Biblid: 1821-4487 (2015) 19; 5; p 245-248
UDK: 582.661
Original Scientific Paper
Originalni naučni rad
THE EFFECT OF CALCIUM SULPHATE, ANIONIC AND CATIONIC
POLYELECTROLYTE IN PHASE OF SUGAR BEET JUICE PURIFICATION
UTICAJ KALCIJUM SULFATA, ANJONSKIH I KATJONSKIH
POLIELEKTROLITA U FAZI ČIŠĆENJA SOKA ŠEĆERNE REPE
Tatjana KULJANIN*, Biljana LONČAR*, Milica NIĆETIN*, Vladimir FILIPOVIĆ*,
Violeta KNEŽEVIĆ*, Rada JEVTIC-MUČIBABIĆ**
* University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia
** University of Novi Sad, Institute for Food Technology, 21000 Novi Sad, Bulevar cara Lazara 1, Serbia
e-mail: [email protected]
ABSTRACT
Compounds with di- and trivalent cations as well as cationic and anionic polyelectrolytes could be used for purification of raw
sugar beet juice.
The new purification method based on the application of CaSO4, cationic and anionic polyelectrolytes are presented. Studies
were performed with 9 different concentrations of CaSO4 (50-450 g/dm3) with the addition of anionic or cationic polyacrylamide (3
mg/dm3). Two pectins were isolated from fresh sugar beet pulp. The efficiency of pectin precipitation was monitored by measuring the
zeta potential.
The highest efficiency of purification was noticed by applying cation polyelectrolyte and CaSO4: 280-320 g/dm3. These quantities
are significantly lower than the average amount of CaO used in the conventional purification process (about 9 g/g pectin of juice).
The practical application of this research in sugar industry would reduce the cost of removal of pectin and other undesirable
compounds from sugar beet juice while protecting the environment.
Key words: pectin, sugar beet juice, CaSO4, cationic, anionic, polyelectrolyte, zeta potential.
REZIME
Čišćenjem sirovog soka šećerne repe se uklanjaju nesaharozne materije, prvenstveno pektini. Za ovu svrhu, dosad je najčešće
korišćen CaO u obliku Ca(OH)2. Međutim, afinitet vezivanja kalcijumovih jona iz CaO je relativno mali. Taloženje pektina bi se
mogla izvoditi postupkom razelektrisanja primenom jedinjenja sa dvo- i trovalentnim katjonima kao i katjonskim polielektrolitima.
Takođe, taloženje pektina bi se moglo izvoditi i mehanizmom međučestičnog vezivanja (efekat premošćavanja) primenom anjonskih
polielektrolita.
U ovom radu, predstavljen je novi metod čišćenja soka šećerne repe baziran na primeni CaSO4 kao i katjonskih i anjonskih
polielektrolita. Iz sveže pulpe šećerne repe izolovana su dva pektinska preparata. CaSO4 je u vidu precipitanta dodat u 100 cm3
rastvora pektina (0,1% mas.). Ispitivanja su izvedena sa 9 različitih koncentracija CaSO4 (50-450 g/dm3) uz dodavanje anjonskog i
katjonskog polielektrolita (poliakrilamid, PAM) koncentracije 3 mg/dm3. Efikasnost taloženja pektina je praćena merenjem zeta
potencijala pektinskih rastvora.
Optimalne količine precipitanta CaSO4, bez upotrebe polielektrolita su bile u intervalu: 410 – 440 g/dm3. Nakon upotrebe
anjonskog polielektrolita, optimalna količina CaSO4 se smanjila na vrednosti: 360-390 g/dm3. Najveća efikasnost čišćenja pektinskih
rastvora postignuta je upotrebom katjonskog polielektrolita (koncentracija 3 mg/dm3). Zeta potencijal je, u ovom slučaju, dostigao
nultu vrednost pri najmanjoj količini CaSO4: 280-320 g/dm3. Ove količine su znatno manje od prosečne količine CaO utrošene u
klasičnom postupku čišćenja soka šećerne repe (oko 9 g/g pektina u soku).
Praktičnom primenom ovog istraživanja u industriji šećera, smanjili bi se troškovi uklanjanja pektina i drugih nepoželjnih
jedinjenja iz soka šećerne repe uz očuvanje životne sredine.
Ključne reči: pektini, sok šećerne repe, CaSO4, katjonski, anjonski, polielektroliti, zeta potencijal.
INTRODUCTION
Charge neutralization plays a major role in undesirable
macromolecules removal in water treatment (Hilal et al., 2008;
Duan and Gregory, 2003). Precipitation of pectins in sugar beet
juice can be also performed by charge neutralization. It is known
that the colloidal particles in the solution surrounded by an
electric double layer that is composed of a stationary and diffuse
layer. The potential at the interface between these layers is easily
measurable size and it is known as zeta potential. The key to
effective removal of pectins from sugar beet juice is reduction of
the zeta potential. Carboxylic acid groups can take a part in the
complexation of divalent and trivalent cations which leads to
discharging negative charge on the surface of the pectin and
Journal on Processing and Energy in Agriculture 19 (2015) 5
decrease the value of zeta potential (Wiedemer et al., 2000;
Dronet et al., 1996). Once the charge is eliminated, no repulsive
forces exist and the conditions for effective coagulation and
precipitation of pectin will be achieved (Koper, 2007; Schneider
et al., 2011).
Another mechanism that causes the coagulation and
precipitation of the macromolecules is interparticle bridging.
Interparticle bridging occurs using high molecular weight
polyelectrolytes where colloids are adsorbed into the polymers
branches or share ions directly to form ionic bridges.
Polyelectrolytes which have a preponderance of negatively
charged sites are called anionic (eg. partially hydrolysed
polyacrylamide). Anionic polyelectrolytes have to have a large
molecular weight (minimum of 106 kg / kmol) to obtain a high
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Kuljanin, Tatjana et al. / The Effect of Calc. Sulphate, Anionic and Cationic Polyelectrolyte in Phase of Sugar Beet Juice Purification
enough kinetic energy to overcome the energy barrier between
the negatively charged particles (Baraniak and Walerianczyk,
2003; Hilal et al., 2008). Polyelectrolytes with positive sites are
called cationic (eg. acrylamide polymer or copolymer). Earlier
studies in application of polyelectrolytes with compounds such
as alum and ferric chloride were related to purification of waste
water (Baraniak and Walerianczyk, 2003; Pattabi et al., 2000).
Cationic and anionic polyelectrolytes have been claimed to
enhance the flocculation in sugar cane juice processing (Doherty
et al., 2003). In the article of Loseva, 1990, the classic cleaning
process of raw sugar beet juice by lime using anionic flocculants
based on polyacrylamide was studied. Industrial research has
confirmed the technological and economic feasibility of this
procedure. Also, anionic polyelectrolyte (Magnafloc LT-25)
proved to be very efficient for precipitation and separation of
proteins from crop (Baraniak et al., 2009). In the papers of
Nasser et al., 2013 and Theng, 2012, were studied the cationic
polyacrylamides in papermaking and clay-cationic polymer
complexes. Sargent et al., 1998 and Carlson and Samaraweera,
2009, were studied the use of cationic polyelectrolytes in sugar
beet juice clarification according to conventional method.
Industrial trials confirmed the technological and economic
justification of this method. Investigation performed in previous
works (Kuljanin et al., 2014; Kuljanin et al., 2015), suggest that
cationic polyelectrolyte used in combination with CaSO4 is more
efficient in pectin precipitation than commonly used CaO in
sugar beet juice processing.
In this study, new sugar beet juice purification method based
on the application of CaSO4 and anionic polyelectrolytes are
presented. The aim of this study was to compare effects of
anionic with cationic polyelectrolytes in combination with
CaSO4, on the efficiency of pectin separation from sugar beet
juice.
MATERIAL AND METHOD
calculated using equivalents of free (modified method of Deuel)
and esterified carboxy groups (method of Shultz) (Poel et al.,
1998).
The molecular weight pectin preparation was determined by
the experimental method of Kar and Arslan (Kar and Arslan,
1999). The refractometric determination of dry matter pectin
solution was carried out by a refractometer of type Abbe,
manufacturer Carl Zeiss. The turbidity of the solution (τ) was
measured on the spectrophotometer of type SPEKOL 202
manufacturers "Iskra", Kranj. The mean molecular weight,
according to this method was calculated from the analytical
expressions and the mean value was read from the graph
(Kuljanin, 2008; equations 25, 26 and figure 19).
In the experiment, nine different CaSO4 concentrations
within the interval from 50 to 450 mg/dm3were prepared. Thus
prepared solutions were added to 50 cm3 of 0.1 % (w/w) pectin
solutions. The pH of solutions with CaSO4 was regulated with
pH METER IskraMA5740. All measurements were performed at
pH = 7. The solutions were stirred for 30 min on a high-speed
magnetic stirrer (TEHNICA, Železniki, MM-520) (500 rpm).
Then, the solutions were slowly manually stirred by a glass rod
in 50 cm3 Erlenmeyer flask for 5 min and left to rest another 5
min. Zeta potential of clear part of the solution was measured.
In the second phase of the experiment, the anionic or cationic
polyelectrolyte (MAGNAFLOC LT-27; MAGNAFLOC LT-24)
was added. The starting solution was prepared by dissolving 0.5
g of cationic or anionic polyelectrolyte in 100 cm3 of distilled
water and left overnight at room temperature to swell. Operating
solutions were prepared by separation of 10 cm3 of starting
solutions and dilution into distilled water up to 100 cm3. From
that solution 0.3 cm3 (polyelectrolyte concentration 3 mg/dm3)
was taken by pipetting and added to 50 cm3 pectin solution with
CaSO4 (Kuljanin, 2008). Zeta potential of clear part of the
solution was measured. It was determined by electrophoretic
method using a commercial apparatus ZETA-METER ZM 77
(Riddick, 1975). Measurements with anionic and cationic
polyelectrolyte were performed under the same conditions. A
method for preparing of solutions and measurement procedure
was presented in the paper of Kuljanin et al., 2014.
Pectin preparations were extracted from pressed sugar-beet
slices (Beta vulgaris L. ssp. vulgaris var. Altissima Doell)
obtained during the industrial processing of sugar beet (factory
Žabalj, Serbia). The metal salt CaSO4 in crystal hydrate form
(CaSO4 x 2H2O) (manufacturer's "Zorka Pharma", Šabac) was
RESULTS AND DISCUSSION
used for preparation of the studied solutions. The purity of salt
Due to differences in the conditions of extraction, the
was 99.0 % w/w.
obtained pectin preparations had a different composition and
Magnafloc LT27 is an anionic polyelectrolyte – copolymer
of sodium acrylate and acrylamide production of "Low Moor," degree of esterification (Table 1).
Bradford, England (molecular weight of
Table 1. Physical-chemical properties of pectin preparations
linear polymer, 106 – 7 106 g/mol).
Equivalent Equivalent of Content of
Degree of Mean molar
Magnafloc
LT24
is
a
cationic Type of Solid content of free COOH ester. COOH galacturonic esterification mass MWsr
pectin SC (g/100g)
groups X 105 groups Y 105 acid (%)
DE
(kg/kmol)
polyacrylamide (PAM) - vinyl monomer
and cationic acrylamide copolymer [P1
81.55
16.83
19.74
63.45
53.98
64 500
CH2-CH(CONH2)]n, production of "Low
P2
80.35
24.58
16.05
72.24
39.50
87 720
Moor," Bradford, England (molecular
The content of galacturonic acid in the tested preparations is
weight of linear polymer, 5 106 – 1,5 107 g/mol). The solid
in accordance with the mean content of pectin found in raw
content of polyelectrolyte: ≥ 90 %, ion degree: 30 % - 80 %.
Pectin preparations were isolated by extraction in acidic sugar beet juices from diffuser reported in literature (Šušić et al.,
condition by standard laboratory procedure AOAC (2000). 1980; Poel et al., 1998). Degree of esterification depends on the
Pectin preparation P1 was extracted at: pH = 1, t = 85 °C, τ = 2.5 biological origin of raw material, sugar beet ripeness, extraction
conditions and procedure (Levigne et al., 2002). In the tested
h. Pectin preparation P2 was extracted at: pH = 3.5, t = 85 °C, τ
pectin preparations it corresponds to the mean value of the
= 2.5 h. The extraction was performed as in our previous work
degree of esterification in sugar beet raw juice (Levigne et al.,
(Kuljanin et al., 2014). The dry matter content was determined
2002; Poel et al., 1998). In the experiments, the used
gravimetrically by drying the samples within 12 hours at 105 °C
concentration of the polyelectrolytes (MAGNAFLOC LT27;
(Kuljanin et al., 2015). The purity of pectin preparations is MAGNAFLOC LT24) was 3 mg/dm3, since this concentration
determined by the content of galacturonic acid. Titration method have proved to be the most favourable in the previous study with
was applied (Walter, 1991). Degree of esterification was
the same type cationic polyelectrolyte (Kuljanin et al., 2014).
246
Journal on Processing and Energy in Agriculture 19 (2015) 5
Kuljanin, Tatjana et al. / The Effect of Calc. Sulphate, Anionic and Cationic Polyelectrolyte in Phase of Sugar Beet Juice Purification
Zeta potential (mV)
Zeta potential (mV)
Table 2 is used in calculation the optimum values of pure
Influence of CaSO4 amount to change the zeta potential of
CaSO4 and CaSO4 with the addition of anionic and cationic
pectin solutions without the addition of polyelectrolyte and with
polyelectrolyte (concentration 3 mg/dm3) for each of the pectin
anionic and cationic polyelectrolytes at 3 mg/dm3 concentration
solution in order to obtain zero zeta potential. Without the
is shown in Figures 1 and 2. Influence of cationic
polyelectrolyte on the change of zeta potential of
Table 2. Optimal concentration of pure CaSO4 and CaSO4 with anionic and
pectin solutions using the same type of
cationic
polyelectrolyte
polyelectrolyte (concentrations: 1, 3 and 5
3
Pectin preparations P1
mg/dm ) was studied in previous works
Zero zeta potential (0 mV)
and P2
(Kuljanin et al., 2014; Kuljanin et al., 2015). On
P1
P2
the Figures 1 and 2, it is marked by a line with
with precipitants:
mg/dm3 mg/gp mg/dm3 mg/gp
the squares (–■–). Change the sign of zeta
CaSO4 without polyelectrolyte
440
680
410
618
potential indicates the charge inversion on the
CaSO4 + 3 mg dm-3 anionic polyelectrolyte
390
610
360
545
surface of the pectin particles. Charge inversion
was observed within the whole series of tested
CaSO4 + 3 mg dm-3 cationic polyelectrolyte
320
504
280
425
CaSO4 concentrations (Figures 1 and 2).
addition of polyelectrolyte, the amount of CaSO4 for
10
achieving zero zeta potential was the largest (440 and
Pectin solution without
410 mg/dm3 for P1 and P2, respectively). This is
polyelectrolyte
explained by a simple charge neutralization mechanism
Pectin solution with 3 mg/dm33
5
cationic polyelectrolyte
as well as the specific adsorption of Ca2+ ions
3
Pectin solution with 3 mg/dm3
(complexation with COO- groups of pectin
anionic polyelectrolyte
macromolecules). With the application of a anionic
0
50
100
150
200
250
300
350
400
450 polyelectrolyte, the amount of CaSO4 is necessary to
bring to zero zeta potential values was reduced for 50
-5
mg/dm3 (Table 2). The effect of anionic polyelectrolyte
can be explained through the phenomenon of charge
inversion. The phenomenon of charge inversion where
-10
changes in the sign of the zeta potential (»-« to »+«),
has not been yet sufficiently clarified from the physicalchemical point of view (Schneider et al., 2011). In
-15
addition to the charge neutralization in small areas on
the surface of pectin macromolecules, also probably
-20
came up to the inversion charge. This allows the
electrostatic interaction of negatively charged surface
active groups of the anionic polyelectrolyte to these
-25
areas on the surface of pectin macromolecules. Due to
3
Concentration of CaSO4 (mg/dm )
high length of the anionic polymer, after the
Fig. 1. The effect of the CaSO4 concentration without
electrostatic interaction, there is a well-known effect of
polyelectrolyte and with cationic and anionic polyelectrolyte
crosslinking molecules in solid and easy separable
on the change of Zeta potential: pectin type P1
flocks. Using the anionic polyelectrolyte with
polyacrylamide composition, an increase in the number
of H - bond between the amide groups polyacrylamide
10
Pectin solution without
compounds and OH - sites on the surface of pectin
polyelectroyte
macromolecules occurs, created after the addition of
3
Pectin solution with 3 mg/dm3
5
Ca2+ ions from CaSO4. This increases the interaction
cation polyelectrolyte
and dehydration of pectin macromolecules and
Pectin solution with 3 mg/dm33
anionic polyelectrolyte
improves the sedimentation properties of pectin
0
solution. This means that the anionic polyelectrolytes
50
100
150
200
250
300
350
400
450
can improve the removal of pectin from sugar beet
juice. With the addition of a cationic polyelectrolyte,
-5
the amount of CaSO4 is necessary to bring to zero zeta
potential was the lowest and reduced in the interval of
-10
120 up to 130 mg/dm3 (Kuljanin et al., 2014; Kuljanin
et al., 2015). This means that the cationic
polyelectrolyte can function as both coagulant (through
-15
charge neutralization) and flocculants (through
interparticle bridging) of pectin solutions. Cationic
polyelectrolytes act via complexation–flocculation
-20
mechanism. Such a process is of potential interest for
the removal of pectin during sugar beet juice
-25
clarification. In this study the anionic polyelectrolyte
(MAGNAFLOC LT-27) had a lower effect of a cationic
Concentration of CaSO4 (mg/dm3)
polyelectrolyte (MAGNAFLOC LT-24), under the
same experiment conditions. This can be explained by
Fig. 2. The effect of the CaSO4 concentration without
the smaller molecular weight of used anionic
polyelectrolyte and with cationic and anionic polyelectrolyte on
polyelectrolyte (MWsr = 4 x 106 g/mol) relative to the
the change of Zeta potential: pectin type P2
Journal on Processing and Energy in Agriculture 19 (2015) 5
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Kuljanin, Tatjana et al. / The Effect of Calc. Sulphate, Anionic and Cationic Polyelectrolyte in Phase of Sugar Beet Juice Purification
cationic (MWsr = 107 g/mol) which leads to weaker effect of
crosslinking chains of polygalacturonic acid (mechanism
interparticle bridging). Better results of pectin removal from
sugar beet juice could be obtained by using an anionic
polyelectrolyte higher molecular weight and a higher degree of
anionic charge. It seems that zeta potential reaches zero most
promptly when using pectin P2. The pectin preparation P2
showed better cation-binding characteristics in relation to the
pectin P1. This is understandable, since the pectin P2, has a
higher content of galacturonic acid (72.24 %) and a lower degree
of esterification (39.50). Also, due to higher molar mass of this
type of pectin (heavy chain length of polygalacturonic acid) and
higher density of charges on the pectin macromolecule surfaces
(larger number of free COO- groups), stronger is the effect of
inter-particle bridging. With proper dosing of CaSO4 and with
the addition of anionic or high molar mass cationic
polyelectrolyte (concentration of 3 mg/dm3), with control of zeta
potential, the consumption of precipitant could be reduced.
Compared with classical process where is approximately used 9
g CaO per g of pectin, the amount of precipitant CaSO4 (in the
form of pure salt or salt with anionic or cationic electrolyte) was
significantly lower, ranging in the interval of 425 – 680 mg per g
pectin. With this, significant economic effect would be achieved
because the consumption of CaSO4 was 13 - 21 times lower
compared to the consumption of conventional coagulant CaO.
CONCLUSION
The influence of CaSO4, anionic and cationic polyelectrolyte
on zeta potential of sugar beet pectin solution has been
investigated. Cationic polyelectrolyte (MAGNAFLOC LT-24) in
combination with CaSO4, produced better charge neutralization
and inter-particle bridging of pectin macromolecules in
comparison with anionic polyelectrolyte (MAGNAFLOC LT27). The consumption of CaSO4 (in the form of pure salt or salt
with anionic or cationic electrolyte) was about 13 - 21 times
lower compared to the consumption of conventional coagulant
CaO. The practical application of this research would reduce the
cost of removal of pectin from sugar beet juice which would
have a special practical significance for the sugar industry.
ACKNOWLEDGMENT: This research is part of the project
supported by the Ministry of Education, Science and
Technological Development of the Republic of Serbia, Project
TR - 31055.
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Received: 4.3.2015.
Accepted: 24.11.2015.
Journal on Processing and Energy in Agriculture 19 (2015) 5