|Numéro de publication||WO1997036799 A1|
|Type de publication||Demande|
|Numéro de demande||PCT/US1997/005520|
|Date de publication||9 oct. 1997|
|Date de dépôt||1 avr. 1997|
|Date de priorité||1 avr. 1996|
|Autre référence de publication||WO1997036798A1|
|Numéro de publication||PCT/1997/5520, PCT/US/1997/005520, PCT/US/1997/05520, PCT/US/97/005520, PCT/US/97/05520, PCT/US1997/005520, PCT/US1997/05520, PCT/US1997005520, PCT/US199705520, PCT/US97/005520, PCT/US97/05520, PCT/US97005520, PCT/US9705520, WO 1997/036799 A1, WO 1997036799 A1, WO 1997036799A1, WO 9736799 A1, WO 9736799A1, WO-A1-1997036799, WO-A1-9736799, WO1997/036799A1, WO1997036799 A1, WO1997036799A1, WO9736799 A1, WO9736799A1|
|Inventeurs||Srinivas K. Mirle|
|Exporter la citation||BiBTeX, EndNote, RefMan|
|Citations de brevets (5), Référencé par (4), Classifications (13), Événements juridiques (8)|
|Liens externes: Patentscope, Espacenet|
MODIFIER TRANSFER FILM AND METHOD OF COOKING A FOOD PRODUCT
BACKGROUND INFORMATION 1. Field of the Invention
This invention generally relates to packaging films and to processes employing such films More specifically, this invention relates to films that can retain and then, during a cook-in process, transfer a modifier to a food product as well as to methods of cooking and transferring a modifier to a food product in such films
2 Background of the Invention
Food products often are processed in thermoplastic film packages by subjecting the packaged products to elevated temperatures For example, such packaged products can be immersed in hot water or placed in a steam-heated environment Such thermal processing often is referred to as "cook-in", and films used in such processes are known as cook-in films The processed and packaged food product can be refrigerated, shipped, and stored until the processed food is to be consumed or, for example, sliced and repackaged into smaller portions for customer display (Many sliced luncheon meats are processed in this fashion.) Alternatively, the processed food can be removed immediately from the cook-in package and consumed or further processed for customer display (e.g , sliced and repackaged)
Cook-in films must be capable of withstanding exposure to rather severe temperature conditions for extended periods of time while not compromising their ability to contain the food product Cook-in processes typically involve a long cook cycle Submersion in hot water for up to about 4 hours at about 55° to 65°C is common, and submersion in water or steam at 70° to 100°C for up to 12 hours is possible. Following the cook-in process, the film preferably conforms, if not completely then at least substantially, to the shape of the contained food product. Often, such conformation is achieved by allowing the film to heat shrink under cook-in conditions to form a tightly fitting package. In other words, the cook-in film desirably possesses sufficient shrink energy such that the thermal energy used to cook the food product also shrinks the packaging film snugly around the contained product. Alternatively, the cook-in film package can be caused to shrink around the contained food product prior to initiating the cook-in procedure by, for example, placing the package in a heated environment prior to cooking.
The cook-in film also preferably possesses sufficient adherence to the food product to inhibit or prevent "cook-out" during the cook-in process. Cook-out involves the collection of juices (sometimes referred to as "purge") between the surface of the contained food product and the food-contact surface of the packaging material Preventing cook-out can increase product yield and provide a more aesthetically appealing packaged product.
Often, application of a modifier (i.e., a substance that can change the odor, color, taste, texture, etc., of the packaged product) to the outer surface of a packaged food product is desired. For example, where the food product is poultry or ham, one might wish to impart a smoke color, flavor, and/or odor to the outer surface thereof. This can be accomplished by applying a substance referred to as "liquid smoke" to the outer surface of the food product, normally after the cooking process. Certain characteristics of conventional cook-in films can limit their range of potential uses. For example, many films cannot successfully transfer modifier(s) to a food product during the cook-in process.
Previous attempts have been largely unsuccessful, resulting in (at best) non-uniform transfer of modifier. Several explanations have been posited.
Merely identifying materials that can sorb and retain a modifier and then, during the cook-in process, transfer the same to a food product has proven problematical. In addition to this selective retention requirement, O 97/36799 PC17US97/05520
the ultimate location of the material further complicates the search for prospective candidates. Specifically, such a material necessarily contacts the packaged food product. As such, it must be capable of being formed into the food-contact layer of a cook-in film, withstanding the rather extreme conditions involved in cook-in processes, and providing a sufficient level of adhesion with the packaged food product. Sufficient adhesion can be a particularly difficult requirement to meet. Specifically, the film must be able to prevent cook-out and also be removable from the cooked food product. Some presently available cook-in films can prevent cook-out. However, such films tend to adhere to the surface of the food product with such tenacity that portions, or even an entire surface layer, of the food product are torn away when the film is peeled from the food product. As a result, product yield is reduced, and the resulting food product has an unsightly appearance (e.g., a pitted surface).
Because conventional cook-in films have not heretofore successfully transferred modifier to a food product during cook-in, any desired modifier generally must be applied to the food product after the cook-in process. This necessitates stripping the cook-in film from, applying the modifier to the surface of, and then repackaging the cooked food product which adds time, expense, and complexity to the cooking/packaging process. This procedure also increases the likelihood that the food product, which is sterilized by the cooking process, will become contaminated. Eliminating the necessity of removing the food product from its cook-in package, handled, and potentially exposed to microbial contact prior to its consumption or processing for retail display is highly desirable.
Accordingly, a need exists for a cook-in packaging film that can facilitate the transfer of a modifier to a food product during the cook-in process, minimize or prevent cook-out, and yet still peel away from the food product without tearing portions from the surface thereof. SUMMARY OF THE INVENTION
Briefly, the present invention provides a film article having a food- contact layer that includes a substantially water-insoluble PVOH with an acidic food-modifying substance (i e , a modifier) retained therein The modifier has a pH of no more than about 5 0, preferably no more than about 4 0, and includes at least one compound that includes an aldehyde functional group The PVOH retains the modifier in such a manner so that at least a portion thereof can be transferred to a food product in contact with the food-contact layer The food-contact layer optionally can further include one or more adjuvants such as, for example, plasticizers, humectants, and release agents
In another aspect, the present invention provides a method of cooking a food product A food product is enclosed in the above- described film and heated so as to at least partially cook the food product During this cooking process, at least some of the modifier is transferred from the food-contact layer to the food product
The film article of the present invention is particularly well suited for use as a cook-in film The film is capable of retaining and then transferring a modifier to a packaged food product in sufficient quantity that a separate, post-cooking application of modifier to the food product is unnecessary This eliminates the contamination risks associated with such an operation Thus, only one package is necessary to cook, ship, and store the food product until it is to be consumed or further processed for retail display
Also, the film provides a desirable level of adhesion with the packaged food product The film adheres sufficiently to the food product during cook-in to minimize or prevent cook-out but still can be peeled from the cooked food product without tearing away a surface layer or portions of the food product The film article also can be made shrinkable and is capable of withstanding the rather severe conditions associated with cook-in procedures
To assist in understanding the more detailed description of the invention that follows, certain definitions are provided immediately below These definitions apply hereinthroughout unless a contrary intention is explicitly indicated
"polymer" means the polymerization product of one or more monomers and is inclusive of homopolymers, copolymers, terpolymers, tetrapolymers, etc , and blends and modifications of any of the foregoing, "mer unit" means that portion of a polymer derived from a single reactant molecule (e g , a mer unit from ethylene has the general formula _CH2CH;>— ),
"homopolymer" means a polymer consisting essentially of a single type of repeating mer unit, "copolymer" means a polymer that includes mer units derived from at least two reactants (normally monomers) and is inclusive of random, block, segmented, graft, etc , copolymers,
"polyvinyl alcohol", abbreviated herein as "PVOH", means the material formed by partial or complete hydrolysis of poly(vιnyl acetate), "hydroxy propyl cellulose", abbreviated herein as "HPC", means a thermoplastic, non-ionic cellulose ether formed by the reaction of propylene oxide with alkali cellulose slurried with an aliphatic hydrocarbon and alcohol or propylene oxide,
"polyolefin" means a polymer in which some of the resulting mer units are derived from an olefinic monomer, which can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted (e g , olefin homo-polymers, copolymers of two or more olefins, copolymers of an olefin and a non-olefinic comonomer such as a vinyl monomer, and the like), "(meth)acrylιc acid" means acrylic acid and/or methacrylic acid,
"(meth)acrylate" means acrylate and/or methacrylate, O 97/36799 PC17US97/05520
"(meth)acrylamιde" means acrylamide and methacrylamide, "anhydride-modified polymer" means one or more of the following (1) a polymer obtained by copolymeπzing an anhydride-containing monomer with a comonomer, (2) an anhydride-grafted copolymer, and (3) a mixture of a polymer and an anhydride-containing compound;
"hygroscopic" means the ability to sorb and retain water (in either liquid or gaseous form) and/or aqueous solutions,
"water insoluble" means the ability to substantially resist dissolution in water and/or aqueous solutions, "free shrink" means the percent dimensional change, as measured by ASTM D 2732, in a 10 cm x 10 cm specimen of film when subjected to heat,
"laminate" means to affix or adhere two or more layers of a film article to one another and can be accomplished by a variety of means including, for example, coextrusion, casting and coating, adhesive bonding, pressure bonding (e g , via calendering), etc , and
"cook" means to heat a food product thereby effecting a change in one or more of the physical or chemical properties thereof (e g , color, texture, taste, and the like)
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Films used in the food packaging industry often are categorized according to the number of layers that make up the film Some films are made from a single polymer or blend of polymers and thus have only one layer However, most films include more than one layer and are referred to as multilayer films
In general, the layers of a multilayer film can be classified as "interior" or "exterior" An interior layer is one in which each of the primary surfaces of the layer directly contacts some other layer of the film In other words, an interior layer is sandwiched by two other layers of the film On the other hand, an exterior layer is one in which only one of O 97/36799 PC17US97/05520
the principal surfaces of the layer is adhered directly to another layer of the film while the other principal surface of each of the two exterior layers forms a principal exterior surface of the film
If desired, one or more additional interior layers can be included to provide additional or different properties to the film In addition, any number of tie layers (i e , internal layers having the primary purpose of adhering two other layers to one another) can be included in the film Such tie layers can be present primarily on the outside of an interior layer or can be a layer itself The tie layer preferably includes modified polyolefin and/or polyurethane, more preferably at least one of modified ethylene/α-olefin copolymer, modified ethylene/unsaturated ester copolymer, and modified ethylene/unsaturated acid copolymer Anhydride-modified ethylene/α-olefin copolymer and anhydride-modified enthylene/unsaturated ester copolymer are particularly preferred Specific examples include anhydride-grafted linear low density polyethylene (LLDPE) or anhydride-grafted ethylene/vinyl acetate copolymer
With respect especially to films to be used for cook-in processes, one exterior layer acts as a food-contact layer while the other acts as an outer layer The former serves as the inner layer of a package formed from the film and is in direct contact with the packaged food product The latter provides abuse resistance by serving as the outer layer of the package, i e , that layer which is most distant from the food-contact layer
To form a multilayer film, the individual layers are laminated, i e , bonded together Lamination can be accomplished through the use of adhesives, the application of heat and/or pressure, corona treatment, and even spread or extrusion coating Lamination also can be accomplished by coextrusion, which involves extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before cooling Coextrusion can be employed in film blowing, free film extrusion, and extrusion coating processes
Some films, including many which are used in cook-in processes, are oriented prior to use Orientation involves stretching a film at an elevated temperature (the orientation temperature) followed by setting the film in the stretched configuration (e g , by cooling) When an unrestrained, unannealed, oriented polymeric film subsequently is heated to its orientation temperature, heat shrinkage occurs and the film returns almost to its original, i e , pre-oπented, dimensions An oriented film has an orientation ratio which is the multiplication product of the extent to which the film has been expanded in several directions, usually two directions perpendicular to one another Expansion in the longitudinal direction, sometimes referred to as the machine direction, occurs in the direction the film is formed during extrusion and/or coating Expansion in the transverse direction means expansion across the width of the film and is perpendicular to the longitudinal direction
Turning now specifically to the films of the present invention, the food-contact layer includes PVOH Preferably, the PVOH is chemically or radiatively crosslinked to an extent sufficient to render the food-contact layer substantially water insoluble In this manner, the food-contact layer remains substantially intact and does not dissolve in the food product Suitable chemical crosslinking agents include metal complexes of inorganic salts, glyoxal, boric acid, sodium borate, as well as any multifunctional compound that can react with hydroxyl groups Those compounds that include aldehyde groups are preferred Advantageously, certain modifiers (e g , liquid smoke) contain compounds that comprise aldehyde functional groups
PVOH resins that are either partially or completely hydrolyzed are commercially available, although PVOH that is completely or nearly completely hydrolyzed (i e , substantially hydrolyzed) is preferred for use as the food-contact layer in the present invention PVOH resins which include no more than about 2%, preferably no more than about 1%, non-hydrolyzed acetate groups are preferred Such PVOH resins have been found to form food-contact layers that have sufficiently low levels of water solubility PVOH resins can be obtained from a variety of commercial sources including Air Products and Chemicals (Allentown, Penna ) under the trade name AIRVOL™, from DuPont de Nemours (Wimmgton, Del ) under the trade name ELVANOL™, and from Hoechst AG (Frankfurt, Germany) under the trade name MOWIOL™
The PVOH from which the food-contact layer is formed can have a wide range of viscosities Specifically, a 4% (by wt ) aqueous solution at
20°C can have a viscosity of from about 3 to about 70 mPa.s, preferably from about 5 to about 60 mPa.s, more preferably from about 9 to about 30 mPa.s Other polymers optionally can be blended with PVOH to obtain either a diluted effect or a synergistic effect Thus, moisture absorbing polymers or relatively water-insoluble polymers can be blended with PVOH to form the food-contact layer The blend can include any desired amount of additional polymer Suitable water-insoluble polymers include polyolefins, polyamides, polyesters, etc , with polyamides being preferred Suitable moisture absorbing polymers can include one or more of the following water-soluble polymers poly(ethylene imine), poly( acrylic acid), polyacrylamide, poly( methacrylic acid), polymethacrylamide, poly(N,N-dιmethylacrylamιde), poly(N-ιsopropylacryiamιde), poly(N-acrylylglycιnnamιde), poly(N- methacrylylglycinnamide), poly(vιnyl acetate), polyvinylpyrrolidones, polyvinyloxazolidone, polyvinylmethyloxazolidone, poly(ethylene sulfonic acid), poly( phosphoric acid), poly(sιlιcιc acid), poly(styrenesulfonιc acid), polyvinylamme, poly(2-vιnylpyrιdιne), poly(4-vιnylpyrιdιne), poly(vιnyl sulfuric acid), poly(vιnyl alcohol-co-vinyl sulfuric acid), poly(N,N-dιmethyl-3,5- methylenepipeπdiπium chloride), poly(ethylene-phosphonιc acid), poly(maleιc acid), poly(2-methacryloyloxyethane-1 -sulfonic acid), poly(3- methacryloyloxypropane-1 -sulfonic acid), poly(4-vιnylbenzoιc acid), poly(4- vinylbenzyltπmethylammonium salts), poly[3-(vιnyloxy)propane-1 -sulfonic acid], poly(4-vιnylphenol), poly(4-vιnylphenyl sulfuric acid), poly(2- vinylpipeπdine), poly(4-vιnylpιperιdιne), and poly(N-vιnylsuccιnamιdιc acid) In some circumstances, forming the food-contact layer solely from one or more of the foregoing moisture absorbing polymers might be possible If desired, a variety of other adjuvants can be included in the food- contact layer, i e , blended with PVOH Examples of potentially useful adjuvants include, but are not limited to, plasticizers such as, for example, glycerol and polyethylene glycol, humectants such as, for example, silica and starch, and release agents such as, for example, stearates, silicones, and certain organic fluorochemicals The skilled artisan can envision a number of other potentially useful adjuvants
In general, the food-contact layer can have a thickness ranging from about 025 to 250 μm (001 to 10 mils), preferably from 1 3 to 25 μm (005 to 1 mil), more preferably from 25 to 13 μm (0 1 to 05 mils), and most preferably from about 5 to 7 5 μm (about 02 to 03 mils)
Advantageously, the food-contact layer of the film article of the present invention not only can transfer modifier to a packaged food product but also can provide purge resistance, i e , inhibit or prevent cook-out during the cook-in process This is a significant advantage, especially where the food product is meat, poultry, or fish Preferably, the film article results in less than 20 weight percent cook-out, i e , less than 20% (by wt ) of the original weight of the food product is lost as purge More preferably, the film article results in less than 10% cook-out, even more preferably less than 5%, more preferably still less than 2% cook-out, and most preferably less than 1 % cook-out
To assist in reducing or eliminating cook-out, a food-contact layer having a surface energy of greater than 34 dynes/cm, preferably greater than 38 dynes/cm, more preferably greater than 42 dynes/cm, even more preferably greater than 46 dynes/cm, and most preferably greater than 50 dynes/cm is preferred At such surface energies, the food-contact layer O 97/36799 PC17US97/05520
is believed to provide sufficient adhesion with the food product to prevent or substantially eliminate cook-out.
If the film adheres so strongly to the cooked food product such that it cannot be peeled therefrom without tearing away portions of the same, the PVOH of the food-contact layer can be blended with one or more polymers that lower its adhesion. In this regard, less polar polymers such as polyolefins having a surface energy of about 36 dynes/cm or less can provide beneficial results. On the other hand, if adhesion between the film article and food product is too low, the surface energy of the food- contact layer can be increased. This can be accomplished by, for example, subjecting the surface of the food-contact layer to sufficient energetic radiation (i.e., of sufficiently high intensity or for a sufficiently long period of time) to achieve a desired increase in surface energy. Examples of radiative techniques include plasma and corona treatments. Alternatively, the surface energy of the food-contact layer can be increased by including one or more polar additives such as polyesters, polyamides, polylactic acid, and polar polyolefins such as ethylene/ unsaturated acid copolymers, modified polyolefins, and blends thereof. When formed into a food-contact layer, PVOH advantageously has been found to provide sufficient adhesion with a packaged food product during cook-in to substantially prevent cook-out without the need for corona treatment. At the same time, adhesion between PVOH and the food product is sufficiently low that the film article can be peeled from the food product after cook-in without substantial tearing of particles from the food product.
As mentioned previously, modifiers are substances that can . change the odor, color, taste, texture, etc., of a packaged product. Normally, the modifier effects a change in the surface of the product to which it is applied when sorbed by that surface. This sorption can occur either without, but preferably with (in the case of meat, poultry, or fish), a concurrent cook-in process. Any desired acidic modifier(s) that include
l l O 97/36799 PC17US97/05520
aldehyde functional groups can be included in the food-contact layer, especially those that are dissolved or suspended in an aqueous medium (Of course, basic modifiers, especially strongly basic modifiers, that include aldehyde groups also are potentially useful ) Non-limiting examples include colorants (e g , caramels, dyes, or pigments such as β- carotene), odorants, flavorants, antioxidants (to control rancidity), antimicrobial agents, enzymes, odor absorbents, or blends of any of the foregoing materials as long as the mateπal(s) has/have a pH of no more than about 5 0, preferably no more than about 4 0, more preferably no more than about 3 5 Most preferably, the modifier has a pH in the range of from about 2 0 to about 3 5 Modifiers which impart more than one of the above properties also can be used
An example of a modifier commonly used in the packaged food industry is "liquid smoke", a substance derived from wood and capable of being sorbed (i e , absorbed or adsorbed) by a food product such as, for example, beef, mutton, poultry, fish, cheese, and the like Liquid smoke is a colorant-flavorant-odorant which imparts a wood-smoked quality to red meat, poultry, ham, sausage, etc Various liquid smoke modifiers, as well as the other modifiers listed above, are available from a number of different commercial sources Most, if not all, liquid smoke modifiers are acidic and include at least one compound that includes aldehyde functional groups
The modifier can be sorbed into the food-contact layer during production of the film article, e g , by adding modifier to the pelletized or molten resin from which the food-contact layer is formed prior to extrusion or coextrusion thereof More specifically, a blend of PVOH and modifier at a temperature of from about 150° to about 250°C, preferably from about 180° to about 220°C, can be extruded by standard techniques known in the art Preferably, the food-modifying substance is added to the blend just prior to (i e , within about five minutes of, preferably within about two minutes of) extrusion Adjuvants such as those listed previously can be added to the the extrudable blend if so desired. For example, use of a plasticizer can reduce the extrusion temperature of PVOH
Altematively, the modifier can be incorporated into the food- contact layer during formation thereof by means of solvent casting, a procedure well known to those of ordinary skill in the art. This can be done by preparing a solution of PVOH and modifier in an appropriate solvent. Because of its relative environmental friendliness, water is a preferred solvent. The PVOH-modifier solution then is cast and allowed to dry into a sheet material. The drying step can be done at a temperature of from about 25° to about 200°C. The resulting PVOH sheet material can be laminated to one or more other layers so as to form a multilayer film with a PVOH food-contact layer. A preferred method of lamination is adhesive bonding. (Of course, if desired, the modifier need not be included in the
PVOH solution. Rather, the resulting cast film subsequently can be impregnated with modifier by one of the methods discussed infra, either before or after the PVOH layer is laminated to one or more other layers.) Simple coextrusion can result in a multilayer film that includes a PVOH food-contact layer. Such a film article then can be impregnated with modifier. This can be accomplished by any suitable means whereby a modifier or modifier solution is brought into contact with the food- contact layer for a time sufficient to allow the food-contact layer to sorb a desired amount of modifier (e.g., dip coating). Where the film article is in the form of a flat sheet, it can be immersed in a bath of a modifier solution so as to impregnate the food-contact layer with modifier. This can be done as a batch or continuous process. Where the film is in the form of a tube with the food-contact layer on the inner surface thereof, the modifier can be contacted with the tube inner surface and sorbed thereby. This can be accomplished in a number of ways such as, for example, by introducing a slug of modifier solution at a low position within a vertically oriented section of tube in the tube processing system, with a nip roll as a liquid seal at the lower end, and then passing the tube through the stationary slug See, e g , U S Pat No 2,901 ,358 Where the film article is fabricated into a bag, the modifier can be added by simply filling the bag or, as disclosed in U S Pat No 5,484,001 , partially filling the bag and then squeezing the modifier between a moveable external roller and backing plate so that it is dispersed along and absorbed into a desired portion of the inside (i e , food-contact layer) of the bag Other impregnating the food-contact layer with modifier include coating a modifier solution onto the food-contact layer with, for example, a flexographic printing press and spraying a modifier solution into the inside of a tube or bag formed from the film article
Regardless of how the film is made and when the modifier is incorporated therein, the pH of the modifier preferably is less than about 3 5 Liquid smoke modifiers are a particularly preferred type of modifier Surprisingly, the food-contact layer of the film article of the present invention has been found to be capable of sorbing, retaining, and then transferring a relatively large amount of modifier as a percentage of the total weight of the food-contact layer For example, a PVOH food-contact layer can sorb and retain between about 200 and 450 weight percent of a liquid smoke modifier, based on the weight of the PVOH The amount of modifier retained by the food-contact layer often can vary with the viscosity of the modifier Generally, lower viscosity modifiers are sorbed and retained to a greater degree than higher viscosity modifiers The values provided in the foregoing paragraph are based on the amount of modifier retained by the food-contact layer shortly after soaking the film article in a liquid smoke solution, i e , with little or no drying of the film article However, where a film article is allowed to dry (e g , at room temperature for a period of 12 to 18 hours), the amount of liquid smoke modifier retained by the food-contact layer is somewhat lower. The amount of modifier retained after drying can range from about 150 to 200 weight percent, based on the weight of the PVOH.
The foregoing sorption percentages are illustrative only. Depending upon a particular set of circumstances (e.g., the type of modifier, the composition of the food-contact layer, cook-in conditions, etc.), observed values can be higher or lower. Actual sorption values can vary from 0.1 to 10,000 weight percent but generally range between 0.5 to 1000, or even 1 to 500, weight percent.
The degree of sorption also can vary somewhat depending on the amount of time that the food-contact layer is exposed to the modifier as well as the temperature experienced during the sorption process. The values reported above are based on soak times ranging from 30 seconds to 10 minutes. (Generally, most sorption occurs within about 2 minutes of the time that soaking is initiated.) Where the modifier is a liquid smoke, sorption times can range from seconds to several hours, e.g., 5 seconds to 24 hours. Preferred sorption times range from about 30 seconds to 30 minutes, more preferably from about 1 to about 10 minutes, most preferably from about 2 to about 5 minutes. As illustrated in the Examples below, the film articles of the present invention advantageously provide adequate sorption of liquid smoke within about 1 to 10 minutes. Sorption temperatures generally range from about 0° to 70°C, with a temperature range of about 10° to 30°C being more preferred. Depending on the circumstances, higher or lower temperatures also can be employed. The food-contact layer preferably transfers at least 1 % (by wt ), more preferably at least 5% (by wt.), even more preferably at least 10% (by wt.), more preferably still at least 20% (by wt.), even more preferably at least 30% (by wt.), yet more preferably at least 40% (by wt ), and most preferably at least 50% (by wt.) of the modifier retained therein is transferred to a food product packaged within the film article. In general, a greater proportion of the retained modifier is transferred to the food O 97/36799 PC17US97/05520
product where a food product is cooked and packaged within the film article than where an already cooked food product is simply packaged within the film article. About 45 to 95% (by wt.) of a liquid smoke modifier retained in the food-contact layer of a film article of the present invention is believed to be transferred to a food product cooked in the film article. The film article of the present invention can have a single layer or include a number of layers. Preferably, the film article is a multilayer film having an outer layer which can include at least one of polyolefin, polystyrene, polyamide, polyester, poly(ethylene/vinyl alcohol), polyvinyHdene chloride, polyether, polyurethane, and polycarbonate. The outer layer preferably provides abuse resistance to the film article when it is formed into a cook-in package. Polyolefins and/or polyamides often prove to be particularly useful in this regard.
Suitable polyolefins include polyethylene homopolyer or copolymer, polypropylene homopolymer or copolymer, and polybutene homopolymer or copolymer. Preferred examples include ethylene/α-olefin copolymer, propylene/α-olefin copolymer, butene/α-olefin copolymer, ethylene/ unsaturated ester copolymer, and ethylene/unsaturated acid copolymer. Specific examples of preferred polyolefins include one or more of LLDPE, ethylene/vinyl acetate copolymer (EVA), propylene/ethylene copolymer, and propylene/butene copolymer. An ethylene/α-olefin copolymer includes mer units derived from ethylene and from one or more C3 to C2o α-olefins such as 1 -butene, 1 -pentene, 1 -hexene, 1 -octene, 4-methyl-1- pentene, and the like. The resulting polymer molecules include long chains with relatively few side chain branches and the side branching that is present is short compared to non-linear polyethylenes (e.g., low density polyethylene homopolymer). Ethylene/α-olefin copolymers generally have a density in the range of from about 0.86 g/cc to about 0.94 g/cc. LLDPE generally is understood to include that group of ethylene/α-olefin copolymers which fall into the density range of about 0.915 to about 0.94 g/cc. Sometimes, linear polyethylene having densities of from about 0.926 to about 0.94 are referred to as linear medium density polyethylene (LMDPE). Lower density ethylene/α-olefin copolymers can be referred to as very low density polyethylene (VLDPE, typically used to refer to ethylene/butene copolymers available from Union Carbide with a density ranging from about 0.88 to about 0.91 g/cc ) and ultra-low density polyethylene (ULDPE, typically used to refer to ethylene/octene copolymers supplied by Dow Chemical Co.).
Ethylene/α-olefin copolymers also include homogeneous polymers such as metallocene catalyzed EXACT™ linear homogeneous ethylene/α-olefin copolymers (Exxon Chemical Co.; Baytown, Texas); TAFMER™ linear homogeneous ethylene/α-olefin copolymers (Mitsui Petrochemical Corp.; Tokyko, Japan); and AFFINITY™ long-chain, branched homogeneous ethylene/α-olefin copolymers (Dow Chemical Co.; Midland, Michigan). Homogeneous polymers have relatively narrow molecular weight and composition distributions. Homogeneous polymers are structurally different from heterogeneous polymers (e.g., ULDPE, VLDPE, LLDPE, and LMDPE) in that homogeneous polymers exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of length of all chains, i.e., a narrower molecular weight distribution. Furthermore, homogeneous polymers are typically prepared using single-site type catalysts (e.g., metallocenes) rather than Ziegler-Natta catalysts. Such single site catalysts typically have only one type of catalytic site, which is believed to be the basis for the homgeneity of the polymers produced thereby.
Suitable polyamides from which the outer layer can be formed include one or more of the following: polyamide (i.e., nylon) 6, polyamide 66, polyamide 9, polyamide 10, polyamide 11 , polyamide 12, polyamide 69, polyamide 610, polyamide 612, polyamide 61, polyamide 6T, polyamide MXD6, and copolymers thereof. More preferably, the polyamide is selected from the group consisting of polyamide 6, polyamide 66 and polyamide 6/66 Even more preferably, the polyamide in the outer layer comprises a blend of polyamide 6, 66 or 6/66 with a second polyamide having a different crystalline structure from the first polyamide, including one or more of the following polyamide 6, polyamide 66, polyamide 9, polyamide 10, polyamide 11 , polyamide 12, polyamide 69, polyamide 610, polyamide 612, polyamide 61, polyamide 6T, polyamide MXD6, and copolymers thereof
If the outer layer includes a polyamide, adding polymers that are compatible with the polyamide or polyamide blend so as to modify the properties of the polyamides can be beneficial for some applications
Suitable polymers include polyolefins, such as those incorporating acids, esters, anhydrides or salts of carboxylic acids, and polar, non-polyolefinic materials such as polyesters, EVA, etc
If desired, additional layers can be included as interior layers Preferred materials from which such interior layers can be formed include polyolefin, particularly EVA, ethylene/alkyl acrylate copolymer (e g , ethylene/methyl acrylate, ethylene/ethyl acrylate, ethylene/butyl acrylate, etc ), LDPE, and ethylene/α-olefin copolymer (e g , LLDPE or VLDPE), polyamide, polyurethane, and blends of any of the foregoing In addition, any of the materials described above as suitable for use in the outer layer also can be used to form one or more interior layers
If desired, the film article can contain an interior layer that acts as a barrier (Barrier layers inhibit the transmission of one or more gases, e g , 02 ) Such a layer may be advantageous for extending the shelf-life of an oxygen-sensitive product, such as beef, poultry, pork, or fish, when packaged in the film article of the present invention Such an oxygen barrier layer preferably is formed from at least one material selected from the group consisting of ethylene/vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, PVOH, polyhydroxyaminoether, polyalkylene carbonate, or a blend of any of the foregoing If desired, oxygen barrier functionality also or alternatively can be provided by appropriate material selection for the outer layer or other interior layers Each of the foregoing materials from which the film article may be constructed are commercially available from a number of suppliers Specific examples are listed in the Examples below
If heat shrinkable, the film article preferably has a free shrink at 85°C (185°F), determined according to ASTM D 2732, of from about 5 to 70%, more preferably from about 10 to 50%, and most preferably from about 15 to 35% in at least one direction (i e , the longitudinal (L) or transverse (T) directions) Preferably, the film article is biaxially oriented, and preferably the film has a free shrink at 85°C of at least 10%, more preferably at least 15%, in each direction in each direction (L and T) Preferably, the film article has a total free shrink (L+T) of from about 30 to 50% at 85°C The film preferably is stretched in both the L and T directions at ratios ranging from about 1 1 5 to 1 7 and, more preferably, from about 1.2 to 1 4 Stretch orienting in the L and T directions can be followed by rapid quenching to lock in the molecular orientation The resulting film article is an oriented film which is heat shrinkable, preferably at the conditions at which the cook-in procedure is performed Alternatively, the oriented film article can be heat-set Heat-setting can be done at a temperature from about 60° to 200°C, more preferably from about 70° to 150°C, and even more preferably from about 80° to 90°C
In general, the film article of the present invention can have any total thickness desired, as long as the film provides the desired properties for the particular packaging operation in which it is used Preferably, the film article has a total thickness (i e , a combined thickness of all layers) of from about 13 to 250 μm (05 to 10 mils), more preferably from about 25 to 130 μm (1 to 5 mils), and still more preferably from about 50 to 75 μm (2 to 3 mils) The film article preferably has a Young's modulus ranging from about
34 to 10,000 MPa, more preferably from about 70 to 2100 MPa, and most preferably from about 280 to 1400 MPa The food-contact layer itself can have a Young's modulus ranging from about 20 to 10,000 MPa
Preferably, the material from which the food-contact layer is formed has a melt flow index ranging from about 0 1 to 1 ,000 g/10 minutes, more preferably from about 0 5 to 500 g/10 minutes, and most preferably from about 1 to 50 g/10 minutes (ASTM D-1238, 235°C/1 kg)
Illustrated below are preferred examples of film structures in accordance with the present invention In each of these structures, the following abbreviations are used FC food-contact layer, as described above,
PA polyamide-containing layer, preferably having a thickness of from 2 5 to 130 μm (0 1 to 5 mils), more preferably from 5 to 75 μm (02 to 3 mils), most preferably from 13 to 25 μm (05 to 1 mils),
PO polyolefin-containing layer, preferably having a thickness of from 25 to 130 μm (0 1 to 5 mils), more preferably from 5 to 75 μm (02 to 3 mils), most preferably from 13 to 25 μm (05 to 1 mils),
B oxygen barrier layer, preferably having a thickness of from 025 to 130 μm (001 to 5 mils), more preferably from 1 3 to 13 μm (005 to 05 mils), most preferably from 2 5 to 7 5 μm (0 1 to 0 3 mils), and TIE tie layer having a preferred thickness of 025 to 25 μm (001 to
1 mils), more preferably 1 3 to 13 μm (005 to 0 5 mils), most preferably
In the following film structures, the individual layers are shown in the order in which they would appear in the film FC (monolayer)
FC / PA
FC / PO
FC / TIE / PO
FC / B / PA FC/TIE/PA
FC/PO / PA
FC / B / PO
FC / PA / B / PA
FC / TIE / PO / TIE / PA
FC/ TIE /PA /TIE /PA FC /TIE/ B /PA /TIE /PA
FC / TIE / PO / TIE / B / PA / TIE / PO
These representative film structures are intended to be illustrative only and not limiting in scope
Where a multilayer film is desired, it can be produced by any suitable technique known in the art of film making, such as, for example, coextrusion, extrusion coating, or lamination Where the PVOH- containing food-contact layer is laminated to a mono- or multilayer film, any suitable adhesive can be used, although polyurethane (e g , Tycel™ two-part adhesives from Liofol Co (Cary, NC) and Adcote™ 530S adhesive from Morton International (West Alexandria, OH)), styrene- butadiene rubber (e g , Hycar™ 2570X59 adhesive from B F Goodrich (Cleveland, OH)), and acrylic (e g , Duroflex™ 72-8660 adhesives from National Starch (Bπdgewater, NJ)) are preferred
If desired, the film article can be chemically or electronically crosslinked When radiatively crosslinked, the film is subjected to an energetic radiation treatment, such as high energy electron treatment, which induces crosslinking of molecules of the irradiated material The irradiation of polymeric films is disclosed in U S Patent No 4,064,296 (Bornstein et al ), incorporated herein in its entirety by reference thereto Bornstein et al discloses the use of ionizing radiation for crosslinking the polymer present in the film Radiation dosages often are expressed in terms of the radiation unit "RAD", megarads (MR), or kiloGrays (kGy), with one MR being equivalent to 10 kGy A suitable radiation dosage of high energy electrons is in the range of from about 16 to 166 kGy, more preferably from about 44 to139 kGy, and still more preferably from about 50 to 80 kGy Preferably, irradiation is carried out by an electron accelerator with the dosage level being determined by standard dosimetry methods
In carrying out a cook-in process in accordance with the present invention, a food product is enclosed in a film article as described above, with the food-contact layer being in contact with the food product Any suitable means of enclosing the food product in the film article can be employed Preferably, the film article is in the form of a bag or casing with a single opening Such a bag or casing (i e , package) can be formed by, for example, heat sealing one end of a length of tubular film or by sealing both ends of the tube and then slitting one edge to form the bag mouth Where the film article is made in the form of flat sheets, bags can be formed therefrom by heat-sealing three edges of two superimposed sheets of film That the food-contact layer be capable of being heat-sealed to itself is preferred PVOH, even with modifier included therein, can be heat sealed under certain circumstances The food product is placed inside of the bag or casing and the opening is sealed closed, e g , by heat-sealing or clipping, so that the resultant enclosure is substantially liquid-tight The enclosed food product is then heated for a time and at a temperature sufficient to at least partially, but preferably fully, cook the food product During this process, at least some of the modifier retained within the food-contact layer is transferred to the food product Any suitable means of heating may be employed, including immersing the enclosed food product in a bath of heated water or steam, or placing the enclosed food product in a hot air or steam cabinet In one preferred embodiment, the film article is heat shrinkable so that the food-contact layer will be in close contact with the food product, thereby facilitating transfer of the modifier If the film is not heat shrinkable, the inside of the bag or casing may be evacuated and collapsed against the food product prior to sealing the bag or casing closed.
After the desired degree of cooking has been achieved, the processed and packaged food product is removed from the heating means and allowed to cool. The film article can be stripped from the food product at any desired time after the cooking process has been completed. That is, the film article immediately can be stripped and the food product then can be either consumed or further processed, e.g., sliced and repackaged into smaller portions for customer display by a retailer. Alternatively, the processed and packaged food product can be refrigerated, shipped to a retailer, and stored until the processed food is to be consumed or further processed as described above.
Food products which can be packaged and cooked in accordance with the present invention can be any of those foods which are amenable to cook-in packaging, including whole muscle or chopped red meat, poultry, pork, or fish. Also included are foods which are not intended to be cooked-in but simply stored within the package, during which time a modifier is to be transferred to the packaged food product. Such foods include cheese, vegetables, fruits, and already cooked meat, poultry, pork, or fish. In general, however, the invention is most advantageous when used as a cook-in package for, e.g., poultry, ham, beef, lamb, goat, horse, fish, liver sausage, mortadella, and bologna; more preferably, poultry, ham, beef and bologna; even more preferably, poultry and ham. The invention will now be described with reference to the following examples, which are intended to be illustrative only and not limiting in scope.
EXAMPLES Example 1
A 6-layer film having the following structure was prepared: FC / I / TIE / B / TIE / O wherein FC represents a 38 μm (1.5 mils) thick food-contact layer of PEBAX™ MX 1074 poly(ether block amide) copolymer; I represents a 76 μm (3.0 mils) thick internal layer made from a blend of TYMOR™ 1203 anhydride-grafted LLDPE (Morton Intemational; Chicago, IL) and EXACT™ 4011 homogeneous ethylene/α-olefin copolymer (Exxon Chemical Co.; Baytown, TX); each TIE represents a 28 μm (1.1 mils) thick tie layer of TYMOR™ 1203 anhydride-grafted LLDPE; B represents a a 28 μm (1.1 mils) thick oxygen barrier layer of EVAL™ LC-E105A ethylene/vinyl alcohol copolymer (Eval Co. of America, Lisle, IL); and O represents a 190 μm (7.5 mils) thick outer layer made from a blend of PE 5269T™ ethylene/vinyl acetate copolymer (Chevron Chemical Co.; Houston, TX) and FORTIFLEX™ J60-500C-147 high density polyethylene (Solvay Polymers, Inc.; Deer Park, TX). This film was prepared by coextruding each polymer (or polymer blend) at between 193° and 277°C (380° and 530°F) through a circular die held at a temperature of approximately 216°C (420°F). The extruded tube of film was cooled with water and flattened to a width of about 6 cm. The flattened film was passed through the scanned beam of an electronic crosslinking unit where it received a total dosage of about 105 kGy. After irradiation, the flattened tube was passed through hot water having a temperature of from about 97° to 99°C (206° to 210°F), inflated into a bubble, and oriented to result in a tube of oriented film, the tube having a lay flat width of about 16.5 cm (6.5 in ), with the multilayer film having a total thickness of 56 μm (2.2 mils).
The resulting film had about 20% free shrink in the longitudinal direction and about 30% free shrink in the transverse direction when immersed in hot water at 85°C (185°F) using ASTM method D 2732-83. O 97/36799 PC17US97/05520
Example 2 Multilayer films made according to the teaching of Example 1 and monolayer PVOH films were subjected to cook-in testing by soaking 15 cm x 15 cm (6 in 6 in ) film samples in a Charsol Select™ 24 liquid smoke solution having a pH of 2 4 (Red Arrow Products Co Ine ,
Manitowoc, WI) for a predetermined period of time ranging from 1 to 10 minutes to allow the PEBA or PVOH food-contact layer to sorb some of the liquid smoke Some of the samples were simply shaken dry and then weighed to determine the amount of liquid smoke absorbed by the food- contact layer Others were allowed to dry for at least 12 hours before weighing This was done to replicate actual use conditions where, in some instances, the food-contact layer is impregnated with modifier shortly before packaging a food product (and will therefore be wet with modifier solution during the transfer of the modifier to the food product) and in other instances the modifier-soaked food-contact layer is dried by the time a food product is packaged in the film article
A chicken breast emulsion having 3% salt, 05% phosphate, and 35% water, the balance being defatted chicken breast meat (all percentages based on the total weight of chicken breast), was prepared Sections of 10 cm (4 in ) diameter poly(vιnyl chloride) pipe were stuffed with the chicken breast emulsion and capped on one end with a 15 cm x 15 cm sample of liquid smoke-impregnated film The other end was capped with a control film having a food-contact layer comprising a 50 50 blend of nylon 12 and nylon 6/12 The control film did not contain modifier but was used as a basts for comparison of the meat-adhesion/ cook-out prevention capabilities of the films of the present invention Restraining plates were placed over the capped ends of the stuffed pipe sections, and the resultant sample assemblies were subjected to a cook-in procedure wherein the sample assemblies were immersed in a hot water bath at 60°C (140°F) for 30 minutes, 65°C
(149°F) for an additional 30 minutes, and then 70°C (158°F) for a final 30 minutes The sample assemblies then were chilled in an ice bath until cool, at which time the restraining plates were removed
Each of the tested film samples were inspected visually for their ability to prevent cook-out This was done by noting the extent to which any purge was trapped between the surface of the cooked chicken and the film The samples then were peeled from the cooked chicken During this procedure, the degree to which the food-contact layer of the film samples adhered to the surface of the chicken also was noted, in terms of the ability of the film to prevent cook-out by strong adherence with the chicken and also in terms of the ability of the film to release from the chicken without tearing away a surface layer or pieces therefrom After the films were removed, the chicken was examined to determine the extent to which the food-contact layer transferred liquid smoke to the chicken during the cook-in process The test results are summarized in Tables 1 and 2, wherein each value is an average from three identically tested samples Table 1 sets forth the test results for film samples (identified according to their respective food-contact layers) which were allowed to dry for at least 12 hours after soaking in liquid smoke before initiating the cook-in procedure described above
Table 2 sets forth test results for films samples which had not been dried prior to commencement of the cook-in procedure Table 2
PEBA PEBA PVOH-13 PVOH-2b
Soak time (min) 1 10 1 10
Initial film wt. (g) 3.20 2.80 1.23 1.25
Wet film wt.c (g) 6.04 5.5 5.36 4.84
Modifier sorbed (wt. %) 89 96 336 287
Adhesion moderate moderate low low
Transfer good good good good
a) Same as in Table 1. b) Same as in Table 1. c) The weight of the film immediately after soaking, with excess liquid smoke having been only shaken off of the film.
The data of Tables 1 and 2 show that films of the present invention exhibit a high degree of modifier sorption and transfer. In addition, the films provide a desirable balance of food adhesion, i.e., cook-out is substantially prevented but removal of the film does not result in tearing of chicken particles.
With respect to the films having a PEBA food contact layer, the percent absorption in Tables 1 and 2 is expressed as a percentage of the entire film weight. In such films, the PEBA-containing food-contact layer accounted for approximately 10% of the total weight and thickness of the film. Thus, the amount of liquid smoke sorbed by the PEBA as a percentage of the weight of the PEBA alone is much higher than the values reported in Tables 1 and 2.
Example 3 About 14 parts by weight MOWIOL™ 28-99 PVOH resin was dissolved in 100 parts by weight water. The water was held at 95° to 99°C and was agitated. The solution was cooled to room temperature before about 28 parts by weight of one of a series of modifiers (listed O 97/36799 PC17US97/05520
below in Table 3) were added and mixed until homogeneous Monolayer films were cast from these solutions by means of a draw down bar The films were allowed to dry overnight in a fume hood at room temperature The various films were dried in a vacuum oven overnight at 60°C before being cut into three samples each with an approximately 3 cm diameter die Each sample was weighed before being immersed in 80°C water for about two hours Those samples that did not dissolve then were dried for 24-48 hours in a 60°C oven until repeated weighings showed that a steady weight had been obtained By comparing these weight measurements with those measurements taken prior to immersion, the percent weight loss was calculated This was used to determine the degree to which the modifier had crosslinked the PVOH
The water from some of the heated baths also was analyzed Specifically, the bath water was analyzed against neat PVOH by gel permeation chromatography. The quantifiable limit of this test was 0.045 mg/mL Results were recorded as "detected" or "undetected".
The results from this testing are given below in Table 3 From this data, at least two conclusions can be drawn First, PVOH food-contact layers that include modifiers having a very low pH (i e., about 3 5 or less) are less likely to dissolve in water than are food-contact layers that include modifiers that are only moderately acidic (i e , a pH of about 5 5 or greater) Second, liquid smoke modifiers seem to provide PVOH food-contact layers that are less water soluble than those PVOH food- contact layers that contain a caramel modifier This is believed to result from the presence of aldehyde groups present in most liquid smoke modifiers Table 3
Modifier Wt. loss after PVOH pH exposure to H20 (%) detected?
None — 100 YES
Charsol™ 24a 2.3 - 3.5 45 NO
LFB Supreme0 2.0 - 2.4 43 NO
LFB Special Ac 2.0 - 3.0 25 NO
Charsol™ 55d 5.5 - 6.5 100 ~
CS N-52e 5.5 - 6.5 100 —
LFB N' 5.5 - 7.0 100 —
Maillose9 2.5 - 3.5 100 —
602h 4.8 - 6.0 100 —
a) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. b) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. c) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. d) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. e) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. f) A liquid smoke solution manufactured by Red Arrow Products Co. Inc. g) A caramel color manufactured by Red Arrow Products Co. Inc. h) A powdered, double strength caramel color manufactured by D.D. Williamson & Co. Inc. (Louisville, KY)
Example 4 Ten percent (by wt.) solutions in ethanol of two common aldehydes, p-anisaldehyde (designated "PA" below) and 3,4- dimethoxybenzaldehyde (designated "DMB" below), were prepared. These were used as comparatives to test the efficacy of Charsol™ 24 liquid smoke as a crosslinking agent for PVOH (i.e., so as to make PVOH more insoluble in water). Four samples were cut from an M1030 PVOH film (Mono-Sol
Division of Chris-Craft, Inc.). One sample was soaked in the PA solution for about 15 minutes at ambient temperature, one was soaked in the DMB solution for about 15 minutes at ambient temperature, one was soaked in the liquid smoke modifier for only about one minute at ambient temperature, and one was left untreated These samples then were dried, and their resistance to water was measured This was done by performing a weight loss test similar to the one described in Example 3 Specifically, each film sample was weighed when dry before being immersed in room temperature water for about 24 hours Thereafter, the film samples were removed from the water, dried, and reweighed to determine the amount of film sample that had been lost due to exposure to water The results of these tests are given below in the table that follows
Pretreatment Wt loss after exposure to H20 (%) none 25
DMB 5 liquid smoke 5
The data of Table 4 show that a liquid smoke modifier such as Charsol™ 24 liquid smoke is as good as, if not better than, common aldehydes in lessening the water solubility of PVOH films
While the invention has been described with reference to illustrative examples, those skilled in the art will understand that various modifications may be made to the invention as described without departing from the scope of the claims which follow
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|Classification internationale||A22C13/00, B32B27/08, B65D65/40, B65D81/34|
|Classification coopérative||A22C2013/0053, A22C2013/0046, A22C13/0013, B32B27/08, B65D2581/345, B65D81/3415|
|Classification européenne||B32B27/08, A22C13/00D, B65D81/34B|
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