Indian Journal of Pure & Applied Physics
Vol. 48, August 2010, pp. 539-542
Ultrasonic and viscometric study of soya protein in aqueous solution
Sarat K Swain* & Pragnya P Priyadarshini
Department of Chemistry, North Orissa University, Takatpur, Baripada 757 003, India
*E-mail: [email protected]
Received 3 September 2009; revised 3 March 2009; accepted 30 March 2010
The interaction of proteins, compatibility of biomaterials and molecular dynamics, solute in solvent have been
investigated by ultrasonic technique. Ultrasonic velocities, viscosities and densities of aqueous solution of soya protein were
measured as a function of concentration and resonance frequencies in the range 3-10 MHz ultrasonic waves. The acoustic
parameters such as adiabatic compressibility, aquatic impedance and viscosity relaxation time were calculated at different
aqueous concentration of soya protein. The adiabatic compressibility of soya protein has been found to decrease with rise in
concentration at both frequencies. However, the decreasing tendency was stiffer at 10 MHz as compared to 3 MHz. It may
be due to the weak interaction of water molecules with protein chains at 3 MHz. The acoustic impedance (Z) increases with
increase in concentration at both frequencies of ultrasound. The viscosity relaxation time of soya protein decreases with
concentration at ultrasonic frequency of 10 MHz, however, at lower frequency of ultrasound at 3 MHz, the value τ increases
linearly with concentration.
Keywords: Acoustic impedance, Adiabatic compressibility, Relaxation time
1 Introduction
The soyabean is one of the most nutritious foods
which belong to the family of legumes or pulses1. It is
grounded up to make soya flour which is then mixed
with water to remove the soluble carbohydrate. The
residue is formed into its final shape - chunks, mince
or flakes2. Soya protein is called as intact protein that
means these are polypeptides containing purified
forms of native proteins.
The application of ultrasonic methods for probing
the structural dynamics3 of biopolymers such as
proteins and polysaccharides has been the subject of
wide research. The study of ultrasonic absorption of
macromolecules including proteins was likely to have
a contribution from a coupling between the thermal
motion of the protein and water molecules, which
changes the strength of their interaction with the
protein4. Only a few biologically important
macromolecules have been subjected to thorough
ultrasonic experiments. For hemoglobin5, protein
6 and
dextran13
, the interaction between solvent and solute
is probably the principal mechanism of acoustic
absorption. Several researchers have used ultrasonic
velocity (υ) together with density (ρ) and viscosity (η)
measurements to study protein-solvent interaction7,8
.
The study of viscometric9,10
on the interaction and
compatibility of protein solution has already been
investigated. The compatibility and interaction studies
of protein probed by sound velocity and related
acoustic parameters are reported in Refs 11 and 12.
Polymers which are water soluble such as soya
protein, have been studied because of their versatile
pharmaceutical, biomedical and industrial
applications. These include the preparation of many
biomedical products, such as biocompatible
hydrogels13
and anticoagulants14
through degradation
and grafting onto these proteins. Because of this
extensive applicability, a comparative study of υ,
related acoustic parameters and viscosity of the
pharmaceutically active soya protein in aqueous
solution have been reported in the present paper. The
protein-water compatibility and their acoustic
properties by ultrasonic technique have been studied.
2 Experimental Details
Soyabean protein sample was supplied by the
HiMedia Laboratories Pvt Ltd, Mumbai, India and
used without further purification. The water used for
the experiments was doubly distilled over alkaline
permanganate and deionized.
An ultrasonic interferometer (Mittal Enterprises,
New Delhi, India) is a simple and direct device to
determine the ultrasonic velocity in liquids with a
high degree of accuracy. The principle used in the
measurement of velocity (U) is based on the accurate
determination of the wavelength (λ) in the medium.
Ultrasonic waves of known frequency (f) are
produced by a quartz plate fixed at the bottom of the
cell. The waves are reflected by a movable metallic
plate kept parallel to the quartz plate. If the separation
INDIAN J PURE & APPL PHYS, VOL 48, AUGUST 2010
540
between these plates is exactly a whole multiple of the
sound wavelength, standing waves are formed in the
medium. The acoustic resonance gives rise to an
electrical reaction on the generator driving the quartz
plate and the anode current of the generator becomes
maximum.
Ultrasonic velocity of soya protein was measured at
frequencies of 3 and 10 MHz with varying the
concentration (C) at temperature of 30°C. The
viscosity (η) of the sample solution was measured at
30°C with an Ubbelohde suspended level viscometer.
The density (ρ) of the sample solution was determined
with a specific gravity bottle with a 25 ml capacity.
The ultrasonic acoustic parameters were calculated
using the standard formulae as follows.
(a) Ultrasonic velocity (υ) — If the distance is
increased or decreased and the variation is exactly
one half wavelengths (λ/2) or multiple of it, anode
current again becomes the maximum.
υ = λ × f
where λ is the wavelength in mm and f is frequency in
MHz
(b) Adiabatic compressibility (βS) — βS=1/ρυ2, where
ρ is the density and υ is the ultrasonic velocity
(c) Acoustic impedance (Z) — Z = ρ × υ, where ρ is
the density and υ is the ultrasonic velocity
(d) Viscosity relaxation time (τ) — τ = 4η/3ρυ2,
where ρ is the density and η is the viscosity
3 Results and Discussion
The values of ultrasonic velocity (υ) in viscosity (η)
and density (ρ) of soya protein are presented in
Table 1. To understand the structural effect and
molecular interactions occurring in aqueous solution
of soya protein, several acoustic and thermodynamical
parameters were derived from different experimental
results of ultrasonic velocities, viscosities and
densities. The variation of density in aqueous solution
of soya protein is shown in Fig. 1. It is found that
density of soya protein increases gradually with
increasing concentration of the solution in the range
0.01-0.1(w/v) %.
In Fig. 2, viscosities of soya protein progressively
have been found to increase with variation of
concentrations. It is noticed that viscosity of the
solution increases by 10% with increasing
concentration 0.01-0.1 (w/v) %. This increase in
viscosity with the rise of concentration may be due to
the enhanced tendency of protein molecule to
associate in the protein-water system.
Ultrasonic velocities were measured with frequency
of ultrasound i.e. at 3 and 10 MHz with variation
Fig. 1 — Variation of densities with concentration in aqueous
solutions of soya protein
Table 1 — Comparative values of ultrasonic velocity υ at frequency of 3 and 10 MHz, density (ρ), viscosity (η), adiabatic compressibility
(βs), acoustic impedance (Z), viscosity relaxation time (τ) for soya protein at different concentrations ( wt/v%)
C ρ ×10−3 η, SI λ/2, mm υ, m/s βs×1010 N m−2 Z, SI unit τ ×107 min
(w/v)% Kg/m3 Unit f, MHz λ/2 f, MHz υ f, MHz βs f, MHz Z f, MHz τ
0 0.9562 1 3 0.493 3 1480 3 4.77 3 1415.17 3 6.36
10 0.148 10 1480 10 4.77 10 1415.17 10 6.36
0.01 0.9570 1.023 3 0.252 3 1512 3 4.57 3 1446.98 3 6.23
10 0.070 10 1400 10 5.33 10 1339.80 10 7.27
0.025 0.9583 1.058 3 0.253 3 1518 3 4.52 3 1454.69 3 6.38
10 0.072 10 1440 10 5.03 10 1379.98 10 7.09
0.05 0.9598 1.079 3 0.254 3 1524 3 4.48 3 1462.73 3 6.45
10 0.075 10 1500 10 4.63 10 1439.70 10 6.66
0.075 0.9613 1.089 3 0.255 3 1530 3 4.44 3 1470.78 3 6.45
10 0.077 10 1540 10 4.38 10 1480.40 10 6.36
0.1 0.9639 1.126 3 0.257 3 1542 3 4.36 3 1486.33 3 6.55
10 0.079 10 1580 10 4.15 10 1522.96 10 6.23
SWAIN & PRIYADARSHINI: ULTRASONIC STUDY OF SOYA PROTEIN
541
Fig. 2 — Variation of viscosities with concentration in aqueous
solutions of soya protein
Fig. 3 — Variation of ultrasonic velocities with concentration in
aqueous solutions of soya protein.
of concentration of the solution. At both the
frequencies, ultrasonic velocities increase gradually
with increase of concentrations. However, increase of
velocity at low frequency i.e. 3 MHz is proportionally
less than the velocity at high frequency. That means
the plot at frequency of 3 MHz is stiffer as compared
to the velocity at 10 MHz (Fig. 3). This may be due to
active interaction of ultrasound wave with the
aqueous solution of soya protein. The protein chain
may have hindered rotation or conformational inter
conversion that occurred at high frequency of sound
wave. At all concentrations, the velocities vary almost
linearly which indicated the compatible nature of
protein in aqueous solution.
Fig. 4 — Variation of adiabatic compressibility with
concentration in aqueous solutions of soya protein
Fig. 5 — Variation of acoustic impedance with concentration in
aqueous solutions of soya protein
The protein chain assumes a variety of
conformational changes under different experimental
conditions. Protein chains are more compressible
because of their chain like structure. It can be shown
by a decrease in adiabatic compressibility with
increase in concentration (Fig. 4). This result was
verified at both frequency of concentration (3 and
10 MHz) with different values of concentration.
Comparing the results at frequency 3 and 10 MHz,
it is assumed that the acoustic sound wave was
perturbed at 3 MHz, the segmental motion of soya
protein chain was in such a way as to cause
rearrangement of the water molecules which are
weakly interacting with the protein chain. This result
INDIAN J PURE & APPL PHYS, VOL 48, AUGUST 2010
542
was in good agreement with the result obtained due to
the ultrasonic relaxation in aqueous solution of
dextran4 and PVA-Dextran bending
12.
In Fig. 5, the acoustic impedance (Z) of soya
protein increase with increase in concentration at both
frequency of ultrasound. The increasing trend of Z
with concentration could be interpreted on the basis
that most of the solvent molecules were engaged in
interaction with them by cross-linking via hydrogen
bond and compatible in all range of concentration and
ultrasound.
The variation of τ with concentration is shown in
Fig. 6. It is found that viscosity relaxation time
decreases with concentration at ultrasonic frequency
of 10 MHz. But at low frequency ultrasound of 3
MHz, the value of τ increases linearly with
concentration. This indicates that the interaction and
compatibility of water-protein solution were
prominent via structural change.
4 Conclusions
The ultrasonic results are described in this paper
with acoustic thermodynamical magnitudes of the
interaction parameters between the protein and the
water. So a remarkable compatibility in aqueous
solution in all range of concentration, the interesting
and significant outcome of our study may enable the
development of pharmaceutically active molecules
and various biomedical applications.
Acknowledgement
Authors express their thanks to Department of
Atomic Energy, BRNS, Government of India for
providing financial assistance.
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Fig. 6 — Variation of viscosity relaxation time with concentration
in aqueous solutions of soya protein