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DESALINATION
ELSEVTER Desalination 148 (2002) 93-98
www.elsevier.com/locate/desal
Cold sterilization and clarification of pineapple juice by
tangential microfiltration
Lucia Carneiro, Iralla dos Santos Saa, Flhia dos Santos Gomesb,
Virginia Martins Mattab, Lourdes Maria Correa Cabralb*
Food Technology Department, UFRRJ, Rodovia BR465 Km7,
Seropedica, Brazil Tel./Fax +55 (21) 26821220; entails:
[email protected], [email protected]
hBrazilian Agricultural Research Corporation, Av. das Americas,
29501, Guaratiba, 23020-470 Rio de Janeiro, Brazil Tel. -1-55 (21)
24107435; Fax +55 (21) 24101090; emails: [email protected];
vmattaQctaa.embrapa.61;
[email protected]
Received 5 February 2002; accepted 25 March 2002
Abstract
Pineapple is a very appreciated tropical fruit due to its unique
aroma and flavour. Pineapple juice was cold sterilised and
clarified by crossflow microfiltration associated with an enzymatic
treatment. A tubular polyethersulfone 0.3 pm pore size membrane
with effective filtration area of 0.05 m* was used in the pilot
system. Ten experiments were carried out under the same operational
conditions, 25C and 100 kPa, in order to evaluate the cold
sterilisation and clarification of pineapple juice by
microfiltration. It was observed that the permeate flux did not
change significantly after fifteen minutes of processing time. It
was stabilised around 100 L/hm. The clarification process was
considered very efficient due to the great reduction of haze and
viscosity, and by showing no significant changes in pH, acidity,
sugar and soluble solid content of the juice. The permeate of the
process was collected in sterile bottles inside a laminar flow
station and kept under refrigeration (8C) for a period of 28 d. The
samples were submitted to microbiological evaluations in intervals
of seven days. The microbiological analysis of the microfiltered
pineapple juice showed that it was in agreement with the
requirements by the Brazilian Legislation for juices and
drinks.
Keywords: Pineapple; Microfiltration; Sterilization;
Clarification; Enzymatic treatment
*Corresponding author.
Presented at the International Congress on Membranes and
Membrane Processes (ICOM), Toulouse, France, July 7-12, 2002.
OOll-9164/02/$- See front matter 0 2002 Elsevier Science B.V.
All rights reserved PII: SO0 1 I-9 164(02)00659-8
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94 L. Carneiro et al. /Desalination 148 (2002) 93-98
1. Introduction
Pineapple is one of the most appreciated tropical fruit due to
its very attractive aroma and very nice flavour. The Smooth Cayenne
variety is known as one of the best for juice production. Its
chemical composition shows a good equilibrium between acid and
sugar: 4.50; 2.21; 1.45; 0.80 wt.% sucrose, fructose, glucose,
citric acid, respectively
111. Fruit juices world market is about US$ 5.0
billions/y, in which Brazil is responsible for 33%. Brazil is
the most important of exporter in the world, and exports 50% of the
total orange juice, besides of passion fruit, pineapple, banana and
acerola products [2].
There is, indeed, a crescent demand for fruit juices with the
original characteristics of the fresh fruits and free from chemical
additives. This results in the search of new technologies that are
able to improve the sensorial, nutritional and microbiological
quality of the fruit juices.
Since thermal processes largely affect the characteristics of
fruit juices, microfiltration can be an alternative to fruit juice
preservation and conservation, because it does not involve the use
of heat treatment. The advantages of micro- filtration in relation
to the thermal processes are the use of mild temperature and
pressure conditions, which maintain the nutritional quality and the
sensorial attributes of the products.
One of the disadvantages of microfiltration is the decline of
the permeate flux along the pro- cessing (fouling), caused by the
retention of some feed components on the membrane surface or in
membrane pores. During microfiltration of pulpy juices the fouling
is caused by pectins, tannins, proteins, starch, hemicellulose and
cellulose. Therefore, it is important to introduce actions to
minimise fouling, such as enzymatic hydrolysis prior to membrane
filtration.
The application of microfiltration process to fruit juices
produces two fractions: a clarified and sterile juice (permeate)
and a fibrous concentrated pulp one (retentate). The concentrated
pulp can
be pasteurised and added to the permeate sterile juice in order
to obtain the reconstituted juice [3].
Microfiltration is already applied in industrial scale for
fruits like apple, pear, grape, orange and lemon [4]. In Brazil,
there are few industries applying microfiltration to clarify apple,
acerola, lemon and orange juices [5].
In previous works, it was studied the influence of membrane pore
size and transmembrane pressure on the clarification of pineapple
juice [3,6,7]. It was verified that juice quality (Brix, pH, acidy,
total sugar, colour, haze) was independent of the applied
transmembrane pressure and the process used, microfiltration or
ultrafiltration. The investigated microfiltration membrane
presented the best permeate flux. So, the present work aimed to
study the use of the microfiltration for the stabilisation and
clarification of pineapple juice.
2. Material and methods
2. I. Material
Pineapple from the variety Smooth Cayenne was used as raw
material. The juice was obtained from the pressing of the fresh
fruits in a depulping machine with a sieve of 0.8 mm and it was
kept in a freezing chamber at -18C until its processing.
2.2. Enzymatic treatment
Before the microfiltration process, the pineapple juice was
submitted to an enzymatic treatment with 0.03% (v/v) of two
enzymatic preparations (Pectinex SP-L and Celuclast 1.5 L, from
Novo Nordisk), at 30C for 60 min. The enzymatic treatment reduces
the viscosity and the suspended solids (pulp) content of the juice,
and, consequently, decreases the fouling in the microfiltration
process. The hydrolysis was carried out in a stainless steel
mixture tank with controlled temperature and agitation. The
hydrolysis condition was defined in a previous work [3].
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L. Carneiro et al. /Desalination 148 (2002) 93-98 95
2.3. Microfiltration
A tubular polyethersulfone membrane from Koch Membrane Systems
with an effective filtration area of 0.05 m2 and 0.3 pm pore size
was used in the pilot system. The process conditions were feed
velocity of 6 m/s, temperature of 25C and applied transmembrane
pressure of lOOkPa. During the process, the permeate was continu-
ously collected and the retentate stream was re- circulated. The
process performance was evaluated by permeate flux behaviour. The
experimental design consisted of a set of ten microfiltration
experi- ments in the pilot unit under the same operational
conditions. After each process alkaline/acid/alkaline cleaning
steps were used to recover the water permeability of the membrane
(1800 L/hm2bar).
The volumetric concentration factor (VCF) is defined as the
initial volume divided by the retentate volume at any time. The
retentate volume was determined by the difference between the
initial feed and permeate volumes. All the processes were finished
when the concentration factor was equal to 2.
2.4. Analytical procedures
Samples from the feed, retentate and permeate were analysed in
relation to pH, titrable acidity, soluble and total solids content
[8]. Instrumental colour and haze evaluations were carried out in a
Hunter system [9]. Glucose, fructose and sucrose concentrations
were measured by HPLC [lo].
The permeated juice was collected in sterile bottles inside a
laminar flow station and kept under refrigeration for a period of
28 d. They were submitted to microbiological evaluations in inter-
vals of 7 d (total count, mould and yeast count, fecal and total
coliforms counts). The microbio- logical analyses were performed in
clarified juices following the methodology described in American
Public Health Association [ 111.
3. Results
An enzymatic treatment was associated with
microfiltration of pineapple juice to improve the filtration.
The treatment consisted of hydrolysing soluble polysaccharides,
which are responsible for the high viscosity of the juice, as well
as liquefying the non soluble polysaccharides such as non soluble
pectins, cellulose, hemicellulose and lignin from cell [12].
The enzymatic treatment did not result in significant
differences on the physical and chemical characteristics of the
single strength and hydrolysed juices. As it was expected, the
excep- tions were the viscosity and pulp content values. The
average reduction of the viscosity from the single strength juice
to the hydrolysed one was 29.6% and for the pulp content was
22.0%.
Table 1 shows the main physical and chemical characteristics of
the pineapple juice along all the steps of the processing: single
strength (juice), hydrolysed (feed), clarified (permeate) and
retentate.
Acidity, pH and soluble solids did not change during the
processing and presented average values of 0,80 w/w % citric acid,
3.7 and lO.OBrix, respectively. Glucose, fructose and sucrose con-
centrations were maintained constant along the process steps,
presenting average values of 5.4 w/w %, 2.4 w/w % and 2.2 w/w %,
respectively. As the sugar and acid concentrations remained
unchanged the microfiltered juice maintained the same flavour
characteristics of the single strength one.
It was verified an increase in the luminosity and a decrease in
the haze of the permeate juice when compared to the single strength
one (Table I). The pineapple juice became clearer and brighter.
It was also observed a reduction of the pulp content in the
hydrolysed juice (5.7 g/100 g) and the permeate (0.0 g/100 g) when
compared to the single strength juice (7.4 g/100 g). The
clarification process completely removed the suspended pulp in the
permeated juice, as it was already observed by Matta et al.
[2].
Fig. 1 shows the behaviour of the permeate flux during one of
the microfiltration processes. It could be separated in two steps.
First there was
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96 L. Carneiro et al. /Desalination 148 (2002) 93-98
Table 1 Average physical-and chemical characteristics of single
strength (juice), hydrolysed (feed), clarified (permeate) and
retentate pineapple juice during all the steps of microfiltration
processes
Parameters Juice Feed Permeate Retentate
Total solids content, w/w% 10.1 10.2 9. la,c 10.6
PH 3.6 3.6 3.6 3.6 Acidity, w/w % citric acid 0.8 0.8 0.8 0.8
Soluble solids, Brix 10.0 10.1 9.9 10.0 Viscosity, mPa.s 6.3 4.4b
1.1 10.4* Sucrose, w/w % 5.7 5.4 5.3 5.1 Glucose, w/w % 2.1 2.3 2.6
2.7 Fructose, w/w % 2.0 2.1 2.3 2.5 Pulp content, w/w % 7.4 5.7b
0.0 10.3* LUNTBR 16.8 17.2 97.gb 9.9 aHUNTER -0.6 -0.6 -3.8b 1.4 b
3 HUNTER 6.8 6.6 12.4b 6.2 Haze 97.2 97.3 3.3b 98.7
Averages at the same line with different letters are different
(p< 0,05, Tukey test)
J-UNTER - luminosity (0 = black and 100 = white)
aHNlER - (from -80 to zero = green, from zero to +lOO = red);
jb,,, - (from -100 to zero = blue, from zero to +70 = yellow)
15 min of process, and it was equal to 100 L/hm*.
01
0 30 60
Processing time (min)
90
The main factors that contribute to the flux decay are the
concentration polarisation, the pore blocking and the juice
viscosity increase due to the increase of the concentration factor.
The main disadvantage of microfiltration of pulpy juice is the
fouling on the membrane surface, which results in the flux decline
[12].
Fig. 1. Permeate flux during a microfiltration process of
pineapple juice.
an acute decay of the permeate flux followed by a period when
the flux decay was less pronounced tending to stabilisation. Other
authors like Itoua Gassaye et al. [ 131 who also studied the
clarification process of pineapple juice have described the same
behaviour.
The clarified juice presented a great reduction in the viscosity
value due to the removal of pulp and macromolecules from the single
strength juice. As observed in Table 1, the apparent viscosity
value of the microfiltered juice was 1.1 mPa.s. The clarified juice
presented the rheological characteristics of a Newtonian fluid
(Fig. 2). The same behaviour was verified by Hemandes et al. [ 141,
who studied orange juice ultrafiltration, and by Matta et al. [2]
during the investigation of acerola juice by microfiltration.
In the beginning of the microfiltration process The
characteristics of the permeated juice the permeate flux was around
232 L/hm*. After showed that microfiltration was effective for the
five minutes of processing, this parameter reduced commercial
sterilisation of the juice. The micro- 52%. The average permeate
flux stabilised after filtered pineapple juice presented
microbiological
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L. Carneiro et al. /Desalination 148 (2002) 93-98 97
0 500 IO00 1500 2000
Velocity gradient (s)
Acknowledgements
The authors wish to tank CNPq and FAPERJ for the financial
support of this project.
Fig. 2. Rheological behaviour of the clarified pineapple juice.
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during the storage period. These results indicate that
microfiltration can be used as an alternative process for fruit
juice conservation in substitution to the thermal
pasteurisation.
4. Conclusions
Pineapple juice was successfully clarified. Its haze changed
from 97.2 to 3.4 and the luminosity from 16.8 to 97.9. The
clarified product presented also commercial sterilisation grade,
which fulfils the requirements of microbiological safety. The
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