JPH0233414B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to microencapsulation processes, and more particularly to methods for encapsulating microscopic droplets of hydrophilic liquids in a hydrophobic continuous phase. In the prior art, microcapsules containing an aqueous amine solution are emulsified in an organic liquid with the aid of suitable surfactants, and a polymer film is formed around the droplets by interfacial polymerization. It has been proposed to produce it by forcing. For example, it has been proposed to add sebacoyl chloride to the continuous phase to produce polyamide membranes, or to add polyisocyanate to the continuous phase to produce polyurethane membranes. Once the microcapsules have been produced, it is often desirable to change the continuous phase from a hydrophobic liquid to a hydrophilic liquid, especially water. This usually involves removing most of the hydrophobic liquid by decanting or centrifuging and washing and redispersing the microcapsules several times in a hydrophilic liquid containing large amounts of surfactant. It will be implemented accordingly. In the methods proposed in the prior art, the capsules are brought close to each other and, for example, free acid chloride groups in the polymer membrane of one capsule are absorbed by, for example, free amino residues in the polymer membrane of another capsule. Care has been taken to avoid agglomeration of the microcapsules, especially during the phase inversion step, condensing with groups and thereby forming chemical bonds between the capsules. According to the prior art, the microencapsulation process uses low temperatures on the order of 0°C (the reaction is usually carried out in an ice bath) and the acid chloride is added quickly to limit the reaction time within a limited range. and after the polymerization reaction has progressed to the desired degree in the phase conversion step,
It is necessary to carry out the conversion to terminate the polymerization as quickly as possible. In many cases where microcapsules are used, it is essential that the capsules be fully suspended in water after which phase inversion surfactants are completely removed. Complete removal is particularly difficult and generally requires repeated cleaning over a long period of time. Until now, prior art techniques have also used polar solvents as a hydrophobic phase such that trace amounts of amine compounds diffuse out of the emulsified droplets and are utilized, for example, in reactions with acid chlorides to form polymer films. It was considered necessary to use it. Thus, for example, in interfacial polymerization reactions in which protein amines are polymerized by reacting with sebacoyl chloride, the solvent used in the hydrophobic phase (and in which sebacoyl chloride is conveniently introduced into the emulsion) is usually a proportion by weight of cyclohexane and chloroform. is a mixture of 3:1 to 4:1, or a solvent of similar polarity that has a small degree of solubility for the amino component. It has often been found that when operated in this manner, the microcapsule walls become thick, rough, and brittle, which makes cleaning the solvent difficult and results in low yields of capsules. This effect is particularly significant when using an amino component containing a large amount of protein. The present invention is based on the unexpected finding that it is possible for the amino component to actually undergo an interfacial polymerization reaction at the interface of the hydrophilic and hydrophobic phases without substantial diffusion into the hydrophobic phase. In preparing microcapsules containing an aqueous solution of a hydrophilic protein having a large number of free amine groups, the present invention involves forming an emulsion of an aqueous protein solution as a dispersed phase in a substantially non-polar solvent as a continuous phase; A manufacturing method is provided which comprises adding to this emulsion a solution of a compound containing a large number of groups capable of reacting with amino groups to produce a polymer, in particular a polyamide. Examples of substantially non-polar solvents include cyclohexane, n-decane, 40/60 petroleum ether, and other solvents that are likewise non-polar. Cyclohexane alone provides an ideal carrier for acid chlorides such as sebacoyl chloride and adipoyl chloride. This prevents rapid diffusion of proteins from the aqueous phase during the initial emulsification step. For example, when using certain reactants that are not soluble in pure cyclohexane, such as succinic anhydride,
It may also be necessary to use mixed solvents containing polar components in which the reactants are soluble. In such a case,
The type and amount of the polar solvent present in the mixed solution is as follows:
It would have a lower polarity than the 1w/w mixture. The use of a substantially nonpolar solvent, such as cyclohexane alone as the continuous phase, inhibits protein diffusion and provides a strong, smooth wall over a wide range of temperatures and reactant addition rates, concentrations, and properties. It becomes possible to produce sticky capsules. Although the polymerization reaction appears to initiate at the interface between the aqueous phase and the continuous solvent phase, polymerization does not occur in the aqueous phase since protein diffusion is severely limited by the low affinity of the substantially non-polar solvent. proceed. This results in a smooth outer surface of the capsule from which the solvent can easily escape. Moreover, since sebacoyl chloride and other chlorides have low permeability in water, polymerization is localized at the interface and controlled by diffusion of the protein in the aqueous phase inside the capsule. Cross-bonding of the walls is thus confined to narrow areas, resulting in a stronger, less brittle structure. The protein used in this reaction is a hydrophilic protein that contains free amino groups, ie, a water-soluble or water-dispersible protein. When the substance to be encapsulated is a food or a food ingredient such as a flavoring, or a drug, preferably the membrane must biodisintegrate in the mouth or stomach to release the contents of the microcapsules. . In the present invention this is achieved. This is because the proteins are hydrolyzable or otherwise disintegrative, causing the polymer chains that form the membrane to rupture and the membrane to disintegrate. It goes without saying that the protein used in the method of the invention must be capable of producing an aqueous phase that is sufficiently stable for emulsification of the aqueous phase into a non-polar solvent.
For this purpose, the protein must be hydrophilic, ie water-soluble or water-dispersible. Also, in order to ensure sufficient cross-linked structures around the emulsion droplets, the molecules of the protein in the emulsified aqueous phase should lie along the surface of the droplets, and therefore preferably The protein should not be a completely globular protein, where the molecule is spherical. If there are sufficient free amino groups in each reacting molecule, the protein will have a substantially linear structure, i.e. it will have one or more substantially linear fragments attached to the globular protein fragment. Proteins can be used. Unprocessed globular proteins themselves are not suitably used in the method of the present invention, but they can also be used in conjunction with or mixed with substantially linear proteins. However, in this case they usually play little or no role in the wall-forming reaction. It is possible, and often preferred, in this method to use modified globular proteins that have been denatured or degraded to at least a partial tertiary amine structure. This causes collapse of the globular structure, providing linear fragments and elongating the molecule by providing free amino groups for reaction. The proteins used in the method of the present invention are preferably naturally produced proteins rather than synthetic protein-type substances. This is because natural proteins are generally easily degraded by enzymatic activity or other biological degradation processes, and their fractions are usually tolerated by living organisms, whereas synthetic protein-type substances are This is because they often cannot or will not biodegrade, producing toxic or harmful or indigestible fragments. In order for a protein to have free amino groups for reaction with another compound, it must have a relatively high proportion of amino acids with two amino groups, especially lysine, arginine or histidine, or aspartate or glutamic acid. with amide,
That is, it should be contained in the form of asparagine or glutamine. It is not essential that the protein material used in this reaction consist of pure protein; in fact, it is often preferred if the protein is used in the form of a component of a complex naturally occurring mixture. Examples of such mixtures include eggs, egg yolks,
Mention may be made of fish eggs such as cod, and certain forms of modified whey. be hydrophilic and meet substantially linear requirements, or
Examples of proteins that can be treated to become hydrophilic and substantially linear include hemoglobin, protamines such as salmin, histones such as liver histones, globulins and β-lactoglobulins. , alpha-lactalbumin, albumin such as ovalbumin or serum albumin, glutelin, which are preferably disrupted and solubilized scleroproteins. As previously mentioned, the protein can be used neat or as a component of a complex mixture containing the protein. As examples of hydrophilic proteins or mixtures containing hydrophilic proteins, mention may be made of whole eggs, egg yolks, hemoglobin, full cream condensed milk, modified whey materials and homogenized cod roe.
Any hydrophilic protein with sufficiently reactive NH ₂ groups can be used to form the capsule wall. Aqueous protein solutions and dispersions having a protein concentration of 20% by weight or more are effectively used in this method. As previously mentioned, proteinaceous materials that are not suitable for wall-forming reactions may be included in the aqueous phase to be encapsulated;
Generally, such proteins do not participate in reactions that form the capsule wall. When edible proteins are encapsulated in accordance with the present invention, biodegradable edible microcapsules are thus easily produced, and these microcapsules can contain the life of aquatic animals such as fish or crustaceans or their larvae. It is particularly useful for dispersing water in the presence of animals as food in order to maintain it. Di- or polybasic carboxylic acids, preferably C ₄ to C ₁₄ as compounds having amino-reactive groups;
Acid chlorides or anhydrides of dicarboxylic acids, for example sebacic acid, adipic acid, phthalic acid, terephthalic acid or succinic acid, or chlorides of tricarboxylic acids such as citric acid are preferably used. An example of a preferred acid anhydride is succinic anhydride. The size of the microcapsules can be varied within a wide range, depending on their final purpose, by varying the size of the dispersed droplets of the amine-containing aqueous phase. Thus, capsules between about 10 microns and about 500 microns in diameter can be prepared as desired by controlling the degree of dispersion of the aqueous phase. The use of surfactants is useful to control capsule size during emulsion production and also affects the rate of wall formation. This is likely because it aids contact between the aqueous and solvent phases. The most suitable surfactants include, for example, the product name “Span”.
85", lecithin, and lactic acid glyceride ester, sold under the trade name "Lactodan". However, surfactants are not essential to the method and may be omitted. In a phase inversion operation, the capsules are allowed to settle and the excess suspended phase is decanted.The capsules are then washed with fresh organic liquid, especially cyclohexane, to remove traces of surfactant, and For example, it may be separated from the solvent by sedimentation or centrifugation and then redispersed in a hydrophilic liquid such as water. It is usually necessary to provide a surface-active substance to aid in dispersion, as was previously thought to be necessary when the capsule is intended for human or animal use. Preferably, the surface-active substance is not a protective colloid, such as polyvinyl alcohol or gelatin, or It can be a material such as lecithin, or an ester of a glyceride, such as a lactate ester of a monoglyceride. It has been found that such materials can be easily removed or otherwise do not need to be removed.
Also, during and after the phase inversion operation, it is often preferred to equilibrate the osmotic pressure by adding solute to the suspended phase to avoid rupturing the capsule. This can be accomplished using high surfactant levels or by adding appropriate amounts of inorganic solutes in the absence of surfactant. The method of the present invention is virtually temperature independent;
It has been successfully implemented in a temperature range up to Although the lower temperatures commonly used in the prior art may be used in the process, it will be clear that it is advantageous to work at room temperature. Polymerization proceeds rapidly at high temperatures. However, the end point of the reaction is generally determined by the inefficiency of the reactants, so there is little advantage in using high temperatures. The method of the present invention provides numerous benefits over prior art operations for microencapsulating various substances in aqueous solution. These benefits include: (a) A wide variety of protein materials can be encapsulated, ie, used for capsule production, without requiring precise temperature measurement and control or precise acid chloride concentrations and addition rates; ( b) The polymerization concentration in the interfacial area between the phases creates a sufficiently strong wall to withstand drying; (c) The method uses short-chain highly reactive diamines and chloroform, both of which are highly toxic. (d) The absence of short-chain diamines allows the creation of a wall that is enzymatically digested in the stomach by cross-linking of pure proteins; ( e) The capsules after washing are dried so that they can be sufficiently rehydrated without agglomeration and thus can be stored and bulked indefinitely; (f) The capsules can be stored in fresh water, salt solution for 6 months. below,
(g) In prior art methods, the continuous phase, i.e. the suspended phase, is
Although often large quantities were required, e.g., a 12:1 volume ratio to the discontinuous phase, i.e., the suspended phase, the proportion of using the present invention is cyclohexane), it can be reduced to 6:1. The detailed examples described below are provided for a better understanding of the invention and its benefits. Unless otherwise specified, all "parts" mentioned in examples are "volume parts."
, and all "percentages" are "weight percentages"
It is. Example 1 5 parts of a 30% by weight aqueous solution of spray-dried whole eggs,
It was emulsified in 25 parts of cyclohexane to which 2% by weight of lecithin was added. The emulsion was produced using a two-blade thruster, the emulsion time was 4 minutes, and the emulsion obtained consisted of droplets with a diameter of 50 to 100 microns. 0.15 parts of adipoyl chloride in 10 parts of cyclohexane was added steadily to the emulsion over a period of 10 seconds. The reaction is
Lasted for 10 minutes at 23.5°C. The resulting microcapsules are left to settle,
Then the cyclohexane was decanted. The capsules were then washed twice with 25 parts of cyclohexane and finally with 25 parts of cyclohexane containing 0.25 part of lecithin. The final settling took about 3 minutes, after which all the cyclohexane was decanted. The capsules were taken up in 50 parts of a 15% by weight warm aqueous gelatin solution and stirred rapidly for 2 to 3 minutes. Next, 750 parts of water at about 35°C was added with stirring. Pale yellow, non-agglomerated capsules with a diameter between 50 and 100μ were obtained. The capsules were separated from the water on a nylon screen and dried overnight after washing with water to remove excess gelatin. Dried capsules could be rehydrated by stirring them in hot water. Examples 2-16 The procedure of Example 1 was generally carried out using various reactants and reaction conditions as shown in the table below. In each case, excellent capsules were obtained that could be dried and rehydrated.

【table】

【table】

[Table] Example 17 100 g of frozen cod roe was thawed and homogenized using a tube and plunger. The resulting mixture was passed through a 0.5 mm nylon mesh sieve and mixed with 5 ml of glycerin. The total amount of material recovered is
It was 63g. Put this in a 500ml beaker,
250 ml of cyclohexane and 0.5% egg lecithin were added and homogenized for 10 minutes using a high speed stirrer to produce an emulsion with a droplet size of 50-150μ.
1.5g succinoyl chloride in 80ml cyclohexane
was added and the reaction continued for 8 minutes. The capsules were allowed to settle and the cyclohexane was decanted. The capsules were then washed four times with 50 ml each of cyclohexane, and then processing continued as in Example 1.

Claims (1)

[Scope of Claims] 1. In producing microcapsules containing an aqueous solution of a hydrophilic protein having a large number of free amino groups, cyclohexane or cyclohexane, which is a non-solvent for the protein and is substantially non-polar, is used. An emulsion of said aqueous solution as a dispersed phase is formed in a liquid as a continuous phase having a polarity lower than that of a 4:1 w/w mixture of chloroform and , its acid halide, or its acid anhydride, so that
A microencapsulation process comprising causing interfacial polycondensation between said protein and said compound to form microcapsules having walls consisting essentially entirely of cross-linked protein. 2. The process according to claim 1, wherein the protein is a protein having a substantially linear structure. 3. The process according to claim 1 or 2, wherein the protein is a globular protein and is denatured to at least partially have its tertiary amine structure. 4. The process according to any one of claims 1 to 3, wherein the protein is a naturally produced protein. 5. Any one of claims 1 to 4, wherein the protein contains a relatively high proportion of amino acids having two amino groups, or contains at least some amino acids in the form of amide. The process described in Crab. 6. A process according to any of claims 1 to 5, wherein the protein is present in the form of a component of a complex naturally occurring mixture. 7. The process of claim 6, wherein the mixture is egg, egg yolk, denatured whey, whole cream condensed milk, or fish roe. 8 Claim 7, wherein the fish roe is cod roe
Process described in section. 9. The process according to any one of claims 1 to 5, wherein the protein is hemoglobin. 10 Claims 1 to 9, wherein the encapsulated aqueous phase contains, in addition to the protein or protein-containing substance, other components that do not participate in the polymerization reaction.
The process described in any of the sections. 11. A process according to any of claims 1 to 10, wherein the aqueous protein solution has a concentration of at least 20% by weight. 12. The process according to any one of claims 1 to 11, wherein the compound that reacts with the protein is an acid chloride of a di- or polybasic carboxylic acid. 13. Claim 12, wherein the compound is sebacoyl chloride, adipoyl chloride, succinoyl chloride, terephthaloyl chloride or succinic anhydride.
Process described in section. 14 The continuous phase liquid is cyclohexane, n-
14. A process according to any of claims 1 to 13 in which decane or 40/60 petroleum ether is used. 15. A process according to any of claims 1 to 14, wherein after the completion of the reaction, the capsules are separated from the continuous phase and dispersed in water. 16. The process according to claim 15, in which a surface-active compound is made to coexist to aid dispersion in water. 17. The process of claim 16, wherein the surface-active substance is a non-detergent compound. 18. The process of claim 17, wherein the surface-active substance is a protective colloid. 19. The process of claim 18, wherein the protective colloid is polyvinyl alcohol or gelatin. 20. The process of claim 17, wherein the surface-active compound is an ester of lecithin or glyceride. 21. A process according to any of claims 15 to 20, wherein a sufficient amount of solute is present in the water to balance the osmotic pressure inside and outside the capsule.