Food Hydrocolloids 35 (2014) 115e121
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Food Hydrocolloids
journal homepage: www.elsevier.com/locate/foodhyd
Dissolution behaviors of waxy maize amylopectin in aqueous-DMSO
solutions containing NaCl and CaCl2
Ju Hun Lee a, SangGuan You b, Dong-Keon Kweon c, Hyun-Jung Chung d, Seung-Taik Lim a, *
a
Graduate School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, South Korea
Department of Marine Food Science and Technology, Kangnung-Wonju National University, Gangneung, Gangwon 210-702, South Korea
c
Kolon Life Science Inc., Yongin 446-797, South Korea
d
Division of Food and Nutrition, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 500-757, South Korea
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 January 2013
Accepted 7 May 2013
Dissolution behavior and molecular conformation of waxy maize amylopectin in aqueous DMSO solutions containing different amounts of water and salts (NaCl or CaCl2 up to 0.2 M) were characterized
using multi-angle laser light scattering (MALLS; micro-batch mode) and dynamic light scattering (DLS)
detectors. The solubility of amylopectin decreased and the molecular size measured increased when the
water content in the DMSO increased, indicating that amylopectin chains tended to be less dissociated or
aggregate by the excess amount of water. The amylopectin in aqueous DMSO solutions (10e50% water)
had a spherical shape with a regular star structure, but the individual amylopectin chains were not
affected by water content. Minor addition of salts facilitated the dissolution of amylopectin in aqueous
DMSO solutions, possibly due to water cluster formation by the salt ions. However, a minute presence of
salts (0.01 and 0.05 M) could induce the chain association even in 90% DMSO solution.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Amylopectin
Waxy maize
DMSO
Conformation
Light-scattering
Salts
1. Introduction
Amylopectin, a branched and high-molecular weight starch
molecule, has a tendency to aggregate in aqueous solutions through
its inter-chain hydrogen bonds. For an accurate analysis of amylopectin structure, thus, a complete dissolution in solvent is required.
Inaccurately high molar mass may result from the incomplete
dissolution, whereas artifact molar mass reduction may also result
from chain degradation induced during physical treatments for
dissolution and chromatographic separation (Han & Lim, 2004;
Yokoyama, Renner-Nantz, & Shoemaker, 1998). Various chemicals
such as alkali, urea, and dimethyl sulfoxide (DMSO) have been
suggested to disrupt the hydrogen bonds between starch chains for
their complete dissolution. Aqueous DMSO solutions, in particular,
have been widely used to dissolve starch molecules, because a
minor presence of water in DMSO could enhance the dissolution of
starch (Jackson, 1991; Leach & Schoch, 1962). Since starch is a hydrophilic polymer, its dissolution behavior is influenced by the
ionic characteristics of solution (Jane, 1993; Lee, Han, & Lim, 2009;
Lii & Lee, 1993). Molecular conformation of starch may be changed
* Corresponding author. Tel.: þ82 2 3290 3435; fax: þ82 2 921 0557.
E-mail address: [email protected] (S.-T. Lim).
0268-005X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.foodhyd.2013.05.003
by the presence of salts, as a result from the change in the ionic
property of solution. However, the function of salts and their effects
on starch dissolution and chain structure in aqueous DMSO solutions have not been fully understood.
Chain structure of amylopectin varies according to its botanical
source (Hizukuri, 1985). Molar size and branch-chain length of
amylopectin affect the dissolution behavior of waxy starches
(Kalichevsky, Orford, & Ring, 1990). Rheological properties of the
pastes and gels prepared with waxy starches were also dependent
on the size and chain composition of the constituting amylopectin
molecules (Chung, Han, Yoo, Seib, & Lim, 2008). Numerous researches have been performed for characterizing the chain structure of amylopectin. Weight-average molecular weights (Mw) of
waxy maize amylopectin varied from 53 106 (Bello-Perez,
Paredes-Lopez, Roger, & Colonna, 1996) to 76.9 106 g/mol
(Aberle, Burchard, Vorwery, & Radosta, 1994) when static light
scattering detectors were used for the analyses. Waxy maize
amylopectin dispersed in 100 C 90% aqueous-DMSO solution with
a mechanical stirring (1 h) at room temperature showed its average
molar mass and radius of gyration (Rg) to be 560 106 g/mol and
349 nm, respectively (Millard, Wolf, Dintzis, & Willett, 1999). Yang
et al. (2006) reported that the Mw, Rg and hydrodynamic radius (Rh)
of waxy maize amylopectin dissolved in 0.5 M NaOH solution with
extensive stirring (18 h) at 25 C were 530 106 g/mol, 276 nm and
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J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
282 nm, respectively. However, those values for the same amylopectin dissolved in a 90% aqueous DMSO solution were much
smaller: 150 106 g/mol, 238 nm and 190 nm, respectively. Yoo &
Jane (2002) reported the Mw and Rg of the amylopectin dissolved in
water to be 830 106 g/mol and 372 nm, respectively. Han, Lim,
and Lim (2005) dissolved waxy maize starch in 90% DMSO by
heating in a boiling water-bath for 1 h and stirring for 8 h at room
temperature, and reported 254 106 g/mol for Mw using a sizeexclusion chromatography connected to multi-angle laser light
scattering (MALLS) and refractive index (RI) detectors, and
274 106 g/mol using a micro-batch MALLS detector. Those molar
size values for waxy maize amylopectin obtained from the analyses
using light scattering detectors vary in a wide range. One of the
major reasons for the discrepancy is the dissolution processes
different in the solutions and physical treatments.
Light scattering analysis has been extensively used for assessing
the size and conformation of various polymers in solution. Structural characteristics of starch such as Mw and Rg can be determined
in the absence of reference compounds because the parameters to
explain the structural feature of starch are theoretically obtained
from a static light scattering (SLS) system. On the other hand, the Rh
measured using a dynamic light scattering (DLS) detector can
complement the SLS data and be used to understand the aggregation behavior of starch in dilute solutions. Callaghan, Lelievre,
and Lewis (1987) reported that wheat amylopectin in DMSO solutions existed as an oblate ellipsoid conformation, whereas the
molecules dispersed in water aggregated to yield a more spherical
shape. Lelievre, Lewis, and Marsden (1986) introduced the amylopectin in DMSO has a flat-sheet or disc-like structure based on the
sedimentation- and diffusion-coefficient data. The conformation of
amylose in aqueous solutions was reported to be random coil, and
more or less extended in KOH or DMSO solutions (Nakanishi,
Norisuye, Teramoto, & Kitamura, 1993). The transitional conformation of amylose from helix to random coil was observed
with increasing the water content (w50%) in DMSO (Cheetham, &
Tao, 1997).
In the present study, effects of water and salts (NaCl and CaCl2)
present in DMSO solution on the dissolution behavior and chain
conformation of waxy maize amylopectin were investigated using
MALLS and DLS detectors.
2. Materials and methods
2.1. Materials
Waxy maize starch was obtained from Samyang Genex Company (Seoul, Korea). Sodium chloride and calcium chloride (ACS
reagent grade) were purchased from Sigma Chemical Co. (St. Louis,
MO, USA). Dimethyl sulfoxide (DMSO, 99.9%, HPLC and spectroscopic grade) was supplied by Honeywell Int. Inc. (Muskegon, MI,
USA). Amylopectin in waxy maize starch was purified in DMSO and
ethanol solutions. The starch (1 g, dry solids) was dispersed in 90%
(v/v) aqueous DMSO solution (100 ml) with a mild stirring using a
magnetic stirrer in a boiling water-bath for 1 h, and then stirred at
room temperature for 24 h. Absolute ethanol (300 ml each for three
times) and then acetone (300 ml, once) were used to precipitate
and wash the amylopectin. The purified amylopectin was then
dried in a convection oven at 30 C.
2.2. Micro-batch MALLS & DLS analyses
Purified amylopectin (10 mg, dry solids) was wetted with
ethanol (0.1 ml) and then dissolved in an aqueous DMSO solution
(50, 70, or 90% DMSO, 5 ml) with magnetic stirring in a boiling
water-bath for 1 h, and then filtered through a
Polytetrafluoroethylene (PTFE) membrane (5 mm pore size). The
filtrate solutions were then mildly stirred at 200 rpm for 8 h at
room temperature. The amylopectin in the filtrate (dissolved
amylopectin) was quantified by the phenol-sulfuric acid method
(Dubois, Gilles, Hamilton, Rebers, & Smith, 1956) to measure the
degree of dissolution. A stock solution for analyses was prepared by
diluting the amylopectin-DMSO solution to 0.2% solids. The
amylopectin sample solutions were prepared by diluting the stock
solution with aqueous DMSO solution to a concentration range of
0.5e1.33 g/L, and the ASTRA 4.90.07 program (Wyatt Technology,
Santa Barbara, CA) was used for data analyses. The molecular
characteristics were determined by MALLS with a micro-batch
mode using a syringe pump (0.4 ml/min). The values of the Mw
and Rg were determined by the Zimm method (Berry formalism)
using a multi angle laser light scattering (MALLS) detector based on
the RayleigheGanseDebye theory for the light scattering technique
(Wyatt Technology, Santa Barbara, CA).
The Rh and size distribution were measured using a DLS detector
(Dynapro Titan, Wyatt Technology, Santa Barbara, CA) which was
set at 1.4785 and 2.14 cp for refractive index (589 nm) and viscosity
at 20 C, respectively. The size of particles in a solution can be
measured by exploiting the physical process of Brownian motion:
the particles are migrating as a function of time, and the rate of
motion is related to be their size. The measurement of the decay
rates in correlation function, which is an exponential function
consisted of correlation coefficients (y-axis) dependent on the
delay time (x-axis), is related to the particle sizes, and the result of
the analysis of the correlation function is a size distribution. The
amylopectin stock solution (0.2% w/v) was used for the measurement using disposable cuvettes (UVette, Eppendorf, Germany). All
measurements were carried out at 25 C using the Dynamics 6.9.2.9
software (Wyatt Technology, Santa Barbara, CA) in triplicate. The Rh
was derived from the diffusion coefficient (D) using the Einsteine
Stokes equation for polysaccharides: Rh ¼ kT/6phD, where T was
the absolute temperature, k was the Boltzmann constant, and h was
the solvent viscosity.
2.3. Effects of salts on amylopectin structure
The purified amylopectin (40 mg, dry solids) was wetted with
ethanol (0.1 ml) and then dissolved in aqueous DMSO solution (50
or 90%, 10 ml) with magnetic stirring in a boiling water-bath for 1 h.
The starch solution was filtered through the PTFE membrane (5 mm
pore size), and then the equivalent DMSO solution (10 ml) containing salt (NaCl or CaCl2) was added to make the salt concentrations to be in a range of 0.0e0.2 M. The amylopectin solutions
were then stirred for 8 h at room temperature prior to the light
scattering measurements.
3. Results and discussion
3.1. Molecular characteristics by micro-batch MALLS and DLS
The molecular characteristics of amylopectin in aqueous DMSO
solutions were analyzed using micro-batch mode MALLS and DLS
detectors. Waxy maize amylopectin was dissolved in aqueous
DMSO solutions containing different amounts of water by stirring
in a boiling water-bath for 1 h, and then the solutions were filtered
through a membrane filter and stirred another 8 h at room temperature for complete dissolution of amylopectin (Han & Lim 2004).
The solubility of amylopectin in different DMSO solutions was
measured by filtering the solutions after the 8 h stirring. The solubility of amylopectin gradually increased (from 76% to 95%) as the
water contents in DMSO decreased from 50% to 10% (Table 1). To
evaluate the effect of filtration followed by 1 h boiling-stirring on
J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
117
Table 1
Molecular characteristics of waxy maize amylopectin in various aqueous DMSO
solutions measured with micro-batch mode MALLS and DLS detectors.
Rg (nm)
Mw
(106, g/mol)
50% DMSO 192.7 14.1
70% DMSO 57.5 10.3
90% DMSO 15.3 1.4
a
Rh (nm)
ra (¼ Rg/Rh) Solubility
(%)
182.8 10.9 201.2 19.0 0.91 0.11 76.1 1.6
182.3 25.8 173.5 8.6 1.06 0.19 89.4 2.3
99.8 5.5 107.0 5.9 0.93 0.06 95.4 3.0
Relationship between Rg and Rh: r ¼ Rg/Rh.
solubility of amylopectin, the solubilities in aqueous DMSO solutions without filtering after 1 h boiling-stirring were measured,
which were 62.3%, 73.9%, and 93.4% in 50%, 70%, and 90% DMSO,
respectively (data not shown). Even with the additional stirring at
room temperature, the presence of excess water in the DMSO
reduced the solubility of amylopectin. A small amount of water in
DMSO is required to inhibit the formation of gel layer in the starch
granules and particles, but excess water usually tends to retard the
dissolution of starch (French, 1984).
The Mw and Rg of amylopectin in the DMSO solutions (50e90%)
calculated by the Zimm plot with the Berry formalism (Fig. 1) which
was adequate for the analysis of large molecules (Hanselmann,
Burchard, Ehrat, & Widmer, 1996) ranged from 15.3 106 to
192.7 106 g/mol and from 99.8 to 182.8 nm, respectively. This plot
is the relationship of the square root of K$c/R(q) vs. sin (q/2) for
amylopectin, where K is the optical constant, c is concentration and
R(q) is the scattering intensity at scattering angle q, and presents a
good theoretical agreement of the scattering intensity for the Mw
calculation. The Mw and Rg values obtained by the micro-batch
mode were quite smaller than the results in previous researches
(Han et al., 2005; Millard et al., 1999). This discrepancy could be
attributed to the difference in sample dissolution procedure. In the
micro-bath mode, the insoluble amylopectin was removed by
filtration following the thermal dissolution (1 h in a boiling waterbath) and then the filtrate was further dispersed for 8 h at room
temperature prior to analysis. The relatively low molar mass of
amylopectin might be induced by removing the large insoluble
amylopectin fraction by filtration. In the case of amylopectin
dispersed in 50 or 70% DMSO solutions, the Mw and Rg were much
higher than those measured in 90% DMSO solution (Table 1). It was
supposed that the amylopectin in the DMSO solution containing
excess amount of water tended to aggregate forming larger mass.
Any amylopectin remaining insoluble after the initial heating for
1 h had been removed by filtration, and the soluble fractions were
subjected to the dissolution procedure at room temperature.
Therefore, the larger Mw and Rg values in the DMSO solution containing higher water content indicates the presence of the formation of amylopectin aggregates. The decreased solubility as the
water content increased in DMSO solution supported the possibility of aggregation. Vorwerg, Radostar, and Leibnitz (2002) reported that the insoluble amylopectin chains retained on the filter
usually had larger Mw than soluble amylopectin chains, and thus
Mw became lower when amylopectin solubility was lower because
the insoluble amylopectin can be removed by filtration.
Chamberlain and Rao (1999) reported that waxy maize starch in
pure water was more aggregated than that in 90% DMSO, based on
the rheological properties of the starch dispersions. Kim, Xu,
Biswas, and Willett (2006) reported that shear force could induce
aggregate formation of amylopectin which became less soluble.
Therefore, the high values of Mw and Rg when relatively higher
amount of water was present in the DMSO solution was induced by
the aggregation of dissolved amylopectin.
The Rh values determined using a DLS detector and the r values
(the ratio of Rg and Rh) are also shown in Table 1 Usually, Rh data can
Fig. 1. Zimm plot with Berry formalism from light scattering data: square root K.c/R(q)
vs. sin2(q/2) of waxy maize amylopectin in 50%(6), 70%(>) and 90%(B) aqueous
DMSO solutions.
be obtained from angular distribution of scattered light using
multi-angle light scattering detectors and have been reported using
a correlation with fitting data (Millard et al., 1999; Yang et al., 2006).
Even though the DLS detector used in this work is equipped with
only one angle (90 ), the Rh value can theoretically be calculated by
correlating the time-dependent fluctuations in the scattering
intensity due to the random motion of amylopectin molecules. It
represents the radius of a sphere with the same diffusion
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J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
coefficient, whereas Rg is the mass-averaged distance of each endpoint in a molecule from the center. Unlike the Rg values obtained
by SLS, the Rh values calculated from the diffusion coefficient using
DLS indicate the dimension of starch molecules occupied in solution, which provide the hydrodynamic radius of polymers and are
used as parameters for elucidating the structural feature of polymer
in solution (Buchard, Schmidt & Stockmayer, 1980; Millard et al.,
1999). The Rh values of amylopectin in 50%, 70% and 90% DMSO
solutions were 201.2, 173.5 and 107.0 nm, respectively. The increase
in Rh with increasing water content indicates that the amylopectin
molecules were less dispersed, existing as larger particles, which
suggested the possibility of aggregate formation. The changes in Rh
and size distribution induced by the filtration and additional
stirring (8 h at room temperature) are shown in Figs. 2 and 3,
respectively. In 70 and 90% DMSO solutions, the Rh values was not
changed by filtering, but decreased after 8 h stirring. As shown in
Fig. 3, the large particles which had the size around 1000 nm
observed in the 70 and 90% DMSO solutions disappeared by the
additional stirring at room temperature. The size distribution data
show that the micro-sized large particles still remained in the
solution after the filtration. The decreases in Rh as well as the
population of the micro-particles, however, indicate that the
amylopectin aggregates could be somewhat dispersed by the
additional stirring. In 50% DMSO solution, the Rh values slightly
decreased by the filtration and the additional stirring (Fig. 2).
However, the large particles, possibly aggregates, were still present
in the 50% DMSO solution (Fig. 3), and complete dissolution could
not be attained by the extended stirring.
The r value, the ratio of Rg to Rh, provides qualitative information about the structure of macromolecules. Generally, it is
inversely proportional to the degree of branching density (Buchard
et al., 1980). The r values of amylopectin in 50%, 70% and 90% were
0.91, 1.06 and 0.93, respectively (Table 1). These values were close to
1.08, which corresponds to a regular star structure, thus revealing
that the amylopectin molecules existed as densely branched
structures in these aqueous DMSO solutions. The observation of
such a structure for waxy maize amylopectin in aqueous DMSO
solutions is consistent with that reported by Millard et al. (1999).
However, the minor differences in the r values among these DMSO
solutions possibly indicate that the individual shapes of amylopectin molecules was not overly affected by the difference in water
content, whereas the dissolution behavior of the amylopectin aggregates was affected by the presence of water. Therefore, the
Fig. 2. Hydrodynamic radius (Rh) of waxy maize amylopectin treated by stirring for 1 h
in a boiling water-bath, filtering through a filter (5.0 mm), and then stirring at room
temperature for 8 h in aqueous DMSO solutions containing different amounts of water.
aggregated or insoluble amylopectin moiety from the low degree of
dissolution did not affect the chain conformation of individual
amylopectin molecule. The conformation of each amylopectin
molecules was relatively stable against the varying water contents
(50e90%) in the aqueous DMSO solutions even though the interactions between amylopectin molecules was facilitated as the
water content increased. It is hypothesized that the chain conformation of amylopectin dissociated in aqueous DMSO solutions is
relatively stable because amylopectin consists of a large number of
short chains connected by alpha-1,6 branch linkages. It was reported that the shorter chains with the larger degree of branching
usually hindered the chain association (Jane & Chen, 1992).
3.2. Effects of salts
Fig. 4 shows the Mw, SVg and r values for amylopectin in various
aqueous DMSO solutions containing NaCl or CaCl2. Mw of amylopectin in 90% DMSO solution varies from 15.3 106 to 38.8 106 g/
mol as the salt concentration was increased up to 0.2 M. When
amylopectin was dissolved in 90% DMSO solution, a minor addition
of salts, up to 0.05 M of NaCl or CaCl2, induced a slight increase in
Mw. When no salt was present, the amylopectin in 90% DMSO was
not fully soluble, and the insoluble molecules, typically large molecules, were removed by filtration, resulting in the low Mw measurement. However, when the a minor amount of salt was present,
the amylopectin molecules could be more soluble and thus the
large molecules could be measured, resulting in high Mw values. On
the other hand, with the increase of salt concentration up to 0.2 M,
the Mw appeared relatively unaffected by the changes in salt content. The stable molar mass might result from the balance of ionic
properties among the amylopectin, water, DMSO and salts, which
seemed to be adequate to stabilize the amylopectin molecules in
the solution. In contrast, the amylopectin in 50% DMSO solution
exhibited larger Mw (192.7 106 g/mol) than those in 90% DMSO
solution. As discussed previously, this difference could be attributed to the lower degree of amylopectin dissolution and/or the
formation of amylopectin aggregates in 50% DMSO solution. The
Mw of amylopectin measured in 50% DMSO changed abruptly by the
addition of salts (Fig. 4). The presence of low concentrations of salt
resulted in a substantial decrease in Mw (100.5 106 and
110.5 106 g/mol in the presence of 0.01 M NaCl and CaCl2,
respectively), which was opposite to the change observed in 90%
DMSO. In addition, the Mw values of amylopectin in 50% DMSO
solution containing NaCl were smaller than those in solutions
containing CaCl2 at all concentrations. Furthermore, the variation of
Mw according to the salt concentration was much greater with
CaCl2 than that with NaCl. This may imply that the structure of
amylopectin might be less stable in the presence of CaCl2 compared
to that in NaCl solution, possibly due to the difference in the ionic
strengths of the two salts. The charged ions derived from these salts
have a tendency to make strong interactions with water molecules.
These ions, named as ‘structure makers’, reduce the fraction of free
water and thus the water activity (Jane, 1993). Therefore, salt
addition may be expected to have the same effect on amylopectin
solubility as does reducing the water content in DMSO solutions.
For the 50% DMSO solution, the salt addition thus resulted in
improving dissolution of amylopectin, and thus the Mw became
similar to those observed in 90% DMSO solution (Fig. 4).
The specific volume of gyration (SVg ¼ 2.522 R3g =Mw ), which
provides the mass-based information on the density and degree of
branching, for the amylopectin dissolved in 90% DMSO solution was
not much changed by the presence of salts, and it ranged from 0.15
to 0.21, similar to the results in other reports (Han et al., 2005; You
& Lim, 2000). It reveals that the amylopectin molecules remain
compact and that their structural conformation is relatively stable
J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
119
Fig. 3. Particle size distribution of waxy maize amylopectin in aqueous DMSO solutions containing different amounts of water.
to the salt addition in 90% DMSO solution. The SVg values of
amylopectin in 50% DMSO were smaller than those in 90% DMSO
solution, ranging from 0.08 to 0.16, indicating that the amylopectin
existed in more compact shape in 50% DMSO solution, suggesting
the possible formation of amylopectin aggregates. The specific
volume was increased with a minor addition of salts (up to 0.01 M).
An increase in Mw was also found by the initial addition of salts. The
presence of salts, even in a minor content, could induce structural
changes for amylopectin. The increase in Mw might suggest association of amylopectin molecules. However, SVg values are independent to changes in molar mass, and thus the increase in SVg
indicates that the amylopectin chains became more extended by
the presence of salts. As shown in both Mw and SVg data, salt
addition above 0.01 M induced no significant changes in amylopectin structure. Overall dissolution behavior of amylopectin
affected by the presence of water in DMSO produced a greater effect on the chain conformation of amylopectin than did the presence of salts.
The r values are also related to the physical conformation: 1.08
for regular star structure, 0.78 for homogeneous spheres, and 2.05
for random coils in good solvents (Buchard & Richtering, 1989). In
the absence of salts, the r values of amylopectin in 90% and 50%
DMSO were 0.93 and 0.91, respectively, indicating that amylopectin
exhibited a compact regular star structure, in agreement with the
data reported by Millard et al. (1999) and Yang et al. (2006). In
the presence of NaCl, changes of the molecular conformation of
amylopectin in 50% DMSO were related to those of Mw (R2 ¼ 0.93,
data not shown). However, there were no strong correlations between the Mw and r values for amylopectin in other solutions (50%
DMSO with CaCl2, and 90% DMSO with NaCl or CaCl2, R2 0.75,
data not shown). Amylopectin was evidently well dispersed in 90%
DMSO, and the dispersed shape of amylopectin chains appeared to
be relatively unaffected by the salts. On the other hand, salt effects
appeared more significant in 50% DMSO solution, as indicated by
the positive correlation between Mw and r values, especially
with NaCl.
The molecular conformation of amylopectin might be affected
by the salts, in two directions: water cluster formation and direct
interaction to amylopectin. Cations such as Naþ or Ca2þ tend to
be attracted to the OH groups on the starch molecules and
destabilize them, whereas anions such as Cl repel the OH
groups to make molecules dispersed and more stable. If salt ions
repel the OH groups of starch or bind to free water molecules, the
starch molecules may tend to associate together. On the contrary,
attracting the OH groups or breaking water clusters may make
starch molecules unstable and readily dissociated. These effects
seemed not to be evident to the amylopectin in 90% DMSO solution. However, amylopectin molecules might be slightly
aggregated at low salt concentrations (relatively high Mw and SVg
at 0.01 M), but seemed to be more highly dissociated at high salt
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J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
Fig. 4. Changes in weight-average molecular weight (Mw), specific volume of gyration (SVg) and r value (Rg/Rh) of waxy maize amylopectin in 50%(:) and 90%(C) aqueous DMSO
solutions in the presence of different concentrations of salts (NaCl and CaCl2).
concentrations (low Mw and SVg at 0.10 and 0.20 M, Fig. 4). It
could be suggested that salt ions may act either as ‘structure
maker’ or as ‘structure breaker’, depending on their concentrations. It was clear that the amount of water present in the DMSO
solutions may influence the susceptibility of the amylopectin
structure to the salt ions. The effects of salt ions on amylopectin
molecules in solution thus may conflict with one another
depending on their types and the ionic strength. Additional study
is needed for a clear understanding of the complicated mechanism of salt ions in relations to water effects on chain conformation of starch.
4. Conclusions
The dissolution of amylopectin in aqueous DMSO solutions was
affected by the water present in the solutions. A level of approximately 10% water appeared optimal for the dissolution of amylopectin. The larger amounts of water in DMSO may not only reduce
the dissolution of amylopectin but also lead to the formation of
aggregates. From light scattering analyses, however, the compact
and regular star shape of amylopectin was not affected by the water
content (10e50%) in DMSO solutions. In 90% DMSO, a minor
presence of salts such as NaCl or CaCl2 tended to induce
J.H. Lee et al. / Food Hydrocolloids 35 (2014) 115e121
amylopectin chain association. The addition of salts could minimize
the adverse effect of the water in amylopectin dissolution in DMSO
solutions.
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