CA1041536A - Dewaxing process for vegetable oils - Google Patents

Abstract

IMPROVED DEWAXING PROCESS
FOR VEGETABLE OILS

Abstract of the Disclosure This invention relates to an improved process for dewaxing vegetable oils containing free fatty acid impurities, wax and other insoluble matter, which comprises: chilling a refined and water-washed or filtered vegetable oil, mixing the chilled vegetable oil with a dilute alkaline solution; gently agitating the resulting mixture, centrifuging the mixture and separating a heavy phase which contains wax and other impurities from a light phase which may then be bleached and deodorized to form a clear oil. The invention further relates to a reliable process for producing salad oils and other clear oils which remain clear at ambient to refrigerator temperatures.

Description

104i~3~i Background of the Invention This invention relates to an improved process for dewaxing vegetable oils and more particularly to a process in which consistently efficient separation of undesirable waxes can be achieved for oils such as sunflower, safflower, and corn oil. Vegetable oils, and more particularly edible vegetable oils, are used as salad oils, cooking oils, margarine constit-uents and the like. Safflower, sunflower and corn oil in particular are often used in these and other food applications.
For purposes of this application the terms "wax"
and "high melting material" are used interchangeably and are intended to be generic to the many substances which can cause clouding in oils at temperatures of less than about 60F.
A problem which arises in the purification of vegetable oils is that the crude oils tend to have high contents of undesirable insoluble material. Natural vegetable seed oils are composed of mixtures of many naturally produced chemical compounds including not only the oily constituents, but also usually, small percentages of natural phosphatides, ' -vegetable waxes, pigments, and many other compounds. The oily constituents, namely the glyceride esters of the long chain fatty acid of the saturated and unsaturated types make up the largest fraction of vegetable oils. Such materials to a large extent determine the properties of the oil, but the remaining constituents also exert a marked and sometimes detrimental effect, depending upon the use to which the oil -is put. ~ -Some natural vegetable oils of commercial grades such as safflower, sunflower, cottonseed oil, soybean oil, peanut oil and corn oil become cloudy after having been 10(~
chilled or cooled to somewhat lower than room temperatures as in a refrigerator and remain cloudy when returned to ordinary (room) temperatures. The cloudiness may be followed by a settling out of an opaque layer, a particularly disadvantageous occurrence when the oil is packed in glass and where clarity and brightness are of importance.
A large portion of the high melting material can be removed from oils by a process known as "winterizing" in which the oils are carefully cooled to low temperatures for extended periods of time to permit precipitation of solid material.
Solid material can then be removed by pressing or other separa-tion procedures. However, not all of the high melting solid material is removed from oils by winterizing, and the oil still tends to cloud when stored for extended periods of time at low temperature. Moreover, the usual winterizing treatment undesirably tends to remove by entrainment a substantial portion of the olein fraction of the oil.
The process of this invention presents a process for producing a salad oil whiah remains clear at ambient to refriger-ator temperatures. This process is useful for processingoils which contain waxes such as sunflower, safflower, or corn oil. A number of oils such as those mentioned above contain small quantities of waxes which are derived from the seed coats during crude oil extraction. These waxes precipitate at room temperatures or lower, making the oils unsuitable for use in salad oils. In the past these waxes have been partially removed by expensive processes involving low temperature crystallization and filtration at very slow rates.
The dewaxing process of this invention is useful primarily for oils which have been previously refined and

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either water-washed or filtered. It is important that the oils have a low fatty acid content of less than about 0.1%
and in addition the oils should have a low soap content of less than about 0.1%. The use of normal crude oils in the process of this invention is practically impossible because of the many impurities present.
Many previous attempts have been made to remove wax fractions from crude vegetable oils by mechanical separation such as centrifuging and filtration at low temperatures. These techniques have been unsuccessful due in part to the small differences in specific gravity between the wax and the vegetable ,

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oil and also due to the compaction of the vegetable oil wax under pressure in a filter to a slime or grease con-sistency which resists the passage therethrough of the vegetable oil.
Refining techniques previously in general use, such as alkali treatment of oil, will not remove wax from vegetable oils sufficiently to eliminate the cloudy appearance of the oils due to the presence of wax, part-icularly at lower temperatures. Treatment of vegetable oils with bleaching earth reported as an effective method of removing mucilaginous materials is not effective at low temperatures, as the slimy nature of the vege-table oil wax prevents satisfactory removal of the treat-ment material. Another common approach to refining of oils is the hydration of gumming material, making them insoluble. However, addition of water to vegetable oil per se does not render the wax any more oil insoluble or more readily recoverably by any mechanical methods.
In view of the above, it is an object of this invention to provide an improved process for the dewaxing of refined and water-washed or filtered vegetable oils.
It is a further object of this invention to provide a dewaxed vegetable oil which is suitable for use as a salad oil after it has been bleached and deodorized.
It is an additional object of this invention to provide a dewaxed vegetable oil having excellent re-frigerator clarity of greater than 100 hours at 32F
and greater than 2 weeks at 40F.
These and other objects will become apparent from the discussion below.
Summary of the Invention According to the present invention a refined

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- vegetable oil containing less than 0.1~ free fatty acid and less than 0.1% soap is chilled to a temperature of less than 60F. and held for a time period of greater than 1 hour. The resulting chilled vegetable oils is mixed with an aqueous alkaline solution and subjected to agitation in a low shear-high circulation manner for at least 1/2 hour to uniformly disperse the alkaline solution without forming an inseparable emulsion. The mixture is then separated into a water phase containing the wax of the natural vegetable oil and a dewaxed oil phase. This oil phase may be later bleached and deodorized to form an improved clear oil, e.g. salad oil.
Description of the Preferred Embodiments This invention comprises a process for dewaxing a vegetable oil by successively chilling, diluting with an alkali solution, agitating, centrifuging, separating and finally bleaching and deodorizing to provide a finished salad oil.
Oils which are suitable for salad use frequently are stored in refrigerators. The prolonged cooling of such oils to temperatures normally encountered in re-- frigerators such as from about 30F to about 50F generally results in the deposition of crystalline material, usually solid triglycerides or waxes ~linear esters) from the oil.
This material may appear in the form of a cloud, or as -clusters of crystals and is considered objectionable by the housewife. In general, the tendency to form solid triglycerides in oils also adversely affects the suitability of the oil for use in mayonnaise emulsions.
Mayonnaise emulsions prepared from such oils tend to be unstable at low temperatures and are more easily broken.

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The proccss of this invcntion, a procedurc known as "dewaxing", has been developec7 to process those oils which con-tain waxes which precipitate at refrigerator temperatures. The most common of such oils are sunflower, safflower and corn oils, although many other vegetable oils encounter similar problems.
As mentioned previously, it is necessary for the practice of the present invention that the oil to be dewaxed have a low soap content and a low free fatty acid content in addition to being refined or water-washed. The low soap and fatty acid content of course are a direct result of the refining and/or water wash-ing procedures. More particularly, a refining procedure which has been found suitable for the practice of this invention is described in U.S. Patent 3,102,898 (1963) issued to Schmitt and entitled "Process for the Purification of Glyceride Oils".
"Refining" is commonly referred to as the removal of gross impurities, gummy or mucilaginous material and the free fatty acids from oils and as herein used the term excludes "bleaching" (color removal) and odor removal. Known methods of refining include contacting the oil with strong or dilute alkaline material followed by separation of impurities, by liquid-liquid extraction of impurities from the oils, or by some form of steam distillation, and/or by contacting the glycer-ide oils with acids. The ultimate objective of a refining oper-ation is to remove every undesirable impurity completely, while at the same time maintaining intact all of the desirable oil.
The particular process used with a given oil is determined by the foregoing consideration of maximum impurity removal wlth a minimum of oil loss.

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The vegetable oil aftcr refining and/or water washing operations must contain less than about 0.1% of free fatty acids and preferably from about 0.01% to about 0.05%. In addi~
tion the soap content must be less than about 0.1% and prefer-ably less than about 0.05%. It has been shown that if thelimits of either of these ranges are not observed an almost inseparable emulsion forms upon dewaxing with an alkali solution.
The refined and/or water washed oil is then chilled using standard chilling apparatus to less than 60F. and held at these chilled temperatures for longer than 1 hour. A pre-ferred range of chilling temperatures is from about 30F to about 50F. Optimum results are obtained by chilling the oil : to 40F. Upon completion of chilling an alkali solution is added amounting to from about 10% to about 30/O of the oil by weight.
A preferred alkaline material is sodium hydroxide although others are viable substitutes. Alkali solutions that have been found - acceptable for purposes of this invention include, but are not limited to sodium hydroxide, sodium bicarbonate, calcium hydrox-ide, potassium hydroxide, magnesium hydroxide, ammonia, and some organic alkalies. When sodium hydroxide is used as the alkali material it must be mixed to a concentration within the range of from about 1~0% to about 2.5% by weight of lye in water. This concentration range is important as above 2.5% and below 1.0% chill test results are unsatisfactory. When other alkali agents are used correspondingly different concentration ranges are used.
The chilled oil and alkali solutions are then mixed with gentle agitation. The alkali solution is added until- it : ~ . ~ . , ~ . .
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forms from about l~/o to about 30/O by weight of the total mixture.
A preferred range is from about 15% to about 25%. Agitation may be provided by any suitable means although rotary mixers operating to provide low shear and high circulation are preferred, - 5 i.e. Twin 6" Marine impellers operated at 100 rpm. The aqita-tion must be strong enough to uniformly disperse the alkali ; solution without, at the same time, forming an inseparable emulsion. The alkali solution is kept in contact with the oil ;~ for a minimum of 1/2 hour. If high shear mixing is employed the alkali solution and the oil form a virtually inseparable emul-sion making further separation difficult. The low shear - high circulation mixing necessary for the practice of this process is normally provided by operating rotary mixers having relatively large blades at a relatively low speed (rpm). As mentioned previously, Twin 6" Marine impellers operated at 100 rpm provide the necessary low shear-high circulation mixing to avoid creat-ing an inseparable emulsion of the oil-alkali mixture. The actual rotary mixer used is not critical as long as the blade size, speed (rpm) and container size are combined to give low shear and high circulation.
The mixture is then centrifuged using continuous centrifugation apparatus. A heavy phase (overflow) and light phase (underflow) are formed. The heavy phase contains the wax and other impurities while the light phase is clear. The light phase may then be further processed to form a salad oil, clear cooking oil or whatever product is desired. Separation into the layers is very distinct with less than 1.5% by weight of the desirable oil being lost with the heavy phase. Likewise, :

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the amount of unremoved impurities is low being in the range of less than 0.03% soap and less than 0.3% water in the light phase.
These levels are judged to be satisfactory. The clear oil resulting from this invention after drying and bleaching exhibits excellent chill test results as evidenced by refrigerator clarity of longer than 100 hours at 32F and longer than 2 weeks at 40F.
, These oils may then be bleached and deodorized and used in the formation of edible products such as salad oils.
; A bleaching operation suitable for practice of this invention is described in U.S. Patent 3,673,228 (1972) issued to Harris and Levine and entitled "Process For Adsorbent Bleaching of Edible Oils". In a typical bleaching process the dewaxed oil is mixed with adsorbent. This mix is heated, main- -tained in heated condition for a period Or time, and then filtered to separate the spent adsorbent and decolorized oil. Traditionally, much of the bleaching action occurs during the filtering process because of the high concentration of bleaching adsorbent compared to oil which can be present in this process.
In addition, a deodorization operation as described 20 in U.S. Patent 3,506,969, issued to BaXer et al. and entitled "Continuous High Temperature Steam Deodorization of Edible Oils"
can be used to deodorize oils. Steam deodorization of edible - oils is removal, by various kinds of steam contacting, of free fatty acids and volatile odoriferous and flavorous materials which are responsible for the smell and taste of undeodorized oil.
Upon completioll of the above-mentioned bleaching and deodorization operation a finished salad oil is obtain~d wllich - :

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has excellent refriyerator clarity over extended periods of time. Specifically, refrigerator clarity of greater than 100 hours at 32F and longer than 2 weeks at 40F is considered acceptable.
The process of this invention may be operated in batch or in continuous fashion. In addition, it has been performed on refined and bleached oils provided that the free fatty acid content is within the stated ranges, but the soap in this ; process must then be removed before deodorization in order to form an acceptable salad oil.

Example 1 A batch of sunflower oil was obtained. The oil was refined according to the process taught by U.S. Patent 3,102,898 until analysis showed a free fatty acid content of 0.02% and a soap content of less than 0.05%. The batch of oil was divided into five portions which were labeled Samples A through E, respectively. Each sample was then identically processed with the single exception that a different sodium hydroxide concen-tration was used for each during dewaxing.
Each sample was chilled to 30F and held for three hours. After the chilled time had expired, a dilute solution of sodium hydroxide was added to each sample. The dilute sodium hydroxide solution consisted of 1.5% by weight lye in ` water. The final oil to water ratio for each sample was 4:1 thus the water amounted to 20% by weiyht of the mixture. The dilute NaOH solution for each sample consisted of:

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10~1S3f~i WEIGHT PERCENTAGE OF ADDED ALKALI SOLUTION
. . _ Sample A 2.5% by weight of water phase Sample B 2.0% by weight of water phase Sample C 1.75% by weight of water phase Sample D 1.5% by weight of water phase Sample E 1.0% by weight of water phase Each sample was then agitated for 1 hour at 100 rpm with two 6" Marine impellers, said impellers providing mixing that was both low shear and high circulation. At this time a centrifuge was used to separate the heavy phase containing the wax from ~ ' -the light phase which was the purified oil. Each was bleached according to the process taught by U.S. Patent 3,673,228 and deodorized according to the process of U.S. Patent 3,506,969.
The samples were then tested for the amount of soap ~ -and water which had not been separated. The soap contents of Sample B, C and D were all found to contain less than the acceptable level of 0.03%. Samples A and E contained more than 0.03% soap and were judged unacceptable. Water levels were judged acceptable for all samples. In addition, 32F and 40F
chill tests were run. All samples were satisfactory at 32F;
but only Sample B, C and D were satisfactory at 40F.
This example shows that the practice of the process of this invention is effective only in the concentration rarige of greater than 1.0% to less than 2.5% by weight lye in water.
Example 2 An experiment was run using the same conditions as in Example 1 with the single exception being that agitation was at 200 rpm. Resultsobtained from 32F and 400F chill tests - - - - - . . .
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showed that the increased rate of agitation caused the $ormation of an unsatisfactory clear oil product. The chill test time decreased with each successive increase in agitation rate.
The conclusion was reached that mild agitation, i.e. less than 200 rpm, such that low shear and high circulation are produced and are essential to the successful operation of the process of this invention.

Example 3 The procedure of Example 1 is repeated with the single exception being the samples are initially cooled to 40F and held instead of 30F. Slightly improved chill test results are obtained in comparison to those obtained by Example 1.

Example 4 The procedure of Example 1 is repeated with the - 15 single exception being that the dilute alkali solution of 1.5%
by weight of sodium bicarbonate in water. Substantially similar results to those obtained in Example 1 are found.

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Example 5 The procedure of Example 1 is repeated with the single exception being that the dilute alkali solution is composed of 1.5% by weight calcium hydroxide in water. Sub-stantially similar results to those found in Example 1 are obtained.

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Example 6 The procedure of Example 1 is repeated with the ; single excepting being that the dilute alkali solution is ' .

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1~)4~S36 composed of 1.5% by weight ammonia in water. Substantially similar results to those found in Example 1 are obtained.
Example_7 The procedure of Example 1 is repeated with the single exception being that the dilute alkali solution is composed of 1.5% by weigh~ magnesium hydroxide in water. Substantially similar results to those found in Example 1 are obtained. --, '- ' ' ' -:, .

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for dewaxing vegetable oils comprising the steps of:
(a) providing a vegetable oil prerefined until analysis of said oil shows less than 0.1% soap and less than 0.1% free fatty acid content, said oil being chilled to a temperature of less than about 60°F;

(b) holding said refined oil at said temperature for longer than one hour;

(c) mixing said refined vegetable oil of step (b) with an aqueous alkaline solution;

(d) agitating in a low shear-high circulation manner the mixture of step (c) for at least 1/2 hour, to uniformly desperse the alkaline solution without forming an inseparable emulsion;
and (e) separating the agitated mixture to provide a wax-containing water phase and a dewaxed oil.

2. The process of claim 1 wherein the vegetable oil of step (a) contains less than 0.05% soap.

3. The process of claim 1 wherein the vegetable oil of step (a) contains less than 0.05% free fatty acid content.

4. The process of claim 1 wherein the oil tem-erature of step (a) is from about 30° to about 50°F.

5. The process of claim 1 wherein the oil tem-perature of step (a) is 40°F.

6. The process of claim 1 wherein the aqueous alkaline solution of step (c) comprises from about 10 to about 30% of the combined weight of vegetable oil and alkaline solution.

7. The process of claim 6 wherein the aqueous alkaline solution is sodium hydroxide in a concentration of from about 1 to about 2.5% by weight of sodium hydroxide in water.

8. The process of claim 1 wherein the agitation in step (c) is provided by two 6-inch marine impellers operated at about 100rpm.

9. The process of claim 1 wherein the process is continuous.

10. The process of claim 1 wherein the process is conducted in batch fashion.

11. A process for dewaxing vegetable oils previously refined and which contain waxes which precipitate at refrigerator temperatures comprising the steps of:
(a) providing a vegetable oil pre-refined until analysis of said oil showed less than 0.05% soap from about 0.01% to less than about 0.05% free fatty acid content, said oil being chilled to a temperature of about 30° to about 50°F.;

(b) holding said refined oil at said temperature for longer than 1 hour;

(c) diluting said refined vegetable oil of step (b) by admixing with from about 10 to 30% by weight of an aqueous alkali solution of about 1.5% by weight concentration of an alkali selected from the group consisting of sodium hydroxide, sodium bicarbonate, potassium hydro-xide, magnesium hydroxide and ammonia, (d) agitating in a low shear-high circulation manner the mixture of step (c) for at least 1/2 hour, to uniformly disperse the alkali solution without forming an inseparable emulsion; and (e) then centrifuging the agitated mixture to separate the wax-containing water phase and to provide a dewaxed oil in which the soap content is less than 0.03% by weight, water is less than 0.3%, and which oil after conventional blending and deodorization is suitable for use as a salad oil and has excellent refrigerator clarity of greater than 100 hours at 32°F and longer than 2 weeks at 40°F.