The present invention relates to using metal-ion sequestering agents in a container filling process for removing bio-essential designated metal-ions from a liquid nutrient for inhibiting growth of microbes in the liquid nutrient.
During the process of filling containers with certain beverages and foodstuffs, air borne micro-organisms may enter the containers after the flash pasteurization or pasteurization part of the process. These micro-organisms such as yeast, spores, bacteria, etc. will grow in the nutrient rich beverage or food, ruining the taste or even causing hazardous micro-biological contamination. While some beverages are packaged by aseptic means or by utilizing preservatives, many other beverages for example fruit juices, teas and isotonic drinks are “hot-filled”. “Hot-filling” involves the filling of a container with a liquid beverage having some elevated temperature (typically, at about 180-200° F.). The container is capped and allowed to cool, producing a vacuum therein. The process of hot filling of beverages and foods is used to kill micro-organisms that enter the container during the filling of the beverage or food containers. Hot filling requires containers be made of certain materials or constructed in a certain fashion such as thicker walls to withstand the hot filling process. The energy required for hot filling adds to the cost of the filling process. Temperatures required for hot filling have a detrimental effect on the flavor of the beverage. Other methods of filling, such as aseptic filling, require large capital expenditures and maintenance of class 5 clean room conditions.
It has been recognized that small concentrations of metal-ions play an important role in biological processes. For example, Mn, Fe, Ca, Zn, Cu and Al are essential bio-metals, and are required for most, if not all, living systems. Metal-ions play a crucial role in oxygen transport in living systems, and regulate the function of genes and replication in many cellular systems. Calcium is an important structural element in the formation of bones and other hard tissues. Mn, Cu and Fe are involved in metabolism and enzymatic processes. At high concentrations, metals may become toxic to living systems and the organism may experience disease or illness if the level cannot be controlled. As a result, the availability and concentrations of metal-ions in biological environments is a major factor in determining the abundance, growth-rate and health of plant, animal and micro-organism populations. It has been recognized that iron is an essential biological element, and that all living organisms require iron for survival and replication. Although, the occurrence and concentration of iron is relatively high on the earth's surface, the availability of “free” iron is severely limited by the extreme insolubility of iron in aqueous environments. As a result, many organisms have developed complex methods of procuring “free” iron for survival and replication.
Methods for packaging drinks and liquid foodstuffs are needed that are able to improve food quality, to increase shelf-life, to protect from microbial contamination, and to do so in a manner that is safe and environmentally clean. Methods are needed that are able to target and remove specific, biologically important, metal-ions while leaving intact the concentrations of beneficial metal-ions.
“Hot filling” provides various advantages over aseptic or preservative packaging, among them lower capital and operational cost (over aseptic systems), and the elimination of the need for preservatives (the heat of the beverage has a sanitizing effect). The hot headspace in the filled bottle also reduces the carrying capacity of oxygen therein, limiting oxidation of the contents. There is however a problem in the hot filling of beverages and foods when used to kill air borne micro-organisms that enter the containers during the filling process after the flash pasteurization or pasteurization of the beverage or food. Hot filling requires containers be made of certain materials or constructed in a certain fashion such as the use of thicker walls, more material, and specific shapes to withstand the hot filling process. The energy required for hot filling adds to the cost of the filling process. Temperatures required for hot filling have a detrimental effect on the flavor of the beverage. Hot filling adds additional time to the manufacturing process in both the heating and cooling of the containers. The manufacturers of the beverages and foodstuffs are loathe to add antimicrobial materials directly to the beverages and foods because these may potentially alter the color or taste of items such as beverages and foodstuffs, and in the worst case may be harmful to the persons using or consuming those items. The wide spread use of antimicrobial materials may cause further problems in that disposal of the items containing these materials cannot be accomplished without impacting the biological health of the landfill or other site of disposal, and further the antimicrobial compounds may leach into surrounding rivers, lakes and water supplies. The wide spread use of antimicrobial materials may cause yet further problems in that micro-organisms may develop resistance to these materials and new infectious microbes and new diseases may develop.
In accordance with one aspect of the present invention, there is provided a method of removing a selected metal-ion from a solution, comprising the steps of:
In accordance with another aspect of the present invention, there is provided a method for bottling a liquid having a pH equal to or greater than about 2.5, comprising the steps of:
In accordance with still another aspect of the present invention, there is provided an article for inhibiting the growth of microbes in a liquid nutrient when placed in contact with the liquid nutrient, the article having a metal-ion sequestering agent and an antimicrobial agent such that when the article is placed in contact with the liquid nutrient the metal-ion sequestering agent and the antimicrobial agent inhibits the growth of microbes in the liquid nutrient.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims and by reference to the accompanying drawings.
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings in which:
Referring to
Referring to
The term inhibition of microbial-growth, or a material which “inhibits” microbial growth, is used by the authors to mean materials which either prevent microbial growth, or subsequently kills microbes so that the population is within acceptable limits, or materials which significantly retard the growth processes of microbes or maintain the level or microbes to a prescribed level or range. The prescribed level may vary widely depending upon the microbe and its pathogenicity. Generally it is preferred that harmful organisms are present at no more than 10 organisms/ml and preferably less than 1 organism/ml.
Antimicrobial agents which kill microbes or substantially reduce the population of microbes are often referred to as biocidal agents, while materials which simply slow or retard normal biological growth are referred to as biostatic agents. The preferred impact upon the microbial population may vary widely depending upon the application. For pathogenic organisms (such as E. coli O157:H7) a biocidal effect is more preferred, while for less harmful organisms, a biostatic impact may be preferred. Generally, it is preferred that microbiological organisms remain at a level which is not harmful to the consumer or user of that particular article
A fluid container, such a container 12 illustrated in
It is preferred that the fluid container made in accordance with the present invention comprises a polymer containing said metal-ion sequestrant. The container may comprise the polymer itself containing said metal-ion sequestrant, or alternatively, the metal-ion sequestrant may be contained with a polymeric layer attached to a support structure. It is preferred that said polymer is permeable to water. It is important that the polymer is permeable to water because permeability facilitates the contact of the target metal-ions with the metal-ion sequestrant, which, in turn, facilitates the sequestration of the metal-ions within the polymer or polymeric layer. A measure of the permeability of various polymeric addenda to water is given by the permeability coefficient, P that is given by
P=(quantity of permeate)(film thickness)/[area×time×(pressure drop across the film)]
Permeability coefficients and diffusion data of water for various polymers are discussed by J. Comyn, in Polymer Permeability, Elsevier, N.Y., 1985 and in “Permeability and Other Film Properties Of Plastics and Elastomers”, Plastics Design Library, NY, 1995. The higher the permeability coefficient, the greater the water permeability of the polymeric media. The permeability coefficient of a particular polymer may vary depending upon the density, crystallinity, molecular weight, degree of cross-linking, and the presence of addenda such as coating-aids, plasticizers, etc. It is preferred that the polymer has a water permeability of greater than 1000 [(cm3 cm)/(cm2sec/Pa)]×1013. It is further preferred that the polymer has a water permeability of greater than 5000 [(cm3 cm)/(cm2sec/Pa)]×1013. Preferred polymers for practice of the invention are polyvinyl alcohol, cellophane, water-based polyurethanes, polyester, nylon, high nitrile resins, polyethylene-polyvinyl alcohol copolymer, polystyrene, ethyl cellulose, cellulose acetate, cellulose nitrate, aqueous latexes, polyacrylic acid, polystyrene sulfonate, polyamide, polymethacrylate, polyethylene terephthalate, polystyrene, polyethylene, polypropylene or polyacrylonitrile. It is preferred that the metal-ion sequestrant comprises 0.1 to 50.0% by weight of the polymer, and more preferably 1% to 10% by weight of the polymer.
In a preferred embodiment, the container 12 comprises a plurality of layers having an outer layer having a metal-ion sequestering agent. In another preferred embodiment, the container comprises a plurality of layers comprising a barrier layer for contact with said beverage or foodstuff and an inner layer having said sequestering agent, said inner layer having a first side adjacent said barrier layer, and said barrier layer allowing liquid to pass through to said inner layer. Multiple layers may be necessary to provide a rigid structure able to contain foodstuffs and to provide physical robustness. In a particular case there may be provided a second outer layer on the second side of said inner layer. It is preferred that both the first and second outer layer comprise a barrier layer that allows liquid to pass through to said inner layer. The barrier layer does not contain the metal-ion sequestrant. However, the primary purpose of the barrier layer is to provide a barrier through which micro-organisms cannot pass. It is important to limit or eliminate, the direct contact of micro-organisms with the metal-ion sequestrant or the layer containing the metal-ion sequestrant, since many micro-organisms, under conditions of iron deficiency, may bio-synthesize molecules which are strong chelators for iron and other metals. These bio-synthetic molecules are called “siderophores” and their primary purpose is to procure iron for the micro-organisms. Thus, if the micro-organisms are allowed to directly contact the metal-ion sequestrant they may find a rich source of iron there and begin to colonize directly at these surfaces. The siderophores produced by the micro-organisms may compete with the metal-ion sequestrant for the iron (or other bio-essential metal) at their surfaces. The barrier layer of the invention does not contain the metal-ion sequestrant, and because micro-organisms are large, they may not pass or diffuse through the barrier layer. The barrier layer thus prevents contact of the micro-organisms with the polymeric layer containing the metal-ion sequestrant of the invention.
It is preferred that the metal-ion sequestrant has a high-affinity for biologically important metal-ions such as Mn, Zn, Cu and Fe. A measure of the “affinity” of metal-ion sequestrants for various metal-ions is given by the stability constant (also often referred to as critical stability constants, complex formation constants, equilibrium constants, or formation constants) of that sequestrant for a given metal-ion. Stability constants are discussed at length in “Critical Stability Constants”, A. E. Martell and R. M. Smith, Vols. 1-4, Plenum, NY (1977), “Inorganic Chemistry in Biology and Medicine”, Chapter 17, ACS Symposium Series, Washington, D.C. (1980), and by R. D. Hancock and A. E. Martell, Chem. Rev. vol. 89, p. 1875-1914 (1989). The ability of a specific molecule or ligand to sequester a metal-ion may depend also upon the pH, the concentrations of interfering ions, and the rate of complex formation (kinetics). Generally, however, the greater the stability constant the greater the binding affinity for that particular metal-ion. Often the stability constants are expressed as the natural logarithm of the stability constant. Herein the stability constant for the reaction of a metal-ion (M) and a sequestrant or ligand (L) is defined as follows:
M+nL⇄MLn
where the stability constant is βn=[MLn]/[M][L]n, wherein [MLn] is the concentration of “complexed” metal-ion, [M] is the concentration of free (uncomplexed) metal-ion and [L] is the concentration of free ligand. The log of the stability constant is log βn, and n is the number of ligands which coordinate with the metal. It follows from the above equation that if βn is very large, the concentration of “free” metal-ion will be very low. Ligands with a high stability constant (or affinity) generally have a stability constant greater than 1010 or a log stability constant greater than 10 for the target metal. Preferably the ligands have a stability constant greater than 1015 for the target metal-ion. Table 1 lists common ligands (or sequestrants) and the natural logarithm of their stability constants (log βn) for selected metal-ions.
EDTA is ethylenediamine tetra acetic acid and salts thereof, DTPA is diethylenetriaminepentaacetic acid and salts thereof, DPTA is Hydroxylpropylenediaminetetraacetic acid and salts thereof, NTA is nitrilotriacetic acid and salts thereof, CDTA is 1,2-cyclohexanediamine tetra acetic acid and salts thereof, PDTA is propylenediammine tetra acetic acid and salts thereof. Desferroxamine B is a commercially available iron chelating drug, desferal®. MECAMS, 4-LICAMS and 3,4-LICAMS are described by Raymond et al. in “Inorganic Chemistry in Biology and Medicine”, Chapter 18, ACS Symposium Series, Washington, D.C. (1980). Log stability constants are from “Critical Stability Constants”, A. E. Martell and R. M. Smith, Vols. 1-4, Plenum Press, NY (1977); “Inorganic Chemistry in Biology and Medicine”, Chapter 17, ACS Symposium Series, Washington, D.C. (1980); R. D. Hancock and A. E. Martell, Chem. Rev. vol. 89, p. 1875-1914 (1989) and “Stability Constants of Metal-ion Complexes”, The Chemical Society, London, 1964.
In many instances, the growth of a particular micro-organism may be limited by the availability of a particular metal-ion, for example, due to a deficiency of this metal-ion. In such cases it is desirable to select a metal-ion sequestrant with a very high specificity or selectivity for a given metal-ion. Metal-ion sequestrants of this nature may be used to control the concentration of the target metal-ion and thus limit the growth of the organism(s), which require this metal-ion. However, it may be necessary to control the concentration of the target metal without affecting the concentrations of beneficial metal-ions such as potassium and calcium. One skilled in the art may select a metal-ion sequestrant having a high selectivity for the target metal-ion. The selectivity of a metal-ion sequestrant for a target metal-ion is given by the difference between the log of the stability constant for the target metal-ion, and the log of the stability constant for the interfering (beneficial) metal-ions. For example, if a treatment required the removal of Fe(III), but it was necessary to leave the Ca-concentration unaltered, then from Table 1, DTPA would be a suitable choice since the difference between the log stability constants 28-10.8=17.2, is very large. 3,4-LICAMS would be a still more suitable choice since the difference between the log stability constants 43-16.2=26.8, is the largest in Table 1.
It is preferred that said metal-ion sequestrant has a high-affinity for iron, and in particular iron(III). It is preferred that the stability constant of the sequestrant for iron(III) be greater than 1010. It is still further preferred that the metal-ion sequestrant has a stability constant for iron greater than 1020. It is still further preferred that the metal-ion sequestrant has a stability constant for iron greater than 1030.
It is preferred that the container comprises derivatized nanoparticles comprising inorganic nanoparticles having an attached metal-ion sequestrant, wherein said inorganic nanoparticles have an average particle size of less than 200 nm and the derivatized nanoparticles have a stability constant greater than 1010 with iron (III). It is further preferred that the derivatized nanoparticles have a stability constant greater than 1020 with iron (III). The derivatized nanoparticles are preferred because they have very high surface area and may have a very high-affinity for the target metal-ions. It is preferred that the nanoparticles have an average particle size of less than 100 nm. It is further preferred that the nanoparticles have an average size of less than 50 nm, and most preferably less than 20 nm. Preferably greater than 95% by weight of the nanoparticles are less than 200 nm, more preferably less than 100 nm, and most preferably less than 50 nm. This is preferred because as the particle size becomes smaller, the particles scatter visible-light less strongly. Therefore, the derivatized nanoparticles can be applied to clear, transparent surfaces without causing a hazy or a cloudy appearance at the surface. This allows the particles of the present invention to be applied to packaging materials without changing the appearance of the item. It is preferred that the nanoparticles have a very high surface area, since this provides more surface with which to covalently bind the metal-ion sequestrant, thus improving the capacity of the derivatized nanoparticles for binding metal-ions. It is preferred that the nanoparticles have a specific surface area of greater than 100 m2/g, more preferably greater than 200 m2/g, and most preferably greater than 300 m2/g. For applications of the invention in which the concentrations of contaminant or targeted metal-ions in the environment are high, it is preferred that the nanoparticles have a particle size of less than 20 nm and a surface area of greater than 300 m2/g. Derivatized nanoparticles are described at length in U.S. patent application Ser. No. 10/822,940 filed Apr. 13, 2004.
It is preferred that the derivatized nanoparticles have a high stability constant for the target metal-ion(s). The stability constant for the derivatized nanoparticle will largely be determined by the stability constant for the attached metal-ion sequestrant. However, the stability constant for the derivatized nanoparticles may vary somewhat from that of the attached metal-ion sequestrant. Generally, it is anticipated that metal-ion sequestrants with high stability constants will give derivatized nanoparticles with high stability constants. For a particular application, it may be desirable to have a derivatized nanoparticle with a high selectivity for a particular metal-ion. In most cases, the derivatized nanoparticle will have a high selectivity for a particular metal-ion if the stability constant for that metal-ion is about 106 greater than for other ions present in the system.
Metal-ion sequestrants may be chosen from various organic molecules. Such molecules having the ability to form complexes with metal-ions are often referred to as “chelators”, “complexing agents”, and “ligands”. Certain types of organic functional groups are known to be strong “chelators” or sequestrants of metal-ions. It is preferred that the sequestrants of the invention contain alpha-amino carboxylates, hydroxamates, or catechol, functional groups. Hydroxamates, or catechol, functional groups are preferred. Alpha-amino carboxylates have the general formula:
R —[N(CH2CO2M)-(CH2)n—N(CH2CO2M)2]x
where R is an organic group such as an alkyl or aryl group; M is H, or an alkali or alkaline earth metal such as Na, K, Ca or Mg, or Zn; n is an integer from 1 to 6; and x is an integer from 1 to 3. Examples of metal-ion sequestrants containing alpha-amino carboxylate functional groups include ethylenediaminetetraacetic acid (EDTA), ethylenediaminetetraacetic acid disodium salt, diethylenetriaminepentaacetic acid (DTPA), Hydroxylpropylenediaminetetraacetic acid (DPTA), nitrilotriacetic acid, triethylenetetraaminehexaacetic acid, N,N-bis(o-hydroxybenzyl) ethylenediamine-N,N diacteic acid, and ethylenebis-N,N′-(2-o-hydroxyphenyl)glycine.
Hydroxamates (or often called hydroxamic acids) have the general formula:
where R is an organic group such as an alkyl or aryl group. Examples of metal-ion sequestrants containing hydroxamate functional groups include acetohydroxamic acid, and desferroxamine B, the iron chelating drug desferal.
Catechols have the general formula:
Where R1, R2, R3 and R4 may be H, an organic group such as an alkyl or aryl group, or a carboxylate or sulfonate group. Examples of metal-ion sequestrants containing catechol functional groups include catechol, disulfocatechol, dimethyl-2,3-dihydroxybenzamide, mesitylene catecholamide (MECAM) and derivatives thereof, 1,8-dihydroxynaphthalene-3,6-sulfonic acid, and 2,3-dihydroxynaphthalene-6-sulfonic acid.
In a preferred embodiment the metal-ion sequestrant is attached to a nanoparticle by reaction of the nanoparticle with a silicon alkoxide intermediate having the general formula:
Si(OR)4-xR′x;
wherein x is an integer from 1 to 3;
The antimicrobial active material of antimicrobial agent may be selected from a wide range of known antibiotics and antimicrobials. An antimicrobial material may comprise an antimicrobial ion, molecule and/or compound, metal ion exchange materials exchanged or loaded with antimicrobial ions, molecules and/or compounds, ion exchange polymers and/or ion exchange latexes, exchanged or loaded with antimicrobial ions, molecules and/or compounds. Suitable materials are discussed in “Active Packaging of Food Applications” A. L. Brody, E. R. Strupinsky and L. R. Kline, Technomic Publishing Company, Inc. Pennsylvania (2001). Examples of antimicrobial agents suitable for practice of the invention include benzoic acid, sorbic acid, nisin, thymol, allicin, peroxides, imazalil, triclosan, benomyl, metal-ion release agents, metal colloids, anhydrides, and organic quaternary ammonium salts. Preferred antimicrobial reagents are metal ion exchange reagents such as silver sodium zirconium phosphate, silver zeolite, or silver ion exchange resin which are commercially available. The antimicrobial agent may be provided in a layer 15 having a thickness “y” of between 0.1 microns and 100 microns, preferably in the range of 1.0 and 25 microns.
In another preferred embodiment, the antimicrobial agent comprising a composition of matter comprising an immobilized metal-ion sequestrant/antimicrobial comprising a metal-ion sequestrant that has a high stability constant for a target metal ion and that has attached thereto an antimicrobial metal-ion, wherein the stability constant of the metal-ion sequestrant for the antimicrobial metal-ion is less than the stability constant of the metal-ion sequestrant for the target metal-ion. These are explained in detail in U.S. Ser. No. 10/868,626 filed Jun. 15, 2004.
In a preferred embodiment, the antimicrobial agent comprising a metal ion exchange material is exchanged with at least one antimicrobial metal ion selected from silver, copper, gold, nickel, tin or zinc.
Referring to
Still referring to
In the embodiment shown in
In another embodiment of the present invention, the sequestering agent 95 may be in a hydrophilic polymeric insert 115 that is placed in the bottle 12 as illustrated in
Referring to
By using the metal-ion sequestering agents 95 to remove “free” iron 85 as the method for eliminating the micro-organisms 80 that enter the bottles 12 between the filling station 25 and the capper 30, the “hot fill” portion 40 of the process shown in
Materials:
Colloidal dispersions of silica particles were obtained from ONDEO Nalco Chemical Company. NALCO® 1130 had a median particle size of 8 nm, a pH of 10.0, a specific gravity of 1.21 g/ml, a surface area of about 375 m2/g, and a solids content of 30 weight. N-(trimethoxysilylpropylethylenediamine triacetic acid, trisodium salt was purchased from Gelest Inc., 45% by weight in water.
Preparation of derivatized nanoparticles. To 600.00 g of silica NALCO® 1130 (30% solids) was added 400.00 g of distilled water and the contents mixed thoroughly using a mechanical mixer. To this suspension, was added 49.4 g of N-(trimethoxysilyl)propylethylenediamine triacetic acid, trisodium salt in 49.4 g distilled water with constant stirring at a rate of 5.00 ml/min. At the end of the addition the pH was adjusted to 7.1 with the slow addition of 13.8 g of concentrated nitric acid, and the contents stirred for an hour at room temperature. Particle size analysis indicated an average particle size of 15 nm. The percent solids of the final dispersion was 18.0%.
Preparation of the immobilized metal-ion sequestrant/antimicrobial: 200.0 g of the above derivatized nanoparticles were washed with distilled water via dialysis using a 6,000-8,000 molecular weight cutoff filter. The final ionic strength of the solution was less than 0.1 millisemens. To the washed suspension was then added with stirring 4.54 ml of 1.5 M AgNO3 solution, to form the immobilized metal-ion sequestrant/antimicrobial.
Preparation of Polymeric Layers of Immobilized Metal-Ion Sequestrants and Sequestrant/Antimicrobials.
Coating 1 (comparison). A coating solution was prepared as follows: 8.8 g of a 40% solution of the polyurethane Permax 220 (Noveon Chemicals) was combined with to 90.2 grams of pure distilled water and 1.0 g of a 10% solution of the surfactant OLIN 10G was added as a coating aid. The mixture was then stirred and blade-coated onto a polymeric support using a 150 micron doctor blade. The coating was then dried at 40-50° C., to produce a film having 5.4 g/m2 of polyurethane.
Coating 2. A coating solution was prepared as follows: 171.2 grams of the derivatized nanoparticles prepared as described above were combined with 64.8 grams of pure distilled water and 62.5 g of a 40% solution of the polyurethane Permax 220 (Noveon Chemicals). 1.5 g of a 10% solution of the surfactant OLIN 10G was added as a coating aid. The mixture was then stirred and blade-coated onto a polymeric support using a 150 micron doctor blade. The coating was then dried at 40-50° C., to produce a film having 5.4 g/m2 of the derivatized nanoparticles and 5.4 g/m2 of polyurethane.
Coating 3. A coating solution was prepared as follows: 171.2 grams of the derivatized nanoparticles prepared as described above were combined with 33.5 grams of pure distilled water and 93.8 g of a 40% solution of the polyurethane Permax 220 (Noveon Chemicals). 1.5 g of a 10% solution of the surfactant OLIN 10G was added as a coating aid. The mixture was then stirred and blade-coated onto a polymeric support using a 150 micron doctor blade. The coating was then dried at 40-50° C., to produce a film having 5.4 g/m2 of the derivatized nanoparticles and 8.1 g/m2 of polyurethane.
Coating 4. A coating solution was prepared as follows: 138.9 grams of the derivatized nanoparticles prepared as described above were combined with 97.1 grams of pure distilled water and 62.5 g of a 40% solution of the polyurethane Permax 220 (Noveon Chemicals). 1.5 g of a 10% solution of the surfactant OLIN 10G was added as a coating aid. The mixture was then stirred and blade-coated onto a polymeric support using a 150 micron doctor blade. The coating was then dried at 40-50° C., to produce a film having 4.4 g/m2 of the derivatized nanoparticles and 5.4 g/m2 of polyurethane.
Coating 5. A coating solution was prepared as follows: 12.8 grams of the immobilized metal-ion sequestrant/antimicrobial suspension prepared as described above was combined with to 77.4 grams of pure distilled water and 8.8 g of a 40% solution of the polyurethane Permax 220 (Noveon Chemicals). 1.0 g of a 10% solution of the surfactant OLIN 10G was added as a coating aid. The mixture was then stirred and blade-coated onto a polymeric support using a 150 micron doctor blade. The coating was then dried at 40-50° C., to produce a film having 2.7 g/m2 of the immobilized metal-ion sequestrant/antimicrobial, 0.06 g/m2 silver-ion and 5.4 g/m2 of polyurethane.
A test similar to ASTM E 2108-01 was conducted where a piece of a coating of known surface area was contacted with a solution inoculated with micro-organisms. In particular, a piece of coating 1×1 cm was dipped in 2 ml of growth medium (Trypcase Soy Agar 1/10), inoculated with 2000 CFU of Candida albicans (ATCC-1023) per ml. Special attention was made to all reagents to avoid iron contamination with the final solution having an iron concentration of 80 ppb before contact with the coating.
Micro-organism numbers in the solution were measured daily by the standard heterotrophic plate count method.
BAR GRAPH 1 demonstrates the effectiveness of the inventive examples. The yeast population which was exposed to the comparison coating 1 (which contained no derivatized nanoparticles) showed a growth factor of one thousand during 48 hours (a 1000-fold increase in population). The yeast population which was exposed to the example coatings 2-4 (containing derivatized nanoparticles) showed growth factors of only 1-4. This is indicative of a fungostatic effect in which the population of organisms is kept at a constant or near constant level, even in the presence of a medium containing adequate nutrient level. The yeast population which was exposed to the example coating 5 (derivatized nanoparticles that had been ion exchanged with silver ion—a known antimicrobial) showed a fungicidal effect (the yeast were completely eliminated). The low level of silver when coated by itself without the nanoparticles would not be expected to exhibit this complete fungicidal effect, and there appears to be a synergistic effect between the iron sequestration and the release of antimicrobial silver.
As can be seen from BAR GRAPH 1, significant improved results may be obtained when a metal-ion sequestering agent is used in conjunction with an antimicrobial agent. The combined agents reduced the level of microbes to lower level than when first introduced and then maintained the reduced level of microbes in the liquid nutrient.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention, the present invention being defined by the claim set forth herein.
This is a continuation-in-part of U.S. patent application Ser. No. 10/823,443 filed Apr. 13, 2004 entitled USE OF DERIVATIZED NANOPARTICLES TO MINIMIZE GROWTH OF MICRO-ORGANISMS IN HOT FILLED DRINKS by Richard W. Wien. Reference is made to commonly assigned U.S. patent application Ser. No. ______ filed herewith entitled ARTICLE FOR INHIBITING MICROBIAL GROWTH by Joseph F. Bringley, David L. Patton, Richard W. Wien, Yannick J. F. Lerat (docket 87834), U.S. patent application Ser. No. ______ filed herewith entitled CONTAINER FOR INHIBITING MICROBIAL GROWTH IN LIQUID NUTRIENTS by David L. Patton, Joseph F. Bringley, Richard W. Wien, John M. Pochan, Yannick J. F. Lerat (docket 87472); U.S. patent application Ser. No. ______ filed herewith entitled ARTICLE FOR INHIBITING MICROBIAL GROWTH IN PHYSIOLOGICAL FLUIDS by Joseph F. Bringley, David L. Patton, Richard W. Wien, Yannick J. F. Lerat (docket 87833) the disclosures of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | 10823443 | Apr 2004 | US |
Child | 10936915 | Sep 2004 | US |