Encapsulation in natural products

United States Patent Office _{B 4} 3,137,631

Patented June 16, 1964

3,137,631

ENCAPSULATION IN NATURAL PRODUCTS Saul Soloway, New Rochelle, N.Y., assignor, by mesne assignments, to Faberge, Inc., Ridgefield, N.J., a corporation of Delaware

No Drawing. Filed Dec. 1, 1959, Ser. No. 856,379 11 Claims. (Cl. 167—83)

This invention relates to encapsulating water insoluble organic liquids and the resulting products.

Those liquids, compounds or mixtures, which have appreciable vapor pressures or which are subject to chemical change by reaction with some atmospheric constituent, may be protected from volatilization or reaction with the environment by enclosure in inert capsules. Solids, having similar properties, may be dissolved in appropriate liquids and then encapsulated as solutions. Some of the volatile essential oils of commerce which could be encapsulated to advantage for applications to be discussed later are: oils of lemon, orange, anise, pine, almond, thyme, rose, jasmine and citronella. In fact one might include all the oils used in the perfume, flavor, food and allied industries. Specific types of compounds such as aldehydes, olefins, acetylenes, mercaptans, amines, ethers and phenols are readily protected against autoxidation by encapsulation. Protection of oxygen sensitive compounds without the use of an anti oxidant is particularly desirable for the preservation of animal fats, vegetable oils and vitamins such as A, E, and C. The general use of anti oxidants in these instances is viewed as that of a necessary contaminant.

It is often desirable to envelop substances, which ma; or may not be stable, in capsules which are frangible. Such capsules may be integrated into a fabric, woven or non-woven, so that the application of pressure will release the material. This concept constitutes a novel way of dispensing perfume and certain types of medication. The encapsulation of such voltile compounds as menthol, camphor, pine oil, oil of eucalyptus, etc. offers a most convenient mode of dispensing alleviants for ⁴θ respiratory disease.

The separate encapsulation of two or more potential reactants offers many possibilities. Carbonless “Carbon Paper” can be made by coating the under side of one sheet of paper with capsules containing a potential color forming reactant. The top side of a second sheet is impregnated with capsules containing the developing reagent. The application of pressure to the pair of sheets in contact causes both types of capsules to rupture, thereby releasing the contents with consequent color ⁵⁰development.

For the reasons given above, many attempts have been made to encapsulate organic substances which are insoluble in water and are liquid at temperatures at which water is liquid. (Such substances are hereinafter called ⁵⁵water insoluble organic liquids.) For example, efforts have been made to encapsulate such substances in gels or encompass them in waxes. Such efforts have not been adequately successful because of rapid leakage through the gel and structural weakness of the wax. Waxes are also readily dissolved by most organic oils and hence are only limited to use for encapsulating polar liquids.

It is a principal object of this invention to overcome, or at least abate the drawbacks heretofore associated with encapsulating water insoluble organic liquids. It is a special object of this invention to provide an encapsulating process which can be carried out at the mild temperature at which water is liquid. It is a special object of this invention to encapsulate volatile substances such as perfume coils or substances which favorably affect respiration. Other objects and features of the invention will become apparent from the more detailed description of the invention which follows.

In my copending application Serial No. 846,535, filed October 15, 1959, now abandoned, it was disclosed 5 that the aforesaid objectives can be obtained by encapsulating water insoluble liquids, such as mentioned above, in solid shells of cross-linked synthetic resins. These encapsulating cross-linked synthetic resin shells, as is known, are water insoluble and are insolu10 ble in usual organic solvents. In order to encapsulate the water insoluble organic liquids in the synthetic crosslinked resin shells, the water insoluble organic liquid was dispersed in an aqueous solution of compounds capable of forming cross-linked synthetic resins by the 15 application of heat or catalyst or both and then the resinforming compounds were polymerized in the presence of the dispersed water insoluble liquids to thereby encapsulate them. Urea-aldehyde prepolymers are disclosed as being especially suitable for use in such a 20 process but water soluble resins forming compounds capable of forming melamine, epoxy, thiourea, polyamide, dicyanodiamidealdehyde resins are likewise disclosed as being suitable.

In special embodiments of that invention, the water 25 insoluble organic liquids were disclosed as being encapsulated in a plurality of concentric shells made of the same or different resin-forming compounds or in a composite shell composed of a plurality of resin-forming compounds. In a particular embodiment of that invention, 30 it was disclosed that the water insoluble organic liquids could be encapsulated in a water insoluble composite shell derived conjointly from water soluble heat denaturable proteins and water soluble compounds which form cross-linked synthetic resins.

In accordance with this invention, the objectives set out above, and other valuable objectives, are obtained by encapsulating water insoluble organic liquids in water insoluble shells derived from water soluble heat denaturable proteins. In order to encapsulate the water insoluble organic liquids, they are dispersed in an aqueous solution of the water soluble proteins and the proteins are then denatured in the presence of the dispersed particles of water insoluble organic liquids to thereby encapsulate the particles in a water insoluble solid protein shell. In an important method of practicing the invention, the proteins are denatured by the application of heat but they can be denatured by use of other kinds of energy as by use of ultraviolet light or ultrasonic sound or by chemicals as by acid or alkali denaturing. Although valuable substances in capsule form may be obtained by encapsulating the water insoluble organic liquids in shells derived from water soluble heat denaturable proteins alone, known cross-linking agents for proteins such as formaldehyde, glyoxal and the like may be used to react with the proteins during the formation of the shell, or after the shell is formed,, to impart increased stability to the capsule. By following the process hereof water insoluble organic liquids are encapsulated in a substantially impermeable shell of a denatured denaturable protein.

.While no theory is necessary to an understanding of this invention, it is felt that the dissolved water soluble proteins normally have some affinity for the diluted dispersion of globules of water insoluble organic liquids and, therefore, tend to concentrate at the interface between the globules and the continuous aqueous phase. In this way, the proteins form a coating around the globules and, when denatured, form a solid water insoluble capsule therearound.

τη ^des/^ecl’ known emulsifying agents, which are usually 70 of an oily or fatty nature, may be used to facilitate the formation of an aqueous dispersion.

Egg albumin has proven especially valuable as a source

3,137,631

Λ a water bath. At 65° C. coagulation began to set in, After the temperature reached 90° C., the reaction mixture was poured into 800 ml. of tap water. Two solid phases formed. One was lighter and the other, heavier than the aqueous medium. The less dense solid was washed extensively with methanol. . The heavier solid was washed with water several times by decantation. Both washed solids were dried at 50° C. with air circulating through the oven. The odorless mass liberated the odor of methyl benzoate on rubbing the solid particles against one another.

EXAMPLE 2

Pinene Encapsulated in Egg Albumin

One hundred (100) grams of pinene were emulsified in a solution of 45 grams of egg albumin dissolved in 900 grams of water. The resulting suspension was heated on a water bath at a rate of 2 to 3 degrees C. per minute. When the temperature reached 75° C., it was held there for ten minutes. /

A small portion of the formed solids were separated by decantation and washed with water and acetone. This product yielded no pinene odor on crushing.

The main batch of solids was split into two parts. 25 One was treated with 30 grams of 37% aqueous formaldehyde and the other with 40 grams of 30% glyoxal. Both batches were heated to 60-70° C. for 15 minutes. The separation and drying steps were the same as described in the first preparation. The resulting dried 30 glyoxal treated material was quite hard and difficult to break by crushing with the fingers. Both preparations yielded odor on the application of frictional forces,

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of heat denaturable protein for, among other things, the egg albumin is a good emulsifying agent and the water insoluble organic liquid can be easily dispersed m the aqueous body in the presence of egg albumin by mechanical agitation with a conventional high speed mix- 5 er. Other water soluble and heat denaturable proteins suitable for use in the process of this invention include blood, other albumins, blood plasma, globulin, myosin, glutelin, excelsin, edestin, arachin, casein and like water soluble proteins and their mixtures which become de- 10 natured by heating.

In the encapsulating process disclosed above, the water soluble proteins may be effectively and economically denatured by the application of heat to thereby form a water insoluble solid shell around the water insoluble 15 liquid. On the other hand, other forms of energy or chemical means may be used to denature the proteins and render them water insoluble as by the use of ultraviolet light, ultrasonic sound or by the use of chemicals such as acid or alkali denaturants. 20

Thus, broadly considered, the present invention relates to a process for encapsulating, or coating, particles of water insoluble organic liquids with denatured and water insolubilized proteins and to. the resulting encapsulated product. In accordance with a more limited aspect of the invention, the invention relates to a process involving dispersing particles of a water insoluble organic compound in an aqueous solution of a water soluble heat denaturable protein thereby applying to and absorbing on the surfaces of the dispersed particles the heat denaturable protein and denaturing the protein on the surfaces of the particles until it becomes substantially water insoluble, i.e., cross-linked.

If desired, the dispersion of the water insoluble organic liquid in the aqueous media may be facilitated by using 35 a water soluble thickening agent, or an agent imparting colloidality to the media. Compounds found very useful as thickening agents include methyl cellulose, hydroxyethyl cellulose and sodium carboxymethyl cellulose and similar compounds known to improve the suspend- 40 ing capacity of aqueous media. Although these colloids are water soluble, they also have some affinity for the water insoluble organic liquid. Thus, these colloids facilitate the formation of an aqueous dispersion of the organic liquid and have a tendency to concentrate at the 45 interface between the dispersed water insoluble organic liquid and the continuous aqueous phase. In this way, the encapsulation is aided.

In many instances sequential coating of the dispersed, water insoluble organic liquid particles gives an importantly improved encapsulated material enclosed in concentric shells. In this way, two or more concentric shells composed of water insolubilized proteins may be formed around the water insoluble organic liquid as disclosed herein or concentric shells respectively composed of 55 water insolubilized proteins and cross-linked resins may be obtained by following the teachings herein set out with the teaching of the above identified application.

Under certain circumstances,(especially, when the capsules are very thin, it may be desirable to form a final θθ overcoat of inorganic compounds such as colloidal silica, titanium dioxide, barium sulfate or the like. These materials yield a drier more powdery product and perhaps serve as fillers for any imperfectly formed capsules containing micro cracks.

The meaning and significance of the invention will become even more apparent from the following illustrative examples.

EXAMPLE 1

Methyl Benzdate Encapsulated in Egg Albumin

Twenty-seven (27) grams of methyl benzoate were added to a solution of 20 grams of egg albumin in 230 ml. of water at room temperature. The mixture was stirred at approximately 300 r.p.m. and heated on

EXAMPLE 3

Encapsulation of Bornyl Acetate in Egg Albumin

Bornyl acetate was successfully encapsulated in egg albumin in weight ratios of 1:1 and 2:1 and thereafter treated with formaldehyde by following the procedure as disclosed in Example 2. An experiment using a 3 to 1 ratio had a tendency to oil out.

In these preparations the intial oil dispersion was passed through a colloid mill before the heating step.

The final preparation consisted of particles of about 1 cm. in diameter. These were broken up in an dsterizer as a suspension in benzene.

The separated particles were odor free on drying, but readily released the odor of bornyl acetate on inter particle friction.

EXAMPLE 4

Encapsulation of Bornyl Acetate in Albumin and UreaFormaldehyde Polymer

Forty-five (45) grams of bornyl acetate were emulsified in a solution of 45 grams of egg albumin dissolved in 900 grams of water. The resulting' dispersion was passed through a colloidal mill and the suspension was then heated on a water bath at a rate of 2 to 3 degrees C. per minute. When the temperature reached 75° C., it was held there for ten minutes. After the coagulation was completed, 10 grams of urea, 25 ml. of 35% formaldehyde, and 1 mol of concentrated hydrochloric acid were added in succession and the heating was continued oh the water bath until solid urea-formaldehyde resin was no longer formed. The encapsulated solids were separated in the same manner as in the preceding examples.

EXAMPLES

Encapsulation of a Mixture of Essential Oils in UreaFormaldehyde and Albumin

Two (2) grams of a mixture of mono and dilauryl phosphates were dissolved in 25 grams of an oily mass consisting of a perfume oil prepared from 20% of each of the following natural oils and synthetic compounds: 75 B-phenyl ethyl alcohol, geraniol, linalool, altar of Rose

3,137,631 and oil of Neroli. This solution was added to a solution of 20 grams of urea in 300 ml. of water, followed by an addition of 50 ml. of 37% formaldehyde. While the above dispersion was being stirred, a solution of 10 grams of alubumin in 100 ml. of water was added dropwise over a period of 2 minutes. The albumin caused the oil to become more finely dispersed and seemed to coagulate around the droplets at room temperature. The preparation was heated in the manner as described in the preceding examples, filtered, washed with water and isopropanol and dried.

Stable capsules of the perfume oil were obtained.

EXAMPLE 6

Encapsulation of a Mixture of Essential Oils in UreaFormaldelryde, Albumin and Barium Sulfate

Fifty (50) ml. of water was used to dissolve 5 grams of urea, 12.5 grams of 37% aqueous formaldehyde, and 2.5 grams of sodium sulfate. Ten grams of the perfume oil of Example 5 and 1 gram of a mixture of mono and dilauryl phosphates were stirred into the aqueous solution while stirring with a stirrer rotating at 200-300 r.p.m. Then 5 grams of egg albumin in 25 ml. of water was added, and the stirring at 200-300 r.p.m. continued for a half hour. After reaction period induced by heating the reaction mass, the urea formaldehyde resin and the denatured egg albumin were formed into a shell around the oil. A dilute barium chloride solution was then added to form a final coat of barium sulfate with the aqueous sulfate ion present. A very stable encapsulated perfume oil was obtained encased in the cross-linked resins and the coating of barium sulfate.

Colloidal silica or powdered titanium dioxide could be added, at this point in the procedure, in lieu of barium chloride.

EXAMPLE 7

Encapsulation of Normally Solid Volatile Compounds

A liquid mixture of 30 grams of menthol, 10 grams of camphor, and 10 grams of bornyl acetate was stirred and dispersed in 50 grams of 10% methyl cellulose (15 c.p.s.) in water. Fifty grams of an aqueous acidic colloidal solution containing 10% of an urea-formaldehyde prepolymer was added to this dispersion. After stirring, at room temperature, for a half hour, 50 grams of a 10% aqueous egg albumin solution was added and the stirring continued for an equal period. The resulting suspension of capsules may be washed free of mother liquid or used as such for spray-drying, brush or blade application to the surface of paper or other non-woven or woven fibrous ⁵θ materials.

This preparation can be made odor free by air-drying the filtered, or centrifuged, capsules overnight in an oven kept at 50 to 60° C.

Also, where it is desired to obtain an intimate admix- ⁵⁵ture of the encapsulated material and the carrier, such as in the production of paper for producing a paper handkerchief it is possible to introduce the capsules into the carrier during its manufacture such as by mixing together an aqueous paper pulp and the aqueous suspension of 60 capsules during the processing of the pulp to paper.

A very satisfactory product for the alleviation of colds has been obtained by incorporating the capsules of this example in non-woven paper tissue. Other types of nonwoven fibrous tissue may be used in the same way. 65

While the preceding examples have related to encapsulating volatile water insoluble organic liquids, especially perfume oils and aromatics, it will be understood that other types or water insoluble liquids, mentioned herein, may be encapsulated by following the same procedure. Also, 70 water soluble heat hardenable proteins may be dissolved in the aqueous medium in place of the egg albumin in equivalent proportions, to encapsulate the water insoluble organic liquids in the other types of denatured proteins derived from the other proteins disclosed above. Like- 75 wise, other resins typified by those disclosed hereinbefore, may be substituted for the urea-formaldehyde resins of the examples to modify the denatured protein capsules.

It is apparent from the foregoing discussion that “encapsulation” and “encapsulate” has reference to the formation of solid shells or capsules around the dispersed globules of water insoluble organic liquids. As pointed out in the body of the specification and in the specific examples, a dilute suspension of the organic liquid is first formed in an aqueous solution of the heat denaturable protein. These water soluble heat denaturable proteins can concentrate at the oil-water interface where they are insolubilized and formed into a denatured protein shell encapsulating the water insoluble oil by the action of heat or by other methods set out above.

It will be understood the foregoing general description as complemented by the specific examples has served to illustrate the invention and its principles. However, many modifications and variations in the details of the disclosure will occur to those skilled in the art to which the invention appertains and still remain within the principles of the invention and its scope. For instance, the illustrative embodiments of the invention have been concerned primarily with encapsulating water insoluble organic compounds which are liquid at temperatures at which water is liquid and with encapsulating such compounds containing dissolved, or otherwise dispersed therein, additional ingredients which are readily dispersed in the water insoluble organic compounds. It will be apparent, however, that the principles of the invention can be applied to encapsulating ingredients which are more difficult to disperse in the water insoluble organic liquids. Broadly considered, the principles of this invention can be applied to the encapsulation of any ingredient which has a greater affinity for the water insoluble organic liquid than it has for water. For example, when the water insoluble organic compound is an oil any ingredient may be kept in dispersion in the dispersed oil phase which is more lipophilic than hydrophilic. Predominantly lipophilic emulsifiers could be used to assist in the dispersion of the substances in the oil phase. The same principle may be used to encapsulate solids which are insoluble both in the oil phase and in the water. For example, the absorption, or coating, of a substance onto the solid particles being dispersed in the oil phase which has an affinity for oil and then dispersing the solid in the oil before it is, in turn, dispersed in the water for encapsulation. This latter principle can be used even to disperse and then encapsulate water soluble solids.

Thus, it will be seen the invention is capable of many modifications as to details and still remain within the scope of the invention as defined in the claims.