Biomedical Engineering Reference
In-Depth Information
groups in the protein molecules and sulfate groups in DSS. At a higher SC concentration (4
wt %) SC-DSS associates forms a pore structure with a diameters of the holes of about 2-3
um. Such structure is usual for many water soluble protein-polysaccharide complexes. Data of
chromatography indicate that DSS interacts first with SC associates having higher molecular
weight. The degree of the protein conversion in the complex increases from approx. 30 % to
80% when the concentration of SC in the system grows from 1 to 2 wt %. Phase separation of
semidilute ternary water-biopolymer 1-biopolymer 2 systems in the presence of DSS is
observed here to be a rather common phenomenon, observed for different types of
biopolymers, e.g. SC-gelatin type-A, gelatin type A-SA. Therefore the use of DSS as a
decompatibilizer for semidilute biopolymer systems can find applications in processes for
concentrating biological materials in two phase systems, because DSS induced demixing
allows decreasing the critical concentration of the phase separation significantly.
It is important to note that complex formation of SC with DSS in dilute and semidilute
solutions has been studied for the first time long ago[20] and recently in details by Dickinson
[21,22]
The dominant mechanism controlling the phase separation involves the creation of water
soluble protein-sulfate polysaccharide associates. Such systems forms the pore structure with
a diameter of holes about 2-3 um. Thermodynamic incompatibility of biopolymers in such
systems develop symbasis with the density of the network, and slop opposition with the
diameters of the network holes[18].
In this work we examine the issue of whether of low-volume fractions of nano- and
microparticles can lead to phase separation in semidilute biopolymer mixture. To do that, we
determine the phase diagrams and ESEM images of aqueous semidilute and weakly structured
sodium caseinate-sodium alginate-dextran sulfate (SC-SA-DSS) system in the presence of
several micro particles containing the functional groups of different origin and sign of charge
with a diameter less, higher, and comparable with the size of the system network holes (2-3
um).
We demonstrate that 3 um particles (both negatively and positively charged) help to
enhance phase separation, and increase the viscoelastic properties of the emulsion. We found
evidence that the dominant mechanism responsible for decrease thermodynamic compatibility
in such system is perfect build 3 um particles into the holes (2-3 um in diameter) of the weak
network of SC enriched phase, and reinforcement of this network.
M
ATERIALS AND
M
ETHODS
The sodium caseinate sample (90% protein, 5.5% water content, 3.8% ash, 0.02%
calcium) was purchased from Sigma Chemical Co. The isoelectric point is around pH = 4.7-
5.2.The weight average molecular mass of the sodium caseinate in 0.15 M NaCl solutions is
320 kDa[18]. The medium viscosity sodium alginate, extracted from brown seaweed
(
Macrocystis pirifera
), was purchased from Sigma. The weight average molecular weight of
the sample in 0.15 M NaCI, M
w
was 390 kDa. Dextran sulfate, DSS (M
W
= 500 kDa, M
n
=
166 kDa, η (in 0.01 M NaCl) = 50 mL/g, 17% sulfate content, free SO
4
less than 0.5%) was
produced by Fluka, Sweden (Reg. №. 61708061 A, Lot No. 438892/1). Surfactant free
particles contains a negatively charged SO
4
2-
groups grafted to the surface of the polymer
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