Concentration of Pulpy Pineapple Juice Using Osmotic Evaporation

Concentration of Pulpy Pineapple Juice Using Osmotic Evaporation

Chularat Hongvaleerat 1, Lourdes M.C. Cabral 2, Manuel Dornier 3, Max Reynes 3, and
Suwayd Ningsanond 4

1Department of Food Science, Burapha University, Saensook, Amphoe Muang, Chonburi 20131, Thailand
2Embrapa Food Technology, Food Engineering Department, Rio de Janeiro, Brazil.
3CIRAD UPR24, ENSIA-SIARC, TA 50PS/4, F-34398 Montpellier cedex 5, France
4School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology,
Nakhon Ratchasima 30000, Thailand – Email: suwayd@yahoo.com

Abstract
Performance of pineapple juice concentration using osmotic evaporation (OE) was
evaluated. The juice concentration was carried out in a laboratory unit composed of two
independent circuits, pineapple juice and brine. Calcium chloride solution was used as
brine. The flat module containing one PTFE/PP membrane was used for concentrating
single strength pineapple juice. Two optimal operating parameters: juice temperature at
35°C and brine velocity at 2 ms-1 were employed. The evaporation flux ranged from 5.5
kg h-1 m-2 to 8.5 kg h-1 m-2 allowed concentration of the juice up to 55 °Brix. The OE
process showed a potential in industrial scale concentration of pulpy pineapple juice.
Keywords: Pulpy pineapple juice, Osmotic evaporation, Evaporation flux

Introduction
Pineapple juice is industrially concentrated by multi-stage vacuum evaporation.
However, this heating process can affect the product quality, reducing consumer
preference. The process often leads to a considerable loss of aroma compounds (Rao and
Vitali, 1999) as shown in the work of Lin et al. (2002) that an average of 95 % of total
volatile compounds in grapefruit juice was lost during thermal concentration. The color
change of pineapple juice as affected by heat treatment was also investigated
(Rattanathanalerk et al., 2005). In addition, the process requires high energy during
concentration.
Osmotic evaporation (OE), a membrane process, can be carried out at friendly
temperature and pressure, presenting a great potential to be applied in fruit juice
concentration. The advantages of OE process over traditional evaporation include higher
retention of product quality, less energy consumption and ability to reach the
concentration of standard products produced by evaporation at low temperature (less than
40 °C). Osmotic evaporation is based on the use of a porous hydrophobic membrane to
separate two solutions of different concentrations, juice and osmotic agent solution. The
driving force for mass transfer is the different in water activity across the membrane.
There have been a number of publications on pulpy fruit juice concentration by OE. These
have covered passion fruit juice (Vaillant et al., 2001), pineapple juice (Shaw et al., 2002),
camu-camu juice (Rodrigues et al., 2004), melon juice (Vaillant et al., 2005), and orange
juice (Cisse et al., 2005; Alves and Coelhoso, 2006). Nonetheless, all studies were
accomplished by the clarification of the juices before the concentration step. This work,
therefore, evaluate the performance of OE in concentration of pulpy pineapple juice
without prior clarification.

Materials and methods
1. Pineapple juice
Single strength pasteurised pineapple juice (SJ) were bought from a commercial
source (Montpellier, France).
2. Osmotic agent

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Calcium chloride (CASO HT food grade pearls 93-97 %, Solvay S.A., Belgium)
was used as osmotic agent for osmotic evaporation. The concentration of calcium chloride
solution ranged approximately from 5.5 to 6.0 M (aw values: 0.329-0.435). The aw values
of calcium chloride solution at 5.5 M evaluated in this experiment were between 0.412
and 0.427 at 25 °C.
3. Osmotic evaporation (OE) unit: lab scale.
The flat membrane module contained one flat sheet membrane made of thin porous
polytetrafluoroethylene (PTFE) supported by PP net (TF-200, Pall-Gelman, USA) with
0.2 µm average pore diameter, 80% porosity and a thickness of 178 µm. The effective area
of the membrane was 0.005 m2.
4. Juice concentration
The OE unit consisted of two independent circuits, one for the juice and the
other for the brine. The 2-L juice tank was placed on a digital balance connected to a
computer where the decay of the juice mass was continuously registered allowing further
evaporation flux calculations. The 5-L brine tank was used to maintain a nearly constant
salt concentration during the experiments. The volume of the brine was about three times
higher than that of the juice to prevent a significant dilution with consequent decrease of
the driving force (Courel et al., 2000; Alves and Coelhoso, 2004). Both solutions were
circulated co-currently in the membrane module using two independent gear pumps. The
temperatures of the juice and the brine were controlled by two thermostated circulating
water systems. Rotameters were used to give the circulation flow rate in each circuit.
Manometers were used to indicate the pressure difference between both circuits (TMP).
By adjusting the circulation flow rates of the circuits, the TMP was maintained at a
negligible level (< 0.1 bar) to prevent liquid transfer through the pores. Juice conductivity
was measured before and after each concentration trial to ensure integrity and
hydrophobicity and to detect possible salt leakage through the membrane. For brine
regeneration, CaCl2 pearls were added to the diluted brine until the desired concentration
(as aw value) was obtained. After each trial, the OE unit was cleaned by deionized water
for the brine tank and by sodium hydroxide (1 %: 50 ml of 30.5 % NaOH) and then
deionized water (until reach pH 7) for a juice tank.
Single strength pasteurized pineapple juice (SJ) at six concentration levels (10, 20,
30, 40, 50, 60 °Brix) were concentrated to simulate the concentration process. These
experiments were carried out using pre-concentrated juices (20-60 °C) obtained by
thermal concentration (T = 35-40 °C, time = 2.5-3 h). The following operating conditions
were used regarding the results of Courel et al. (2000).
Juice temperature: 35 °C
Brine temperature: 20 °C
Juice velocity: 1.25 ms-1
Brine velocity: 2.00 ms-1
Transmembrane pressure (TMP): < 0.1 bar
The effect of the juice concentration on the flux behavior was also investigated.
The SJ was concentrated under steady-state condition. Due to the small effective area of
the membrane surface compared with the large volume of juice in the OE system,
concentration did not change during 3 h of operation. Six different concentrations (10-60
°Brix) were evaluated.
The parameters to be optimized were juice temperature (20 and 35 °C) and brine
velocity (2-3 ms-1). At the optimal conditions chosen, the SJ was concentrated in two
stages (days) of 8 h each. Since the membrane surface of the flat module was small, the
juice was concentrated in a closed concentration loop continuously fed by the raw juice. In
the first stage, each juice was concentrated by OE from the initial Brix to reach about 30

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°Brix. In the second stage, the juice previously concentrated by thermal evaporation at
around 30 °Brix was concentrated by OE up to 55 °Brix. The pre-concentrated juice by
thermal evaporation was needed because the amount of the concentrated juice obtained
from the first stage of OE was not enough for the subsequent stage of concentration.
5. Analytical procedures
Total soluble solids (TSS) were measured with handy rafractometers (ATAGO,
Japan). Water activity of both juice and brine were measured in an aw-meter Aqualab
(Series 3 Model TE, Decagon Devices, Inc., USA) with a mean error of 0.05. The
equipment was daily calibrated using salt standard solutions with water activity of 0.243,
0.504 and 0.760. Conductivity values of juice and brine were performed in the HANNA
Instruments conductivity equipment, calibrated with standard solutions ranging from 1413
to 12880 µS/cm. The juice conductivity was always monitored during concentration to
ensure membrane integrity and hydrophobicity, and to detect possible salt leakage through
the membrane. The brine conductivity was evaluated regarding dilution problems during
the concentration trials but it was verified that the CaCl2 concentration did not change
more then 10% after an eight hour experiment.

Results and Discussion
1. Effect of juice concentration on flux behavior

In order to understand the effect of juice concentration on flux behavior, the
experiments under steady state (constant feed concentration) were investigated (Fig.1). As
expected, the evaporation flux decreased when the juice concentration increased. These
observations agree with the results obtained for sucrose solutions at a laboratory scale
(Courel et al., 2000) and for passion fruit juice at a pilot scale (Vaillant et al., 2001). The
flux value of SSJ was 8.6 kg h-1 m-2 at 12.5 °Brix, 4.7 kg h-1 m-2 at 40 °Brix, and 3.7 kg h-1
m-2 at 60 °Brix. The decrease in evaporation flux was about 20 %, comparing
concentration at 40 and 60 °Brix. This behavior justifies the interest of a multi-step
process. As can be seen in the work of Vaillant et al. (2001), the two-stage process
provided the higher evaporation flux compared to the one-stage process (0.62 vs. 0.50 kg
h-1 m-2) in the concentration of clarified passion fruit juice. As pointed out by Jiao et al.
(2004) this phenomenon can be attributed to the reduction of the driving force due to the
decrease of the vapor pressure of the juice and to the exponential increase of the viscosity
of the juice. Since many of liquid foods (juices and beverages) contain hydrophilic solutes
such as sugars, polysaccharides and proteins; when these solutes are concentrated to high
levels, solutions of irregular high viscosity are obtained. As such a solution passes through
a membrane-bounded channel, solution near the membrane surface becomes increasingly
concentrated until a critical concentration is reached, resulting in a very rapid increase of
viscosity with further water removal. The flow rate of this viscous layer along the channel
is progressively declined because it is bounded by flowing liquid of lower solute
concentration and viscosity. Finally, stagnation of fluid in the boundary layer occurs to the
membrane surface on the feed side and the less viscous and more diluted solution extends
to the center of the channel with increasing velocity. Reduction of the solution residence
time in the membrane module and blockage of the access of the solution to the membrane
surface lead to a decrease in water transport (Hogan et al., 1998).

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Single strength juice
10
)
-
2
9

m
-
1
8

h
7
g

(
k
6
x
5

f
l
u
n
4
t
i
o
3
r
a
o
p
2
a
v
1
E
0
0
10
20
30
40
50
60
70
Total soluble solids (°Brix)

Fig.1. Evolution of evaporation flux during the concentration of pulpy pineapple juice by
osmotic evaporation
2. Juice concentration
Concentration of SJ at six concentration levels (10-60 °Brix) by OE was
determined to simulate the concentration process. The evaporation fluxes obtained from
the juice of 10-60 °Brix using the flat module were between 8.6 and 3.7 kg h-1 m-2.
The increase of temperature enhanced the evaporation fluxes about two times from
4.5 to 8.6 kg h-1 m-2 for the lower brine velocity and from 3.9 to 9.1 kg h-1 m-2 for the
higher brine velocity, whereas the increase of velocity slightly improved the evaporation
flux (5%). The results are in accordance with the findings of Courel et al. (2000). They
found that the vapor flux increased two times for a temperature different of 12 °C between
the two circulating solutions, water and brine, whereas the evolution of the evaporation
flux was hardly noticeable at brine velocity of 1.7-2.2 ms-1 since the role of concentration
polarization becomes negligible due to strong sheer stress along the concentration size of
the membrane. The increase of flux with temperature was mainly due to the increase in
driving force (Sheng et al., 1991; Mengual et al., 1993; Courel et al., 2000; Vaillant et al.,
2001; Alves and Coelhoso, 2002). Higher temperatures give more kinetic energy to the
water vapor molecules and reduce the viscosity of feed stream causing an increase in mass
transfer coefficient. Therefore, the optimum conditions for further study of OE were the
juice temperature at 35 ºC and the brine velocity of 2 ms-1.

The OE allowed the concentration of the pasteurized juice from 12.5 °Brix to 28
°Brix at the first stage and from 33 to 55 °Brix at the second stage. The average
evaporation fluxes during these trials ranged from 8.5-5.5 kg h-1 m-2. These values were
lower than those (12 to 9 kg h-1 m-2) obtained by Rodridges et al. (2004) that the same
membrane module and similar operating conditions were used but the juice (camu-camu)
was in the clarified form and contained lower initial total soluble solids (6.6 vs. 11 °Brix).
With different membrane and module (PP hollow fibers), the flux values obtained in this
experiment were much higher than those (0.5-0.7 kg h-1 m-2) obtained with other clarified
juices, melon, orange, and passion fruit (Cisse et al., 2005; Vaillant et al., 2001; Vaillant et
al., 2005).
The evaporation flux decreased during the processing time (Fig.2). In general, the
flux decay during membrane filtration is attributed to the concentration polarization and
fouling phenomena due to solute retention on the membrane surface. However, in the case
of osmotic evaporation this decay could be related to the concentration of the juice itself,

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resulting in the increase of the juice viscosity and consequently the increase of the
resistance to mass transfer in the liquid phase and also to a decrease in the driving force,
the water activity difference between both sides of the membrane (Alves et al., 2004).

Single strength juice
16
)
-
2
12.5 to 28°Brix
14

m
-
1
33 to 55°Brix
12

h
g
10

(
k
x
8

f
l
u
n
6
t
i
o
r
a
4
o
p
a
2
v
E
0
0
2
4
6
8
Processing time (h)

Fig.2. Evolution of the evaporation flux during the concentration of single strength
pineapple juice by osmotic evaporation.

Conclusion

The concentration of the single strength pineapple juice could easily reach 55
°Brix using osmotic evaporation. This technique indicated a potential to concentrate the
pineapple juice without the need of prior clarification.

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