Patent Publication Number: US-9832993-B2

Title: Melt processed antimicrobial composition

Description:
BACKGROUND OF THE INVENTION 
     Certain types of botanical oils, such as thymol and carvacrol, are known to be environmentally friendly and effective in combating microorganisms. Unfortunately, however, the use of such oils has been limited in many commercial applications (e.g., wipes) due to their high volatility and instability in the presence of oxygen. Attempts to overcome this problem often involve the use of a larger amount of the botanical oils to prolong antimicrobial activity. Regrettably, this just leads to another problem in that high concentrations of essential oils can cause damage to certain types of food products, such as fruit. Other attempts have involved the encapsulation of the oil component with certain types of polymers, such as proteins. For example, an article entitled “ Encapsulation of Essential Oils in Zein Nanospherical Particles ” (Parris, et al.,  J. Agric. Food Chem.  2005, 53, 4788-4792) broadly describes the encapsulation of thymol in zein nanospheres by mixing the oil with zein particles in the presence of a solvent (e.g., ethanol). The particles are said to be useful for oral or injectable administration of biological materials into the body. Another article entitled “ Controlled Release of Thymol from Zein Based Film ” (Mastromatteo, et al.,  J. Innovative Food and Emerging Technologies  2009, 10, 222-227) broadly describes films formed by dissolving corn zein and glycerol into ethanol, and thereafter adding thymol to form a solution. The solution is poured into a Petri dish and dried to form the film. 
     One problem with the techniques described above is that they generally rely on solvents (e.g., ethanol) to help dissolve the botanical oil into a solution. A disadvantage of the use of solvents is that both the botanical oil and protein must be soluble in a common solvent system, which puts a limit on what type of components may be employed in the composition. Also, solvent-based solutions require a substantial amount of time, energy, and material for processing. Still further, a portion of the botanical oil may escape from the solution when the solvent is evaporated, which requires the use of a greater amount of the oil than would normally be needed. Notwithstanding the above, the ability to use a “solventless” process is complicated by the tendency of proteins to lose their flow properties when exposed to the intense shear and elevated temperature normally associated with melt processing. For example, proteins may undergo a conformational change (“denaturation”) that causes disulfide bonds in the polypeptide to dissociate into sulfhydryl groups or thiyl radicals. Sulfhydryl groups form when disulfide bonds are chemically reduced while mechanical scission of disulfide bonds causes thiyl radicals to form. Once dissociated, however, free sulfhydryl groups randomly re-associate with other sulfhydryl groups to form new disulfide bond between polypeptides. Thiyl radicals can also randomly re-associate with other thiyl radicals forming new disulfide bonds or thiyl radicals can react with other amino acid functionality creating new forms of cross-linking between polypeptides. Because one polypeptide contains multiple thiol groups, random cross-linking between polypeptide leads to formation of an “aggregated” polypeptide network, which is relatively brittle and leads to a loss of flow properties. 
     As such, a need currently exists for a solventless process for forming a stable composition that contains an antimicrobially active botanical oil. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a method for forming an antimicrobial composition is disclosed that comprises dispersively blending a botanical oil, modified starch, and plasticizer within a melt blending device. Botanical oils constitute from about 0.01 wt. % to about 25 wt. % of the composition, modified starches constitute from about 30 wt. % to about 95 wt. % of the composition, and plasticizers constitute from about 0.1 wt. % to about 40 wt. % of the composition. 
     In accordance with another embodiment of the present invention, a melt-processed antimicrobial composition is disclosed that comprises at least one monoterpene phenol in an amount of from about 0.01 wt. % to about 25 wt. %, at least one hydroxyalkyl starch in an amount of from about 30 wt. % to about 95 wt. %, and at least one plasticizer in amount of from about 0.1 wt. % to about 40 wt. %. In yet another embodiment, a method for removing bacteria from a surface is disclosed that comprises contacting the surface with a wipe that comprises a fibrous material that contains the melt-processed antimicrobial composition. 
     Other features and aspects of the present invention are discussed in greater detail below. 
    
    
     DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS 
     Reference now will be made in detail to various embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Generally speaking, the present invention is directed to a method for forming a composition that includes mixing an antimicrobially active botanical oil (e.g., thymol, carvacrol, etc.) and a modified starch polymer within a melt blending device (e.g., extruder). Unlike the problems associated with proteins, the use of starch polymers allows for a greater degree of flexibility in the processing conditions and is still able to achieve good properties in the resulting composition. The present inventors have also discovered that a plasticizer may be employed to facilitate melt processing of the starch, as well as to enhance the ability of the botanical oil to flow into the internal structure of the starch where it can be retained in a stable manner. The composition is also typically generally free of solvents. In this manner, the starch will not generally disperse before use and prematurely release the botanical oil. Due to the water sensitivity of the modified starch, however, it may be subsequently dispersed by moisture when it is desired to release the botanical oil. 
     Various embodiments of the present invention will now be described in more detail below. 
     I. Components 
     A. Botanical Oil 
     Botanical oils are employed in the composition of the present invention as antimicrobial actives. The oil may be an “essential” oil that is extracted from a plant. Likewise, the botanical oil may also be isolated or purified from an essential oil, or it may simply be made synthetically to mimic a compound derived from a plant (e.g., synthetically made thymol). The botanical oils are generally soluble in lipids and believed to exhibit antimicrobial efficacy due to their ability to cause damage to the lipid component of the cell membrane in microorganisms, thereby inhibiting their proliferation. Essential oils are derived from herbs, flowers, trees, and other plants, and are typically present as tiny droplets between the cells of the plants and may be extracted by methods known to those of skill in the art (e.g., steam distillation, enfleurage (i.e., extraction using fat(s)), maceration, solvent extraction, or mechanical pressing). Examples of suitable essential oils for use in the present invention may include, for instance, anise oil, lemon oil, orange oil, oregano, rosemary oil, wintergreen oil, thyme oil, lavender oil, clove oil, hops, tea tree oil, citronella oil, wheat oil, barley oil, lemongrass oil, cedar leaf oil, cedar wood oil, cinnamon oil, fleagrass oil, geranium oil, sandalwood oil, violet oil, cranberry oil, eucalyptus oil, vervain oil, peppermint oil, gum benzoin, basil oil, fennel oil, fir oil, balsam oil, menthol, ocmea origanum oil, Hydastis carradensis oil, Berberidaceae daceae oil, Ratanhiae and Curcuma longa oil, sesame oil, macadamia nut oil, evening primrose oil, Spanish sage oil, Spanish rosemary oil, coriander oil, thyme oil, pimento berries oil, rose oil, bergamot oil, rosewood oil, chamomile oil, sage oil, clary sage oil, cypress oil, sea fennel oil, frankincense oil, ginger oil, grapefruit oil, jasmine oil, juniper oil, lime oil, mandarin oil, marjoram oil, myrrh oil, neroli oil, patchouli oil, pepper oil, black pepper oil, petitgrain oil, pine oil, rose otto oil, spearmint oil, spikenard oil, vetiver oil, or ylang ylang. Still other essential oils known to those of skill in the art are also contemplated as being useful within the context of the present invention (e.g., International Cosmetic Ingredient Dictionary, 10 th  and 12 th  editions, 2004 and 2008, respectively, which are incorporated by reference). 
     In one embodiment, carvacrol and thymol-containing oils are purified from the species Origanum vulgare of a hirtum variety. Ideally this is a hybrid strain that produces high quality oils, but is not limited to this genus, species or strain. The oil extract may also be obtained from a plant of the genus  Nepeta  including, but not limited to species  Nepeta racemosa  (catmint),  Nepeta citriodora, Nepeta elliptica, Nepeta hindostoma, Nepeta lanceolata, Nepeta leucophylla, Nepeta Iongiobracteata, Nepeta mussinii, Nepeta nepetella, Nepeta sibthorpii, Nepeta subsessilis, Nepeta tuberosa, Thymus glandulosus, Thymus hyemalis, Thymus vulgaris  and  Thymus zygis.    
     As indicated above, isolates and/or derivatives of essential oils may also be employed in the present invention. For example, monoterpene phenols are particularly suitable for use in the present invention, which may be isolated and purified from plant oil extracts, or made synthetically by known methods. Suitable monoterpene phenols may include, for instance, thymol, carvacrol, eucalyptol, etc. Thymol (isopropyl-cresol) is one particularly suitable monoterpene phenol, which is a crystalline substance that has a boiling point of about 238° C. at atmospheric pressure. Carvacrol (isopropyl-o-cresol), an isomer of thymol, is another suitable compound. Carvacrol is a liquid with a boiling point of about 233° C. at atmospheric pressure. Thymol and carvacrol, as well as isomers thereof, may be derived from plant oil extracts or synthesized. For example, carvacrol may be synthesized by the reaction of nitrous acid with 1-methyl-2-amino-4-propyl benzene. In addition to being employed in an isolated or pre-synthesized form, essential oils containing the monoterpene phenols as major constituents may be employed, with the final concentrations of the monoterpene phenols being within the ranges provided herein. The term “major constituent” generally refers to those essential oils having monoterpene phenols in an amount of more than 50 wt. %. It is well-known in the art that such essential oils may also contain lesser amounts of other constituents, such as non-aromatic terpene compounds. Essential oils with organic phenolic compounds as the major constituent include, for example, anise oil, bay oil terpineless, clove bud, clove leaf, clove oil, clove stem, origanum oil, Peru balsam, pimento oil, eucalyptus oil, and thyme oil. 
     Due to the stability achieved by the antimicrobial composition of the present invention, a relatively small amount of botanical oils may be employed and still achieve the desired antimicrobial efficacy. More particularly, the composition may employ botanical oils in an amount of from about 0.01 wt. % to about 25 wt. %, in some embodiments from about 0.1 wt. % to about 20 wt. %, and in some embodiments, from about 0.2 wt. % to about 10 wt. %. 
     B. Modified Starch 
     The antimicrobial composition of the present invention also contains a modified starch. Because the botanical oil tends to leach out during storage and before it is used in the desired application, the modified starch polymer helps enhance the long term stability of the oil and, in turn, antimicrobial efficacy. Without intending to be limited by theory, it is believed that the physical structure of the starch can effectively encapsulate the botanical oil and inhibit its premature release. Nevertheless, when it is desired to release the botanical oil prior to and/or during use, the modified starch can disperse (e.g., disintegrate, dissolve, change physical form, etc.) when placed in an aqueous environment. The amount of time needed for dispersal of such polymers so that they release the desired antimicrobial active will depend at least in part upon the particular end-use design criteria. In most embodiments, the modified starch will begin to disperse and release the antimicrobial active within about 5 minutes, suitably within about 1 minute, more suitably within about 30 seconds, and most suitably within about 10 seconds. 
     Although starch polymers are produced in many plants, typical sources includes seeds of cereal grains, such as corn, waxy corn, wheat, sorghum, rice, and waxy rice; tubers, such as potatoes; roots, such as tapioca (i.e., cassava and manioc), sweet potato, and arrowroot; and the pith of the sago palm. Regardless of its source, the starch is modified so that it possesses a higher degree of water sensitivity, which helps facilitate degradation upon contact with water. Such modified starches may be obtained through typical processes known in the art (e.g., esterification, etherification, oxidation, acid hydrolysis, enzymatic hydrolysis, etc.). 
     Starch ethers and/or esters are particularly desirable, such as hydroxyalkyl starches. Without intending to be limited by theory, it is believed that such modified starches possess polar groups (e.g., hydroxy) and nonpolar groups (e.g., alkyl) that are capable of interacting with the polar (e.g., phenolic hydroxyl) and nonpolar (e.g., isopropyl) groups, respectively, found in monoterpene phenolic botanical oils. This enhances the ability of the starch polymer to trap and hold the botanical oil prior to use. Furthermore, the modification of the starch polymer provides enhanced chain flexibility, which even further enhances its trapping efficiency. The hydroxyalkyl group of hydroxylalkyl starches may contain, for instance, 2 to 10 carbon atoms, in some embodiments from 2 to 6 carbon atoms, and in some embodiments, from 2 to 4 carbon atoms. Representative hydroxyalkyl starches such as hydroxyethyl starch, hydroxypropyl starch, hydroxybutyl starch, and derivatives thereof. Starch esters, for instance, may be prepared using a wide variety of anhydrides (e.g., acetic, propionic, butyric, and so forth), organic acids, acid chlorides, or other esterification reagents. The degree of esterification may vary as desired, such as from 1 to 3 ester groups per glucosidic unit of the starch. 
     The starch polymer may contain different weight percentages of amylase and amylopectin, different polymer molecular weights, etc. High amylose starches contain greater than about 50% by weight amylose and low amylose starches contain less than about 50% by weight amylose. Although not required, low amylose starches having an amylase content of from about 10% to about 40% by weight, and in some embodiments, from about 15% to about 35% by weight, are particularly suitable for use in the present invention. Examples of such low amylose starches include corn starch and potato starch, both of which have an amylose content of approximately 20% by weight. Particularly suitable low amylose starches are those having a number average molecular weight (“M n ”) ranging from about 50,000 to about 1,000,000 grams per mole, in some embodiments from about 75,000 to about 800,000 grams per mole, and in some embodiments, from about 100,000 to about 600,000 grams per mole, and/or a weight average molecular weight (“M w ”) ranging from about 5,000,000 to about 25,000,000 grams per mole, in some embodiments from about 5,500,000 to about 15,000,000 grams per mole, and in some embodiments, from about 6,000,000 to about 12,000,000 grams per mole. The ratio of the weight average molecular weight to the number average molecular weight (“M w /M n ”), i.e., the “polydispersity index”, is also relatively high. For example, the polydispersity index may range from about 10 to about 100, and in some embodiments, from about 20 to about 80. The weight and number average molecular weights may be determined by methods known to those skilled in the art. 
     The antimicrobial composition of the present invention typically employs modified starch polymers in an amount of from about 30 wt. % to about 95 wt. %, in some embodiments from about 40 wt. % to about 90 wt. %, and in some embodiments, from about 50 wt. % to about 80 wt. %. 
     C. Plasticizer 
     A plasticizer is also employed in the antimicrobial composition to help render the starch more flowable under melt processing conditions (e.g., rendering the starch thermoplastic) and able to receive the botanical oil within its internal structure. For instance, the plasticizer typically softens and penetrates into the outer membrane of the starch and causes the inner starch chains to absorb water and swell. This swelling will, at some point, cause the outer shell to rupture and result in an irreversible destructurization of the starch granule. Once destructurized, the starch polymer chains, which are initially compressed within the granules, may stretch out and form a generally disordered intermingling of polymer chains. Upon resolidification, however, the chains may reorient themselves to form crystalline or amorphous solids having varying strengths depending on the orientation of the starch polymer chains. 
     Suitable plasticizers may include, for instance, polyhydric alcohol plasticizers, such as sugars (e.g., glucose, sucrose, fructose, raffinose, maltodextrose, galactose, xylose, maltose, lactose, mannose, and erythrose), sugar alcohols (e.g., erythritol, xylitol, malitol, mannitol, and sorbitol), polyols (e.g., ethylene glycol, glycerol, propylene glycol, dipropylene glycol, butylene glycol, and hexane triol), etc. Also suitable are hydrogen bond forming organic compounds which do not have hydroxyl group, including urea and urea derivatives; anhydrides of sugar alcohols such as sorbitan; animal proteins such as gelatin; vegetable proteins such as sunflower protein, soybean proteins, cotton seed proteins; and mixtures thereof. Other suitable plasticizers may include phthalate esters, dimethyl and diethylsuccinate and related esters, glycerol triacetate, glycerol mono and diacetates, glycerol mono, di, and tripropionates, butanoates, stearates, lactic acid esters, citric acid esters, adipic acid esters, stearic acid esters, oleic acid esters, and other acid esters. Aliphatic acids may also be used, such as copolymers of ethylene and acrylic acid, polyethylene grafted with maleic acid, polybutadiene-co-acrylic acid, polybutadiene-co-maleic acid, polypropylene-co-acrylic acid, polypropylene-co-maleic acid, and other hydrocarbon based acids. A low molecular weight plasticizer is preferred, such as less than about 20,000 g/mol, preferably less than about 5,000 g/mol and more preferably less than about 1,000 g/mol. 
     The plasticizer may be incorporated into the antimicrobial composition using any of a variety of known techniques. For example, the starch polymers may be “pre-plasticized” prior to incorporation into the composition to form what is often referred to as a “thermoplastic starch.” The relative amount of the starch and plasticizer employed in the thermoplastic starch may vary depending on a variety of factors, such as the desired molecular weight, the type of starch, the affinity of the plasticizer for the starch, etc. Typically, however, the starch polymer constitutes from about 40 wt. % to about 98 wt. %, in some embodiments from about 50 wt. % to about 95 wt. %, and in some embodiments, from about 60 wt. % to about 90 wt. % of the thermoplastic starch. Likewise, the plasticizer typically constitutes from about 2 wt. % to about 60 wt. %, in some embodiments from about 5 wt. % to about 50 wt. %, and in some embodiments, from about 10 wt. % to about 40 wt. % of the thermoplastic starch. The plasticizers may likewise constitute from about 0.1 wt. % to about 40 wt. %, in some embodiments from about 1 wt. % to about 35 wt. %, and in some embodiments, from about 5 to about 30 wt. % of the antimicrobial composition. 
     D. Other Components 
     In addition to those noted above, still other additives may also be incorporated into the composition. For example, in addition to the modified starch, the composition may also contain other natural biopolymers, such as native starches, cellulose obtained from various plant sources, algae matters from various sources which is mixture of carbohydrates, proteins, and natural oils, hemicelluloses, modified cellulose (hydroxylalkyl cellulose, cellulose ethers, cellulose esters, etc.), and so forth. When employed, the amount of such additional natural biopolymers may ranges from about 0.1 wt. % to about 50 wt. %, in some embodiments from about 0.5 wt. % to about 40 wt. %, and in some embodiments, from about 1 wt. % to about 30 wt. %. 
     Dispersion aids may also be employed to help create a uniform dispersion of the oil/starch/plasticizer and retard or prevent separation of the antimicrobial composition into constituent phases. When employed, the dispersion aid(s) typically constitute from about 0.01 wt. % to about 10 wt. %, in some embodiments from about 0.1 wt. % to about 5 wt. %, and in some embodiments, from about 0.5 wt. % to about 4 wt. % of the antimicrobial composition. Although any dispersion aid may generally be employed in the present invention, surfactants having a certain hydrophilic/lipophilic balance may improve the long-term stability of the composition. As is known in the art, the relative hydrophilicity or lipophilicity of an emulsifier can be characterized by the hydrophilic/lipophilic balance (“HLB”) scale, which measures the balance between the hydrophilic and lipophilic solution tendencies of a compound. The HLB scale ranges from 0.5 to approximately 20, with the lower numbers representing highly lipophilic tendencies and the higher numbers representing highly hydrophilic tendencies. In some embodiments of the present invention, the HLB value of the surfactants is from about 1 to about 15, in some embodiments from about 1 to about 12 and in some embodiments, from about 2 to about 10. If desired, two or more surfactants may be employed that have HLB values either below or above the desired value, but together have an average HLB value within the desired range. 
     One particularly suitable class of surfactants for use in the present invention are nonionic surfactants, which typically have a hydrophobic base (e.g., long chain alkyl group or an alkylated aryl group) and a hydrophilic chain (e.g., chain containing ethoxy and/or propoxy moieties). For instance, some suitable nonionic surfactants that may be used include, but are not limited to, ethoxylated alkyiphenols, ethoxylated and propoxylated fatty alcohols, polyethylene glycol ethers of methyl glucose, polyethylene glycol ethers of sorbitol, ethylene oxide-propylene oxide block copolymers, ethoxylated esters of fatty (C 8 -C 18 ) acids, condensation products of ethylene oxide with long chain amines or amides, condensation products of ethylene oxide with alcohols, fatty acid esters, monoglyceride or diglycerides of long chain alcohols, and mixtures thereof. In one particular embodiment, the nonionic surfactant may be a fatty acid ester, such as a sucrose fatty acid ester, glycerol fatty acid ester, propylene glycol fatty acid ester, sorbitan fatty acid ester, pentaerythritol fatty acid ester, sorbitol fatty acid ester, and so forth. The fatty acid used to form such esters may be saturated or unsaturated, substituted or unsubstituted, and may contain from 6 to 22 carbon atoms, in some embodiments from 8 to 18 carbon atoms, and in some embodiments, from 12 to 14 carbon atoms. In one particular embodiment, mono- and di-glycerides of fatty acids may be employed in the present invention. 
     The composition may also contain a preservative or preservative system to inhibit the growth of microorganisms over an extended period of time. Suitable preservatives may include, for instance, alkanols, disodium EDTA (ethylenediamine tetraacetate), EDTA salts, EDTA fatty acid conjugates, isothiazolinone, benzoic esters (parabens) (e.g., methylparaben, propylparaben, butylparaben, ethylparaben, isopropylparaben, isobutylparaben, benzylparaben, sodium methylparaben, and sodium propylparaben), benzoic acid, propylene glycols, sorbates, urea derivatives (e.g., diazolindinyl urea), and so forth. Other suitable preservatives include those sold by Sutton Labs, such as “Germall 115” (amidazoiidinyl urea), “Germall II” (diazolidinyl urea), and “Germall Plus” (diazolidinyl urea and iodopropynyl butylcarbonate). Another suitable preservative is Kathon CG®, which is a mixture of methylchloroisothiazolinone and methylisothiazoiinone available from Rohm &amp; Haas; Mackstat H 66 (available from McIntyre Group, Chicago, Ill.). Still another suitable preservative system is a combination of 56% propylene glycol, 30% diazolidinyl urea, 11% methylparaben, and 3% propylparaben available under the name GERMABEN® II from International Specialty Products of Wayne, N.J. 
     To better enhance the benefits to consumers, other optional ingredients may also be used. For instance, some classes of ingredients that may be used include, but are not limited to: antioxidants (product integrity); anti-reddening agents, such as aloe extract; astringents-cosmetic (induce a tightening or tingling sensation on skin); colorants (impart color to the product); deodorants (reduce or eliminate unpleasant odor and protect against the formation of malodor on body surfaces); fragrances (consumer appeal); opacifiers (reduce the clarity or transparent appearance of the product); skin conditioning agents; skin exfoliating agents (ingredients that increase the rate of skin cell turnover such as alpha hydroxy acids and beta hydroxyacids); skin protectants (a drug product which protects injured or exposed skin or mucous membrane surface from harmful or annoying stimuli); and thickeners (to increase viscosity). 
     While a wide variety of different components may be employed, it is typically desired that the antimicrobial composition is formed without the use of solvents, particularly organic solvents, such as organic alcohols (e.g., ethanol). Not only does this enhance manufacturing efficiency, but it also limits the evaporation of the botanical oil that might otherwise be encountered during removal of the solvent. While the composition may be generally free of such solvents, it should of course be understood that a small amount may still be present in the resulting composition. Regardless, the composition typically contains solvents in an amount less than about 20 wt. %, in some embodiments less than about 10 wt. %, and in some embodiments, from about 0.01 wt. % to about 5 wt. %. 
     II. Melt Processing Technique 
     As indicated above, the antimicrobial composition of the present invention is formed by processing the components together in a melt blending device (e.g., extruder). The mechanical shear and heat provided by the device allows the components to be blended together in a highly efficient manner without the use of a solvent. Batch and/or continuous melt blending techniques may be employed in the present invention. For example, a mixer/kneader, Banbury mixer, Farrel continuous mixer, single-screw extruder, twin-screw extruder, roll mill, etc., may be utilized. One particularly suitable melt-blending device is a co-rotating, twin-screw extruder (e.g., USALAB twin-screw extruder available from Thermo Electron Corporation of Stone, England or an extruder available from Werner-Pfleiderer from Coperion Ramsey, N.J.). The raw materials (e.g., botanical oil, starch, plasticizer, etc.) may be supplied to the melt blending device separately and/or as a blend. For example, the starch and/or botanical oil may be initially fed to a feeding port of the twin-screw extruder, Thereafter, a plasticizer may be injected into the extruder downstream from the botanical oil and starch. Alternatively, the components may be simultaneously fed to the feed throat of the extruder or separately at a different point along its length. 
     Regardless, the materials may be dispersively blended at a shear/pressure and temperature sufficient to ensure adequate mixing (e.g., at or above the softening point of the starch polymer), but without adversely impacting the physical properties of the starch. For example, melt blending typically occurs at a temperature of from about 50° C. to about 250° C., in some embodiments, from about 70° C. to about 200° C., in some embodiments from about 80° C. to about 150° C., and in some embodiments, from about 80° C. to about 125° C. Lower processing temperature may reduce evaporation of the botanical oil and potential loss during processing. Likewise, the apparent shear rate during melt blending may range from about 100 seconds −1  to about 5,000 seconds −1 , in some embodiments from about 200 seconds −1  to about 2,000 seconds −1 , and in some embodiments, from about 400 seconds −1  to about 1,200 seconds −1 . The apparent shear rate is equal to 4Q/πR 3 , where Q is the volumetric flow rate (“m 3 /s”) of the polymer melt and R is the radius (“m”) of the capillary (e.g., extruder die) through which the melted polymer flows. The apparent melt viscosity of the resulting antimicrobial composition may be relatively low, such as from about 1 to about 100 Pascal seconds (Pa·s), in some embodiments from about 5 to about 60 Pa·s, and in some embodiments, from about 20 to about 50 Pa·s, as determined at a temperature of 160° C. and a shear rate of 1000 see. The melt flow index (190° C., 2.16 kg) of the composition may also range from about 0.05 to about 50 grams per 10 minutes, in some embodiments from about 0.1 to about 15 grams per 10 minutes, and in some embodiments, from about 0.5 to about 5 grams per 10 minutes. 
     Once formed, the antimicrobial composition of the present invention may be used in a variety of forms, such as particles, lotion, cream, jelly, liniment, ointment, salve, oil, foam, gel, film, wash, coating, liquid, capsule, tablet, concentrate, etc. In one particular embodiment, for example, the antimicrobial composition may be formed into a film, either alone or in conjunction with an additional film-forming material. The film may be used in a wide variety of applications, such as in the packaging of items (e.g., food products, medical products, garments, garbage, absorbent articles (e.g., diapers), etc. The film may have a mono-layered or multi-layered structure. Multilayer films normally contain at least one base layer and at least one skin layer, but may contain any number of layers desired. The base layer and/or the skin layer may contain the antimicrobial composition of the present invention. Any known technique may be used to form a film from the compounded material, including blowing, casting, flat die extruding, etc. In one particular embodiment, the film may be formed by a blown process in which a gas (e.g., air) is used to expand a bubble of the extruded polymer blend through an annular die. The bubble is then collapsed and collected in flat film form. Processes for producing blown films are described, for instance, in U.S. Pat. No. 3,354,506 to Raley; U.S. Pat. No. 3,650,649 to Schippers; and U.S. Pat. No. 3,801,429 to Schrenk et al., as well as U.S. Patent Application Publication Nos. 2005/0245162 to McCormack, et al. and 2003/0068951 to Bowls, et al., all of which are incorporated herein in their entirety by reference thereto for all purposes. In yet another embodiment, however, the film is formed using a casting technique. 
     Besides being formed into a film, the antimicrobial composition of the present invention may also be formed into particles and applied to other types of articles. Powderization may be accomplished using any of a variety of known techniques. Suitable pulverizing techniques may include, for instance, cryogenic disk mill or hammer mill, solid state shear pulverization using cold extrusion technology, double stream mills (e.g., Type PSKM or PPSM mills available from Pallmann Industries), and other known powderization methods. Cryogenic downsizing techniques or cold extrusion pulverization techniques may be particularly suitable as such techniques limit the degree to which the volatile botanical oil is heated and lost during powder formation. Examples of such techniques are described in more detail, for instance, in U.S. Pat. No. 5,395,055 to Shutov, et al., which is incorporated herein in its entirety by reference thereto for all purposes. The shape of the particles may vary as desired, such as spherical, nodular, flake, etc. The average size of the particles may also be selected to optimize the ability of the botanical oil to be released during use. More particularly, the present inventors have discovered that smaller particle sizes can generally result in a greater release rate of the oil when dispersed in an aqueous solution due to their high surface area to volume ratio. However, at too small of a size, the botanical oil may become unstable during storage and actually begin to leach out of the particles prior to use. In this regard, the present inventors have discovered that an average size of from about 10 to about 3,000 micrometers, in some embodiments from about 50 to about 800 micrometers, and in some embodiments, from about 100 to about 600 micrometers, can help achieve a good balance between stability and releasibility. 
     Regardless of its particular form, the antimicrobial particles may be applied to a wide variety of different articles for imparting antimicrobial efficacy. In one particular embodiment, the composition is applied to a wipe. Such wipes may be used to reduce microbial or viral populations on a hard surface (e.g., sink, table, counter, sign, and so forth) or surface on a user/patient (e.g., skin, mucosal membrane, such as in the mouth, nasal passage, stomach, vagina, etc., wound site, surgical site, and so forth). The wipe may provide an increased surface area to facilitate contact of the composition with microorganisms. In addition, the wipe may also serve other purposes, such as providing water absorption, barrier properties, etc. The wipe may also eliminate microorganisms through frictional forces imparted to the surface. 
     The wipe may be formed from any of a variety of materials as is well known in the art. Typically, however, the wipe includes a fibrous web that contains absorbent fibers. For example, the wipe may be a paper product containing one or more paper webs, such as facial tissue, bath tissue, paper towels, napkins, and so forth. The paper product may be single-ply in which the web forming the product includes a single layer or is stratified (i.e., has multiple layers), or multi-ply, in which the webs forming the product may themselves be either single or multi-layered. Normally, the basis weight of such a paper product is less than about 120 grams per square meter (“gsm”), in some embodiments less than about 80 gsm, in some embodiments less than about 60 grams per square meter, and in some embodiments, from about 10 to about 60 gsm. Any of a variety of materials can also be used to form the paper web(s) of the product. For example, the material used to make the paper product may include absorbent fibers formed by a variety of pulping processes, such as kraft pulp, sulfite pulp, thermomechanical pulp, etc. The pulp fibers may include softwood fibers having an average fiber length of greater than 1 mm and particularly from about 2 to 5 mm based on a length-weighted average. Such softwood fibers can include, but are not limited to, northern softwood, southern softwood, redwood, red cedar, hemlock, pine (e.g., southern pines), spruce (e.g., black spruce), combinations thereof, and so forth. Exemplary commercially available pulp fibers suitable for the present invention include those available from Kimberly-Clark Corporation under the trade designations “Longlac-19”. Hardwood fibers, such as eucalyptus, maple, birch, aspen, and so forth, can also be used. In certain instances, eucalyptus fibers may be particularly desired to increase the softness of the web. Eucalyptus fibers can also enhance the brightness, increase the opacity, and change the pore structure of the web to increase its wicking ability. Moreover, if desired, secondary fibers obtained from recycled materials may be used, such as fiber pulp from sources such as, for example, newsprint, reclaimed paperboard, and office waste. Further, other natural fibers can also be used in the present invention, such as abaca, sabai grass, milkweed floss, pineapple leaf, bamboo, algae, and so forth. In addition, in some instances, synthetic fibers can also be utilized. 
     If desired, the absorbent fibers (e.g., pulp fibers) may be integrated with synthetic fibers to form a composite. Synthetic thermoplastic fibers may also be employed in the nonwoven web, such as those formed from polyolefins, e.g., polyethylene, polypropylene, polybutylene, etc.; polytetrafluoroethylene; polyesters, e.g., polyethylene terephthalate and so forth; polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, and so forth; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol; polyurethanes; polylactic acid; polyhydroxyalkanoate; copolymers thereof; and so forth. Because many synthetic thermoplastic fibers are inherently hydrophobic (i.e., non-wettable), such fibers may optionally be rendered more hydrophilic (i.e., wettable) by treatment with a surfactant solution before, during, and/or after web formation. Other known methods for increasing wettability may also be employed, such as described in U.S. Pat. No. 5,057,361 to Sayovitz, et al., which is incorporated herein in its entirety by reference thereto for all purposes. The relative percentages of such fibers may vary over a wide range depending on the desired characteristics of the composite. For example, the composite may contain from about 1 wt. % to about 60 wt. %, in some embodiments from 5 wt. % to about 50 wt. %, and in some embodiments, from about 10 wt. % to about 40 wt. % synthetic polymeric fibers. The composite may likewise contain from about 40 wt. % to about 99 wt. %, in some embodiments from 50 wt. % to about 95 wt. %, and in some embodiments, from about 60 wt. % to about 90 wt. % absorbent fibers. 
     Composites, such as described above, may be formed using a variety of known techniques. For example, a nonwoven composite may be formed that is a “coform material” that contains a mixture or stabilized matrix of thermoplastic fibers and a second non-thermoplastic material. As an example, coform materials may be made by a process in which at least one meltblown die head is arranged near a chute through which other materials are added to the web while it is forming. Such other materials may include, but are not limited to, fibrous organic materials such as woody or non-woody pulp such as cotton, rayon, recycled paper, pulp fluff and also superabsorbent particles, inorganic and/or organic absorbent materials, treated polymeric staple fibers and so forth. Some examples of such coform materials are disclosed in U.S. Pat. No. 4,100,324 to Anderson, et al.; U.S. Pat. No. 5,284,703 to Everhart, et al.; and U.S. Pat. No. 5,350,624 to Georger, et al.; which are incorporated herein in their entirety by reference thereto for all purposes. Alternatively, the nonwoven composite may be formed be formed by hydraulically entangling staple length fibers and/or filaments with high-pressure jet streams of water. Various techniques for hydraulically entangling fibers are generally are disclosed, for example, in U.S. Pat. No. 3,494,821 to Evans and U.S. Pat. No. 4,144,370 to Bouolton, which are incorporated herein in their entirety by reference thereto for all purposes. Hydraulically entangled nonwoven composites of continuous filaments (e.g., spunbond web) and natural fibers (e.g., pulp) are disclosed, for example, in U.S. Pat. No. 5,284,703 to Everhart, et al. and U.S. Pat. No. 6,315,864 to Anderson, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Hydraulically entangled nonwoven composite of staple fiber blends (e.g., polyester and rayon) and natural fibers (e.g., pulp), also known as “spunlaced” fabrics, are described, for example, in U.S. Pat. No. 5,240,764 to Haid, et al., which is incorporated herein in its entirety by reference thereto for all purposes. 
     Regardless of the materials or processes utilized to form the wipe, the basis weight of the wipe is typically from about 20 to about 200 grams per square meter (“gsm”), and in some embodiments, between about 35 to about 100 gsm. Lower basis weight products may be particularly well suited for use as light duty wipes, while higher basis weight products may be better adapted for use as industrial wipes. 
     The wipe may assume a variety of shapes, including but not limited to, generally circular, oval, square, rectangular, or irregularly shaped. Each individual wipe may be arranged in a folded configuration and stacked one on top of the other to provide a stack of wet wipes. Such folded configurations are well known to those skilled in the art and include c-folded, z-folded, quarter-folded configurations and so forth. For example, the wipe may have an unfolded length of from about 2.0 to about 80.0 centimeters, and in some embodiments, from about 10.0 to about 25.0 centimeters. The wipes may likewise have an unfolded width of from about 2.0 to about 80.0 centimeters, and in some embodiments, from about 10.0 to about 25.0 centimeters. The stack of folded wipes may be placed in the interior of a container, such as a plastic tub, to provide a package of wipes for eventual sale to the consumer. Alternatively, the wipes may include a continuous strip of material which has perforations between each wipe and which may be arranged in a stack or wound into a roll for dispensing. Various suitable dispensers, containers, and systems for delivering wipes are described in U.S. Pat. No. 5,785,179 to Buczwinski, et al.; U.S. Pat. No. 5,964,351 to Zander; U.S. Pat. No. 6,030,331 to Zander; U.S. Pat. No. 6,158,614 to Haynes, et al.; U.S. Pat. No. 6,269,969 to Huang, et al.; U.S. Pat. No. 6,269,970 to Huang, et al.; and U.S. Pat. No. 6,273,359 to Newman, et al., which are incorporated herein in their entirety by reference thereto for all purposes. 
     The composition may be incorporated into the wipe in a variety of different ways. For example, the composition may be applied to a surface of the wipe using known techniques, such as printing, dipping, spraying, melt extruding, coating (e.g., solvent coating, powder coating, brush coating, etc.), foaming, and so forth. If desired, the composition may be applied in a pattern that covers from about 5% to about 95%, in some embodiments from about 10% to about 90%, and in some embodiments, from about 20% to about 75% of a surface of the wipe. Such patterned application may have various benefits, including enhanced aesthetic appeal, improved absorbency, etc. The particular type or style of the pattern is not a limiting factor of the invention, and may include, for example, any arrangement of stripes, bands, dots, or other geometric shape. The pattern may include indicia (e.g., trademarks, text, and logos), floral designs, abstract designs, any configuration of artwork, etc. It should be appreciated that the “pattern” may take on virtually any desired appearance. The composition may also be blended with the fibers used to form the wipe. This may be particularly useful when the composition is in the form of particles. For example, such particles may be blended with the absorbent fibers (e.g., pulp fibers, staple fibers, etc.) during hydraulic entanglement, coforming, etc. The particles may also be incorporated into the thermoplastic material of the wipe (e.g., meltblown web) using known techniques. 
     The amount of the antimicrobial composition on the wipe may vary depending on the nature of the substrate and its intended application. For example, the add-on level of the composition may be from about 5% to about 100%, in some embodiments from about 10% to about 80%, and in some embodiments, from about 20% to about 70%. The “add-on level” is determined by subtracting the weight of the untreated substrate from the weight of the treated substrate, dividing this calculated weight by the weight of the untreated substrate, and then multiplying by 100%. Lower add-on levels may provide optimum functionality of the substrate, while higher add-on levels may provide optimum antimicrobial efficacy. 
     To use the composition, an aqueous solution may simply be added, thereby dispersing the starch and releasing the botanical oil. The aqueous solution may contain only water, or it may contain water in combination with other components. For example, a weak acid may be employed to help disperse the starch and facilitate the release of the oil upon contact with the aqueous solution. Suitable acids for this purpose may include, for instance, organic carboxylic acids, such as citric acid, oxalic acid, lactic acid, acetic acid, etc. Regardless, the present inventors have surprisingly discovered that the amount of the botanical oil released into the aqueous solution can be even greater than the normal solubility limit of the oil in water. Without intending to be limited by theory, it is believed that this can be achieved because the physical structure of the starch is able to effectively “carry” the volatile into the released solution. For example, the solubility limit of thymol in water (at 25° C.) is typically about 0.1 wt. %. When released from the composition of the present invention, however, the concentration of thymol in the released solution can be greater than 0.1 wt. %, in some embodiments greater than about 0.15 wt. %., in some embodiments from about 0.2 wt. % to about 10 wt. %, and in some embodiments, from about 0.2 wt. % to about 4 wt. %. 
     The present inventors have discovered that the composition of the present invention may inhibit (e.g., reduce by a measurable amount or to prevent entirely) the growth of one or more microorganisms when exposed thereof. Examples of microorganisms that may be inhibited include bacteria, protozoa, algae, and fungi (e.g., molds and yeast). Furthermore is possible to use this invention to inactivate viruses, prions and other infectious particles. For example, the composition may inhibit the growth of several medically significant bacteria groups, such as Gram negative rods (e.g.,  Entereobacteria ); Gram negative curved rods (e.g.,  Heliobacter, Campylobacter , etc.); Gram negative cocci (e.g.,  Neisseria ); Gram positive rods (e.g.,  Bacillus, Clostridium , etc.); Gram positive cocci (e.g.,  Staphylococcus, Streptococcus , etc.); obligate intracellular parasites (e.g.,  Ricckettsia  and  Chlamydia ); acid fast. rods (e.g.,  Myobacterium, Nocardia , etc.); spirochetes (e.g.,  Treponema, Boreilia , etc.); and mycoplasmas (i.e., tiny bacteria that lack a cell wall). Particularly species of bacteria that may be inhibited with the composition of the present invention include  Escherichia coli  (Gram negative rod),  Klebsiella pneumonia  (Gram negative rod),  Streptococcus  (Gram positive cocci),  Salmonella choleraesuis  (Gram negative rod),  Staphyloccus aureus  (Gram positive cocci), and  P. aeruginosa  (Gram negative rod). In addition to bacteria, other microorganisms of interest include fungi (e.g.,  Aspergillus niger ) and yeasts (e.g.,  Candida albicans ). 
     Upon exposure for a certain period of time, the composition may provide a log reduction of at least about 2, in some embodiments at least about 3, in some embodiments at least about 4, and in some embodiments, at least about 5 (e.g., about 6). Log reduction, for example, may be determined from the % population killed by the composition according to the following correlations: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 % Reduction 
                 Log Reduction 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 90 
                 1 
               
               
                   
                 99 
                 2 
               
               
                   
                 99.9 
                 3 
               
               
                   
                 99.99 
                 4 
               
               
                   
                 99.999 
                 5 
               
               
                   
                 99.9999 
                 6 
               
               
                   
                   
               
            
           
         
       
     
     Such a log reduction may be achieved in accordance with the present invention after only a relatively short exposure time. For example, the desired log reduction may be achieved after exposure for only 30 minutes, in some embodiments 15 minutes, in some embodiments 10 minutes, in some embodiments 5 minutes, in some embodiments 1 minute, and in some embodiments, 30 seconds. 
     The present invention may be better understood with reference to the following examples. 
     Materials Employed 
     
         
         
           
             Thymol (99.5% purity) was obtained from Sigma-Aldrich. 
             Native corn starch, Cargill Gum™ 03460, was obtained from Cargill Inc. (Minneapolis, Minn.). 
             Hydroxypropylated starch, Glucosol® 800, was obtained from Chemstar Product Company (Minneapolis, Minn.). 
             Glycerine (or Glycerol) was obtained from Cognis Corp. 
             Excel P-40S (mono-diglyceride dispersion aid) was obtained from Kao Corp. 
           
         
       
    
     Test Methods 
     Thymol Stability 
     Samples were placed in an oven at 40° C., 50° C., or 55° C. for a certain number of days. The residual thymol level was determined through “High Performance Liquid Chromatography (HPLC) analysis.” More particularly, the thymol level in each sample was determined by generating a thymol calibration curve by the following method. Approximately 70 mg thymol was weighed into a 100-mL volumetric flask. Approximately 50-mL of a 0.1% acetic acid:IPA mixture (50:50) was added to the flask and the contents swirled to promote dissolution. The volume was diluted with a 0.1% acetic acid:IPA mixture (50:50) and subsequent dilutions were performed to generate a calibration curve with a concentration range of approximately 700 μg/mL to 70 μg/mL. Samples were prepared as follows. Approximately 100 mg of sample was used for each code, where each code was analyzed in duplicate at every pull point. The measured material was cut up into small pieces and placed into a 40-mL vial. To each vial, 10.0 mL 0.1% acetic acid was added and the contents were shaken and sonicated for 30 minutes periods until the sample is dispersed. To each vial, 10.0 mL IPA was added and the contents were sonicated for 10 minutes to promote mixing and extraction of thymol. The resulting solutions were filtered through nylon filters prior to injection. Thymol levels were calculated using the thymol calibration curve described above. 
     HPLC Equipment &amp; Conditions 
     
         
         Column: Phenomenex NH 2    
         Column Temperature: Ambient 
         Mobile Phase: 50:50 (IPA:0.1% acetic acid) 
         Flow rate: 0.6 mL/min. 
         Injection volume: 15 microliters 
         ELS detection: 280 nm
 
Thymol Concentrations in Extractions
 
       
    
     An aliquot of a sample was centrifuged at approximately 5000 rpm until visible settling occurred (approximately 30 minutes). The solution was filtered using two (2) different types of syringe filters: (1) Pall Life Acrodisc 13 mm 0.2 micron nylon membrane and (2) Whatman Puradisc-0.2 micron polyethersulfone membrane with polypropylene housing. 1.0 mL of the centrifuged solution was pipetted into a 10-mL flask. The contents were dissolved and diluted with a 0.1% AA:IPA (50:50) solution to volume. The solution was then filtered with Pall Acrodisc 0.45 micron nylon membrane. The thymol concentration was determined through “High Performance Liquid Chromatography (HPLC) analysis” according to the following conditions: 
     HPLC Equipment &amp; Conditions 
     
         
         HPLC: Agilent 1100 HPLC system. 
         Column: Phenomenex Luna NH 2  (5 μm, 250 mm×4.6 mm)-ambient 
         Detector: UV/Vis at 280 nm 
         Mobile Phases: (75:25) (IPA: 0.1% acetic acid) 
         Flow Rate: approximately 0.6 mL/min. 
         Injection Volume: approximately 15 μL 
         Run Time: 6 minutes
 
Zone of Inhibition
 
       
    
     To determine antimicrobial efficacy, a zone of inhibition test was performed. More specifically, a 0.05 g sample was placed on a freshly spreading lawn of test microorganism on TSA (Trypticase Soy Agar). Two microorganisms were used,  Staphylococcus aureus  (ATCC #27660) as a Gram positive bacteria and  Escherichia coli  as a Gram negative bacteria (ATCC #25922). After 24 hours incubation at 37° C., plates were measured for clear zones of inhibition surrounding each sample (Clear zone (mm)=diameter of clear zone−sample (wipe) diameter). 
     Microplate Assay 
     To determine the germicidal efficacy of an extracted thymol solution, a microplate germicidal assay was performed. In this method, the test solution was brought into contact with 60 wells of test microorganisms (4*10 6  CFU (colony forming unit)/well) coated on the bottom of 96 well flat plates for 4½ minutes. At the end of the contact time, 200 μL of a “Letheen” neutralizing broth (included 0.5% Tween 80) was added to each well to deactivate the active ingredients. After addition of the neutralizer, 50 μL of TSB (Tryptic Soy Broth) was added and then the microplate was incubated to allow for out-growth of survivors. After incubation, the number of wells showing growth of the target microorganism was recorded. If the media in the well was turbid, then the well was counted as a failure to disinfect. If the well was not turbid after incubation, then the well was recorded as achieving disinfection. All tests were performed against two different microorganisms,  Staphylococcus aureus  (ATCC #6538) as Gram positive bacteria and  Pseudomonas aeruginosa  (ATCC #15442) as Gram negative bacteria. 
     Example 1 
     A ThermoPrism USALab16 extruder (Thermo Electron Corporation, Stone, England) was employed to form the antimicrobial composition. The extruder is a continuous co-rotating twin screw micro extruder, with a screw diameter of 16 mm and a screw length of 640 mm. The extruder has 10 barrels. A K-Tron feeder (K-Tron America, Pitman, N.J.) was used to feed a blend of 74 wt. % Glucosol 800, 1 wt. % Excel P-40S, and 25 wt. % glycerol. Thymol was then added so that it constituted 5 wt. % of the blend. The material feeding rate was kept at 2 pounds per hour. The processing temperatures were 100° C., 110° C., 120° C., 130° C., 135° C., 135° C., 130° C., 125° C., 120° C., and 115° C. for Zones 1 to 10, respectively. The torque was about 40% to 42%, the screw rotation speed was 150 rpm, and the pressure at the die was 8 to 10 bars. The resulting strand was cooled down through a cooling belt (Bondine Electric Co., Chicago, Ill.). A pelletizer (Emerson Industrial Controls, Grand Island, N.Y.) was used to cut the strand from the extruder die and the resulting pellets were collected in a plastic bag for subsequent testing. 
     Example 2 
     An extruded antimicrobial composition was formed as described in Example 1, except that native corn starch was employed, the torque was about 50% to 53%, and the pressure at the die was 13 to 14 bars. The resulting strand was cooled down through a cooling belt (Bondine Electric Co., Chicago, Ill.). A pelletizer (Emerson Industrial Controls, Grand Island, N.Y.) was used to cut the strand from the extruder die and the resulting pellets were collected in a plastic bag for subsequent testing. 
     Once formed, the pellets of Examples 1 and 2 (approximately 3 millimeters in size) were placed in an oven at 40° C. and subjected to the above-described thymol stability test. The results are set forth below in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Thymol Levels After Aging at 40° C. 
               
            
           
           
               
               
               
            
               
                   
                   
                 % Thymol levels after aging for 
               
               
                   
                 Post 
                 specified number of days 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 extrusion 
                 1 
                 5 
                 9 
                 20 
                 61 
               
               
                 Example 
                 % thymol 
                 days 
                 days 
                 days 
                 days 
                 days 
               
               
                   
               
               
                 Example 1 
                 5.2 
                 5.3 
                 5.2 
                 5.3 
                 5.5 
                 5.0 
               
               
                 (modified 
               
               
                 starch) 
               
               
                 Example 2 
                 4.4 
                 3.9 
                 3.4 
                 2.9 
                 1.7 
                 1.6 
               
               
                 (native 
               
               
                 starch) 
               
               
                   
               
            
           
         
       
     
     As indicated, the antimicrobial composition of Example 1 was surprisingly very effective in storing thymol, even after 61 days of aging at elevated temperature. The composition of Example 2 was not nearly as effective in trapping thymol. 
     The pellets of Examples 1 and 2 were also subjected to zone of inhibition (“ZOI”) testing, as described above. The results are set forth below in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Zone of Inhibition Test Results After Aging at 40° C. 
               
            
           
           
               
               
            
               
                   
                 Area of ZOI (mm) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 0 
                 1 day 
                 4 days 
                 12 days 
                 20 days 
                 60 days 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 
                   E. 
                 
                 
                   S. 
                 
                 
                   E. 
                 
                 
                   S. 
                 
                 
                   E. 
                 
                 
                   S. 
                 
                 
                   E. 
                 
                 
                   S. 
                 
                 
                   E. 
                 
                 
                   S. 
                 
                 
                   E. 
                 
                 
                   S. 
                 
               
               
                   
                 
                   coli 
                 
                 
                   aureus 
                 
                 
                   coli 
                 
                 
                   aureus 
                 
                 
                   coli 
                 
                 
                   aureus 
                 
                 
                   coli 
                 
                 
                   aureus 
                 
                 
                   coli 
                 
                 
                   aureus 
                 
                 
                   coli 
                 
                 
                   aureus 
                 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 11 
                 9 
                 8 
                 7 
                 8 
                 8 
                 7 
                 8 
                 6 
                 6 
                 6 
                 6 
               
               
                 (modified 
               
               
                 starch) 
               
               
                 2 
                 11 
                 10 
                 9 
                 9 
                 7 
                 6 
                 5 
                 6 
                 3 
                 2 
                 1 
                 1 
               
               
                 (native 
               
               
                 starch) 
               
               
                   
               
            
           
         
       
     
     As indicated, the antimicromial composition of Example 1 was surprisingly effective in inhibiting the growth of bacteria. For example, even after 60 days at an elevated temperature of 40° C., the zone of inhibition values were 6 for both bacteria species. Howvever, the composition of Example 2 was not nearly as effective with values of only 1 for these two species of bacteria. 
     Example 3 
     A composition of 70% Glucosol® 800, 24% glycerol, 5% thymol, and 1% Excel P-40S was prepared by extrusion, pelletizing, putting the material in a plastic bag, and placing at a temperature of −32° C. for a minimum of 24 hrs. The resulting cooled material was downsized via a Brickmann/Retsch lab scale grinding mill (set speed=1) and collected at a size of &lt;250 microns. The resulting sample was tested for thymol stability at 55° C. using the test method described above. The results are set forth in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Thymol Levels After Aging 
               
            
           
           
               
               
            
               
                   
                 Thymol Level (wt %) 
               
            
           
           
               
               
               
               
            
               
                   
                 0 days 
                 7 days 
                 19 days 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Example 3 
                 5.3 
                 1.2 
                 1 
               
               
                   
                   
               
            
           
         
       
     
     In addition, 100 milliliters of deionized water was added to 20 grams of the non-aged particles. The concentration of thymol in solution was determined after 2, 10, 60 minutes by the method described above giving thymol concentrations by weight of 0.107%, 0.118%, 0.128% respectively. 
     Example 4 
     A composition of 80% Glucosol® 800, 14% glycerol, 5% thymol, and 1% Excel P-40S was prepared as described in Example 3. The resulting cooled material was downsized via a Brickmann/Retsch lab scale grinding mill (set speed=1) and collected at a size of 250-425 micrometers by sieving. The resulting sample was tested for thymol stability at 50° C. using the test method described above. The results are set forth in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Thymol Levels After Aging 
               
            
           
           
               
               
            
               
                   
                 Thymol Level (wt %) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 1 
                 4 
                 5 
                 7 
                 28 
                 48 
               
               
                   
                 days 
                 day 
                 days 
                 days 
                 days 
                 days 
                 days 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 4 
                 5.09 
                 4.81 
                 4.65 
                 4.6 
                 4.47 
                 4.5 
                 4.46 
               
               
                   
               
            
           
         
       
     
     A series of thymol extractions were carried out from the particles prepared in Example 4 that involved various amounts of thymol/modified starch particles, various amounts of water, addition of citric acid particles, and extracting time. The extracting method involved adding specified amount of water to starch/thymol particles and citric acid particles, waiting a specified amount of time while shaking, and centrifuging to collect supernatant. In addition, water was added to neat thymol as a control, shaken for specified amount of time, and centrifuged to collect supernatant. The thymol concentration in supernatant was determined by the method described above. The composition of the solutions and the resulting thymol concentration are set forth in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Thymol Extractions from Particles 
               
               
                 Particle Composition 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                   
                 % Thymol 
               
               
                   
                   
                   
                 Particle 
                   
                 Citric 
                 Deionized 
                 Extracting 
                 (wt/wt) 
               
               
                   
                   
                 % 
                 Size 
                 Amount 
                 acid 
                 water 
                 time 
                 in extract 
               
               
                 Starch 
                 Plasticizer 
                 Thymol 
                 (microns) 
                 (grams) 
                 (grams) 
                 (milliliters) 
                 (mins) 
                 solution 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 80% 
                 14% 
                 5 
                 250-425 
                 0.75 
                 0.38 
                 12.4 
                 30 
                 0.159 
               
               
                 Glucosol 
                 glycerol 
                   
                   
                 1.5 
                 0.38 
                 12.4 
                 30 
                 0.240 
               
               
                 800 
               
               
                 n/a 
                 n/a 
                 100 (control) 
                 &lt;250 
                 2 
                 1.14 
                 97 
                 30 
                 0.081 
               
               
                   
                   
                   
                   
                 2 
                 0 
                 100 
                 30 
                 0.084 
               
               
                   
               
            
           
         
       
     
     The reported solubility limit of thymol in water is normally is 0.1 grams per 100 grams of water (0.1%) at 25° C. As illustrated above, however, the concentrations of thymol in the extract solutions were up to 2.4 times greater than the reported limited solubility. Two of the solutions above (0.159% thymol and 0.240% thymol) were also tested for antimicrobial efficacy according to the microplate assay described above. The results are set forth below in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Efficacy of Thymol Extractions 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 # of wells 
                 # of wells 
               
               
                   
                   
                   
                   
                 Particle 
                   
                 showing growth 
                 showing growth 
               
               
                   
                   
                   
                 % 
                 Size 
                 Amount 
                 after test for 
                 after test for 
               
               
                 Example 
                 Starch 
                 Plasticizer 
                 Thymol 
                 (microns) 
                 (grams) 
                 
                   S. aureus 
                 
                 
                   P. aeruginosa 
                 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 5 
                 80% Glucosol 800 
                 14% glycerol 
                 5 
                 250-425 
                 0.75 
                 9 
                 2 
               
               
                 Example 6 
                   
                   
                   
                   
                 1.5 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
     As indicated, both extracts were shown to have antimicrobial efficacy. Surprisingly, Example 6 had very strong antimicrobial efficacy, showing zero microbe growth. 
     While the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of variations and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.