Note: Descriptions are shown in the official language in which they were submitted.
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NOV~L PROTEIN ISOLATION PROCEDURE
The present invention relates to the isolation
of proteins from source materials.
The i~olation of proteins from source
materials, such as, legumes and oil seeds has been the subject
of considerable research and a number of procedures have
been suggested. One such procedure is the isoelectric
precipitation of the protein by extracting the protein with
aqueous alkali and then acidifying the extract to the iso-
electric point of the protein. A more recent development,described in U.S. Patents Nos. 4,169,090 and 4,208,323, assigned
to the assignee of this application, involves the formation of
an isolate under much milder conditions, using an aqueous
food grade salt solution of ionic strength in excess of 0.2M
15 to extract the protein under weakly acid conditions, and
dilution of the protein solution to form the isolate.
Protein isolates are characterized by high protein
contents, namely at least about 90% by weight (as determined
by Kjeldahl nitrogen x 6.25), and have utility in various
food compositions.
It has now been surprisingly found that the pro-
tein can be isolated from certain selected oil and legume
seeds by a hitherto unknown but very simple and surprising
procedure. In accordance with this invention, a vegetable
25 protein seed selected from the group consisting of rapeseed
(canola), sesame, pea and cottonseed is contacted with
water to dissolve the protein therefrom and water is then
added to the protein solution to precipitate an isolate
of the protein. The isolate which is attained by this
30 procedure is substantially undenatured. Where the protein
source is an oil seed, the seed may be defatted prior to
contact with water.
The process of this invention, therefore, is a simple
operation requiring extraction of the protein from the
35 plant protein source into water and then dilution of the
protein solution with the same solvent, namely water, to
precipitate the isolate.
It is quite surprising that proteins of certain
plant proteins can be isolated by the simple expedient
40 Of diluting an aqueous extract of the proteins, in view of
A ~
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the indications of the prior art, noted above, that alkalin-
ity and/or high ionic strength are required to effect protein
extraction.
Theplant seed proteins to which the invention is
applicable are limited to a defined group, namely, rapeseed
~canola), sesame, peas and cottonseed. The plant
proteins to which the invention is applied include oil
seeds which are valuable sources of vegetable oils for use
in a variety of food products and usually are crushed and/
or solvent extracted to remove the oil.
The initial step of the process of the invention
involves solubilization of the protein in the source material,
usually after initial defatting in the case of oil seeds.
The particulate plant seed ~rotein, in the form of a concen-
trate or meal remaining from oil removal operations, iscontacted with water. The average particle size of the
particulate protein may vary widely, generally between about
10 and about 8QQ mesh, preferably less than about 5Q mesh.
The extraction is effected with water at a concen-
tration of protein source material in the aqueous phase of
about 5 to about 25% w/v, preferably about 10 to about 15%
w/v. The extraction may be accompanied by agitation to
decrease the solubilization time, which is usually about 10
to about 60 minutes. The temperature at which the extraction
is effected is not critical and room temperature (about 20
to 45C) can conveniently be used. Generally, the temperature
of the water used in the extraction step is within the range
of about 15 to about 35C. The water used in the extraction
step may be distilled water or tap water, as desired.
When the protein extraction operation has been
1~39.?0!~
effected, the protein solution is separated from solid phase
extracted material. The protein solution, which may have a
protein concentration of a~out 5 to a~out 100 g/l, preferably
about 2a to a~out 70 g/l, is diluted in the second step of
the process to form a dispersion of protein particles which
are collected.
The dilution of the aqueous protein solution may ~e
effected by passing the protein solution into a body of
water having a temperature ~elow a~out 25C and preferably
about 5 to about 15C. The dilution is effected to cause
the formation of a dispersion of protein aggregates and the
isolate may be collected from the dispersion by permitting
the protein particles to settle or ~y inducing settling, such
as, ~y centrifugation.
The settled protein isolate may be removed from
residual aqueous phase and dried by any convenient technique,
such as, spray drying, freeze drying or vacuum drum drying.
The protein isolate has in common with other protein isolates
a high protein content in excess of about 90~ (as determined
by Kjeldahl nitro~en CTKNl x 6.25), and often much higher.
In addition, the protein isolate is su~stantially undenatured
~as determined by ~el filtration), thereby enhancing its
functional value.
It has previously been suggested in U.S. Patent No.
3,758,452 to produce a rapeseed isolate by a procedure
involving extraction under alkaline pH conditions and then
pH adjustment to acid values. The products of this
procedure are said to contain up to a~out 88% protein (as
determined by TKN x 6.25~. As indicated above, a protein
extract is normally regarded as an isolate only when the
protein content exceeds ~0%. The product formed in this
in~ention conforms with this protein content requirement
whereas the protein produced by this prior art procedure does
not. The product of the process of U.S. Patent No.
3,758,452, therefore, is a concentrate and not an isolate
and,in addition, is substantially denatured.
The present invention, in one aspect, therefore,
relates to a noYel product, namely a substantially undenatured
ll3s~,n~
rapeseed protein isolate.
The invention is illustrated further by the follow-
ing Examples:
Example 1
Solvent extracted rapeseed meal containing about
50 wt.% protein was formed into a 10% w/v suspension in tap
water (pH 5.8) at 20C and the suspension was stirred by
gentle mechanical action for 30 minutes. The slurry was
centrifuged at 10000xg for 20 minutes and the supernatant
protein solution was decanted.
The protein solution was poured into 15 volumes of
cold (about 8C~ tap water resulting in a turbid suspension
of pH 6.3. The protein was collected from the suspension
in two ways. One half of the volume of the suspension was
centrifuged at about 6000xg for 15 minutes while the other
half of the volume of the suspension was allowed to settle
overnight in a refrigerator at about 4C. The settled protein
was separated from the aqueous phase and dried. From 2.2 litres
of extract containing 33.7 mg/ml of protein, there were
collected 27g ~dry weightl of protein.
The protein isolate exhibited a protein content
(as determined by Kjeldahl N x 6.25) of 106 wt.% and was
substantially undenatured (as determined by gel filtration).
Example 2
50g of a pea protein concentrate containing about
55% protein CKjeldahl N x 6.251 were stirred into 500 ml
of water (pH 6.41) for one hour at room temperature (about
25C). After centrifugation to remove insolubles, 370 ml
of extract containing 4.31~ of protein (TKN x 6.25) were
diluted into 25~0 mls of cold tap water (8Cl and a precipitate
conta~ng 91.9~ protein (on a dry weight basis) was formed.
Example 3
30g of a dehulled , solvent extracted sunflower
flour containing 58% protein (TKN x 6.25) was stirred into
300 ml of water (pH 6.25l for 45 minutes at room temperature
(about 25C). After centrifuging to remove insolubles, 240
ml of extract containing 2.61% protein (TKN x 6.25) was
diluted into 1680 ml of cold tap water (8C~. No precipitate
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formed, indicating that the procedure is ineffective in
recovering a protein isolate from sunflower. In a similar
experiment, it was found that a soybean isolate also could not
be formed.
In summary of this disclosure, the present invention
provides a novel process for isolating proteins from certain
p~ntseeds which enables substantially undenatured protein
isolates to be formed by a simple and inexpensive process.
Modifications are possible within the scope of this invention.
