Abstract:
The present invention pertains to a method for preparing a hydrogel in dry conditions that contains high loading of the active ingredient, preferably flavor or fragrance molecules. The hydrogel compositions are initially in solid form and preferably extruded and sized to form the desired shape and size. The actual hydrogel is formed in-situ from the uptake of water that is present in the suspending medium. The hydrogels have the following properties: contain of up to 40% of active ingredient prior to the water uptake; retain color and particle identity in high moisture systems; and retain color and particle identity at elevated temperature.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for preparing a hydrogel and use of the hydrogel in the flavor, fragrance, or pharmaceutical industries. In a preferred embodiment the hydrogel compositions are prepared by extrusion and contain flavor and fragrance products.  
       BACKGROUND OF THE INVENTION  
       [0002]     Hydrogels are colloidal gels in which water is the dispersion medium. Hydrogel products are known in the art and are used in a wide variety of applications and products. Common uses for hydrogels are in disposable diapers, contact lenses, dressings for wounds, and breast implants.  
         [0003]     U.S. Pat. No. 5,489,437 discloses an adhesive hydrogel product comprising a mixture containing water, and a thermoplastic water soluble polymer extruded in a dry state. The mixture is exposed to radiation to provide a breaking strength in excess of at least 10 pounds per square inch.  
         [0004]     In a similar application, as disclosed in U.S. Pat. No. 6,179,862, hydrogels are used to provide in-situ tissue adherent barriers as they are spayed onto tissue and then crosslinked. The crosslinkable solution is kept separate and are atomized and mixed in a gas stream prior to being applied to the tissue.  
         [0005]     Another application of hydrogels is the delivery of therapeutic agents and diagnostic applications at high concentrations in condensate phase microparticles. U.S. Pat. No. 5,654,006 discloses that hydrogels having a particle size of from 0.5 to 5 microns are effective in the delivery of therapeutics, preferably therapeutics having a positive charge.  
         [0006]     Despite the teachings of the above use of hydrogel materials, there is an ongoing need to develop new uses for hydrogel materials.  
         [0007]     Nothing in any of the foregoing references discloses techniques for the production of the hydrogels of our invention or processes for producing same, with said hydrogels having advantageous properties with respect to the delayed release of active materials.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention describes a method for preparation of a hydrogel comprising extruding the functional polymer and the active ingredient in dry conditions and forming a hydrogel in-situ by contacting the extruded material with water provided by the substrate. The unique feature of the invention is that prior to the composition contacting water in the substrate, no water is being added to this composition.  
         [0009]     As an alternative, a hydrogel composition may be prepared by combining the functional polymer and the active ingredient in a spray dry emulsion followed by spray drying. The hydrogel is formed by contacting the dry product with water provided by the substrate.  
         [0010]     A second embodiment of the invention is the use of cross-linking agents to impart thermal stability to the hydrogels, for example with hydrogels made with gelatin. This can be achieved either enzymatically, using transglutaminase or chemically using appropriate cross-linking agents.  
         [0011]     In a third embodiment of the invention the composition of a hydrogel is prepared by admixing the ingredients of the invention together, and providing a heating source such as an extruder to obtain a melted matrix and then creating the desired particle size by forming, cooling, and sizing operations. The extruded material is added to a water-containing medium to form a hydrogel. The hydrogels are formed in-situ.  
         [0012]     The formed hydrogels have the following properties: 
        contain of up to 40% of active ingredient prior to the water uptake;     retain color and particle identity in high moisture systems; and     retain color and particle identity at elevated temperature.        
 
         [0016]     These and other embodiments of the present invention will become apparent by reading the detailed description and accompanying examples. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     The retention of color, particle identity, and actives are provided to the hydrogels through the proper selection and combination of functional polymer, colorant, active ingredient, other functional additives, and processing conditions. Proper selection and combination of the above components of the hydrogel composition and processing conditions allow stable hydrogels to be formed. The hydrogel does not need to be irradiated with ionization energy for the cross-linking to be achieved. Suitable functional polymers include alginate, gelatin, gluten, starch, agar, xanthan gum, gellan gum, pectin, guar gum, hydroxypropyl methylcellulose (HPMC), methyl cellulose, microcrystalline cellulose, soy protein, whey protein, casein, collagen, hydrolyzed gelatin, and the like. The preferred materials are gelatin, gluten, instant starch, and sodium alginate. The level of functional polymer used in the preparation of the hydrogel, before the uptake of water is from about 1 to about 60 weight percent of the material to be extruded. Preferably the amount of the functional polymer ranges from about 7 to about 50 weight percent. The polymer used has a molecular weight of less then 250,000. Preferably, the polymer used has a molecular weight of less than 40,000.  
         [0018]     The active ingredient provided by the present invention is preferably a hydrophobic material. The hydrophobic material is incorporated into a hydrogel composition thereby allowing it to be delivered in hydrophilic systems. The active ingredient may be any suitable material including therapeutic and diagnostic agents, flavors, fragrances and the like.  
         [0019]     A list of suitable fragrances is provided in U.S. Pat. No. 4,534,891. Another source of suitable fragrances is found in Perfumes, Cosmetics and Soaps, Second Edition, edited by W. A. Poucher, 1959. Among the fragrances provided in this treatise are acacia, cassie, chypre, cyclamen, fern, gardenia, hawthorn, heliotrope, honeysuckle, hyacinth, jasmine, lilac, lily, magnolia, mimosa, narcissus, freshly-cut hay, orange blossom, orchid, reseda, sweet pea, trefle, tuberose, vanilla, violet, wallflower, and the like.  
         [0020]     Conventional flavoring materials useful in flavoring products include saturated fatty acids, unsaturated fatty acids and amino acids; alcohols including primary and secondary alcohols, esters, carbonyl compounds including ketones, other than the dienalkylamides of our invention and aldehydes; lactones; other cyclic organic materials including benzene derivatives, acyclic compounds, heterocyclics such as furans, pyridines, pyrazines and the like; sulfur-containing compounds including thiols, sulfides, disulfides and the like; proteins; lipids, carbohydrates; so-called flavor potentiators such as monosodium glutamate; magnesium glutamate, calcium glutamate, guanylates and inosinates; natural flavoring materials such as hydrolyzates, cocoa, vanilla and caramel; essential oils and extracts such as anise oil, clove oil and the like and artificial flavoring materials such as vanillin, ethyl vanillin and the like.  
         [0021]     Specific flavor adjuvants include but are not limited to the following: anise oil; ethyl-2-methyl butyrate; vanillin; cis-3-heptenol; cis-3-hexenol; trans-2-heptenal; butyl valerate; 2,3-diethyl pyrazine; methyl cyclo-pentenolone; benzaldehyde; valerian oil; 3,4-dimethoxy-phenol; amyl acetate; amyl cinnamate; y-butyryl lactone; furfural; trimethyl pyrazine; phenyl acetic acid; isovaleraldehyde; ethyl maltol; ethyl vanillin; ethyl valerate; ethyl butyrate; cocoa extract; coffee extract; peppermint oil; spearmint oil; clove oil; anethol; cardamom oil; wintergreen oil; cinnamic aldehyde; ethyl-2-methyl valerate; γ-hexenyl lactone; 2,4-decadienal; 2,4-heptadienal; methyl thiazole alcohol (4-methyl-5-β-hydroxyethyl thiazole); 2-methyl butanethiol; 4-mercapto-2-butanone; 3-mercapto-2-pentanone; 1-mercapto-2-propane; benzaldehyde; furfural; furfuryl alcohol; 2-mercapto propionic acid; alkyl pyrazine; methyl pyrazine; 2-ethyl-3-methyl pyrazine; tetramethyl pyrazine; polysulfides; dipropyl disulfide; methyl benzyl disulfide; alkyl thiophene; 2,3-dimethyl thiophene; 5-methyl furfural; acetyl furan; 2,4-decadienal; guiacol; phenyl acetaldehyde; β-decalactone; d-limonene; acetoin; amyl acetate; maltol; ethyl butyrate; levulinic acid; piperonal; ethyl acetate; n-octanal; n-pentanal; n-hexanal; diacetyl; monosodium glutamate; mono-potassium glutamate; sulfur-containing amino acids, e.g., cysteine; hydrolyzed vegetable protein; 2-methylfuran-3-thiol; 2-methyldihydrofuran-3-thiol; 2,5-dimethylftiran-3-thiol; hydrolyzed fish protein; tetramethyl pyrazine; propylpropenyl disulfide; propylpropenyl trisulfide; diallyl disulfide; diallyl trisulfide; dipropenyl disulfide; dipropenyl trisulfide; 4-methyl-2-[(methyl-thio)-ethyl]-1,3-dithiolane; 4,5-dimethyl-2-(methylthiomethyl)-1,3-dithiolne; and 4-methyl-2-(methylthiomethyl)-1,3-dithiolane. These and other flavor ingredients are provided in U.S. Pat. Nos. 6,110,520 and 6,333,180.  
         [0022]     Examples of the appropriate therapeutic agents include hypnotics, sedatives, antiepileptics, awakening agents, psychoneurotropic agents, neuromuscular blocking agents, antispasmodic agents, antihistaminics, antiallergics, cardiotonics, antiarrhythmics, diuretics, hypotensives, vasopressors, antitussive expectorants, thyroid hormones, sexual hormones, antidiabetics, antitumor agents, antibiotics and chemotherapeutics, and narcotics.  
         [0023]     Examples of diagnostic agents include, but are not limited to synthetic inorganic and organic compounds, proteins, peptides, polypeptides, polysaccharides and other sugars, lipids, and DNA and RNA nucleic acid sequences having diagnostic activities.  
         [0024]     The level of active ingredient used in the preparation of the hydrogel, before the uptake of water is from about 5 to about 40 weight percent. Preferably the amount of the active ingredient ranges from about 10 to about 20 weight percent. High levels, such as 20 weight percent or greater, of the active ingredient can be achieved by the addition of appropriate functional materials such as modified starch, hydroxypropylcellulose, and/or ethylcellulose.  
         [0025]     The functional additives in the hydrogel compositions are determined by the functional polymer in the composition. For example, a hydrogel composition with sodium alginate as the functional polymer will preferably employ a calcium salt as the functional additive. Calcium functions as a cross-linking agent for the alginate. The invention is advantageous in that the dry extruded composition combines the alginate and calcium in a unique polymer network capable of forming a hydrogel in-situ, thereby eliminating the need to solubilize the alginate and calcium separately prior to forming the hydrogel. The calcium salt must possess certain properties, such as slowly soluble in water and possess desirable melting temperature. The preferred calcium salt is calcium gluconate.  
         [0026]     Another hydrogel composition based on the use of either gelatin or gluten or other protein as the functional polymer will require the use of the transglutaminase enzyme as the functional additive (Activa® Ajinomoto USA, Inc., Chicago, Ill.). This reaction imparts thermal stability to the hydrogel. It also minimizes color leaching from particles containing water miscible colorants such as lakes. Optimum conditions are required to achieve cross-linking within a reasonable amount of time, such as moisture, temperature of about 50° C., pH 6-7, and high enzyme concentration, as described in JP 5292899. U.S. Pat. No. 6,325,951 discloses that it is possible to achieve cross-linking at lower temperatures, such as 5- 10° C., over a 16-hour period or at 5-40° C. for a period of from 10 minutes to 24 hours, see U.S. Pat. No. 5,658,605. In both cases, the level of available moisture is very high. These conditions can be modified depending on the raw materials. Surprisingly, it has been found that cross-linking can be achieved during extrusion, in dry conditions, with the water content of the mixture less then 5%, preferably less than 1%, most preferably no intentionally added water, within the residence time of the materials in the extruder. A powder form of the enzyme is conveniently mixed with the other dry ingredients of the extrusion powder blend. Extrusion is carried out within the time and temperature conditions typically used for melt extrusion.  
         [0027]     It has also been found that enzymatic cross-linking can be achieved using typical conditions for preparing a spray dry emulsion and subsequent spray drying operation. The enzyme preparation is mixed with the dry ingredients and mixed with water to fully hydrate the ingredients. The flavor is added to the mixture and shear is applied to form a pre-emulsion followed by the spray drying operation.  
         [0028]     An alternative functional additive for proteinaceous polymers is glutaraldehyde, formaldehyde or other aldehyde cross-linking materials. The level of functional additive used in the preparation of the hydrogel, before the uptake of water is from about 0.1 to about 20 weight percent of the material to be extruded. Preferably the amount of the functional additive ranges from about 0.5 to about 10 weight percent.  
         [0029]     The colorants of the present invention include, but are not limited to lakes, preparations containing lakes, oleoresins, pigments, and minerals. An example of a preparation containing lakes is Spectra Flecks™ (Sensient Technologies, St. Louis, Mo.). Preferred colorants are botanical materials. Use of botanical materials reduces color leaching. Examples of botanical materials include ground tea leaves, dried parsley, dried red bell pepper, fruit powders, annatto, turmeric, beta-carotene, among others. Examples of pigments are cosmetic colorants identified by their INCI name CI 74260, CI 74160, CI 73360, among others. An example of a mineral is titanium dioxide. The level of colorant used in the preparation of the hydrogel, before the uptake of water is from about 0.01 to about 10 weight percent of the material to be extruded. Preferably the amount of the colorant ranges from about 0.1 to about 5 weight percent.  
         [0030]     In addition to the foregoing components, various optional ingredients such as are conventionally used in the art, may be employed in the matrix of this invention. For example, fillers, diluents, emulsifiers, preservatives, anti-oxidants, stabilizers, lubricants, and the like may be employed herein if desired. Fillers include, for example, materials such as silicon dioxide, titanium dioxide, alumina, talc, kaolin, powdered cellulose and microcrystalline cellulose, as well as soluble materials such as mannitol, urea, sucrose, lactose, dextrose, sodium chloride and sorbitol. Diluents are typically necessary to increase bulk so that a practical size hydrogel is ultimately provided. Suitable diluents include calcium phosphate, calcium sulfate, carboxymethylcellulose calcium, cellulose, cellulose acetate, dextrates, dextrin, dextrose, fructose, glyceryl palmitostearate, hydrogenated vegetable oil, kaolin, lactitol, lactose, magnesium carbonate, magnesium oxide, maltitol, maltodextrin, maltose, microcrystalline cellulose, polymethacrylates, powdered cellulose, pregelatinized starch, silicified microcrystalline cellulose, sodium chloride, sorbitol, starch, sucrose, sugar, talc, hydrogenated vegetable oil, and mixtures thereof. Emulsifiers include mono and di-glycerol esters of fatty acids, modified starch, polyglycerol esters, and sorbitol esters, preferably, the emulsifier is lecithin.  
         [0031]     The formed hydrogels have the following properties: 
        contain of up to 40% of active ingredient prior to the water uptake;     retain color and particle identity in high moisture systems; and     retain color and particle identity at elevated temperature.        
 
         [0035]     Retention of color means that no significant color leaching from the hydrogel occurs. Retention of particle identity means the hydrogel particles maintain their shape and appearance after being exposed to elevated temperatures or stress.  
         [0036]     In another embodiment of the invention, the hydrogel is used for delivering an active ingredient, such as flavor, into an ingestible composition. In this embodiment, the hydrogel is prepared by any of the methods described above and added to an ingestible composition, such as yogurt.  
         [0037]     In all methods of preparation of a hydrogel as described above, spray drying may be used as an alternative to extrusion.  
         [0038]     In order to demonstrate the invention, the following examples were conducted. All U.S. Patent and Patent applications referenced herein are hereby incorporated by reference as if set forth in their entirety. The following disclosures are provided to exemplify the present invention.  
         [0039]     Unless noted to the contrary all weights are weight percent. Upon review of the foregoing, numerous adaptations, modifications and alterations will occur to the reviewer. These adaptations, modifications, and alterations will all be within the spirit of the invention. Accordingly, reference should be made to the appended claims in order to ascertain the scope of the present invention.  
       EXAMPLE 1  
       [0040]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Strawberry Flavor   10           Silicon Dioxide   5           Emulsifier   2           Sorbitol   30.8           Gelatin   50           Transglutaminase   2           Color lake red #40   0.2                         (Extruder zone temperatures ° C.: 1 = 40-50, 2 = 50-60, 3 = 55-65, 4 = 60-75, 5 = 90-105. Extruded melt was cooled, milled, and sized to give a specific particle size.)             
 
       EXAMPLE 2  
       [0041]     Product from Example 1 was incorporated into a lemon-flavored chewy candy base at 100° C. The particles survived the initial mixing and pulling process, retaining their visual identity and color in the candy. When the chewy candy was evaluated, it was observed that the strawberry flavor from the particles was not detected until the particles were masticated. Flavor from the particles continued to increase in intensity as chewing progressed. The example demonstrates that the flavor was protected in the hydrogel at a temperature of 100° C.  
       EXAMPLE 3  
       [0042]     Product from Example 1 was incorporated into a vanilla-flavored yogurt and stored in the refrigerator. The particles survived the mixing process, retaining their visual identity and color in the yogurt. When the yogurt was evaluated after 2 weeks, it was observed that there was a slight leaching of the color and flavor in the base. The particles remained intact and the color distinctly red. The particles retained a high level of strawberry flavor. No further changes were noted after 4 weeks of storage. This example demonstrates the stability of a gelatin-based hydrogel in a high moisture food product.  
       EXAMPLE 4  
       [0043]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Orange Flavor   10           Silicon Dioxide   5           Emulsifier   2           Sorbitol   30.8           Gluten   50           Transglutaminase   2           Color lake yellow #5 &amp; #6   0.2                         (The process followed was similar to that provided in Example 1.)             
 
       EXAMPLE 5  
       [0044]     Product from Example 4 was incorporated into a vanilla-flavored yogurt and stored in the refrigerator. The particles survived the mixing process, retaining their visual identity and color in the yogurt. When the yogurt was evaluated after 2 weeks, it was observed that there was a slight leaching of the color and flavor in the yogurt. The particles remained intact and the color distinctly orange. The particles retained a high level of orange flavor. No further changes were noted after 4 weeks of storage. This example demonstrates the stability of a gluten-based hydrogel.  
       EXAMPLE 6  
       [0045]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Peppermint Flavor   20           Silicon Dioxide   6           Emulsifier   4           Sorbitol   17.99           Gelatin   50           Transglutaminase   2           Color CI #74 160   0.01                         (The process followed was similar to that provided in Example 1.)             
 
       EXAMPLE 7  
       [0046]     Product from Example 6 was incorporated into a model toothpaste base. The particles survived the initial mixing process, retaining their visual identity and color in the toothpaste. This example demonstrates the stability of the hydrogel.  
       EXAMPLE 8  
       [0047]     Product from Example 6 was incorporated into a chewy candy base at 100° C. The particles survived the initial mixing and pulling process, retaining their visual identity and color in the candy. This example demonstrates the stability of the hydrogel.  
       EXAMPLE 9  
       [0048]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Strawberry Flavor   5           Silicon Dioxide   5           Emulsifier   2           Maltitol   37           Starch Advantagel P75   50           Color Red Spectra Flecks ™   1                         (The process followed was similar to that provided in Example 1.)             
 
       EXAMPLE 10  
       [0049]     Product from Example 9 was incorporated into a vanilla-flavored yogurt and stored in the refrigerator. The particles survived the mixing process, retaining their visual identity and color in the yogurt. When the yogurt was evaluated after 2 weeks, it was observed that there was a slight leaching of the color and flavor in the yogurt. The particles remained intact and the color distinctly red. The particles retained a high level of strawberry flavor. At 4 weeks, the particles were softer in texture and color intensity had decreased. This example demonstrates the stability of a starch-based hydrogel.  
       EXAMPLE 11  
       [0050]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Peppermint Flavor   5           Silicon Dioxide   5           Emulsifier   2           Maltitol   75.5           Sodium Alginate   7.5           Parsley, milled   5                         (The process followed was similar to that provided in Example 1.)             
 
       EXAMPLE 12  
       [0051]     Product from Example 11 was incorporated into a vanilla-flavored yogurt and stored in the refrigerator. The particles survived the mixing process, retaining their visual identity and color in the yogurt. When the yogurt was evaluated after 2 weeks, it was observed that there was a slight leaching of the flavor in the yogurt. No parsley flavor was detected in the yogurt. No color leaching was observed. At 4 weeks, the particles were softer in texture and color intensity had decreased. This example demonstrates the color stability of an alginate-based hydrogel using a botanical material as the colorant.  
       EXAMPLE 13  
       [0052]     The following formulation was processed via extrusion:  
                                                             % by weight                                        Strawberry Flavor   5           Silicon Dioxide   5           Emulsifier   2           Maltitol   75.3           Sodium Alginate   7.5           Calcium Gluconate   5           Color Red Spectra Flecks ™   0.2                         (The process followed was similar to that provided in Example 1.)             
 
       EXAMPLE 14  
       [0053]     Product from Example 13 was added to yogurt. Particles formed a fluffy soft gel. This is an example of a calcium alginate hydrogel composition.  
       EXAMPLE 15  
       [0054]     The following formulation was processed via spray drying:  
                                                                                   % by weight                    Formula A   Formula B                            Water   62   62           Strawberry Flavor   11.25   11.25           Modified Starch   21.5   21           Gelatin   5.25   5.25           Transglutaminase   0   0.5                      
 
       EXAMPLE 16  
       [0055]     Products from Example 15 were suspended in water and examined under the microscope. The majority of particles from Formula A dissolved although a few gel-like clusters were formed in sections where there was a collection of powder. Particles from Formula B swelled and formed stable hydrogels.  
         [0056]     The description provided above is not limiting to the scope of the invention. Many other permutations may be specified once the basic concept is understood. These are included although they are not outlined in detail.