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: swainsk2@yahoo.co.in

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