Note: Descriptions are shown in the official language in which they were submitted.
CA 02256246 1998-12-18
1 ) TITLE OF THE INVENTION
Process for The Membrane Filtering of Protein Solutions
2) BACKGROUND OF THE INVENTION
i) Field of the Invention
This invention relates to a process for the treatment of protein solutions.
ii) Description of The Prior Art
Whey proteins are commonly concentrated through the use of
ultrafiltration.However,
attempts to utilize membranes in processes which require the protein to
permeate through
the membrane (e.g., microfiltration (MF) for bacterial removal or selective
fractionation
of proteins by ultrafiltration (UF) have been less successful. Standard
organic membranes
in spiral or flat sheet format exhibit soiling which may be partially due to
the formation
of a secondary membrane layer resulting in the rejection of proteins sized
well below the
molecular weight cut off (MWCO) for that membrane. For example, beta-
lactoglobulin
(MW: 18,000) which exists as a dimer in whey (MW: 36,000) exhibits significant
rejection on membranes with much higher MWCO including even MF membranes. This
fact has been used as the basis for concentrating beta-lactoglobulin relative
to alpha
lactalbumin (MW: 14,000) (see U.S. Patent No. 5,008,374) .
The problem of protein rejection can be controlled in tubular membrane systems
through the use of inorganic membranes employing high product recirculation
rates and
and the possible inclusion of the cocurrent circulation of permeate.This
approach is
characterized by low effeciency and high capital and operating costs. It is
also limited to
microfiltration applications.
3) SL>Z~Y OF THE INVENTION
i) Aims of the Invention
Consequently, since the above-described processes are not completely
successful, it is
the object of this invention to provide a process for the treatment of
proteins involving
the use of the full selection of organic and inorganic membranes available and
is
applicable in both OF and MF.
Another object of this invention is to provide a process for the fractionation
of
individual proteins in milk generally or in whey protein solutions in
particular.
Yet another object of this invention is the provision of a process for the
removal of
lipids and/or bacteria from milk generally or from whey protein solutions in
particular.
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ii) Statement of Invention
The present invention is based on the discovery that, by utilizing a system
that applies a
low tangential velocity at the surface of the membrane and low transmembrane
pressure,
permeation of protein sizes down to the approximate molecular weight cut-off
of the
membrane can be achieved. In other words, the present invention provides an
improvement in a process for the membrane filtration of a protein solution.
Thus, the present invention provides a process for the membrane fractionation
of
protein solutions which comprises applying a low pressure and tangential
velocity at the
surface of the membrane, whereby permeation through the membrane of protein
sizes
down to a pre-selected molecular weight cut-off of the membrane is achieved.
iii) Other Features of The Invention
By one feature of the invention, the protein solution is milk, whey,
concentrated whey or
a purified solution of whey proteins. In one variant of such feature, one or
more proteins
of higher molecular weight are rejected, which lower molecular weight proteins
pass
through the membranes. By one facet of that feature of the invention, the
higher
molecular weight proteins are immunoglobulin and/or bovine serum albumin
proteins,and
the lower molecular weight proteins are beta-lactoglobulin and alpha-
lactalbumin, which
are allowed to pass into the permeate. By another facet of that feature of the
invention the
higher molecular weight protein is beta-lactoglobulin, and the lower molecular
weight
protein is alpha lactalbumin, which is allowed to pass into the permeate. By
another facet
of that feature of the invention the higher molecular weight protein is
phosphocasein and
the lower molecular weight proteins are immunoglobulin,bovine serum
albumin,beta-
lactoglobulin, and alpha lactalbumin proteins.
In another such feature of the invention, the permeate is subjected to at
least one of
further concentration and diafiltration steps to produce a milk or whey
protein isolate
containing greater than 90% protein on a dry basis.
By another feature of the invention, the membrane has a pore size which is
selected to
remove bacteria but will allow substantially all protein to pass through the
membrane.
By a further feature of the invention, the membrane has a pore size which is
selected to
remove residual lipid material,but to allow substantially all protein to pass
through the
membrane.
In other facets of these features of the invention, the resulting concentrates
are dried to
produce individual milk or whey protein fractions, or the permeates are
further
concentrated and dried to produce individual milk or whey protein fractions.
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iv) Generalized Description of the Invention.
The process conditions are most effectively applied by passing a protein
solution
through a membrane pack ( Pall Corporation Cassette Systems, North Carolina
SRT
Cross Flow filter modules, Millipore Prostak membrane module) with a channel
height
greater than O. Smm, a tangential velocity of less than 3.0 meters a second
and a
transmembrane pressure of less than 10 psi.
Accordingly, this invention provides a process for the membrane filtration of
protein
solutions.Such process uses standard flat sheet membrane materials. The
proteins in the
solution of sizes down to the approximate molecular weight cut-off of the
membrane are
able to cross the membrane and may be recovered in the permeate solution
without any
significant rejection of these proteins.
4) DESCRIPTION OF PREFERRED EMBODIMENTS OF TIC INVENTION
The following are examples of the present invention.
Example 1
4 liters of cooled whey protein concentrate (43%) were recirculated through an
ultrafiltration holder ( known by the trdemark North Carolina SRT OPTISEP ) at
a flow
rate of 2.0 U. S. gallons per minute with the temperature maintained at less
than 60
degrees F. The transmembrane pressure was maintained at 6 psi.This unit was
equipped
with 0.2 square feet of 500,000 MWCO PVDF membrane. Permeate was recombined
with the feed to maintain a constant volume and the test was carried out for a
period of 5
hours. Samples were taken for protein analysis every hour and flux
measurements were
taken throughout the run.
Analysis for Bovine serum albumin, alpha lactalbumin, and beta lactoglobulin
revealed
no significant rejection over the course of the test. Bacteria and lipid
removal were shown
to be greater than 99% and the flux remained constant at 1 lml/min for the
duration.
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Example 2
2 liters of defatted protein solution were circulated through an
ultrafiltration holder
( known by the trademark North Carolina SRT OPTISEP ) at a flow rate of 1.9 U.
S.
gallons per minute with the temperature maintained at less than 60 degrees F.
The
transmembrane pressure was maintained at 4 psi. This unit was equipped with
0.2 square
feet of 30,000 MWCO RC membrane. Permeate was recombined with the feed to
maintain a constant volume and the test was carried out over a period of 4
hours. Samples
were taken for protein analysis every hour and flux measurements were taken
throughout
the run. Analysis for beta lactoglobulin and alpha lactalbumin revealed
significant
rejection for the beta lactoglobulin and no significant rejection of the alpha
lactalbumin.
The flux remained constant at 22 ml per minute for the duration.
CONCLUSION
Thus, by the present invention, a process is provided which is particularly
effective with
whey protein solutions and may be used for the removal of bacteria or lipids
or for the
fractionation of individual proteins.
