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Journal of Modern Chemistry & Chemical Technology
ISSN: 2229-6999 (Online), ISSN: 2321-5208 (Print)
Volume 10, Issue 1
www.stmjournals.com
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 28
Intrinsic Viscosity of Stud Plant Mucilage (Dicerocaryum
Zanguebarium): Polymeric Studies at Infinite Dilution.
S. Muyambo1,*, I. Chikurunhe2, D.N. Moyo3
1,3Department of Food Processing Technology, Harare Institute of Technology, P.O. Box BE277
Belvedere, Harare, Zimbabwe
2Department of Polymer Technology and Engineering, Harare Institute of Technology, P.O. Box
BE277 Belvedere, Harare, Zimbabwe
Abstract
Studies on stud plant mucilage (SpM) showed that it constitutes of galactose, mannose and
xylose and it has a molecular weight of 500 kDa. However, the behaviour of the polymer
using intrinsic viscosity, in dilute regime, has not been explored. The research investigated the
intrinsic viscosity of SpM in water, salt and sugar solutions. Salt solutions have poor solvent
properties and hence reduced the intrinsic viscosity of SpM as opposed to sugars which
enhance it. The shape of SpM particles, in water, is either oblate or prolate. The Berry
numbers shows that, all SpM solutions (in water, salt and sugar solvents) were in dilute
domain and the molecules portray a conformation which is between rod-like and random coil.
Keywords: Dicerocaryum zanguebarium, Intrinsic viscosity, Mucilage, Stud plant,
Biopolymers
*Author for Corresponding E-mail: shadiemyambo@hotmail.com
INTRODUCTION
The use of natural or plant–based polymers as
food, food additives, cosmetics and
pharmaceutical additives, lubricants and
medicinal applications has received much
attention in recent times. This has been
attributed to their abundance, biocompatibility,
biodegradability, renewability, cost
effectiveness and complexity. Stud plant (also
known as Seso or Ruredzo and botanically as
Dicerocaryum senecioides or Dicerocaryum
eriocarpum) is a prostrate perennial herb
which grows in grasslands particularly
trampled areas and abandoned fields [1, 2]. It
is one of the most abundant mucilaginous
plants, which are commonly found in
Zimbabwe, and some parts of Southern Africa
and East Africa [3].
The stud plant (Sp) leaves, traditionally, have
been used for several functions: commonly as
food, a side dish called derere [2]; as soap
substitute or for facilitating deliveries in
humans and cows and for bathing babies
suffering from measles [2]; treatment of
wounds [4] and inflammatory disorders[5].
The extracts from Sp species has been shown
to have inherent anti-oxidant, anti-
inflammatory and anti-proliferate properties,
which can act against cancerous cells [1, 5].
Sp extracts has indicated much improvement
on facilitating hair development (improve
curling capacity from 62–86%), loosens the
hair curly, and it also softens skin [1].
According to Benhura and Marume [6] the
mucilaginous material from Sp (stud plant
mucilage, SpM) have molecular weight of 500
kDa and also comprises of monomeric units
such as galactose, xylose, arabinose and
mannose in the ratio of 21:19:12:1. It was
further stated that the mucilage has a specific
optical rotation of +4.5°, ash content of 7.6%,
protein content of 2.1% (Kjeldahl) and 1.8%
(Lowry) and uronic acid content of 8.1% [6].
The emulsifying properties of SpM were
investigated by Benhura and Marume [2]
using corn oil and they found out that the
mucilages have optimum emulsifying
properties at pH 7. The emulsification activity
was enhanced by an increase in the SpM
concentration. The emulsifying properties
Intrinsic Viscosity of Stud Plant Mucilage Muyambo et al.
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 29
were observed to be affected by the presence
of salts (NaCl and CaCl2). A study to optimize
the polymeric properties of SpM was done by
crosslinking the mucilage with
epichlorohydrin [7]. The properties of the
cross-linked mucilage (CLM) were like those
of cross-linked pectate from citrus peels. An
increase in the concentration of the salts
(NaCl) indicated a slight decrease in the bed-
volume of the CLM. The degree of swelling of
the SpM cross-linked mucilage was less
affected by ethanol, NaCl and pH.
The specific structure and molecular identity
of the stud plant mucilage is somewhat
complicated to elucidate due to the presence of
different monomers (heterogeneity) and the
presence of complex branching [1, 6].
However, in trying to explain the polymeric
structure of the stud plant mucilage (SpM),
Benhura and Marume [8] oxidized the
mucilage with periodate. It was observed that
the arabinose ring remained intact (impervious
to acid hydrolysis) and unexpectedly resistant
to periodate oxidation which contrast to most
polymers or other pectic polymeric material.
In conclusion, Benhura and Marume [8],
stated that the resistance to hydrolysis and
periodate oxidation can be significant in
clarifying the overall structure of SpM, where
arabinose residues in the SpM formed sections
of the polymer in which the arabinose residues
were highly substituted, whilst the
galacturonic acid main chain was relatively
unsubstituted.
It was observed that current studies have not
addressed the polymeric structures or
properties of the SpM using intrinsic viscosity
studies, hence limited its use in many possible
industrial applications. Intrinsic viscosity can
be used to explain the hydrodynamic nature of
the polymer, conformity, voluminosity and
shape identity in dilute regime [9–15]. It is
apparent that the properties of the solvent are
very crucial in the determination of intrinsic
viscosity [11]. The addition of sugars and salts
may influence the attractive and repulsive
interactions between chain segments and
therefore affect the solubility of the
polysaccharide during hydration and its
molecular hydrodynamic volume. This change
in molecular hydrodynamic volume,
conformation and macromolecular
associations can be identified by change in the
intrinsic viscosity of the polymer solution [9,
11, 13].
METHODOLOGY
Stud Plant Collection
Stud plant (Sp) was collected from
Gombakomba area in Mutare, Zimbabwe. The
leaves were pruned from the stem and dried
using sunlight for approximately 48 hours. The
dried leaves were grounded and stored in a
cool and dry place for further investigation.
Extraction and Purification of the Stud
Plant Mucilage (SpM)
Modified extraction methods obtained from
Benhura and Marume [2, 6] and Martin et al
[16] were used in the extraction process. The
dried and grounded stud plant (Sp) leaves
measuring 500 g were mixed with distilled
water in the ratio of 1:20 (w/v). The mixture
was heated in a water bath, 60±5oC, for three
hours and filtered using a muslin cloth then
cooled to room temperature. The mucilage
supernatants were precipitated, in the presence
of 0.1 M NaCl to prevent precipitation of
proteins, using ethanol (99.9%), in solvent to
supernatant ratio of 3:1. The precipitate was
recovered through centrifugation at 7000 rpm
for 20 min. The recovered precipitate was
washed in excess fresh ethanol (99.9%),
filtered and dried in an oven at 35–40°C. The
dried mucilages were pounded using pestle
and mortar and screened through a 125 µm
pore size sieve then stored in cool dry place.
Preparation of the SpM Samples
SpM analytes had concentrations ranging from
0.02–0.05 g/dL. Sugars and salts samples were
prepared using SpM sample at 0.03 g/dL as
follows: Lactose (5%, 10% and 15%); Glucose
(10%, 20%, 30% and 40%); CaCl2 (3.75, 7.50
and 15.0 mM) and NaCl (6.5, 12.5, 25.0 and
50.0 mM). The analytes were prepared using
distilled water and allowed to stand for 20
hours at 4±0.2°C, for complete hydration;
thereafter they were filtered using a methyl-
cellulose membrane [9, 11].
Journal of Modern Chemistry & Chemical Technology
Volume 10, Issue 1
ISSN: 2229-6999 (Online), ISSN: 2321-5208 (Print)
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 30
Viscosity Measurements
Ostwald viscometer was used to determine the
time of flow of the analytes. In each trial test,
10 ml aliquots of the sample were dispensed in
the capillary using a pipette and suctioned
using a rubber bulb, to bring the solution to the
meniscus. The temperature of the sample was
equilibrated to 25±0.1°C in a water bath. For
each sample six trials were conducted. The
method for cleaning and setting the viscometer
were adopted from Masuelli [17].
Determination of the Intrinsic Viscosity
Viscosity Ratios
The values of intrinsic viscosity were
calculated using the flow time , of the
solution in the Ostwald capillary viscometer.
The flow time , may be used to calculate
intrinsic viscosity if it is less than 100 s [12].
Eq. 1 and 2 below were used to determine the
relative viscosity ηr, and specific viscosity ηsp,
respectively, by considering flow time of the
sample in Ostwald capillary viscometer [12,
18, 19]. (1)
(2)
Where; and are the respective flow times
of the solution and the solvent (distilled water)
at constant temperature.
Empirical Expressions for Determining
Viscosity
Kraemer, Huggins and Schulz-Blaschke
expressions extrapolate the intrinsic viscosity
at infinite dilutions (i.e. intrinsic viscosity is
the intercept) according to Eq. 3, 4 and 5
respectively [10, 18, 20–22]:
Kraemer’s equation (3)
Huggins’ equation (4)
Schulz-Blaschke (S-B) (5)
where; is the Kraemer constant, is the
Huggins viscosity constant and is the
Schulz-Blaschke constant.
Intrinsic viscosity was also calculated by
measuring the slope of relative viscosity ηr, or
specific viscosity ηsp, with concentration c.
Thus, Eq. 6–8 below were also used for
determination of intrinsic viscosity [9, 10, 21–
23]:
Tanglertpaibul-Rao’s equation
(6)
Higiro’s equation 1 (7)
Hence, the intrinsic viscosity will be the slope
obtained from plotting ln ηr vs c.
Higiro’s equation 2 (8)
Intrinsic viscosity is the slope obtained by
plotting 1-(1/ηr) vs c.
The determination of intrinsic viscosity using
single point method was also considered.
Solomon-Ciuta equation (Eq. 9) was used to
predict the intrinsic viscosity at a specific
polymer concentration [20, 24, 25].
Solomon-Ciuta equation
(9)
Evaluation of the Molecularity of the
Mucilage
A power-law expression, shown in Eq. 10a,
was used to estimate the exponent γ from the
slope of a double logarithmic plot of specific
viscosity against concentration. The parameter
gives an indication of the conformation of the
polysaccharides [9, 21, 26].
(10a)
(10b)
Voluminosity and Shape Factor of the
Polymer Coil
According to Antoniou et al [27] and Joseph et
al [28] the voluminosity VE, was obtained by
plotting factor Y (Eq. 11) against c.
Voluminosity VE, provide information
concerning the polymer conformation in
different solvent conditions.
(11)
VE values for different solvent conditions can
be obtained from the intercept at c=0 of the
line going Y vs c. The intrinsic viscosity and
VE are related as follows [28]:
(12a)
Intrinsic Viscosity of Stud Plant Mucilage Muyambo et al.
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 31
(12b)
where v is the shape factor that gives the idea
of the particle is solution.
Coil Overlap Parameter
In dilute solution the molecules (polymer
coils) exist separately and are free to move
independently. Increase in concentration
causes the coils to start overlapping and
interpenetrate on another. Estimation of the
coil overlap parameter can be found on a
double logarithmic plot (master curve) of
specific viscosity ηsp vs c[η] (Berry number)
derived from the following Eq. 13 [29, 30].
(13)
Statistical Analysis
The intrinsic viscosity was expressed as mean
±SD of the 6 trials performed. The [η] values
were tested for significant dissimilarity using
Euclidean dissimilarity distance δ correlation
with functions in SPSS and XLStat. The
dissimilarity threshold was at 0.95 and as such
values were dissimilar at P>0.05 (null
hypothesis) and similar at P<0.05 (alternative
hypothesis). Statistical software used includes
SPSS (IBM SPSS Statistics, v23.0), Matlab
(Mathworks, R2017a), XLStat (Microsoft,
v2018) and Excel (Microsoft 2016).
RESULTS AND DISCUSSION
Intrinsic Viscosity
The summary of the intrinsic viscosity values
for equation 3–9 are shown in Table 1. The
results show that the approximation of the
intrinsic viscosity [η], of the SpM did not
follow equations which are based on the
intercept (Eq. 3–5), even though the prediction
power increased from
Kraemer<Huggins<Schulz-Blaschke,
considering the magnitude of the correlation
coefficient and root mean square errors,
RMSE (Table 1). Theory pointed to the fact
that the inherent viscosity ( ) changes
less rapidly with concentration as compared to
reduced viscosity ( ), Kraemer’s
equation (based on ) could have given
more accurate predictions of [η] than Huggins
equation (based on ), this was not the
case in this study [12, 18]. This observation
maybe well explained by the polyelectrolyte
nature of the polymeric chain of the SpM,
which makes the chain to become fully
extended and therefore overruling this general
concept [12].
To the contrary, the equations which are based
on deriving the [η] from the slope/gradient
(Tanglertpaibul-Rao, Higiro equation 1 and 2),
as expected showed higher values of R2 and
smaller magnitudes of errors (RMSE). The
same trend was also obtained by Behrouzian et
al [9] on cress seed gums (CSG); Razavi et al.
[11] on wild sage (Salvia macrosiphon) seed
gums (SSG); Khouryieh et al [10] on the
intrinsic viscosity of xanthan gum and
xanthan-guar gum mixtures and McMillan
[31] when determining the methods of
determining intrinsic viscosity of bovine
serum albumin. Razavi et al. [29]; Vahid et al
[23] and Behrouzian et al. [9] further
elucidated that the failure of the Huggins
equation can be attributed to sequential
dilution in sample preparation which may
enhance error in term (this can be
generalized to S-B and Kraemer equations).
The Huggins equation is usually presumed to
be valid for ηsp<0.7 [9], however, the model
still failed despite that ηsp ranged between
0.07–0.2 for this study. Eq. 6–9 were therefore
used for further analysis of the intrinsic
viscosity properties of SpM.
Table 1 also shows the [η] obtained using
single point equation (Solomon-Ciuta model,
Eq. 9). The Solomon-Ciuta model is an easy
alternative and less time-consuming way of
determining the intrinsic viscosity values using
single polymer concentration. The model has
been successfully used to estimate [η] of
various polymers according to Masuelli [24]
and Abel-Azim et al [20]. The results indicated
that the intrinsic viscosity obtained using
Solomon-Ciuta equation were significantly
similar and they were also similar to the values
obtained using Higiro equation 1 (Eq. 7),
Huggins equation (Eq. 4), S-B equation (Eq.
5) and Kraemer’s equation (Eq. 3), using
Euclidean distance (δ) correlation at 0.95
dissimilarity threshold. This means that
intrinsic viscosity values from the Solomon-
Ciuta equation are also comparable to the
Journal of Modern Chemistry & Chemical Technology
Volume 10, Issue 1
ISSN: 2229-6999 (Online), ISSN: 2321-5208 (Print)
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 32
typical models that are commonly used, as
also observed by Masuelli [24]; Pamies et al.
[25] and Abel-Azim et al. [20].
Molecular Conformity (γ), Voluminosity
(VE) and Shape Factor (v)
The conformity of the polymer was
determined as the exponent factor γ, expressed
as the gradient from a power-law model (Eq.
10a and b). The equation for the data collected
was as follows (Eq. 14):
(14)
The value of the exponent factor γ obtained
from the fit of log ηsp and log c was 1.0554.
The voluminosity VE and shape factor v, were
also determined using Eq. 11 and 12a and b
respectively. VE was expressed as the intercept
from the plot of Y and concentration of the
polymer in solution. The equation (Eq. 15) of
the line indicates that the value of VE was
8.6794 (intercept).
(15)
The value of VE was used to calculate the
shape factor v using intrinsic viscosity [η] as
illustrated in Eq. 15. Table 2 shows the values
of v using [η] values obtained from
Tanglertpaibul-Rao equation (Eq. 6), Higiro
equation 1 and 2 (Eq. 7 and 8) and Solomon-
Ciuta expression (Eq. 9).
Table 2 indicated that the values of v ranges
from 0.362–0.464. The mean (±SD) for the v
values which were not significantly dissimilar
(using Euclidean distance correlation at
dissimilarity threshold of 0.95) was found to
be 0.428 (±0.0201). Antoniou et al [27]
categorize the values of v according to shape
of the polymers in solution as follows: v≈2.5-
spherical particles; v>2.5-ellipsoidal particles
and if v values are not within these
specifications then the particles are oblate or
prolate. Values of v in the range of 0.362–
0.464 will suggest that the shape of the SpM
particles are oblate or prolate. This means that
the particles of SpM are lengthened in the
direction of polar diameter (prolate) or rather
flattened at the poles (prolate). Razavi et al
[11] also observed that the shape factor v of
sage seed gums (SSG) follows an oblate or
prolate shape at 20–40oC.
Coil Overlap Parameter
The coil overlap parameter is usually used to
determine the coil overlap concentration or
critical concentration (c*) and shows if the
polymer solution is within dilute Newtonian
domain [29, 32, 33]. A master curve plot of log
(ηsp) against log c[η] is shown in Figure 1,
where c[η] is the dimensionless concentration
also known as Berry number. The Berry
numbers calculated from intrinsic viscosities
obtained from Tanglertpaibul-Rao, Higiro
equation 1 and 2 and Solomon-Ciuta equation
are shown in Table 3. The exponent b was
obtained from the gradient/slope of the power
law model on a master curve (Figure 1). In
general, the Berry number ranges from 0.08–
0.20 for Tanglertpaibul-Rao equation, 0.07–
0.18 for Higiro equation 1 and Solomon-Ciuta
equation and 0.06–0.17 for Higiro equation 2
(Table 3). Behrouzian et al [9], Graessley [34]
and Hager and Berry [35], indicates that the
molecular entanglement occurs when the Berry
number (c[η]) exceeds 1.0 and semi-dilute
regime when c[η] ranges from 1.0–10.0. Berry
numbers for the SpM were below 1.0, as shown
in Table 3, indicating that the polymer solutions
were in the dilute regime (i.e. within Newtonian
domain). Thus, it was presumed to be without
coil overlap and molecular entanglements. The
exponent factor b of Tanglertpaibul-Rao and
Higiro equation 1 and 2 was 1.0554 and 1.039
for Solomon-Ciuta equation. This value was
also observed to be identical to conformity
factor γ and hence provide the same
explanation. Behrouzian et al. [9] indicates that
for the values of b greater than 1.0, the polymer
in dilute regime will assume a random coil
conformation. Morris et al [33] further
explained that values of b greater than 1.0 are
interrelated to entanglement and slopes less
than 1.0 have rod-like conformations. Since the
observed values of exponent b, was greater but
close to 1.0, it was assumed that the conformity
of the molecules of SpM could be between
random coil and rod-like. Behrouzian et al. [9]
obtained a value of 1.08 for CSG and
concluded that the conformity of CSG was
between rod-like and random coil. However,
Higiro et al [21] found the values exponent b of
1.234 and 0.786 for locust bean gum LBG, and
xanthan gum respectively (in dilute regime) and
established that the molecular conformation of
LBG was a random coil and xanthan was a rod
molecule.
Intrinsic Viscosity of Stud Plant Mucilage Muyambo et al.
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 33
Table 1: Summary of Intrinsic Viscosity of the SpM.
Eq. No.
Model
[η] (dL/g)
R2
RMSE
c (g/dL)
3
Kraemer
3.61(±0.120)AD
0.009
0.0977
0.02–0.05
4
Huggins
3.61(±0.128)AD
0.439
0.113
0.02–0.05
5
Schulz-Blaschke
3.61(±0.106)AD
0.503
0.106
0.02–0.05
6
Tanglertpaibul-Rao
4.03(±0.0909)B
0.996
0.0042
0.02–0.05
7
Higiro equation 1
3.55(±0.0792)A
0.995
0.004
0.02–0.05
8
Higiro equation 2
3.14(±0.0696)C
0.994
0.0039
0.02–0.05
9
Solomon-Ciuta
3.65(±0.140868)AD
-
-
0.02
3.60(±0.1223)AD
-
-
0.03
3.80(±0.03269)D
-
-
0.04
3.64(±0.0459)AD
-
-
0.05
Results are expressed as means ± SD for the six trials performed. A-D: the values with the different letter(s) are dissimilar
considering the Euclidean distance (δ) correlation at dissimilarity threshold of 0.95 (P>0.05).
Table 2: Voluminosity (VE) and Shape Factor (v) of the Stud Plant Mucilage (SpM).
Tanglertpaibul
-Rao
Higiro
equation 1
Higiro
equation 2
Solomon-Ciuta
0.02–0.05
0.02–0.05
0.02–0.05
0.02
0.03
0.04
0.05
4.0259
3.5527
3.1376
3.648
3.6032
3.7979
3.6373
8.6794
8.6794
8.6794
8.6794
8.6794
8.6794
8.6794
0.464(±0.0105)
A
0.409(±0.0091)
B
0.362(±0.008)
C
0.420(±0.0162)A
B
0.415(±0.0141)A
B
0.437(±0.0038)A
B
0.419(±0.0053)A
B
Results are expressed as means ±SD for the trials performed. A-C: the values with the different letter(s) are dissimilar
considering the Euclidean distance (δ) correlation at dissimilarity threshold of 0.95 (P>0.05).
Fig. 1: Master Curve of the SpM at 25°C.
Table 3: Berry Numbers (Intrinsic Viscosity x Concentration, c[η]) and Exponent Factor b (Gradient
of Master Curve) of SpM.
Tangertpaibul-Rao
Higiro equation 1
Higiro equation 2
R2
RMSE
Solomon-Ciuta
R2
RMSE
c[η]
0.08–0.20
0.07–0.18
0.06–0.17
0.07–0.18
b
1.0554(±0.03652)
0.997
0.0122
1.039(±0.000991)
1.0
0.00102
Results are expressed as means ±SD considering number of trials (6) performed
Journal of Modern Chemistry & Chemical Technology
Volume 10, Issue 1
ISSN: 2229-6999 (Online), ISSN: 2321-5208 (Print)
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 34
Effects of Salts (NaCl and CaCl2) on the
Intrinsic Viscosity of SpM
As expected, the intrinsic viscosity of SpM
decreases with increasing salt concentration.
The results (Table 4 and Figure 2) shows that
there was a decrease in [η] of SpM on addition
of 6.5 mM of NaCl. However, the [η] slightly
increases as the concentration increased to 25
mM and then decreases again when the NaCl
reaches 50 mM. The same trend was also
observed for CaCl2, though the effects were
more pronounced in CaCl2 than in NaCl at the
same concentration, Figure 2. Behrouzian et
al. [9] investigated the effects of NaCl (0–100
mM) and CaCl2 (0–15 mM) on cress seed
gums (CSG). A decrease in the [η] of CSG on
the addition of 25 mM NaCl and a slight
increase at 50 mM NaCl, then followed by a
moderate decrease at higher NaCl
concentration was observed. However, for
CaCl2 the decrease was observed up to 10 mM
then continued with the addition of CaCl2 up
to 15 mM. A more pronounced effect of
divalent salts (CaCl2) than monovalent salts
have been reported in several studies [9, 13,
23, 29].
The decrease of [η] when salt was added can
be best explained by considering the
interactions of the salts and the polymer. Since
stud plant mucilage (SpM) are polyelectrolytes
i.e. polymeric chain that carries a negative
charge [2], it is known that the coil dimensions
of polyelectrolytes are expanded by
electrostatic repulsion between chain segments
[9, 12]. However, the introduction of the salts
reduces the electrostatic repulsion, due to its
shielding effect, causing contraction of chain
segments-favouring intramolecular
interactions. Khouryieh et al. [10] observed
that when salt was added to xanthan gum
solution, at 25°C, a disordered transition
occurs in which the backbone takes a helical
conformation and the charged tri-saccharide
side chains collapses down onto the backbone
(charge screening effect) and stabilizes the
ordered conformation.
In a good solvent the polymer favour
interactions with the solvents rather than
segments of the polymer or other polymer
chains and this result in increase of the solvent
viscosity [9]. Nevertheless, in poor solvent
(salt solution) polymer-polymer interactions
are rather favoured resulting in the reduction
of the intrinsic viscosity of the solution. The
increase in salts can eventually cause the
polymer molecules to aggregate forming
precipitates [9, 29]. Salt solution proves to be
a poor solvent for SpM and as such the
polymer assumes a tighter configuration and
hence lower intrinsic viscosity [10, 17].
Benhura and Marume [2] investigated the
emulsifying activity of SpM (ruredzo) in the
presents of salts (NaCl-1% and CaCl2–1%) and
observed that there was reduction in the
emulsifying properties and stability of the
formed emulsions (CaCl2 has slightly more
effect than NaCl). A factor, which they also
ascribed to the effect of salts on the
electrostatic interactions between the charged
groups in the polymeric chain.
The physical entanglements of SpM in salt
solution were also determined using the Berry
numbers. The Berry numbers were distributed
as follows 0.089–0.11 for NaCl and 0.085–
0.11 for CaCl2 as demonstrated in Table 5. The
values of c[η] show that there were no
significant physical entanglements of SpM in
the presents of NaCl and CaCl2 salts.
Behrouzian et al [9] observed c[η] values of
CSG, in the order of 0.25–1.02 and 0.24–1.33
for NaCl and CaCl2 respectively and
concluded that there were no physical
entanglements between molecules. The slope
of the power model, exponent b was 1.03 for
both NaCl and CaCl2 and in general the values
were observed to be lower than those of SpM
solution in water solvent as shown in Table 3.
Though there was a reduction in the exponent
b values with the addition of salt, we
anticipated otherwise, since higher values of b
(>1.0) are associated with formation of
entanglements and random coil conformation
of the polymer [33], as polymer-polymer
interactions are supported by the salted
solvent. This was also supported by
Behrouzian et al [9] after explaining that at
higher salt concentration (greater values of
exponent b) the polymer molecules aggregates
forming precipitates. Hence, the addition of
salt should have been accompanied by an
increase in the values of b, as compared to
water solvent.
Intrinsic Viscosity of Stud Plant Mucilage Muyambo et al.
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 35
Effects of Sugars (Glucose and Lactose) on
Intrinsic Viscosity of SpM
The addition of sugars, in contrast to salts, led
to the increase of the SpM intrinsic viscosity
as shown in Table 4 and Figure 3. The
intrinsic viscosity of SpM with addition of
glucose ranges from 3.58–12.16 dL/g whilst
that of lactose from 3.58–10.82 dL/g (Table
4). The [η] of lactose was approximately as
twice as much at the same concentration as of
glucose. The results however, show a slight
decrease in [η] after addition of 10% (w/w) of
glucose but rapidly increase as glucose
concentration was added from 20–40% (w/w)
as shown in Table 4 and Figure 3. Studies also
showed that the addition of sugar (sucrose) up
to 20% (w/w) or 5% (w/w) lactose, to cress
seed gums-CSG solutions, resulted in the
decrease of the intrinsic viscosity, however,
further increase up to 40% w/w (sucrose) or
15% w/w (lactose) resulted in intrinsic
viscosity increment [9, 13]. Razavi et al [29]
also observed that intrinsic viscosity decreases
upon adding sucrose and other low molecular
additives, at lower concentration. Further,
Vahid et al [23] showed that addition of
sweeteners (low molecular weight) like
Aspartame (0–0.2%), Acesulfame-k (0–0.2%),
cyclamate (0–0.2%), Neotame (0–0.002%) had
no significant effect on intrinsic viscosity of
salep gum solutions, indicating that the
sweeteners had less effect on solvent quality
and hydrodynamic volume of salep gum. May
be the extent of intrinsic viscosity
enhancement is directly linked to the
concentration of sugar added as discovered in
this study i.e. the higher the sugar
concentration the greater the intrinsic viscosity
enhancement.
The decrease of the intrinsic viscosity at lower
levels of sugars has no solid explanation but it
can be thought that the reduction in [η] suggest
that 20% sucrose (as also in 10% w/w,
glucose) are poor solvent than water [9]. The
decrease in [η] can be a function of reduction
in the size of polymers in the course of an
increase in the level of macromolecules
(polymer-polymer) association [9, 13]. Thus,
high sugar levels (40% w/w glucose and 15%
w/w lactose) prove to be the best solvent for
SpM. Behrouzian et al. [9] concluded that
there are competing factors associated with
how sugars impact the intrinsic viscosity of
polymer solutions, firstly a decrease in [η] at
lower concentration due to poor solvent
properties, decreases polymer-polymer
association and then at high concentration the
solvent properties are enhanced and therefore
an increase in intrinsic viscosity through coil
expansion.
The Berry numbers varied from 0.11–0.36
(glucose) and 0.11–0.33 (lactose), this
indicates that the SpM polymers are in dilute
domain in the presence of glucose and lactose,
thus, no entanglements or coil-overlapping
was occurred as shown in Table 5. There was
also an increment in the exponent factor of
the power law model, as compared to that of
SpM in water and salt solutions. This increase
was explained by Behrouzian et al [9] that
glucose and lactose could have modified the
SpM polymeric conformation and boost
random coil structure.
Table 4: Intrinsic Viscosity of SpM with salt (NaCl and CaCl2) and Sugar (Glucose and Lactose).
Salts NaCl
CaCl2
c (mM)
0
6.5
12.5
25
50
3.75
7.5
15
3.58(±0.359)
A
3.05(±0.084
)B
3.13(±0.061)
BC
3.33(±0.087
)C
2.96(±0.075)
D
3.06(±0.108
)B
3.13(±0.547)
BC
2.75(±0.026)
D
Sugars Glucose
Lactose
c (%)
0
10
20
30
40
5
10
15
3.58(±0.359)
a
3.34(±0.071
)b
4.13(±0.246)c
8.17(±1.457
)d
12.16(±0.046
)e
3.72(±0.124
)a
6.56(±0.257)f
10.85(±0.088
)g
Results are expressed as means ±SD for the trials performed. The values with the different letter(s) in the same row are
dissimilar considering the Euclidean distance (δ) correlation at dissimilarity threshold of 0.95, P>0.05. (A-D for salts and a-g
for sugars).
Journal of Modern Chemistry & Chemical Technology
Volume 10, Issue 1
ISSN: 2229-6999 (Online), ISSN: 2321-5208 (Print)
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 36
Fig. 2: Changes of Intrinsic Viscosity of SpM with Increase of Salt Concentration.
Table 5: The Berry Numbers c[η] and Exponent b Values for SpM on Addition of Salts (NaCl and
CaCl2) and Sugars (Glucose and Lactose).
Salts
NaCl
CaCl2
c (mM)
0–50
3.75–15
c[η]
0.0888–0.1074
0.0852–0.1074
b
1.03198 (±0.00166)
1.03141 (±0.00224)
Sugars
Glucose
Lactose
c (%)
0–40
5–15
c[η]
0.1074–0.3648
0.1074–0.3254
b
1.064(±0.00189)
1.0618(±0.00125)
Results for exponent b of the power-law model are expressed as means ±SD for the trials performed
Fig. 3: Intrinsic Viscosity of SpM at Varying Sugar (Glucose and Lactose) Concentration.
Intrinsic Viscosity of Stud Plant Mucilage Muyambo et al.
JoMCCT (2019) 28-39 © STM Journals 2019. All Rights Reserved Page 37
CONCLUSION
The mathematical expression which are a
dependent on estimating intrinsic viscosity
from the gradient/slope (Tanglertpaibul-Rao,
Higiro equation 1 and 2) generally show a
better prediction than those which uses the
intercept (Kraemer, Huggins and Schulz-
Blaschke), considering correlation coefficient
R2 and associated errors, RMSE. The shape of
the SpM molecules in water at 25°C were
observed to be either oblate or prolate using
the shape factor v. The molecular conformity γ
(obtained from the slope of log ηsp vs log c)
and the exponent factor b (obtained from
power-law model of log ηsp and log c[η]) were
similar and slightly above 1.0. These
parameters both suggest that the SpM
conformity was between rod-like and random
coil formation in water solvent at 25°C. The
intrinsic viscosity values of SpM were reduced
in the presence of salts (NaCl and CaCl2) and
they were enhanced in presence of sugars
(lactose and glucose), though the distribution
of intrinsic viscosity was not perfect linear
with change in either salt or sugar
concentration. CaCl2 (divalent salt) shows
higher effect than NaCl (monovalent) and in
the same way lactose (disaccharide) shows
higher effect than glucose (monosaccharide).
The Berry numbers (c[η]) for SpM in water,
salt or sugar solution indicated that at each
instant the solutions were in dilute domain
since they were less than unity, 1.0. However,
the exponent b values of SpM in salts were
unexpectedly slightly lower than in water, but
higher in sugars. Nevertheless, the
conformation (rod-like and/or random coil) of
SpM molecules in these three solvents proves
to be the same.
DATA LINK
Muyambo, Shadreck (2018), “Intrinsic
viscosity of stud plant mucilage”, Mendeley
Data, v1 http://dx.doi.org/10.17632/
67wvp69hxm.1
ACKNOWLEDGEMENTS
This research was made possible through the
support from Harare Institute of Technology,
Food Processing Department and Polymer
Technology and Engineering Department
particularly using their laboratory equipment.
We appreciate enormous advice provided by
Professor M. A. N Benhura (University of
Zimbabwe, Biochemistry Department) during
the progression of this research. There are no
special grants or other forms of funding
received for this research and no areas of
conflicts have been recorded to the best
knowledge of the authors.
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Cite this Article
S. Muyambo, I. Chikurunhe, D.N. Moyo.
Intrinsic Viscosity of Stud Plant Mucilage
(Dicerocaryum Zanguebarium): Polymeric
Studies at Infinite Dilution. Journal of
Modern Chemistry & Chemical
Technology. 2019; 10(1) 28–39p.
