercompound separation and lower processing temperatureswere realized by membrane process than by evaporationconcentration (Alvarez, Riera, Alvarez, & Coca, 1998;Alvarez, Riera, Alvarez, & Coca, 2001; Ferrarini, Versari,& Galassi, 2001; Garcia, Gozalvez, & Lora, 2002).

There are two principal models for the transport pro-cess: the solution–diffusion model and the capillary poremodel, both of which describe the reverse osmosis pro-cess. However, the solution–diffusion model is morewidely accepted. The water flux (Fw), and the salt flux(Fs), is linked to the pressure and concentration gradi-ents across the membrane (Jiao, Cassano, & Drioli,2004). From the solution–diffusion model, these termsare described by the equations: Fw = A (Dp � Dp) whereA is the water permeability constant of the membrane,Dp is the pressure differential across the membrane,and Dp is the osmotic pressure difference between theretentate and permeate sides of the membrane. The os-motic pressure is directly dependent on the salt concen-

tration of the process stream (White, Ditgens, &Laufenberg, 2002). The equations describing the saltflux: Fs = B (C1 � C2) where B is the salt permeabilityconstant, and C1 � C2 is the salt concentration differ-ence across the membrane. Thus, the water flux is pro-portional to applied pressure but the salt flux isindependent of the applied pressure (Bogliolio et al.,1996). The salt transport is primarily dependent uponthe concentration of dissolved solids on each side ofthe membrane.

Aroma compounds retention, higher in the retentate,was realized using the composite HR membranes forfruit juice concentration by reverse osmosis (Shen &Wiley, 1983; Chou, Wiley, & Schlimme, 1991; Dasgupta& Jayarama, 1996). Konja et al. reported that retentionof aroma compounds in the retentate was 88% in fruitjuice concentration by reverse osmosis using the mem-brane HR 98 PP (Konja & Clauss, 1991). Many authorsindicated successfully separation and retention of organ-ic components from water solutions during RO concen-tration using different composite membranes (Huang,Guo, Ohia, & Fang, 1998). Pozderovic et al. reportedthe possibility of reverse osmosis and composite mem-brane HR 98 PP application for apple juice aroma con-centration from evaporator condensate (Pozderovic &Moslavac, 1999). Investigation of model solution con-centration of individual esters and aldehydes by reverseosmosis using two different composite membranes wascarried out in this paper as a continuation of the abovementioned investigation. The aim of the research wasstudy of retention and recovery phenomenon and mech-anisms of ester and aldehyde model solutions on mem-branes during the reverse osmosis processes.

2. Materials and methods

2.1. Preparations of ester and aldehyde solutions

Different esters and aldehydes (purity level p.a.) bySigma, Aldrich and Fluka were used for preparation

A. Pozderovic et al. / Journal of Food Engineering 76 (2006) 387–395 389

of model solutions. Model solutions of esters: ethyl ace-tate, butyl acetate, hexyl acetate, amyl acetate, iso-amylacetate, iso-amyl propionate, ethyl butyrate, ethyl 2-methyl butyrate and aldehydes: hexanal, trans-2-hexenalwere prepared. All investigations of reverse osmosis con-centration were realized using water solutions of estersand aldehydes with the concentration of 0.01% v/v,0.05% v/v and 0.1% v/v. The concentration of esters inthe model solutions was 0.01% v/v, 0.05% v/v, 0.1%v/v and of aldehydes was 0.01% v/v, 0.05 %v/v. The bin-ary solutions consisted of the esters or aldehydes andwater. For the model solution deionised water wasmixed with one organic component (binary solution).

Solutions were prepared by using distilled water,cooled at 18 �C, followed by reverse osmosis concentra-tion. Five litres of feed solutions were prepared for theexperiment for all ester and aldehyde solutions of differ-ent concentrations.

2.2. RO equipment

All investigations of model solution concentration ofevery single ester and aldehyde were realized by RO lab-oratory equipment ‘‘Lab Unit M20’’ with plates andframes supplied by DDS (Dow Denmark SeparationSystems De Danske Sukkerfabrikker, Copenhagen,Denmark). High-pressure piston pump Rannie 16.50was used for solution supplying in the experiment. Con-centration of ester and aldehyde water solution was real-ized with composite membranes HR 95 PP and HR 98PP (high resistance polyamide supported on polysul-phone HR membrane) of the same firm, as was theequipment for reverse osmosis (Table 1).

Twelve membranes, total surface of 0.347 m2 were in-serted in a plate module of reverse osmosis plant. Sixmembranes type HR 95 PP and six membranes Hr 98PP were inserted in the module. All experiments werecarried out parallel, by both membranes at the sameworking conditions.

2.3. Concentration procedure

The concentration of each solution was carried outwith retentates recirculation up to the final volumereduction (VR = 3.33). During concentration, the reten-tates was cooled with refrigerating water in a heat chan-ger of the instrument module. Experiments were realized

Table 1Characteristics of the composite HR 95 PP and HR 98 PP membraneselements

Types ofcompositemembranes

Permeability% NaCl

Waterflux(L/m2h)

pH Temperature(�C)

Pressure(bar)

HR 95 PP <5 115–155 2–11 0–60 0–60HR 98 PP <2.5 105–145 2–11 0–60 0–60

with 0.1% v/v of ester model solution (ethyl acetate, bu-tyl acetate, ethyl butyrate) at four operating pressures of10, 20, 30, 40 bar by 0.05% v/v portion at 30 bar pres-sure and by 0.01% v/v portion at 30 and 40 bar pres-sures. The concentration of ester solutions (hexylacetate, ethyl 2-methyl butyrate, amyl acetate, iso-amylacetate, iso-amyl propionate) was realized by 0.01%v/v portion at 40 bar pressure. Aldehyde solutions con-centration by 0.01% v/v and 0.05% v/v portions werecarried out at 40 bar pressure. Permeate samples weretaken for every type of membrane during concentration,up to the final VR of 3.33. The permeate was taken indefined time intervals: at the pressure of 10 bar every10 min, 20 bar every 5 min, 30 bar every 3 min, 40 barevery 2 min. Total permeate of every membrane typewas obtained by mixing all permeates collected duringthe concentration. Retentate samples were taken duringthe process: an initial solution (after recirculation of2 min), an average sample (at VR = 1.6) and a final sam-ple at the end of the concentration process.

2.4. Aroma analysis

The concentration of every single ester and aldehydein the feed water solutions, in permeate and retentatewas determined by gas chromatography with massspectrometry (GC/MS) by a ‘‘head space’’ method. Ananalysis was carried out with gas chromatographyHewlett-Packard 5890 Series II with a mass detectorHewlett Packard 5971 A and a ‘‘head space’’ injectorHP 19395A. The ionisation of the samples was achievedat 70 eV under the SCAN mode. The mass range studiedwas from 10 to 250 m/z. The capillary column used inthis experiment was HP-20M (Carbowax 20M), (length50 m, capillary column diameter 0.2 mm film thicknessin the column stationary phase 0.2 lm). Helium (He)5.0 (purity 99.999%; Messer, Austria) was used as a car-rier gas. Work conditions at GC–MS were the following:the carrier gas flow rate was 50 mL/min split vent, purgevent 1 mL/min, head column pressure 1.379 bar, injec-tor temperature at 250 �C and detector was at 280 �C.The oven temperature at 50 or 70 �C (1 min) to 120 �C(10 �C/min), at 120 �C (1 min). Work conditions of a‘‘head space’’ injector were: bath temperature at 70 �C,valve loop temperature 75 �C, gas pressurization time2 min, injected time 2 min, volume of head space sample2 mL. GC–MS ester and aldehyde analysis was con-ducted for all experiments, after the permeate and reten-tate samples had been collected during and afterconcentration. Aroma compounds (esters and alde-hydes) were registered as chromatograph peaks thatcome out in specific times of retention from the capillarycolumn of the gas chromatograph.

Peak area, received at chromatogram, was propor-tional to the amount of aroma components (esters andaldehydes) in the analysed sample. Database of mass


spectars (WILEY 275.L) (library spectrum) of thehighest number of aroma components (chemical compo-sitions) was used for identification of esters and alde-hydes from the sample based on its received massspectar.

2.5. Data calculations

Chromatogram data obtained by gas chromatogra-phy presented peak areas (impulses) of individual estersand aldehydes as aroma components. To study the pro-cesses of concentration and organic components passage(OCP) of individual esters and aldehydes, the followingparameters were calculated using the equation:

VR ¼ V o

V r

ð1Þ

VR is the volume reduction; Vo is the feed volume (L)and Vr the retentate volume (L)

OCP ¼ Ap

Af

� 100 ð2Þ

OCP is the organic components passage (%); Ap is thepeak area in permeate and Af the peak area of feedsolution.

CFi ¼Ar

Af

� 100 ð3Þ

CFi is the concentration factor of component in reten-tate (%); Ar the peak area in retentate and Af is the peakarea of feed solution.

Microsoft Excel 2000 (Microsoft Corp.), the com-puter program, was used for data calculations.

Thermodynamic parameters: activity (a) and activitycoefficient (c) were calculated for two-component sys-tems that represent water model solutions of individualesters and aldehydes. Mathematical method for UNI-FAC model (Universal functional activity coefficient)was used for calculating the values of these parameters.These could be for example CH3, CH2, CH, CHO, CO,OH, CH3COO, COOH, NH.

The equation for activity coefficient calculation is:

log ci ¼ log cCi þ log cR

i ð4Þindexes C and R present combinatorial and residualcontribution. Combinatorial contribution relates to thedifference in size and shape of molecules and residualcontribution relates to energetic interactions.

Combinatorial contribution is expressed by:

log cCi ¼

XnKo

i¼1

xi ln/i

xiþ z

2

XnKo

i¼1

qi lnhi

/iþ li �

/i

xi

XnKo

j¼1

xjlj

ð5Þwith

li ¼ z=2ðri � qiÞ � ðri � 1Þ ð6Þ

Volume and area parameters are determined byequations

ri ¼XnGr

k¼1

mkiRk; qi ¼XnGr

k¼1

mkiQk ð7Þ

ri and qi are the molecular parameters (volume and sur-face area parameters for each molecular species) dependon the structure of pure components, size and moleculararea. Values of these parameters were taken from corre-sponding tables. Rk and Qk are the group volume andsurface area parameters.

Residual contribution to activity coefficient was cal-culated from the equation:

ln cRi ¼

XnGr

k¼1

mðiÞki ðln Ck � ln CðiÞk Þ ð8Þ

Here vðiÞk is the number of k groups present in species i

and CðiÞk is the residual contribution to the activity coef-ficient of group k in a pure fluid of species i molecules.

Parameter results at the temperature of 20 �C werecalculated by computer analysis using the programMathematica 4.2 (Wolfram Research, USA) for UNI-FAC model.

Osmotic pressure is a critically important property inreverse osmosis that presents the pressure necessary toreverse osmosis process and return to the initial condi-tion. The physical significance of osmotic pressure in re-verse osmosis is that it represents the minimum pressurethat must be applied to a feed solution in order to obtainany permeation of flux (Bouchard & Lebrun, 1999).

Osmotic pressure was traditionally calculated usingthe Van�t Hoff relationship for dilute solutions (Thorne,1992) using

P ¼ M � R � T ð9ÞThe Van�t Hoff model assumes that osmotic pressure

increases linearly with molar concentration of the solute.The solution osmotic pressure is the function of solutionconcentration and temperature (Heldman & Hartel,1997).

3. Results and discussion

Research data of the process pressure influence ondifferent esters portion in the permeate and retentates,in the concentration by reverse osmosis with the mem-branes HR 95 PP and HR 98 PP and with the feed solu-tion 0.1% v/v are shown in Figs. 1–3. The ethyl acetateand ethyl butyrate organic components passage (OCP)in the permeate was reduced by concentration solutionsof every single ester with the pressure increase using themembrane HR 95 PP (Fig. 1). The butyl acetate organiccomponents passage (OCP) in the permeate increasedwhen process pressure increased. Data in Fig. 2 showed

10

20

30

40

50

60

5 10 15 20 25 30 35Pressure (bar)

Org

anic

com

pone

nts

pass

age

(%)

ethyl acetate butyl acetateethyl butyrate

Fig. 1. The influence of pressure on the concentration of differentesters in permeate (membrane HR 95 PP, feed solution 0.1% v/v).

0

5

10

15

20

25

30

35

40

5 10 15 20 25 30 35 40 45Pressure (bar)

Org

anic

com

pone

nts

pass

age

(%)

ethyl acetatebutyl acetateethyl butyrate

Fig. 2. The influence of pressure on the concentration of differentesters in permeate (membrane HR 98 PP, feed solution 0.1% v/v).

100

110

120

130

140

150

160

170

180

190

5 10 15 20 25 30 35Pressure (bar)

Con

cent

ratio

n fa

ctor

of c

ompo

nent

in re

tent

ate

(%)

ethyl acetatebutyl acetateethyl butyrate

Fig. 3. The influence of pressure on the concentration of differentesters in retentate (feed solution 0.1% v/v, membranes HR 95 PP andHR 98 PP).


that the same phenomenon of portion decrease in thepermeate was observed in the concentration with themembrane HR 98 PP for ethyl acetate and butyl acetate.That phenomenon was not expressed that much forethyl butyrate. It was also noticed that values of estersorganic components passage (OCP) in the permeate

were lower with the solution concentration by the mem-brane HR 98 PP than HR 95 PP membrane. Concentra-tion factor of esters in the retentate increased withhigher-pressure application by esters concentration be-cause of membrane selectivity increase (Fig. 3). That re-sulted in greater retention of esters in the retentate thanin the permeate.

Calculated values of thermodynamics parameters,activity coefficient (c) and activity (a) for water modelsolutions of esters and aldehydes at 20 �C temperatureobtained by UNIFAC method, are given in Table 2.Data in that table showed that ester and aldehyde por-tion in solution, molecular mass and molecule structureaffected activity coefficient (c) and activity (a). Higherconcentration of esters and aldehydes in the water solu-tion caused an increase of activity and decrease of activ-ity coefficient. It was also observed that molecular massincrease, at the identical ester and aldehyde portion inthe solution, caused an increase of activity and activitycoefficient. Carelli and Sancho indicated that an increaseof molecular mass of esters and aldehydes in the watersolution and temperature increase resulted in their high-er activity coefficient (Carelli, Crapiste, & Lozano, 1991;Sancho, Rao, & Downing, 1997). Table 2 showed thatthe ester molecule structure affected thermodynamicparameters and because of that the n-form ester (byidentical portion) had lower activity and activity coeffi-cient than the iso-form.

Calculated values of osmotic pressure of ester andaldehyde solutions at 18 �C are shown in Table 3. Tableshowed that smaller molecular weight substances exertgreater osmotic pressure than larger molecules, andhigher concentrations give higher osmotic pressures.

In Figs. 4–8 are presented the research results ofmolecular mass and molecule structure effect on esterand aldehyde organic components passage (OCP) inthe permeate during RO concentration by the mem-branes HR 95 PP and HR 98 PP. Data in Fig. 4 showedthat ester organic components passage (OCP) increasedin the permeate during the ester concentration of acetategroup, using feed solution concentration of 0.01% v/vby 40 bar pressure and by both membrane application.It was observed in Fig. 4 that esters, ethyl acetate andbutyl acetate, had higher permeability through the mem-brane HR 95 PP (bigger portion of esters in the perme-ate) than through the membrane HR 98 PP. Esters, amylacetate and hexyl acetate, have the greater permeabilitythrough the membrane HR 98 PP. It was shown forboth membranes that the organic components passage(OCP) of esters in the permeate was greater and concen-tration factor in the retentate was lower when esters oflower molecular mass, ethyl acetate and butyl acetate,were concentrated (lower activity and activity coeffi-cient, higher osmotic pressure) compared to esters ofgreater molecular mass, amyl acetate and hexyl acetate,(greater activity and activity coefficient, lower osmotic

Table 2Calculated values of activity coefficient (c) and activity (a) for model solutions of ester and aldehyde at 20 �C with UNIFAC method

Concentration % (v/v) Activity coefficient (c) Activity (a)

Ester, aldehyde Water Ester, aldehyde Water

Ethyl acetate 0.01 10.1854 1.0000 0.001019 0.99990.05 10.1718 1.0000 0.005086 0.99950.1 10.1547 1.0000 0.010155 0.999002

Butyl acetate 0.01 13.7732 1.0000 0.001377 0.99990.05 13.7547 1.0000 0.006877 0.99950.1 13.7316 1.0000 0.013732 0.999002

Hexyl acetate 0.01 16.9945 1.0000 0.0016994 0.99990.05 16.9718 1.0000 0.0084858 0.99950.1 16.9435 1.0000 0.0169435 0.999002

Ethyl butyrate 0.01 18.7888 1.0000 0.001879 0.99990.05 18.7567 1.0000 0.009378 0.9995010.1 18.7168 1.0000 0.018717 0.999002

Iso-amyl propionate 0.01 23.1215 1.0000 0.0023121 0.99990.05 23.0825 1.0000 0.0115413 0.9995010.1 23.034 1.0000 0.023034 0.999002

Ethyl-2-methyl butyrate 0.01 21.0412 1.0000 0.0021041 0.99990.05 21.0055 1.0000 0.0105028 0.9995010.1 20.961 1.0000 0.020961 0.999002

Amyl acetate 0.01 15.4305 1.0000 0.0015430 0.99990.05 15.4098 1.0000 0.0077048 0.99950.1 15.3839 1.0000 0.0153839 0.999002

Iso-amyl acetate 0.01 15.4445 1.0000 0.0015444 0.99990.05 15.4238 1.0000 0.0077119 0.99950.1 15.398 1.0000 0.015398 0.999002

Hexanal 0.01 34.5312 1.0000 0.003453 0.99990.05 34.3301 1.0000 0.017165 0.999502

trans-2-Hexenal 0.01 11.055 1.0000 0.001106 0.99990.05 11.037 1.0000 0.005518 0.999501

Table 3Osmotic pressure of ester and aldehyde solutions at 18 �C

Concentration% (v/v)

Ethylacetate(kPa)

Butylacetate(kPa)

Hexylacetate(kPa)

Ethyl-2-methylbutyrate(kPa)

Amylacetate(kPa)

Iso-amylacetate(kPa)

Iso-amylpropionate(kPa)

Ethylbutyrate(kPa)

Hexanal(kPa)

trans-2-Hexenal(kPa)

0.01% 2.74 2.083 1.678 1.859 1.859 1.859 1.678 2.083 2.416 2.4660.05% 13.72 10.419 8.392 9.297 9.297 9.297 8.392 10.419 12.083 12.3310.1% 27.47 20.838 16.780 18.590 18.590 18.590 16.780 20.838


pressure). It was also shown for both membranes, thatpermeability of ethyl acetate was greater compared toother esters of acetate group when 0.01% v/v ethyl ace-tate solution (the lowest molecular mass) was conductedby 40 bar pressure. It was seen that molecular mass,activity and activity coefficient of esters affected on or-ganic components passage in the permeate, while osmo-tic pressure did not has any influence. Data in Figs. 5and 6 showed that the ester molecule structure affectedmore membrane permeability during concentration of0.01% v/v ester solution by 40 bar pressure than the es-ter molecular mass. The ester solution concentration of

the identical molecular mass (ethyl-2-methyl butyrate,amyl acetate, iso-amyl acetate) with the membranesHR 95 PP and HR 98 PP showed that ethyl 2-methylbutyrate had the smallest retention on the membrane(greater portion in the permeate and OCP) because ithad the most branched molecule and the smallest alco-hol radical in molecule structure. It was shown in bothmembrane concentration that iso-amyl acetate, ester ofiso-structural form (bigger activity and activity coeffi-cient), had lower retention on the membrane in theretentate and greater organic components passage(OCP) in the permeate as compared to amyl acetate con-

0

5

10

15

20

25

30

35

40

1 1.5 2 2.5 3 3.5Volume reduction

Org

anic

com

pone

nts

pass

age

(%)

ethyl acetate HR 95 PPethyl acetate HR 98 PPbutyl acetate HR 95 PPbutyl acetate HR 98 PP

amyl acetate HR 95 PPamyl acetate HR 98 PPhexyl acetate HR 95 PPhexyl acetate HR 98 PP

Fig. 4. The influence of molecular mass on different ester portions inpermeate during concentration (membranes HR 95 PP and HR 98 PP,feed solution 0.1% v/v, pressure 40 bar).

0

10

20

30

40

50

60

70


Org

anic

com

pone

nts

pass

age

(%)

ethyl butyrateethyl-2-methyl butyrateisoamyl propionate

isoamyl acetateamyl acetate

Fig. 5. The influence of molecular mass and molecule structure ondifferent ester portions in permeate during concentration (membraneHR 95 PP, feed solution 0.01% v/v, pressure 40 bar).

0

10

20

30

40

50

60

70


Org

anic

com

pone

nts

pass

age

(%)

ethyl butyrate

ethyl-2-methyl butyrate

isoamyl propionate

isoamyl acetate

amyl acetate

Fig. 6. The influence of molecular mass and molecule structure ondifferent ester portions in permeate during concentration (membraneHR 98 PP, feed solution 0.01% v/v, pressure 40 bar).

0

10

20

30

40

50

60

70

80

90

100


Org

anic

com

pone

nts

pass

age

(%)

hexanaltrans-2-hexenal

Fig. 7. The influence of the molecule structure on different aldehydeportions in permeate during concentration (membrane HR 95 PP, feedsolution 0.01% v/v, pressure 40 bar).

0

10

20

30

40

50

60

70

80

90


Org

anic

com

pone

nts

pass

age

(%)

hexanaltrans-2-hexenal

Fig. 8. The influence of the molecule structure on different aldehydeportions in permeate during concentration (membrane HR 98 PP, feedsolution 0.01% v/v, pressure 40 bar).


centration. Membrane HR 98 PP had greater permeabil-ity for these esters having, therefore, a higher portion ofesters in the permeate than the membrane HR 95 PP.Ethyl butyrate has a greater alcohol radical (smallermolecular mass) than ethyl-2-methyl butyrate and ithas been found that smaller organic components pas-sage (OCP) realised in permeate, in concentration byboth membranes. The greater concentration factor inthe retentate as well as smaller organic components pas-sage (OCP) in the permeate were received by iso-amylpropionate concentration, ester with the greatest molec-ular mass, and both membrane application.

Results of the molecule structure effect on the alde-hyde portion in the permeate during the concentrationof 0.01% v/v solution by 40 bar pressure with the mem-branes HR 95 PP and HR 98 PP were shown in Figs. 7and 8. The figures indicated, for both membrane con-centration of aldehyde solutions, bigger retention oftrans-2-hexenal (smaller activity and activity coefficient,higher osmotic pressure) in the retentate and lower in


the permeate than it was with hexanal (bigger activityand activity coefficient, lower osmotic pressure). Betterretention of trans-2-hexenal on the membrane is due todifferent molecule structure, i.e. double bond in the alde-hyde molecule; activity, activity coefficient and osmoticpressure did not have any influence.

At the beginning of the process, organic componentspassage (OCP) was 11.27% by concentrating 0.01% v/vsolution of trans-2-hexenal with the HR 95 PP mem-brane, while at the end of the process organic compo-nents passage (OCP) was 25.34%. Concentration withthe membrane HR 98 PP showed higher OCP (organiccomponents passage) values (from 14.49% to 29.65%).

In Table 4 is shown an influence of initial portion ofesters and aldehydes in binary system on organiccomponents passage (OCP) in the final permeate withmembrane HR 95 PP and 40 bar pressure. Organic com-ponents passage (OCP) in final permeate was insignifi-cantly smaller by greater initial portion of aldehydeand ester in binary solution (greater activity, smalleractivity coefficient, greater osmotic pressure).

Fig. 9 showed the effect of different initial portion ofesters on organic components passage (OCP) in the finalpermeate at both membrane applications. The organiccomponents passage (OCP) in the final permeate wasinsignificantly lower by greater initial portion and

Table 4Effect of initial portion of aldehyde (initial concentration) on organiccomponents passage (OCP) in final permeate with membrane HR 95PP at 40 bar

Compounds Concentration % (v/v) OCP (%)

Hexanal 0.01 77.250.05 63.74

trans-2-Hexenal 0.01 17.740.05 16.77

0

10

20

30

40

50

60

70

0 0.005 0.01 0.015 0.02

Activity

Org

anic

com

pone

nts

pass

age

(%)

Ethyl acetate HR 98Butyl acetate HR 98Ethyl butyrate HR 98Ethyl acetate HR 95Ethyl butyrate HR 95

0.01% 0.05%

0.1%

0.05%0.1%

0.05%0.1%

0.01%0.05%

0.1%

Fig. 9. The influence of initial portion and activity of ester solutionson portion in the final permeate (water solutions 0.01% v/v, 0.05% v/vand 0.1% v/v, both membranes, pressure 30 bar).

activity of esters in the solution. It was pointed out thatorganic components passage in the permeate was lowerat greater activity, osmotic pressure and greater portionof esters and aldehydes in the feed solution.

4. Conclusion

Ester and aldehyde water solutions can be concen-trated with the composite membranes HR 95 PP andHR 98 PP. Retention was greater on the membraneHR 98 PP in the retentate than on the membrane HR95 PP by concentration of the following ester water solu-tions: ethyl acetate, butyl acetate, ethyl butyrate, ethyl 2-methyl butyrate. Higher retention of hexyl acetate, amylacetate, iso-amyl acetate, hexanal and trans-2-hexenalwas on the membrane HR 95 PP. Activity and activitycoefficient of esters in water solutions affected theirretention in the retentate. Concentration factor washigher in the retentate, organic components passage(OCP) was lower in the permeate when ester and alde-hyde activity in feed solution was bigger. Greater esterand aldehyde portion in feed solution increased theiractivity (a) and osmotic pressure but decreased activitycoefficient (c). While concentration factor was higherin the retentate, organic components passage (OCP)was lower in the permeate when ester and aldehyde por-tion was bigger in feed solution (higher activity (a) andlower activity coefficient (c)). Ester concentration factorwas greater in the retentate, organic components pas-sage (OCP) was lower in the permeate by the concentrat-ing ester solution of the higher molecular mass in n-form(greater activity and activity coefficient, lower osmoticpressure) due to lower membrane permeability. An in-crease of molecular mass of esters and aldehydes in-creased their activity (a) and activity coefficient (c) anddecreased osmotic pressure in water solution. Ester con-centration of n-structural form, in case of both mem-brane applications, showed better membrane retentionin the retentate in relation to the iso-form. Ester iso-form had greater activity and activity coefficient in thewater solution. The alcohol radical sharp of ester mole-cule affected membrane retention during concentration.Ester with a smaller alcohol radical in the molecule hadhigher permeability through the membrane and higherportion in the permeate. The branched ester molecule(ethyl 2-methylbutyrat) had lower retention in the reten-tate. Retention was greater in the permeate by the con-centration of aldehyde solutions with the double bond inthe molecule (lower activity). Application of higher pro-cess pressure in ester and aldehyde concentration in-creased selectivity of the composite HR membraneshaving, therefore, better ester and aldehyde retentionin the retentate than in the permeate. Osmotic pressurewas not affect on esters and aldehydes retention onmembrane and in the retentate.


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Apple Juice Conc Using RO