[0001] The present invention relates to an improved process for the purification and/or
decolorization of natural oils such as the edible vegetable oils. It particularly
relates to an improved process for alkali refining triglyceride oils into refined
oils having improved color, color stability, odor and/or flavor.
[0002] Crude vegetable glyceride oils, as they are obtained from their natural sources by
conventional extraction or pressing methods, normally contain various non-glyceride
impurities. These non-glyceride substances include gross material from the source
of the oil, such as xanthophyll or chlorophyll; products obtained by the breakdown
of the glyceride oil during treatment such as free fatty acids and other derivatives
of the glycerides such as phosphatides, sterols, aldehydes and ketones; peroxides;
as well as various other impurities such as metal cations, metal complexes, various
disulfides and related impurities. In addition, many vegetable oils normally contain
natural waxes from the crushing of the coat of the oilseeds employed. Some of these
impurities are desirable in that they help to protect the oil from oxidation or other
adverse processes, but by far the greater amount of these substances must be removed
during processing for edible purposes because they are deleterious to the appearance,
taste; stability and other properties of the oil. It has therefore been conventional
practice to subject the triglyceride oils to an extensive purification. Typically,
this purification has involved a complex multi-step procedure including degumming,
refining, bleaching, deodorization, and optionally hydrogenation and/or selected crystallization
(winterizing).
[0003] One technique for refining triglyceride oils heretofore developed by the prior art
is alkali refining. In this technique, the oil is treated with an aqueous solution
of sodium hydroxide or some other strong alkali in an amount slightly in excess of
the amount of the free fatty acids present in the oil to produce a refined oil and
an impurity-containing soapstock. Typical alkali refining techniques which have previously
been employed to refine triglyceride oils are described in U.S. Patent Nos. 2,702,813;
3,629,307; 3,943,155; 4,150,045 and 4,280,962; as well as in Sullivan, Journal Agricultural
and Oil Chemists Society, page 845A (November 1980).
[0004] While the alkali refining techniques of the prior art have been adequate when employed
in combination with the various other procedures mentioned above to produce triglyceride
oils of acceptable purity, many of the various attempts to improve the basic alkali
refining technique described above are somewhat complicated in nature which has discouraged
their commercial exploitation. In the alkali refining procedure of U.S. Patent No.
3,629,307, for example, following treatment of the oil with alkali to produce an oil-water-soapstock
admixture, the admixture must be first dehydrated to a water content of no more than
3% by weight, and then simultaneously rehydrated and centrifuged in a pressurizing
centrifuge in order to obtain the refined oil. Similarly, in U.S. Patent No. 4,280,962,
the alkali extracted oil must be treated with an aqueous solution of acid before the
refined oil can be separated from the insoluble materials formed during refining.
[0005] While the prior art has also developed less complicated variations of the conventional
alkali refining procedure such as the cold refining technique described in the aforementioned
article by Sullivan, cold refining has in practice resulted in unsatisfactory refining
losses which have likewise discouraged the commercial use of this procedure.
[0006] In addition, it has also previously been known in the prior art that the odor and
color of mink oil (a non-triglyceride oil) may be improved by treating the mink oil
with NaBH
4 subsequent to the conventional neutralization and bleaching steps employed for the
purification thereof. The high cost attendant to the use of such extra process steps,
including material and equipment costs, however, renders the use of such separate
NaBH
4 post-treatment procedures impractical for use in the refining of triglyceride oils.
[0007] The use of alkali metal borohydrides in order to improve the color and odor of soap
has also been suggested in
U.S. Patent No. 3,542,823. As described therein, the alkali metal borohydride treatment
is preferably conducted by treating the saponified soap charge immediately after leaving
the washing unit with the alkali metal borohydride at a pH of at least 9.5. Use of
such a treatment in the purification of triglyceride oils is undesirable, however,
since this procedure requires the addition of a further expensive step to the already
complicated triglyceride oil purification process.
[0008] Accordingly, it is an object of the present invention to provide an improved process
for the purification of natural oils such as the triglyceride oils which obviates
the need for complex refining procedures or undesirable extra steps.
[0009] It is a particular object of the present invention to provide an improved alkali
refining procedure which improves the color, color stability, odor and/or flavor of
natural oils, as well as the production efficiency of the overall purification procedure.
[0010] In accomplishing the foregoing and other objects, theri has been provided in accordance
with the present invention an improved process for alkali refining natural oils, such
as for example the triglyceride oils, wherein the efficiency of the refining process
is improved by extracting the oil with alkali while in the presence of an alkali metal
borohydride. The alkal: metal borohydride is generally employed during the alkali
extraction treatment in an amount sufficient to effect the desired improvement in
the quality of the triglyceride oil. Typically, from about 50 to about 2000 ppm of
alkali metal borohydride (based on the weight of oil) are sufficient for most purposes.
[0011] Oils of superior color and purity may be obtained by employing the alkali refining
treatment of this invention in conjunction with a degumming pretreatment step and
a bleaching step. If required, the bleaching treatment may be followed by a deodorization
treatment as well as by any of the various other treatment steps conventional in the
art. In a preferred embodiment, the present invention thus also provides a process
for the purification of natural oils, such as the triglyceride oils, which comprises
the steps of degumming a crude oil to produce a degummed oil; extracting the degummed
oil with alkali while in the presence of an alkali metal borohydride to produce refined
oil and a soapstock; bleaching the refined oil; and, if required, deodorizing, winterizing,
hydrogenating and/or crystallizing the oil.
[0012] Through the use of the inventive concepts of this invention, oils of excellent purity
and color may readily be obtained by a relatively simple procedure without the requirement
for costly extra steps and the attendant capital investment outlays required therefor.
Vegetable triglyceride oils exhibiting a Lovibond color characterized by a yellow
value of 10 or less and a red value of 1 or less, a bland taste, a lack of any perceptible
odor, and a significantly reduced peroxide content, for example, may readily be obtained
through the use of the process improvements of this invention. In addition, oils subjected
to the alkali metal boroh
ydride/alkali extraction of this invention have also been found to exhibit enhanced
heat stability. Moreover, as a result of the enhanced purification achieved by the
alkali refining procedure of this invention, with some oils it is possible to reduce
the amount of bleaching earth required and/or to reduce the time required for deodorization,
accruing thereby a significant increase in purification efficiency.
[0013] Other objects, advantages and features, as well as the preferred modes of operation
of the present invention, will be apparent to those skilled in the art from the following
detailed description of the preferred embodiments.
[0014] The process improvements of this invention may be successfully utilized with any
of the natural oils well known to those skilled in the art, such as the triglyceride
oils. Of the triglyceride oils, the edible vegetable oils are particularly amenable
to processing according to this invention, examples of which include soybean oil,
corn oil, cottonseed oil, peanut oil, sesame oil, rapeseed oil, canola oil, among
others. As is well known to those skilled in the art, such oils are frequently employed
as salad oils, cooking oils, margarine constituents, and as constituents in various
other food applications, and accordingly must meet stringent requirements in terms
of color, flavor, odor and purity. Industry specifications for the edible vegetable
oils generally require that the purified oil exhibit a color, as evaluated by the
Lovibond Color system, characterized by a yellow value of 10 or less and a red value
of 1.0 or less. In addition, the edible vegetable oils must also desirably have a
bland taste, a lack of any perceptible odor, and a peroxide value of 0 as determined
by standard A.O.C.S. test Cd 8-53.
[0015] The alkali metal borohydride treatment of this invention, as discussed above, is
preferably conducted during alkali refining of the triglyceride or other natural.oil.
While the alkali metal borohydride treatment may be conducted at other points in the
overall oil purification process, the low stability of the alkali metal borohydrides
in non-alkaline environments requires that the alkali metal borohydride treatment
be performed during the alkali refining step, or as a separate post-treatment step.
While this latter type of treatment procedure is within- the purview of this invention
and is desirable for use in the purification of e.g., spoiled refined vegetable oils,
it has been unexpectedly found that utilization of the alkali metal borohydride treatment
during the alkali refining step reduces peroxide build-up in the oil during subsequent
treatment. Moreover, utilization of the alkali metal borohydride treatment during
the alkali refining step avoids the addition of a further costly purification step
to the overall purification process, and further, provides a desirable alkaline environment
which enhances the activity of the alkali metal borohydride. Accordingly, it is preferred
that-the alkali metal borohydride treatment be performed simultaneously with alkali
refining.
[0016] The triglyceride oils or other natural oils utilized in the improved alkali refining
procedure of this invention may comprise a crude oil or a pretreated oil, i.e., a
degummed oil.
Degumming of the oil may be accomplished by any of the various degumming procedures
well known to those skilled in the art. The degumming process is primarily carried
out at the extraction mill, where alkali refining may or may not be carried out. To
a much lesser extent, degumming may be done by the refiner at another location. In
general, degumming is accomplished by hydration of the mucilagineous product impurities
contained in the vegetable oil with from about 1 to about 3% by weight water at elevated
temperatures. Typically, a small amount of a degumming agent, such as for example
acetic acid, acetic anhydride or phosphoric acid is employed during the degumming
step in order to improve the efficiency thereof. As a matter of convenience, the degumming
agents are most easily employed by simply adding them to the crude vegetable oil prior
to the addition of the hydrating water. The resulting admixture is thereafter introduced
into a continuous centrifuge in which it is heated and caused to circulate continuously
whereby the mucilagineous products are completely hydrated and the aqueous phase containing
the precipitated hydrated mucilagineous products are separated from the oil.
[0017] The alkali refining step is conducted according to conventional procedures with the
exception that extraction of the oil with the alkali is performed in the presence
of the alkali metal borohydride. Any of the various art recognized alkali refining
procedures well known to those skilled in the art, including any of the various procedures
described in U.S. Patent Nos. 2,702,813; 3,629,307; 3,943,155; 4,150,045; and 4,280,962;
as well as in Sullivan, Journal Agricultural and Oil Chemists Society, page 845A (November
1980), may thus be employed in conjunction with the alkali metal borohydride treatment
of this invention. The particular operating procedures of this step will usually vary
according to the particular type of oil to be refined, and the facilities and equipment
wherein the oil is refined. In general, the oil is refined by contacting the same
with an aqueous solution of a suitable alkali, such as for example but not limited
to sodium hydroxide, at temperatures which range from as low as 5°C to temperatures
as high as about 100°C for an interval of from several seconds to several hours. The
amount of alkali employed during the refining operation is preferably added in an
amount which is only slightly in excess of that theoretically required (the stoichiometric
amount) for neutralization of the free fatty acids in the oil, ah excess of 0.01%
to 0.5%, and preferably from 0.01 to 0.3%, of alkali being preferred.
[0018] The alkali metal borohydride may be added to the system by a variety of procedures.
Typically, the alkali metal borohydride is added with the addition of the alkali solution
to the oil. In this embodiment, the alkali metal borohydride may be employed in powdered
form, or alternatively may be employed in the form of an alkaline aqueous alkali metal
borohydride solution. Alkali metal borohydride solutions of this type are readily
available commercially, for example, from the Morton-
Thiokol Corporation under the trade designation SWS®. If an aqueous alkali metal borohydride
solution is employed, it is necessary of course to adjust the amount of alkali admixed
with the oil to compensate for the alkali present in the ` alkali metal borohydride
solution.
[0019] In an alternative embodiment, the alkali may be divided into two portions with a
first and larger portion being admixed with the oil. The alkali metal borohydride,
either in powdered form or in the form of an aqueous alkali metal borohydride solution,
is admixed with the remaining portion of alkali, and the combined mixture thereafter
added to the alkali deficient oil-alkali mixture.
[0020] As is well known to those skilled in the art, the reaction of the alkali with the
oil during refining neutralizes the free fatty acids present in the oil and purifies
and improves the flavor, odor and color of the same. This action of the alkali is
enhanced by the alkali metal borohydride treatment of this invention. While not wishing
to be bound by any particular theory or explanation, it is believed that the alkali
metal borohydride reduces various impurities in the oil which are resistant to reduction
with alkali, thereby improving the color, color stability, odor, and/or flavor of
the refined oil. Such impurities comprise, for example, the various aldehydes, ketones,
metal cations, metal complexes, disulfides, and related impurities present in the
oil which are resistant to alkali attack. Reduction of these various impurities has
been found to not only improve the quality of the refined oil, but in addition to
retard the bui-ld-up of peroxides and other decomposition products during subsequent
processing.
[0021] The alkali metal borohydride may be, for example, lithium, potassium, or sodium borohydride.
Of the alkali metal borohydrides, the sodium derivative is commercially readily available.
The alkali metal borohydride may be added to the refining process of this invention
either in solid form, or as discussed above, as an aqueous solution. If desired, the
alkali metal borohydride may also be formed in situ from other borohydrides.
[0022] The alkali metal borohydride is generally employed during the alkali refining step
in an amount sufficient to effect the desired improvement in the quality of the purified
oil. The exact amount required for this purpose varies with the particular vegetable
oil being refined and with the particular characteristics of the oil which require
improvement, e.g., color, flavor, odor, taste, etc. Typically, from about 50 to about
2000 ppm of alkali metal borohydride are sufficient for most purposes, with preferred
amounts ranging from about 250 to 1000 ppm, and most preferably from about 250 to
500 ppm of alkali metal borohydride, based on the weight of the oil.- In processing
the edible vegetable triglyceride oils, it is particularly preferred that the amount
of alkali metal borohydride employed be sufficient to produce a purified oil having
Lovibond color characterized by a yellow value of 10 or less and a red value of 1
or less, as measured by a Lovibond Tintometer using a 5 1/4" cell-at ambient temperature;
a bland taste; a lack of any preceptible odor; and a peroxide value of 0.0 as measured
by AOCS Standard Analytical Method Cd 8-53. For the purposes of the present invention,
these characteristics are based on the purified oil, i.e., after it has been degummed,
refined, bleached, and if required deodorized and and/or winterized, dewaxed, etc.
[0023] Following completion of the combined alkali-alkali metal borohydride treatment of
the improved alkali refining procedure of this invention, the refined and purified
oil is separated from the resulting soapstock by conventional separation procedures,
such as for example, by centrifugation. In accordance with conventional practice,
the refined oil is thereafter typically washed with water to remove any residual traces
of soap and then dried to remove any dissolved or emulsified water which may be present.
[0024] Frequently, the production of a purified oil having an acceptable color requires
the use of a bleaching process in order to remove pigments remaining in the oil after
the refining step, such as various carotenoids and chlorophyll, among others. Typically,
the bleaching step is carried out under vacuum at a moderate temperature in the range
of from about 50 to about 120°C in the presence of a bleaching clay. After bleaching,
the oil is then filtered to remove the bleaching clay and pigment products adsorbed
thereon.
[0025] If required, the oil may be thereafter subjected to a deodorization process, winterizing
process, dewaxing process, etc. by conventional techniques well known to those skilled
in the art in order to further improve the quality of the oil. Some oils may also
require hydrogenation in order to reduce the polyunsaturates. These various additional
processing techniques, however, are well known to those skilled in the art and do
not require detailed discussion.
[0026] The invention is additionally illustrated in connection with the following examples
which are to be considered as illustrative of the present invention. It should be
understood, however, that the invention is not limited to the specific examples.
EXAMPLE I
[0027] A degummed soybean oil was alkali refined in accordance with the present invention.
In the runs of this example, refining was carried out in the presence of 250 - 770
ppm of NaBH
4, which was utilized in the form of an aqueous sodium borohydride solution comprising
approximately 12% NaBH
4 and 40% by weight sodium hydroxide (SWS
® brand, available from the Morton-Thiokol Corporation) and in the presence of 1000
ppm NaBH
4 which was utilized in the form of a dry powder. As a control, a further run was conducted
by an identical procedure, but without the use of NaBH
4 during refining.
[0028] In each of these runs, 500 g of oil was first cooled to 10°C and then refining was
performed by adding a sodium hydroxide solution to the oil with agitation in a commercial
blender. Each sample was thereafter agitated for two four-minute periods at a temperature
maintained below 54.4°C (130°F). Where used, the NaBH
4 was added to the sample after the first four-minute agitation and prior to the second.
In the run employing NaBH
4 powder, a portion of the alkali was retained and used for NaBH
4 addition by admixture therewith. The total NaOH employed was in an amount sufficient
to provide a slight excess of NaOH relative to the free fatty acid concentration of
the oil (0.2% excess).
[0029] At the end of the second four-minute agitation period, each sample was allowed to
sit overnight and then filtered through diatomaceous earth. All samples were then
stirred for two hours with molecular sieve to remove any remaining water. Each of
the resulting samples was then evaluated for peroxide value (A.O.C.S. method Cd 8-53),
free fatty acids, FFA, (A.O.C.S. standard method Ca 5a 40, Ca 9a 52, B.3), odor, color
(Lovibond system using a Lovibond Tintometer with a 5 1/4 inch cell at ambient temperature)
and heat stability. The heat stability test comprised an accelerated heat aging process
wherein the oil was heated for 2 hours at 205°C in air and then analyzed for color,
peroxide value and FFA.
[0030] 300 grams of each of the refined soybean oil samples described above were thereafter
bleached by agitating the oil with 1% by weight of a standard bleaching clay (Filtrol
105) at 110°C under a 5 mm Hg vacuum for one hour. The resulting bleached samples
were then cooled to 40°C and filtered through
Whatman #4 filter paper and diatomaceous earth, after which an analysis for peroxides,
color, and heat stability was performed as described above.
[0031] The results of these experiments are set forth in Tables Ia-Ib. As can be seen therefrom,
vegetable oils alkali refined in accordance with the present invention possess improved
heat stability, color and reduced peroxide build-up as compared with vegetable oils
refined in accordance with the prior art.

EXAMPLE II
[0032] This example demonstrates the effect of various NaBH
4 treatment levels during the alkali refining and subsequent bleaching at various bleaching
clay levels of a partially degummed crude soybean oil.
[0033] 1000 gram samples of the partially degummed oil were treated with 0, 250 and 500
ppm of NaBH
4, based on the weight of oil, by the addition thereto of the required amount of SW#
(
Morton-Thiokol Corporation) aqueous NaBH
4 solution to the caustic refining solution. The total NaOH addition was sufficient
to achieve a 0.05% excess of NaOH, based on the .free fatty acid concentration. Refinement
was carried out for 5 minutes in a commercial blender under rapid agitation while
maintaining the temperature below 54.4°C (130°F). Each of the refined samples was
then allowed to settle overnight, followed by filtering through Whatman #4 filter
paper and washing three times with warm deionized distilled water. Following this
treatment, the color, free fatty acid (FFA), and peroxides were evaluated as described
in Example I.
[0034] After refining, 300 grams of each of the oil samples were bleached by agitation with
0.5 to 3% bleaching clay (Filtrol 105) at 100-110°C for one hour under a 5 mm Hg vacuum.
The samples were thereafter cooled to 40°C and filtered through diatomaceous earth
and Whatman #4 filter paper. At this point, the color, peroxide value, and free fatty
acid concentration were again evaluated as in Example I.
[0035] The accelerated heat aging test of Example I was then performed on each sample and
an analysis of % FFA, peroxide and .color made in order to evaluate to heat stability.
[0036] The results of these experiments are set forth in Tables IIa and IIb. As can be seen
from the data of these tables, soybean oils refined in accordance with this invention
exhibit enhanced heat stability as compared with oils refined by conventional procedures.

1. A process for alkali refining a triglyceride oil by reacting said oil with an alkali
solution to produce a refined oil and a soapstock, characterised by-- conducting said
alkali refining step in the presence of an alkali metal borohydride in an amount sufficient
to improve the purity and/or color of said oil.
2. The process of claim 1, wherein said alkali metal borohydride is present during
said alkali refining step in an amount of from about 50 to about 2000 ppm, based on
the weight of oil.
3. The process of claim 2, wherein said alkali metal borohydride is present during
said alkali refining step in an amount of from about 250 to about 1000 ppm, based
on the weight of oil.
4. The process of claim 1, 2 or 3, wherein said triglyceride oil is an edible vegetable
oil.
5. The process of claim 1,2, 3 or 4 wherein said alkali metal borohydride is added
to said alkali refining step in the form of a solid powder.
6. The process of claim 1,2, 3 or 4 wherein said alkali metal borohydride is added
to said alkali refining step in the form of an aqueous alkaline alkali metal borohydride
solution.
7. A process for purifying and decolorizing a triglyceride oil characterised by-the
steps of:
a. degumming a crude triglyceride oil to produce a degummed oil;
b. refining the degummed oil of step (a) with an alkali solution containing from about
50 to 2000 ppm of an alkali metal borohydride, based on the weight of oil, to produce
a refined oil and a soapstock; and
c. bleaching the refined oil of step (b) to produce a purified/decolorized oil.
8. The process of claim 7, wherein said triglyceride oil is an edible vegetable oil.
9. The process of claim7 or 8, wherein said alkali metal borohydride is employed in
an amount sufficient to produce a purified oil having a color, based on the Lovibond
Color System, characterized by a yellow value in the range of 10 or less and a red
value in the range of 1 or less.
10. The process of claim 9, wherein said alkali metal borohydride comprises from about
250 to about 1000 ppm, based on the weight of oil.