US3491132A - Glyceride oil treatment - Google Patents

Description

United States Patent 3,491,132 GLYCERIDE OIL TREATMENT Robert A. Reiners, Hinsdale, and Frederic J. Birkhaug, La Grange, lll., assignors to Corn Products Company, New York, N.Y., a corporation of Delaware No Drawing. Filed May 1, 1967, Ser. No. 634,864 Int. Cl. C11b 3/00 US. Cl. 260-420 8 Claims ABSTRACT OF THE DISCLOSURE A method for reducing the free fatty acid levels of glyceride oils so that said oils may be subsequently efficiently refined, said method providing combining a cyclodextrin with oil and water mixture, breaking the mixture so formed and obtaining the oil with the desirably reduced levels of free fatty acids. The cyclodextrin is recovered by decomposing the clathrate of the cyclodextrin and the fatty acids.

This invention relates to a method for purifying glyceride oils to a condition where they may be subsequently refined in conventional process steps. The invention particularly relates to reducing the free fatty acid content of edible glyceride oils from undesirably high levels which would handicap or prevent subsequent conventional refining.

Glyceride oils, particularly edible glyceride oils, are conventionally refined by alkali treatment such as with an aqueous solution of sodium hydroxide. The alkali treatment destroys or extracts some of the objectionable color bodies, it precipitates phosphatides, and it neutralizes the free fatty acids by forming soaps. Alkali refining is usually the first of several steps designed to place the oil in a form acceptable to theconsumer. Subsequent treatment such as bleaching, hydrogenating, Winterizing and deodorizing (vacuum stream stripping) are usually employed to make an oil of the desired quality.

The alkali refining step tends to be practiced to disadvantage when the glyceride oil contains free fatty acids of higher levels. The larger amounts of soap which are formed are accompanied by serious oil losses resulting from the neutral oil being entrained or occluded in the formed soap. It has been the experience of the art that when a crude glyceride contains more than about of free fatty acids, problems began to occur in the neutral oil losses; and when the free fatty acids exceeds about 10% by weight of the oil, the neutral oil losses become very serious.

Crude oils having a 10 to 20% free fatty acid content are often considered unrefinable because the neutral oil losses sulfered are so high as to make refining economically undesirable. Not only is there a problem with the higher amounts of soap which are formed, but the greater amounts of added alkali lead to other problems such as hydrolysis of the ester groups in the glyceride oils.

If the free fatty acids are present in smaller and workable levels of less than about 5% by weight of the glyceride oil, only a small amount of neutral oil is lost by entrainment or occlusion in the soap. In general, the neutral oil loss is equivalent to the amount of free fatty acids at the lower levels of said glyceride oils.

The practitioners in this art have exerted many efforts in an attempt to establish an inexpensive method to con vert oils having the undesirable high levels of free fatty acids into edible oils. It is the intention of the art to obtain essentially pure triglycerides in edible oils because the presence of free fatty acids leads to undesirable propice erties, the most objectionable being excessive smoke formation at higher cooking temperatures. Among the unrelated prior art efforts may be mentioned the teaching of US. Patent No. 3,008,972 where oils having a high free fatty acid content are treated conjunctively with sodium hydroxide and concentrated diammonium phosphate solution.

Other approaches of a distinctly different type include Japanese Patent 5532 (1954) in which refined oils of high free fatty acid content were suspended in strong ethanol solutions before being treated with the alkali. Gomez Fabra et al. suggested the use of an anion exchange resin in Anales real soc. expan, fis. y quim., 51B, 291300 (1955) and the use of the urea adducts and crystalline urea for said deacidification is discussed in the same journal in volume 47B on pages 229234 (1951). It is to the benefit of the art to find other unrelated methods, especially methods which can be practiced effectively and economically.

It is therefore one object of the present invention to provide a new method for purifying glyceride oils by reducing their free fatty acid content to a desired level so that said oil may be practically and economically refined.

It is another object of this invention to provide a new method of reducing undesirable levels of free fatty acids in glyceride oils by using a cyclodextrin to form a clathrate with free fatty acids, and then obtaining the oil essentially free of the added cyclodextrin or the formed cyclodextrin and fatty acid clathrate.

A still further object is an improved method of the type described wherein substantial amounts of cyclodextrin may be used for purifying the oil without disadvantage because the unclathrated cyclodextrin may be easily recovered and the clathrated cyclodextrin may be simply split to recover the cyclodextrin for further processing. The efiicient recovery of cyclodextrin contributes to the economies which are realized since the recovered cyclodextrin can be reused or recycled for a subsequent purification.

A still further object of the invention is a new method wherein edible glyceride oils may be purified by reducing their free fatty acid content to desirably low levels so that said glyceride oils may be subsequently alkali refined without encountering untoward or undesirable losses of neutral oils. It is a feature of this object that higher amounts of alkali will not be required for alkali refining which would cause undesirable soap formation and objectionable possibility of hydrolysis of the glyceride ester groups.

The foregoing objects are attained as well as still other objects which will occur to practitioners from considering the invention which will be described in detail.

The method to be described in practiced to particular advantage because a cyclodextrin is used to reduce the undesirably high free fatty acid content in crude glyceride'oils to lower workable levels so that the oil may thereafter be efiiciently refined.

The cyclodextrins are a group of homologous oligosaccharides that are obtained from starch by the action of enzymes elaborated by Bacillus macerans. The cyclodextrins are known as Schardinger dextrins from an early investigator who studied these matetrials. They are homologous cyclic molecules containing 6 or more a-D-glucopyranose units linked together at the 1, 4 positions as in amylose. The cyclic molecule may also be referred to as a torus. As a consequence of the cyclic arrangement, this torus is characterized by having neither a reducing end group nor a non-reducing end group. The torus molecule is depicted in the following schematic formula, where the hydroxyl groups are shown in the 2, 3 and 6 positions in the illustrated anhydroglucose units. The letter n may be a number from 4 to 6, or higher.

When n is 4, the torus molecule is known as u-cyclodextrin or cyclohexaamylose, because the torus contains six anhydroglucose units; when n is 5, the seven unit member is known as ii-cyclodextrin or cycloheptaamylose; and when n is 6, the eight unit member is known as 'y-cyclodextrin or cyclooctaamylose. When reference is made herein to cyclodextrin, it is intended to include the foregoing forms as well as still other tori that have a still larger number of units in the molecule, and, as well, mixtures of these and other homologs.

Cyclodextrin is produced from starch by the action of an enzyme commonly known as cyclodextrin transglucosylase (B. macerans amylase). The source of the enzyme is usually a culture of Bacillus macerans which is grown under conventional conditions on conventional media containing sources of nitrogen, carbon, growth factors and minerals. The cyclodextrin transglucosylase may be produced by following published teachings such as, for example, those described by D. French in Methods in Enzymology, S. P. Colo-wick and N. 0. Kaplan, editors, Academic Press, New York, N.Y., vol. V, 1962, pp. 148-155.

The cyclodextrin transglucosylase activity in cultures of Bacillus macerans may be measured by the Tilden-Hudson procedure as described by these two workers in J. BacterioL, 43, 527-544 (1942). In general, the cyclodextrin transglucosylase is added to a dilute solution of a gelatinized starch, whereupon a conversion to cyclodextrin occurs by enzymolysis. Procedures for making and isolating the cyclodextrins have been variously described as by F. Cramer and D. Stainle, Ann., 595, 81 (1955). If desired, the various homologs such as, for example, the alpha, beta, and gamma, may be fractionated by procedures such as those described by D. French, et al., J. Am. Chem. Soc., 71, 353 (1949).

The various homologous cyclodextrins, having from six to eight units, or higher, and their mixtures, may be used as equivalent materials for the purposes of this invention. In practice, there may be little reason for separating the various fractions, and the cyclodextrin employed may contain a preponderance of B-cyclodextrin, for example. No distinction is intended between the various homologous cyclodextrins or their mixtures unless otherwise indicated, when using the term cyclodextrin.

Cyclodextrin is known as a clathrating compound, that is, it is adapted to form inclusion compounds. In referring to the inclusion and clathrating properties, reference has been made to the torus molecule being a host molecule, and the included or complexed molecule being the guest molecule.

A cyclodextrin or a homologous mixture of cyclodextrins are used to advantage by combining them with the crude glyceride oils, but it has been found to be an important feature of the invention that the cyclodextrin should be combined with an intimate mixture of oil and water. One way in which this mixture may be formed is to prepare a paste of the oil and dry cycladextrin powder in the presence of a lesser amount of water. In general, about equal amounts of the oil the cyclodextrin may be vigorously mixed, as in a mortar, with water in an amount of about one-half of the oil. It is, however, a preferred practice to combine the cyclodextrin with an emulsion of the crude glyceride oil and water. In particular, it has been found that a coarse or unstable emulsion should be formed for combination with the cyclodextrin to attain the advantages of the invention in a more efficient way.

The method of the invention requires that the emulsion be separated or broken down to its aqueous and oil phases, following contact in combination with the cyclodextrin. An unstable emulsion does not effectively resist the ordinary procedures to separate or break down this emulsion into the respective phases. A stable form resists said separation or breakdown to an undesirable or impracticable degree.

Practitioners in the art 'will readily recognize when a glyceride oil and water emulsion assumes the unstable form, and when it passes into the undesirable stable form. One way in which the practitioner may determine whether an unstable or coarse emulsion is obtained is to observe whether the emulsion separates or breaks down upon centrifugation at good operating rates such as 2000 r.p.m. which run for relatively short periods such as 5 minutes or less. Such centrifugation may not nor need not lead to a direct and complete separation of the oil and Water phases because an initial creamy phase may separate from an aqueous phase; but this creamy phase will lead to the final separation of oil and water phases upon recentrifugation with or without dilution with Water. I

While the formed emulsion should be unstable, it still must comprise an effective emulsion, by which is meant that a true emulsion is formed so that there is an intimate extensive contact between the added cyclodextrin and the free fatty acid in the crude glyceride oils. In general,.the unstable emulsion is formed by mixing with a lesser or controlled degree of agitation than would characterize the formation of the stable emulsion.

It is an advantage to add the cyclodextrin after the unstable or coarse emulsion is formed. The emulsion is important for providing adequate contact surface between the free fatty acid and the oil and the cyclodextrin but, additionally, the water phase of the emulsion is necessary for clathration to occur. The use of the emulsion leads to another advantage in practice because the dry cyclodextrin solid is incorporated at a surprisingly rapid rate into the water phase of the emulsion at room temperature. This is in distinction to the slow solubility of cyclodextrin in water at room temperature. The method permits the coarse or unstable emulsion to be formed at room temperature, and then the dry cyclodextrin added thereto without requiring any elevation of temperature or addition of more water. If desired, however, the cyclodextrin could be previously dissolved in water prior to preparing the unstable emulsion.

Large amounts of cyclodextrin and homologous cyclodeXtrin mixtures are used to effectively conclude the purification to desired levels, and said amounts are preferably at least about ten times the amount of the free fatty acid content of the crude oil. It is a further feature of the invention that effective clathration occurs even though a small amount of the added cyclodextrin becomes actually dissolved. It is believed that the presence of the water in the mixture assures the occurrence of effective clathration.

The cyclodextrin is retained in combination with the oilwater mixture for a time suflicient to reduce the free fatty acid content to the desirably low level. In general, the crude glyceride oils may have anywhere from about 10 to 20% by weight of free fatty acids or even higher. The method requires that a sufiicient amount of cyclodextrin be combined with the intimate oil-water mixture and retained in combination for sufficient period of time until the undesirable high levels of free fatty acids be reduced to desirable levels of less than about 5% by weight of the glyceride oil. In practice, the free fatty acid content is reduced to about 2 to 3% by weight, or even less. At these desirably low levels, the purified glyceride oil can be successfully and efliciently refined with alkali and other materials in the conventional refining process steps.

The unstable emulsion may be separated or broken down in various ways, but it has been found that centrifuging has certain advantages because it is quick, and various types of equipment may be adapted to different scales of operations. Recentrifuging may be required on occasion to break some of the unstable emulsions. An initial centrifugation generally leads to a first creamy phase and an aqueous phase. The creamy phase is still in a partly emulsified form, and the aqueous phase contains clathrated and unclathrated cyclodextrin. The creamy phase may again be recentrifuged, preferably with water addition, to separate the oil from the water.

Other means may be adopted and devised by the art for separating or breaking down the emulsions, and these may include the use of extraction with oil solvents, filtration, use of raised temperature and still other means. When the intimate mixture of oil and water is in the form ofa paste, it may be separated by adding water in excess of the mixture and then centrifuging.

While the method requires large amounts of a cyclodextrin, such cyclodextrin is easily recovered and may be recycled in a subsequent processing step in-which additional crude oil is purified. Separation is facilitated because the cyclodextrin has a low solubility in water at room temperature, about 2-3. Once the oil-water emulsion is effectively separated, the cyclodextrin need be isolated essentially only from the aqueous phase. The relatively small amount of cyclodextrin which remains in solution may be discarded, or it may be recovered, at least in part, by lowering the temperature of the solution, concentration, or by other means.

The formed fatty acid-cyclodextrin clathrate is decomposed to separate the fatty acid from the cyclodextrin which can then be recycled in a batch or continuous purification process. A simple and efiicient way to decompose the clathrate is to add the clathrate to a liquid and then heat. In particular, the cyclodextrin may be added to water which is then boiled. The liberated guest fatty acid collects on the surface of the water, and the host cyclodextrin appears both in solution and in a precipitated form. Cooling the water results in more eflicient precipitation because of the poor solubility of the cyclodextrin in cold water, or even water at room temperature. Still other ways may be devised for decomposing the clathrate and collect ing the freed host cyclodextrin. The collected free fatty acids may be discarded or collected for practical utilization, as desired.

It has been indicated that the cyclodextrin should be maintained in combination with the oil-water mixture for a time sufiicient to desirably lower the free fatty acid content to predetermined levels. Such a time period will be readily determined by the practitioner for a particular processing operation which has been devised, considering the oil used, the original high level of free fatty acid in said crude oil and the selection of homologous cyclodextrins or mixtures thereof which are employed. The elfective nature of the emulsion, when use, is also a factor. In general, however, relatively short contact time periods are adequate, such as -20 minutes when using a cyclodextrin equivalent in amount to the weight of the oil which is to be purified. In many operations, the contact time period will be less than about one half hour at room temperature when using the cyclodextrin in said amounts.

The unstable or coarse emulsions may also be formed by incorporating a small, but effective amount of a surface active agent into one of the crude oil or the water which we used to form the emulsion. Including such a small amount of a surface active agent will permit the effective emulsion to be formed with a lowered degree of agitation and mixing, and this is desirable because a greater degree of agitation will, of course, tend to convert the emulsion to a stable form. A wide variety of surface active agents may be employed for this purpose and the amounts actually used can be readily determined by the practitioner by routine observation. In general, such surface active agents may be added in amounts of less than about 1% by weight of the crude glyceride oil. Said surface active agent may include soaps and detergents of the usual nonionic, anionic or cationic types.

The method may be used successfully with crude glyceride oils which have the undesirably high levels of free fatty acids, and it is particularly used with edible crude glyceride oils such as palm kernel oil, babassu oil, coconut oil, rice bran oil, and the like.

The following examples are presented to illustrate the various embodiments of practicing the method, but such examples should not be construed as representing exclusive embodiments. The examples do include the best mode contemplated for practicing the invention, but they are intended only to illustrate various teachings to the art.

EXAMPLE I Corn oil purification To about 5 g. of crude corn oil was added sufiicient oleic acid to bring the free fatty acid (FFA) content up to 7.5% (expressed as oleic acid). The oil was thoroughly mixed with 50 ml. water at 28 C. to obtain a coarse emulsion. fi-cyclodextrin was added in an amount of 4 g., and the mixture was stirred vigorously at 1500 r.p.m. with a turbine-type stirrer for 15 minutes. The mixture was centrifuged at 2000 r.p.m. for 5 minutes in an International No. 2 centrifuge to separate a creamy upper layer. The lower layer was the aqueous phase which contained some insolubles, believed to be the clathrate of 5-cyclodextrin and fatty acid. The creamy phase was diluted with water and recentrifuged. The resulting oil contained 2.2% FFA, a low enough value to permit efficient refining with sodium hydroxide in the conventional way.

EXAMPLE II Corn oil purification The process steps of Example I were repeated except that 5 g. of B-cyclodextrin were used rather than 4 g. The free fatty acid content of the treated oil was 1.97%.

EXAMPLE III Corn oil purification with modified agitation rate The process steps of Example I were repeated except that 30 minutes of moderate stirring at 800 r.p.m. was substituted for 15 minutes of vigorous stirring at 1500 r.p.m. The free fatty acid content of the processed oil was 1.65%.

EXAMPLE IV Use of surface active agent To 5 g. of crude corn oil was added sufiicient oleic acid to raise the FEA content to 7.5%. The oil was coarsely emulsified with 50 ml. water at room temperature by stirring at 1600 r.p.m. for 15 minutes. The water contained 0.02% sodium oleate by weight. B-cyclodextrin in an amount of 5 g. was added and the stirring was continued at 800 r.p.m. for 15 minutes. A cream was removed by centrifugation, the cream was diluted with water, heated and recentrifuged to recover the oil. The EPA content of the processed oil was 1.48%.

EXAMPLE V Use of surface active agent A mixture of 1 part corn oil containing 7.5% FFA and 2 parts of water was coarsely emulsified by rapid stirring. To the water was previously added 0.02% by weight of sodium lauryl sulfate. An amount of this emulsion containing 5 g. oil was added to a solution of 5.6 g. [icyclodextrin in 25 ml. water at 70 C. The mixture was stirred 15 minutes at 70 C., then another 15 minutes without heating. A creamy layer separated on centrifugation. The creamy layer was stirred gently with a rod, then the tube recentrifuged to obtain an oily layer. The free fatty acid content of this process and purified oil was 1.13%.

7 EXAMPLE v1 Palm kernel oil purification with solvent extractions To g. of palm kernel oil having a free fatty acid level of 10.7% by weight was added g. Water containing 0.02% sodium lauryl sulfate, and an unstable emulsion was formed. This emulsion was added to a solution of 5.6 g. of {3-cyclodextrin in 25 ml. water at 70 C., and stirred slowly for 10 minutes. The suspension was filtered and extracted with cyclohexane to recover an oil having a FFA level of 3.62%.

EXAMPLE VII Corn oil purification by filtration B-cyclodextrin in an amount of 5.6 was dissolved in 100 ml. water by heating to 65 C. Crude corn oil was augmented with oleic acid to raise the FFA level to 7.5% by Weight, and the mixture was stirred rapidly for minutes to form an emulsion. The emulsion was cooled to C. in about minutes while being gently agitated. The mixture was filtered to break the emulsion. When most of the water had come through the funnel, oil began to appear. The oil which separated from this water had a free fatty acid content of 0.68%.

EXAMPLE VIII Corn oil purification with solvent extraction [i-cyclodextrin in an amount of 6.0 g. and 4 g. of water were mixed in a mortar with a pestle, and 6 g. of crude corn oil having a FFA of 7.5% by weight was added with continued mixing. The material was pasty, and an additional 6 g. of B-cyclodextrin was added. The mixture remained pasty. Half of this paste was mixed with 25 ml. of water at room temperature and stirred slowly. The mixture was centrifuged and oil separated which had a FFA content of 0.52%. The other half of the pasty material was mixed with 8 g. of diatomaceous earth to obtain a powder which was then slurried in hexane and poured into a glass column with a fritted glass filter in the bottom. Additional hexane was poured through the column to remove the oil which had a free fatty acid content of 2.2%.

EXAMPLE IX Decomposition of clathrate The aqueous phases collected in Example I are heated to boiling to decompose the cyclodextrin and fatty acid clathrate. After boiling for a few minutes, the boiled mixture is cooled to about room temperature and the aqueous phases are then cooled to about 10 C. to obtain additional amounts of insoluble cyclodextrin. The fatty acids are collected on the surface of the boiled water and separated by skimming and decanting. The water is poured off and the unclathrated cyclodextrin is collected for use in a subsequent purification process.

The method described in the foregoing specification is not intended necessarily to place edible glyceride in consumer-acceptable forms, but to purify the oils sufficiently so that they may be refined by the conventional alkali treatment and other steps practiced in the conventional refining art.

When using the term purifying in this disclosure, it is understood that the term is primarily intended to mean such a reduction of free fatty acid levels so that the resulting purified glyceride oil may then be refined.

The term intimate mixture has been used in reference to the mixture of the crude glyceride oil and the water which is then combined with the cyclodextrin. An unstable emulsion is the preferred form of this intimate mixture. It is understood, however, that other types of mixtures, such as the paste, are included within the meaning of this term. In general, an intimate mixture is one where adequate contact is attained between the added cyclodextrin and the crude glyceride oils. It will be appreciated that under proper conditions an adequate inti- 8 mate mixture of the cyclodextrin and the oil will provide a sufficient contact to lead to the desired purification when the preferred amounts of cyclodextrin are added to the glyceride oils for the reasonable time periods which have been described.

Reference has particularly been made to purification of edible glyceride oils, but glyceride oils may also be purified which are not intended primarily as a food. For example, oils may be purified to attain chemical grade or to be used as pharmaceutical carriers or the like.

The examples have particularly illustrated the use of B-cyclodextrin in the purification but other cyclodextrins may be used as well as a mixture of homologous cyclodextrins, said mixtures containing various amounts of 11-, B- and 'y-cyclodextrins, for example.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable-0f further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure :as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.

The invention is hereby claimed as follows.

1. A method for reducing the free fatty acid content of a glyceride oil comprising:

combining cyclodextrin, water, and the glyceride oil to form an emulsion, the amount of water by weight being less than the combined amount of the oil and the cyclodextrin, and the amount of the cyclodextrin being about equal to the amount of the glyceride oil;

[allowing the combination to remain in emulsion form until the desired low levels of free fatty acid are obtained; and

separating the oil from the oil-water mixture, the oil having a free fatty acid content less than about 5% by weight and being substantially free of cyclodextrin.

2. A method :as in claim 1 wherein the glyceride oil is emulsified with the water and then the cyclodextrin is added to the emulsion with mixing.

3. A method as in claim 1 wherein the cyclodextrin is added to the water and then the water-cyclodextrin mixture is emulsified with the oil.

4. A method as in claim 1 wherein a small amount of surface active agent selected from the group consisting of soaps and detergents is incorporated into the oil and water mixture.

5. A method as in claim 1 wherein said glyceride oil is selected from the group consisting of crude corn oil, crude rice bran oil, crude palm kernel oil, crude coconut oil and crude babassu oil.

6. A method as in claim 1 wherein the glyceride oil is separated from the emulsion by centrifugation to obtain an aqueous phase comprising cyclodextrin clathrated with the free fatty acids and water, and an oil phase.

7. A method as in claim 6 wherein the cyclodextrin clathrated with the fatty acid is separated from the aqueous phase of the unstable emulsion and free cyclodextrin is recovered after decomposing the clathrate by combining the clathrate with water and heating the combination until the cyclodextrin is free of the clathrate.

8. A method as in claim 7 wherein a creamy phase is initially obtained together with an aqueous phase and further comprises the steps of diluting said creamy phase with water and recentrifuging the water-diluted creamy phase to obtain a subsequent aqueous phase and oil phase, wherein said oil phase has reduced levels of free fatty acids and said :aqueous phase contains free fatty acids clathrated with cyclodextrin.

(References on following page) 9 10 References Cited 2,867,639 1/1959 Watts 260-428 UNITED STATES PATENTS 3,008,972 11/1961 Mitani 260425 2,462,923 3/1949 Thurman 260-428 XR N ZITVER, p i Examiner 2,639,289 5/1953 Vogel 260-428 2,653,122 9/1953 Arnold et a1. 260-420 XR 5 MARS Assistant Examine