FIELD OF INVENTION:
The present invention relates to a process of pectin separation/membrane clarification of
citrus fruit juice by advantageous application of the electric field assisted Ultra filtration or
electro-ultrafiltration system having favored variable trans-membrane pressure difference,
to effect significant cross-flow velocity and thereby achieving substantial improvement in
the filtration speed and time. The pectin, a complex polysaccharide, present in fruit juices,
carries negative charge which is higher at higher pH value and lower degree of
methoxylation and the invention is directed to method of clarification of citrus fruit juice
involving such charge carried by the gel forming pectin to benefit the clarification process.
In particular under the invention, a suitable electric field is provided to assist migration of
the pectin molecules away from the membrane surface leading to a reduction in gel layer
resistance and substantial increase in filtration rate and increased productivity of the
filtration process. Also, the removal of pectin by the present process increases the shelf life
of the clarified fruit juice and thus having wide application in allied industries.
BACKGROUND ART:
The conventional method for clarification of fruit juice includes the steps such as : (i)
Centrifugation, (ii) addition of fining agents like bentonite, gelatin, etc. for removal of haze,
(iii) removal of fining agents by coarse filtration using diatomaceous earth. Each batch
operations consume much of time and labor. The whole processing requires 30-36 hours
time.
Energy efficient membrane based separation technology is a novel and highly innovative
unit operation. These processes include reverse osmosis, ultrafiltration and microfiltration.
Off late, these processes are becoming attractive alternative to the conventional separation
processes like distillation, centrifugation, extraction etc. Membrane processes have found
wide applications in clarification of fruit juices, removal of products from fermentation
broths, desalination of brakish water , removal of dye from textile effluents etc.
Ultrafiltration and microfiltration processes have been investigated for clarification by
H.Yukawa, K. Shimura, A. Maniwa et al in "Cross-flow electro-ultrafiltration for colloidal
solution of protein"pournal of Chemical Engg.,Japan, 16(4)(1983)305]. Ultrafiltration is also
investigated for the clarification of juice from lemons, grapefruit, apple, papaya, pineapple
etc. In addition, ultrafiltration is used to prepare flavor and aroma concentrate as food
ingredients. The main bottleneck of such processes is the decline in permeate flux with time
due to concentration polarization and membrane fouling during operation. The presence of
2

high molecular weight pectin (molecular weight 30-100 KDa) in fruit juice is the main cause
of low productivity of clarified juice. During ultrafiltration, pectin and its derivatives form a
gel layer in the presence of Calcium ions or sugar and acid over the membrane surface
which offers extra resistance to the permeate flow.
Several studies have been attempted to predict the flux decline during ultrafiltration of fruit
juices. The most conventional models include gel-polarization model by V.S. Minnikanti, S.
Dasgupta and S.De in their publication titled "Prediction of masstransfer co-efficient with
suction for turbulent flow in cross-flow ultra filtration" [Journal of Membrane Science,
137,227] and boundary layer model by S.De and P.K. Bhattacharaya their publication in
"Flux prediction of Black Liquor in cross flow ultrafiltration using low and high rejecting
membranes" [ Journal of Membrane Science,109(1996),109]. A number of techniques have
been investigated to enhance the permeate flux. These techniques include-(i) change of
hydrodynamic condition in the flow channel, e.g. introduction of fluid particles or
intermittent jet in the flow chamber as reaveled in the publication titled "Basic transport
mechanism of ultrafiltration in presence of fluidized particles" by G.M. Rios, H. Rakotoarisoa
and B.T. de Fuente [ Journal of Membrane Science,34(1987)331], insertion of promoter in
the flow channel as dealt with in the article titled "Screw thread flow promoters:An
experimental study of ultrafiltration and microfiltration performance"[Journal of Membrane
Science 106(1995)269], gas sparging [Flux enhancement with gas sparging in downward
cross-flow ultrafiltration: performance and mechanism by F.Cui and K.I.T. Wright, Journal
of Membrane Science,117(1996)109], pulsatile flow as disclosed in "Improving permeating
flux by pulsed reverse osmosis" by TJ. Kennedy, R.L. Merson and B.J. Mc Coy, Chemical
Engg. Science, 29(1974)1927], combination of pulsatile flow with baffles such as disclosed
by J.A. Howell and S.M. Finnigan in their article "The effect of pulsed flow on ultrafiltration
fluxes in a baffled tubular membrane system", Desalination, 79(1990)47; (ii) modification
of membrane material, (iii) application of d.c. electric field etc.
The technique of electro-ultrafiltration is developed to reduce the concentration polarization
in the close vicinity of membrane by applying external d.c. electric fileld across the
membrane in case of filtration of charged particles. The direction of electric field is such
that electrically charged particles tend to move away from the membrane surface by
electrophoretic migration.
3

A number of excellent publications on electro-ultrafiltration have appeared in literature. A
simple mathematical model based on film theory for cross-flow electro-ultrafiltration under
gel polarization domain for kaolin clay suspension and oil-in-water emulsion is presented by
henry et al in the literature titled "A solid/liquid separation process based on cross-flow and
electrofiltration" by D. J. Henry, L.F. Lawler C.H.A. Quoch, AIChE J.23(6)(1977)851. Yukawa
et al have studied cross-electro ultrafiltration in a tubular module for gelatin solution [H.
Yukawa, K. Shimura, A. Maniwa in their literature titled "Cross-flow electro-ultrafiltration
for colloidal solution of protein" , J. Chem. Eng. Jpn., 16(4)(1983)305]. Mullon et al have
conducted experiments on prevention of protein and paint fouling using electric
field[C.Mullon, J.M. Radovich and B. Behnam in their literature titled "A semispherical model
for electro-ultrafiltration-diafiltration, Sep. Sci. Technol, 20(l)(1985)63]. Jagannath et
alhave reviewed in detail the electro kinetic method to control membrane fouling[S.N.
Jagannath H.S. Muralidhara in the article titled "Electrokinetics method to control membrane
fouling, Ind.Eng. Chem. Res, 35(1996)1133]. Mameri et al. have shown the impact of
electric field on fouling of BSA[ N.Mameri, S.M.oussedik, A.Khelifa, D. Bethocine,H. Ghrib
and H. Lounici in the literature titled "Electric field applied in the ultra-filtration process,
Desalination, 138(2001)291. The separation of suspended bentonite particles by forced-flow
electrophoresis is investigated by Moulik et al[S.P. Moulik, F.C. Cooper, M.Bier, forced-flow
Electrophoretic Filtration of clay Suspentions, J. Colloid Sci.,24(1967)427. However, to the
best of the prior knowledge in the related field, electro-ultrafiltration has not been used for
clarification of fruit juice.
Us patent no. 5064515(1991), US Patent no. 3945900(1976), US Patent no.
4758320(1988) etc. are all directed to process and apparatus for electrofiltration or electro
ultra-filtration for preventing filter fouling in cross flow filtration or for separation of solid
particles or macromolecules in solution by electrofiltration. Again the patent documents like
US4643902(1987), US6355284(2002), US6465026(2002) are directed to making sterile
and concentrated juice from fruits and vegetables and the like. The present invention is thus
having distinctly different direction in terms of inventive intent to apply electro ultrafiltration
for favored pectine separation for fruit juice clarification.
There had been therefore a need to develop a process for electric field assisted membrane
separation or electro-ultrafiltration of citrus fruit juices and, in particular, achieve faster
clarification involving separation of pectin and its derivative and thereby increasing the shelf
life of fruit juices.
4

OBJECTS OF THE INVENTION:
The basic object of the present invention is therefore directed to electrical field assisted
membrane separation/clarification of citrus fruit juice by advantageous separation of
negatively charged pectin and its derivatives.
A further object of the present invention is to achieve increased productivity by way of
faster filtration and enhanced throughput for the process of clarification of citrus fruit juice
employing preferred migration of charged pectin and its derivatives under a properly applied
electric field between two electrodes, across the permeate flux and the membrane.
A further object of the present process of electro ultra-filtration of fruit juices is to eliminate
the use of any fining agent such as gelatin, bentonite etc and also the use of diatomaceous
earth required for separation of the fining agents, and thus save loss of fruit juice yield lost
by absorption.
A still further object of the present invention is directed to a combination of optimum
process parameters to achieve the favored complete pectin removal and enhance the
productivity leading to nil pectin in the clarified juice from a level of wt % of pectin around
0.24 in the raw fruit juice.
A still further object of the present invention directed to a process and system for electro-
ultrafiltration adapted to increase the throughput by about 30% over the conventional zero
electric field permeate flux, with a juice yield in the range of 96 to 98% and with a
processing time of 8 to 10 hours, as compared to 30 to 36 hours in conventional juice
clarification.
A further object of the present invention process and system for electro ultra-filtration of
citrus fruit juices is by eliminating the pectin and its derivatives, the shelf life of the clarified
juice is enhanced.
A still further object of the present process and system for electro ultra-filtration of citrus
fruit juices, wherein membrane fouling is minimized and frequent cleaning and /or
5

replacement of the membrane can be avoided leading to an augmentation of the membrane
life.
Yet another object of the present invention is directed to provide clarified fruit juice
substantially free of pectin and with increased shelf-life of the clarified juice for wide scale
application of such process and provision of fruit juices in a form which would be storage
stable.
SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention there is provided a method of
separation of pectin during membrane clarification of fruit juice comprising:
subjecting the fruit juice to electric field assisted ultra filtration for separation of the
negatively charged gel forming pectin away from the membrane leading to reduction in gel
layer resistance in such membrane separation and substantial increase in filtration rate.
A further aspect of the present invention directed to said method of separation of pectin
during membrane clarification of fruit juice wherein the trans membrane pressure difference
is in the range of 220-500kPa, cross flow velocity is in the range of 0.09 m/s to 0.148m/s
and electric field applied is in the range of upto 400 V/m preferably 200 to 400 V/m for
enhanced separation of pectin.
A still further aspect of the present invention directed to a method of membrane clarification
of fruit juice comprising:
subjecting the fruit to juice extraction;
subjecting the extracted juice to enzymatic treatment; and
subjecting the enzyme treated juice to electric field assisted ultra filtration to thereby obtain
the clarified fruit juice.
A further aspect of the method of membrane clarification of fruit juice, according to the
present invention, comprising:
6

providing the fruit juice in a feed tank;
providing a cross -flow ultra filtration unit having the filtration membrane;
allowing the fruit juice to flow tangentially over the membrane surface with said membrane
supported on a cathode substrate;
an anode mounted in parallel position just above the ultra filtration channel;
applying an external electric field across said membrane surface whereby the said electric
field applies perpendicular to the flow direction such that the pectin molecules migrate away
from the membrane surface and the permeate generated free of any resistance from the
gel formable pectin is collected from the bottom of the unit while the retentate form the
unit is recycled to the feed tank.
Another aspect of the present invention is directed to said method of membrane clarification
of fruit juice wherein external electric field from regulated d.c. power supply is applied
across the membrane surface.
A still further aspect of the present invention is directed to a method of membrane
clarification of citrus fruit juice wherein the process parameters maintained such as trans
membrane pressure difference is in the range of 220-500 kPa , cross flow velocity is in the
range of 0.09 m/s to 0.148 m/s and the electric field is upto 400 V/m.
According to yet another aspect of said method of membrane clarification of citrus fruit juice
wherein the juice yield is in the range of 96-98%.
A still further aspect of the present invention is directed to a system for carrying out the
method of membrane clarification of fruit juice, comprising:
a feed tank for said fruit juice to be clarified;
a cross-flow electro-ultrafiltration unit operatively connected to said feed tank;
pump means to feed the juice from said tank to the electro-ultrafiltration unit;
7

regulated D.C. Power supply for applying electric field during the clarification process in said
electro-ultra filtration unit;
a permeate outlet at the bottom of said electro- ultra filtration unit and a retentate outlet at
the top of said electro- ultra filtration unit.
A further aspect of the present invention directed to said system comprising a by pass
control valve and supply to said feed tank is operatively connected to said juice supply line
from said feed to said
electro- ultra filtration unit; and
said retentate outlet is operatively connected to the feed tank via a flow control valve and a
rotameter.
A still further aspect of the present invention is directed to said system for carrying out the
method of membrane clarification of fruit juice wherein said cross flow electro-ultrafiltration
unit comprises:
a positive electrode preferably a Platinum coated Titanium sheet and a stainless steel
support as negative electrode with an intermediate membrane preferably polyethersulfone
membrane of cut off (MWCO) 50000, with preferably a gasket disposed there between said
membrane and said positive electrode , said positive and negative electrodes being
operatively connected to a DC power supply.
Importantly the above invention thus favors obtaining clarified fruit juice substantially free
of pectin and with improved shelf life.
The details of the invention, its objects and advantages are explained hereunder in greater
detail in relation to non-limiting exemplary illustrations in relation to the following
accompanying figures:
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: is the flow chart for conventional clarification process of fruit juice.
8

Figure 2: is the flow chart of eloctro-ultrafiltration of fruit juice according to the present
invention.
Figure 3: is the schematic block diagram of electro-ultrafiltration system, according to the
present invention.
Figure 4: is the illustration of the schematic diagram of the experimental cross-flow cell,
according to the present invention.
Figure 5:is the graphical presentation of variation of zeta potential with pectin concentration
at different sucrose contents at a pH range of 3.3 to 3.5.
Figure 6: is the illustration of the permeate flux profile of mosambi juice at a pressure of
360 Kpa and cross-flow velocity of 0.15m/s.
Figure 7: illustrates the graphical presentation of the variation of steady state permeate flux
with electric field at a cross flow velocity 0.118m/s.
Figure 8:illustrates the effect of pressure on permeate flux at a cross-flow velocity of 0.089
m/s.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS AND EXAMPLES:
As already described that the traditional fruit juice clarification process is a slow and low
productive one involving the steps like- (i) centrifugation,(ii) addition of fining agents like
bentonite, gelatin etc. for removal of haze,(Mi) removal of fining agents by coarse filtration
using diatomaceous earth. Each batch operations are time and labour consuming. The whole
process requires 30-36 hours which is quite lengthy indicative of low productivity. Attention
is now invited to the accompanying Figure 1, wherein the process steps along with some of
the principal parameter values are illustrated with the flow diagram for conventional fruit
juice clarification method.
9

The present invention is therefore basically directed to eliminating the limitations with
respect to the time and increasing productivity of the process by preferred application of
electrical field assisted pectin separation from the fruit juice without the requirement of the
addition of fining agent or their removal by using diatomaceous earth, and more importantly
by the favored separation of pectin and its derivatives because of their electronegativity,
separated by means of electro ultrafiltration system of the present invention. Focus of this
invention is rather directed to the enhancement of solvent flux with electric field that gets
adversely affected by the gel forming pectin layer on the membrane. Application of a
suitable electric field would lift the electrically charged pectin and move them away from the
membrane surface. So under the applied dc electric field gel layer formation of pectin is
restricted and hence filtration rate increases.
The pectin separation from the fruit juice has the added advantage of enhancing shelf life of
the clarified fruit juice. The accompanying Figure 2, illustrates the flow diagram for the
steps involved in said electro ultrafiltration of the present invention, alongwith the important
process parameter values used in such elctric field assisted membrane separation. The
preferred range of values for the parameters like the strength of the applied d.c. electric
field, trans-membrane pressure difference or the cross-flow velocity is so selected such as
to implement faster clarification of the fruit juice and desired removal of pectin and its
derivative directed to increase the productivity of the unit operation and reduce the
processing time substantially. The through put of the present system is increased by about
30% achieving an yield of 96 to 98% clarified juice within a batch processing time in the
range of 8 to 10 hours. Moreover, during electro-ultrafiltration, membrane fouling is
minimized and frequent cleaning and/ or replacement of the membrane can be avoided
leading to an augmentation of the membrane life.
In the process of clarification of citrus fruits, the fruit extracts contains Pectin, which is a
complex polysaccharide, composed of a rhamno-galacturonan backbone in which 1-4 linked
a-D- galacturonan chain are intercepted by the insertion of 1-2 linked a-L-rahmnopyranosyl
residue. One of the most important properties of pectin is that its chain carries negative
charge and its charge density is higher at higher pH and lower degree of methoxylation.
Pectin being negatively charged, application of external electric field during membrane
separation is advantageously applied in several ways. The present invention utilizes the
charged nature of pectin. A typical application of this concept is in clarification of fruit juice.
In citrus fruit, there are present in the extracts, lower molecular weight components like
10

sugar, acid, salt, flavor and aroma compounds on one hand and the high molecular weight
components like pectin and its derivatives, protein, spoilage microorganisms, on the other
hand. These higher molecular weight components, mainly pectin, causes decline in the
filtration rate and a consequent reduction in throughput of the system during operation.
Pectin and its derivatives are well known gel forming materials. In the present invention
invention, a suitable electric field has been applied to cause appreciable migration of the
pectin molecules away from the membrane leading to a reduction in gel layer resistance and
substantial increase in filtration rate.
During the electro ultrafiltration of fruit juices, the smaller components (which are
electrically neutral) preferentially permeate through membrane while the large species;
mainly pectin and its derivatives are retained. In fruit juice,typical concentration of pectic
substances is up to 1.0%. Pectins are considered to be a complex polysaccharide
composed of a rhamno-galacturonan backbone in which 1-4 linkeda-D- galacturonan chain
are interepted and bent at the intervals by the insertion of 1-2 linked a-L-
rahmnopyranosyl residue. Other sugar such as D-galactose, L-arabinose and D-xylose
are present as side chain. The carboxyl groups present in the pectin structure dissociates
in aqueous solution and gives the molecule electric charge and its charge density is pH
dependent at its natural pH, the application of external electric field during cross-flow
ultrafiltration of fruit juice is thus promising improvement in yield and productivity.
The present process for fruit juice clarification and the pectin separation employing electro
ultrafiltration is entirely different from the existing conventional process. The working or the
manner of implementation of the present invention has been experimentally verified. The
effect of operating conditions such as the pressure, cross flow velocity, external d.c. electric
field etc., on the permeate flux during electro-ultrafiltration are extensively studied. In the
present invention the operating pressures are chosen from among 220 KPa, 360 KPa and
500 Kpa; the cross flow velocities are selected from among 0.089 m/s, 0.118 m/s, 0.15 m/s
and the strength of the applied d.c. electric fields selected from among 0 V/m, 200 V/m,
300 V/m, and 400 V/m. All experiments are conducted at a temperature range of 32±2° C.
The schematic diagram of an embodiment of the system of the continuous cross flow
electro-ultrafiltration according to the present invention, is illustrated in the accompanying
Figure 3. The feed solution is pumped out from the feed tank(l) by means of a feed
pump(2), the flow rate being controlled by the by pass control valve (3) and allowed to flow
11

tangentially over the membrane surface through a thin channel of 37 cm in length, 3.6 cm
in width and 6.5 mm in height, inside the cross flow electro-ultrafiltration module(6)
through the feed inlet (4). Said cross flow electro-ultrafiltration module or the experimental
cross-flow cell of the present invention has been schematically illustrated in the
accompanying Figure 4; such a cell comprises a polyethersulfone membrane of molecular
weight cut-off (MWCO) 50000, obtained from M/S Permionics, Boroda (India), is placed on a
porous stainless steel support, which is used as cathode. The permeability is found to be
1x10-10 m/ (Pa s) using distilled water. The anode is platinum coated titanium sheet of size
having length 33.5 cm, width 3.4 cm and thickness 1.0 mm) obtained from Ti Anode
Fabricators, Chennai (India), mounted in parallel position just above the ultrafiltration
channel. Referring back to figure 3, an external electric field from regulated d.c. Power
supply(9) is applied across the membrane surface of the unit/module(6). The electric field
acts perpendicular to the flow direction. The retentate(5) is recycled to the feed tank
through a flow control valve(8). A rotameter (11) in the retentate line measures the flow
rate. The operating pressure inside the electro-ultrafiltration cell is maintained by operating
the bypass valve and is measured by a pressure gauge (10). The Permeate (7) is collected
from the bottom of the cell. The effective filtration area is about 133.2 cm2. The direction of
electric field is such that electrophoretic pectin molecules tend to migrate away from the
membrane surface. The electrophoretic and convective flux of pectin molecules are acting in
opposite direction and hence pectin gel layer thickness over the membrane surface is
reduced and consequently higher permeate flux is achieved.
The purpose of the application of electric field between the electrodes across the cross-flow
cell , is to reduce gel layer thickness of pectin as much as possible. During electric field
assisted ultra filtration the electric field strength (voltage applied per unit distance between
the electrode) is an important controlling parameter. The distance between two electrodes
can be varied. In the present experimental study it is maintained at 6.5 mm, which
corresponds to field strength of upto 400 V/m for an applied voltage upto 2.6 V. The
deposited gel thickness (in the order of microns) over the membrane surface decreases with
increasing applying electric field.
During such experimentation for the study of working embodiment of the present system of
electro ultrafiltration, a significant permeate flux enhancement is observed during cross flow
electro- ultrafiltration of Mosambi fruit juice compared with the permeate flux of
conventional ultrafiltration (without electric field). From the experiment it is observed that
12

at selective values of transmembrane pressure difference of 360 kPa and at a cross flow
velocity of 0.118 m/s, by applying dc electric field 400 V/m, the permeate flux increased
from 8.9 L/m2-hr (without electric field in conventional clarification) to 11.7 L/m2-hr. Similar
flux enhancement is also noticed at other operating pressures for the same cross flow
velocity and the resultant variation of the steady state permeate flux has been illustrated
graphically in the accompanying Figure 7.
Testing procedure for the claimed improvement in efficiency of the cross flow electro
ultrafiltration unit of the invention for favored faster fruit juice clarification and pectin
separation.
The following operational steps are involved for test evaluation the effects of electric field in
terms of an increase in permeate flux for cross flow electro-ultrafiltration acoording to the
present invention.
(i) Preparation of feed solution:
Mosambi fruit (sweet orange, citrus Sinensis (L.) Osbeck) juice is extracted by manually
operated 'screw type juice extractor'. For enzymatic treatment of mosambi juice, pectinase
from aspergillus nigar with activity 3.5-7.0 units/mg (protein Lowry) is used as obtained
from SIGMA-ALDRICH (USA). The enzymatic treatment of mosambi juice is done using an
enzyme concentration of 0.01% v/v at 44°C (in a constant temperature bath) for 120
minutes. At the end of the enzyme treatment, the suspension is heated to 90°c for 5 mints
in a water bath to inactivate the remaining enzyme in the sample. The decanted,
depectinized juice is used for electro-ultrafiltration.
(ii) Operating Conditions:
The effect of operating conditions (pressure, cross flow velocity, external d.c. electric field)
on the permeate flux during electro-ultrafiltration are extensively studied. Operating
pressures are chosen as 220 KPa, 360 KPa and 500 KPa. Cross flow velocities are selected
as 0.089 m/s, 0.118 m/s, 0.15 m/s and electric fields of 0 V/m, 200 V/m, 300 V/m, and
400 V/m. All experiments are conducted at 32±2°c.
13

(iii) Analytical methods used for interpretation:
Clarified juice samples are analyzed for color, clarity, total soluble solid, titrable acidity, pH,
viscosity, alcohol insoluble solid, and conductivity . Color is measured by absorbance at 420
nm and clarity by transmittance at 660 nm using Genesys2 Spectrophotometer. Total
soluble solid is measured by Refractometer, (Thermospectronic). Acidity of the sample is
determined by titration with 0.1(N) NaOH and expressed as % of anhydrous citric acid.
Viscosity is measured by Ostwald viscometer. Conductivity is measured by Autoranging
Conductivity meter, Toshniwal Instrument (India). Alcohol Insoluble Solid (AIS) is a
measure for pectin content in juice. AIS values are measured by boiling 20gm juice with
300 ml 80% alcohol solution & simmering for 30 mints. The filtered residue is washed with
80% alcohol solution. The residue is dried at 100°c for 2 hour and is expressed in % by
weight. Pectin in the juice is about 0.38 times of AIS value obtained by a calibration curve.
The zeta potential of pectin-sucrose mixture at pH 3.3-3.5 is measured by Zeta meter
(Malvern Zeta Sizernano).
(iv) Results , observations & Interpretations:
The zeta potential variation with solution composition is illustrated graphically in
accompanying Figure 5. It can be observed from the figure that the pectin-sucrose
agglomerates become more positive as the pectin concentration increases. Similarly, for
fixed pectin concentration and with decreasing sucrose concentration these agglomerates
become more negative. These agglomerates remains negative within the range of pectin
concentration normally found in fruit juice.
The permeate flux profile for different electric field is presented in accompanying Figure 6
for a transmembrane pressure (TMP) of 360 KPa and a cross flow velocity of 0.15 m/s.
There is a sharp decrease in permeate flux at the early stage of experiment which may be
due to absorption of colloidal species and build up of concentration polarization layer on the
membrane surface. Afterward, a smoother and slower decline towards the steady state is
observed. This is believed to be due to pore blocking and gel layer formation. Under applied
electric field, gel layer formation is restricted and hence a clear change in permeate flux
with smoother and slower zone is observed.
14

Accompanying Figure 7 represents the variation of permeate flux with electric field.
Application of electric field would potentially lift the electrically charged pectin molecules
from the membrane surface and carry then with the bulk flow. Thus gel layer formation is
restricted. With increasing pressure, driving force across the membrane increases. So
increased pressure and higher electric field both facilitate enhancement of permeate flux.
Hence maximum flux is observed at highest applied pressure and electric field. It may also
be observed from this figure that at low pressure, increase in permeate flux with electric
field is gradual. At higher pressure and at higher electric field, this increase is sharp. The
reason is, increased pressure leads to more severe concentration polarization and also
facilitates the convective flux through the membrane due to availability of enhanced driving
force. Electric field becomes more pronounced in higher concentration polarization and
hence greater permeate flux is achieved. From the experiment it is observed that at
selective values of transmembrane pressure difference of 360 kPa and at a cross flow
velocity of 0.118 m/s, by applying dc electric field 400 V/m, the permeate flux increased
from 8.9 L/m2-hr (without electric field in conventional clarification) to 11.7 L/m2-hr.
The accompanying Figure 8, shows the variation of steady state permeate flux with
transmembrane pressure. From this figure it may be observed that permeate flux increases
with pressure but at higher pressure this increase is gradual. At high TMP, the
macromolecules, mostly pectin, which are already on the membrane surface as well inside
the membrane pores get compressed more tightly. These densely packed gel of pectin form
a barrier across the membrane surface and reduces the flow of permeate flux, showing a
decreasing trend with increasing pressure. For operating pressures used in present
investigation, with increasing electric field, permeate flux increases as with electric field
densed gel layer becomes loose due to electrophoretic mobility of pectin molecule.
The properties of the raw juice and enzyme treated juice are summarized in the following
Table 1 and the properties of clarified juice at different operating conditions are compiled in
following Table 2, as obtained by the experimental application of the process according to
the present invention.
Table 1:
Fruit Color Clarity TSS Acidity as pH Density Viscosity Pecti Conductivity
juice (A420) (T660) (°Brix) Citric acid (Kg/m3) (Pa s) (wt%) m mho/cm
wt% xicr3 xl10+3
Actual 1.33 35.5 8.60 0.71 3.74 1.04 2.39 0.24 3.20
iuice
Enzyme 0 96 40 4 8 60 0 54 3 84 1 033 0 93 0 15 3 20
treated
iuice
15

Table 2:
Pressure Cross Electric Color Clarity TSS Acidity as pH Density Viscosity Pectin Conductivity
(KPa) flow field (A420) (T660) (°Brix) Citric acid (Kg/m3) (Pa-s) (wt %) m mho/cm
velocity (V/m) wt% xirr3 xlO+3
(m/s)
220 0.15 0 0.20 95.3 8.0 0.37 4.2 1.03 0.86 Nil. 3.2
220 0.15 200 0.20 95.5 8.0 0.37 4.2 1.03 0.86 Nil. 3.2
220 0.15 300 0.20 96.4 8.0 0.37 4.2 1.03 0.86 Nil 3.2
220 0.15 400 0.20 96.5 8.0 0.37 4.2 1.03 0.86 Nil 3.2
360 0.15 0 0.20 94.1 8.1 0.37 4.3 1.03 0.86 Nil. 3.2
360 0.15 200 0.19 94.9 8.1 0.37 4.3 1.03 0.86 Nil. 3.2
360 0.15 300 0.20 95.0 8.1 0.37 4.3 1.03 0.86 Nil 3.2
360 0.15 400 0.20 95.0 8.1 0.37 4.3 1.03 0.86 Nil 3.2
500 0.15 0 0.20 94.3 8.0 0.37 4.3 1.03 0.86 Nil 3.0
500 0.15 200 0.19 94.1 8.0 0.37 4.2 1.03 0.86 Nil 3.0
500 0.15 300 0.20 94.8 8.0 0.37 4.2 1.03 0.86 Nil 3.0
500 0.15 400 0.20 94.8 8.1 0.37 4.3 1.03 0.86 Nil 3.0

Thus following the above invention the process of clarification of fruit juice is simplified and
made faster and importantly does not require any fining agents. Advantageously, the
processing time could be substantially reduced to only about 8-10 hours with maximizing
the juice yield in the range of 96-98%.Moreover, the throughput of the system (permeate
flux) is increased approximately 30% by applying d.c electric field of 400 V/m compared to
zero electric field permeate flux. Furthermore, in absence of pectin, increase of shelf life of
the clarified juice is achieved. Also, during electro-ultrafiltration, membrane fouling is
minimized and frequent cleaning and/ or replacement of the membrane can be avoided
leading to an augmentation of the membrane life.
17

We Claim:
1. A method of separation of pectin during membrane clarification of fruit juice comprising:
subjecting the fruit juice to electric field assisted ultra filtration for separation of the
negatively charged gel forming pectin away from the membrane leading to reduction in gel
layer resistance in such membrane separation and substantial increase in filtration rate.
2. A method of separation of pectin during membrane clarification of fruit juice as claimed in
claim 1 wherein the trans membrane pressure difference is in the range of 220-500kPa,
cross flow velocity is in the range of 0.09 m/s to 0.148m/s and electric field applied is in the
range of upto 400 V/m preferably 200 to 400 V/m for enhanced separation of pectin.
3. A method of membrane clarification of fruit juice comprising:
subjecting the fruit to juice extraction;
subjecting the extracted juice to enzymatic treatment; and
subjecting the enzyme treated juice to electric field assisted ultra filtration to thereby
obtain the clarified fruit juice.
4. A method of membrane clarification of fruit juice comprising:
providing the fruit juice in a feed tank;
providing a cross -flow ultra filtration unit having the filtration membrane;
allowing the fruit juice to flow tangentially over the membrane surface with said
membrane supported on a cathode substrate;
an anode mounted in parallel position just above the ultra filtration channel;
applying an external electric field across said membrane surface whereby the said
electric field applies perpendicular to the flow direction such that the pectin
18

molecules migrate away from the membrane surface and the permeate generated
free of any resistance from the gel formable pectin is collected from the bottom of
the unit while the retentate form the unit is recycled to the feed tank.
5. A method as claimed in anyone of claims 1 to 4 wherein external electric field from
regulated d.c. power supply is applied across the membrane surface.
6. A method as claimed in anyone of claims 1 to 5 wherein trans membrane pressure
difference is in the range of 220-500 kPa , cross flow velocity is in the range of 0.09 m/s to
0.148 m/s and the electric field is upto 400 V/m.
7. A method as claimed in anyone of claims 1 to 6 wherein the juice yield is in the range of
96-98%.
8. A system for carrying out the method of membrane clarification of fruit juice as claimed
in anyone of claims 1 to 7 comprising:
a feed tank for said fruit juice to be clarified;
a cross-flow electro-ultrafiltration unit operatively connected to said feed tank;
pump means to feed the juice from said tank to the electro-ultrafiltration unit;
regulated d.c. Power supply for applying electric field during the clarification process
in said electro-ultra filtration unit;
a permeate outlet at the bottom of said electro- ultra filtration unit and a retentate
outlet at the top of said electro- ultra filtration unit.
9. A system as claimed in claim 8 comprising a by pass control valve and supply to said feed
tank is operatively connected to said juice supply line from said feed to said
electro- ultra filtration unit; and
said retentate outlet is operatively connected to the feed tank via a flow control valve and a
rota meter.
19

10. A system as claimed in anyone of claims 7 or 8 wherein said cross flow electro-
ultrafiltration unit comprises:
a positive electrode preferably a Platinum coated Titanium sheet and a stainless steel
support as negative electrode with an intermediate membrane preferably polyethersulfone
membrane of cut off (MWCO) 50000, with preferably a gasket disposed there between said
membrane and said positive electrode, said positive and negative electrodes being
operatively connected to a DC power supply.
11. Clarified fruit juice substantially free of pectin having higher shelf life obtained following
the method as claimed in anyone of claims 1 to 7.
12. A method of separation of pectin during membrane clarification of fruit juice and a
method and system for use in such separation of pectin from fruit juices substantially as
herein described and illustrated with reference to the accompanying figures and examples.
Dated this the 7th day of May, 2007.

20

The present invention relates to a process of pectin separation during membrane
clarification of citrus fruit juice by advantageous application of the electric field assisted
Ultra filtration system operated at variable trans-membrane pressure difference, to effect
significant cross-flow velocity and thereby achieving substantial improvement in the
filtration speed and time. The negatively charged pectin in fruit juices, higher at higher pH
value. Application of external electrical field during membrane separation in the present
invention advantageously utilizes the charged nature of pectin. Moreover, pectin and its
derivatives being gel forming materials, it has tendency to decrease the filtration rate and
the throughput of the filtration process. A suitable electric field utilized to assist migration of
the pectin molecules away from the membrane surface, reducing gel layer resistance and
consequent increase in productivity of the filtration process. The removal of pectin by the
present process increases the shelf life of the clarified fruit juice and thus having wide
application in allied industries.