FIELD OF THE INVENTION

The present invention relates to edible pre-formed film barrier materials and methods to make edible film barrier materials which films can be used to stabilize vapor pressure gradients existing between individual components of a multicomponent food product separated by the edible film.

3ACKGR0UND OF THE INVENTION

Deleterious changes in the quality of food products can occur with inadvertent alteration of the moisture content of the food product. The driving force for moisture transfer in food pro-ducts is primarily due to moisture partial pressure gradients existing between the food product and the environment and/or between components of a multicomponent food product. The partial pressures involved can be expressed in terms of water activity, a which equals the partial pressure of water vapor exerted by the food material divided by the vapor pressure of pure water at the same temperature. Prevention of. moisture transfer between the food product and the environment can be accomplished by using a moisture impermeable packaging

material, either edible or inedible. Prevention of moisture exchange among individual components of a multicomponent food product is more difficult.

Edible food coatings have been used to retard moisture transfer within foods. However, the ability of sucn coatings to maintain vapor pressure gradients among components for extended periods has not been proven. The prior art is generally cognizant of the use of carbohydrate, protein, and lipid coatings to retard moisture transfer in foods. Lipids include hydrophobic compounds such as fats, oils, and waxes, and are especially effective in retarding moisture transfer in foods. However, when lipids such as waxes were applied to food products, the coatings were not continuous, but contained pinholes and cracks wnich provided routes for moisture transfer. Carbohydrate compounds are capable of forming continuous coatings, but these compounds are generally hydrophilic and hence less effective in retarding moisture transfer in foods. Therefore, in the past, lipids have been used in conjunction with carbo.hy rates in order to form a continuous coating to prevent moisture transfer in foods.

In U.S. Patent No. 2,909,435 to atters, et al, a double layer coating was applied sequentially on foods such as raisins. The-first layer consisted of a polysaccharide, upon which was applied a second layer of a melted wax composition. The layers were applied to the food by brushing, spraying, or dipping, and were dried after application. In U.S. Patent No. 3,323,922 to Durst, an aqueous solution was prepared from starch or a carboxymethyl cellulose, a plasticizer, and a lipid. The coating was then applied to a food product by brushing, dipping, or spraying ^' , and the coating was dried after application on the food product. U.S. patents number 3,471,303 and 3,471,304 to Hamdy,

~e—t- ——a — —l • disclose two *t _* ypes of coating co *mpositions having as one constituent a cellulose ether. The cellulose etner was plasticized by various fatty acid derivatives such as

(1) an ester of a linear polysaccharide having alpha-glucoside linkages and a fatty acid having between 8 to 26 carbon atoms, or (2) a glyceride containing a fatty . acid having between 6 to 20 carbon atoms, together with a fatty acid metal salt wherein the fatty acid contains between 16 and 22 carbon atoms. Tne coating composition in the Ha dy patents could be extruded as a molten sheet over the food to be coated, and then dried.

U.S. patent number 3,997,674 to Ukai , et al discloses an aqueous solution used to coat foods such as fresh fruits. The coating solution contained a water soluble high polymer such as methyl cellulose and also hydrophobic substances such as waxes or oils. ^■ In Ukai , the food product was coated and then dried. Drying a food coating after application on a food has several disadvantages. It is difficult to control the thickness of such coatings. Furthermore, drying coated foods adds time and hence cost to the manufacture of such foods. Therefore, it would be advantageous to provide off-the-shelf, pre-formed films which could effectively retard or prevent moisture transfer between components having different vapor pressures in a mύlticomponent food product.

SUMMARY OF THE INVENTION

The present invention is summarized as an edible pre-formed and dried film for retarding moisture transfer among components of a multicomponent food product. The film includes a hydrophilic polymer layer selected from the group consisting of edible, film-forming carbohydrates and proteins and a lipid layer adhered to the hydrophilic polymer layer such that the film comprising the hydrophilic polymer layer and the lipid layer has a ^• thickness in the range of 0.035 millimeters to 0.150 millimeters, the lipid layer having a concentration of at least approximately 0.8 milligrams of ^' lipid ^' per square centimeter of hydrophilic polymer layer. When the film is

placed between components of food having different vapor pressures, the lipid layer is oriented toward the food component possessing the greater water activity so that the film can maintain the existing vapor pressure gradient for substantial periods of time, thereby retarding moisture transfer among the food components.

It is an object of the present invention to provide an edible pre-formed and dried film whicli can retard moisture transfer among components of a multicomponent food product during extended storage times, and over changing temperatures and humidities, and yet which film can be absorbed in the food product during heating or other preparation of the food product or if not fully absorbed, will be unobjectionable during consumption of the food. It is a further object of the present invention to provide a method for making edible pre-formed films capable of retarding moisture transfer among components of a multicomponent food product over extended storage times. It is a still further object of the present invention to provide a food product and method to make a food product which includes a plurality of components having different vapor pressures together with edible films separating individual components, which films can maintain existing vapor pressure gradients for substantial periods of time, and thereby retard moisture transfer among the food components.

Other objects, advantages, and features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present ^' invention discloses an edible film for retarding moisture transfer among components of a multicomponent food product. The film includes a hydrophilic polymer layer, and a semi-solid, edible lipid layer adhered to the hydrophilic polymer layer such that

the film, comprising the hydrophilic polymer layer and the lipid layer, has a thickness in the range of 0.035 millimeters to 0.10 millimeters. The hydrophilic polymer layer can be formed from any edible, water soluble, film 5 forming carbohydrate or protein. Suitable polymers would include, for example, starch, cellulose ethers such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, and methyl cellulose, and also albumen. The lipid layer is comprised of semi-solid, edible lipids of plant or 0 animal origin such as hydrogenated oils (e.g., palm oil and soybean oil), saturated fatty acids, and edible waxes (e.g., beeswax and paraffin wax). The lipid layer has a concentration of at least approximately 0.8 milligrams of lipid per square centimeter of hydrophilic polymer layer. 5 The surface of the lipid layer is hydrophobic, whereby when the film is placed between components of food having different vapor pressure, the film can maintain the existing vapor pressure gradient for substantial periods of time, and thereby retard moisture transfer among the 0 food components.

There are two methods to prepare an edible film according to the present invention. The first method is called the Layer method. In the first step of the Layer method, a film-forming solution-is provided, consisting of 5 a hydrophilic polymer and water. The film-forming solution is then spread on a plate, preferably to a depth of approximately 0.75 millimeters. The plate is then dried for a time sufficient to form a cohesive hydrophilic polymer layer on the plate. Finally, a lipid layer is _Q applied to the hydrophilic polymer layer by brushing, dipping, or spraying; the lipid layer is then solidified. The lipid layer concentration should be at least approximately 4.0 milligrams of lipid per square centimeter of hydrophilie- polymer layer. The dried film 5 consisting of a hydrophilic polymer layer and a lipid layer should have a thickness in the range of 0.10 to 0.15 millimeters. The dried film is finally removed from the plate and positioned on the food material. Alternatively,

such films can be stored until the components of the food material are assembled. Preferably, alcohol such as ethanol is added to the. film-forming solution to decrease drying time. The ideal alcohol to water ratio by volume is approximately 2 to 1. In addition, polyethylene glycol can be added to the film-forming solution to aid in removal of the dried films from the plates and to improve adhesion between the lipid and non-lipix. layers. The ideal hydrophilic polymer to polyethylene glycol ratio by weight is approximately 9 to 1.

The second method for making an edible film according to the present invention is the Emulsion method. According to the Emulsion method, a film-forming solution is provided, consisting of a hydrophilic polymer, water, and a lipid. The solution is warmed, if necessary, to melt lipids having high melting points. The film-forming solution is then spread on a plate, preferably to a depth of approximately 0.75 millimeters. The film-forming solution on the plate is then dried for a time sufficient to form a cohesive edible barrier film having the thickness desired and a lipid concentration in the range of 0.8 to 1.0 milligrams lipid per square centimeters of hydrophilic polymer layer. A thickness in the range of 0.035 millimeters to 0.045 millimeters is preferred. After drying, the plate is cooled and the film is removed from the plate. The film can then be positioned on the food material, or stored until the food components are assembled. As in the Layer techique, alcohol and/or polyethylene glycol can also be added to the film forming solution in the ratios given above.

In both the Layer and Emulsion methods, the preferred hydrophilic polymer is a cellulose ether, specifically, hydroxypropyl methylcellulose. In both methods, the preferred lipids are selected from the group consisting of hydrogenated oils (specifically, hydrogenated soybean oil and hydrogenated palm oil), saturated fatty acids, and edible waxes. The preferred saturated fatty acids are stearic acid and a mixture of stearic and palmitic acids;

the ratio of stearic acid to palmitic acid in the mixture is not critical.

Temperature control is important in preparing a film by the Emulsion method. Emulsions containing fatty acids with high melting points require high temperatures to melt and disperse the fatty acid. However, high temperatures result in a low viscosity of the film-forming solution and poor control over film thickness during plating. Also, •high temperatures must be avoided during plating, otherwise vaporization of the alcohol will occur resulting in bubbles in the solution and possibly pin holes in the dried film. However, the solution must be warm enough to prevent solidification of the fatty acids during plating. Within seconds after plating, the fatty acids orient at the emulsion surface such that the hydrophobic portion of substantially all of the fatty acids in the fatty acid layer is oriented away from the hydrophilic polymer layer.

Example 1 — Layer Method

Nine grams of the cellulose ether hydroxypropyl methylcellulose were dissolved in 100 milliliters of 90°C distilled water. After the hydroxypropyl methylcellulose was completely dissolved, 200 milliliters of 95% ethanol was added. The solution was thoroughly mixed and then one gram of polyethylene glycol was dissolved in the solution. Air bubbles in the solution were removed by reducing the pressure over the solution.

One hundred milliliters of the film forming solution were added to a spreader for thin layer chromotography (TLC) and, the solution was plated onto three 8 inch by 8 inch TLC glass plates at a thickness of 0.75 millimeters. The plates were dried in an oven -at approximately 90°C for 15 minutes, at which time a cohesive cellulose ether layer formed. The plates were then cooled to room temperature and the hydroxypropyl methyl cellulose layers were removed and weighed. 3.3 grams of a lipid material was painted onto the surface of each 8 inch by 8 inch hydroxypropyl

methyl cellulose layer. The film thickness {hydroxypropyl methyl cellulose layer plus lipid layer) averaged 0.1 millimeters. The two layers were then reweighed. The concentration of lipid deposited was 8 milligrams lipid per square centimeters of hydroxypropyl methyl cellulose layer.

Example 2 — Emulsion Method

The film-forming solution was prepared by dissolving 9 - grams of hydroxypropyl methylcellulose in 100 milliliters of 90°C distilled water. After the hydroxypropyl methylcellulose was completely in solution, 200 milliliters of 95% ethanol was added. Next, 1 gram of polyethylene glycol was added to the solution. Finally, 3.4 grams of stearic acid was added to the solution. The solution was warmed to between 70 - 75°C in order t.o melt the stearic acid.

One hundred milliliters of the film-forming solution was added to the TLC spreader and plated onto three 8 inch by 8 inch glass TLC plates at a thickness of 0.75 millimeters. The coated plates were then dried in an oven at approximately 90°C for 15 minutes, at which time a cohesive edible barrier film formed. After drying, the plates were cooled and the films were peeled from the plates. The films had an average thickness of 0.04 millimeters, and an average stearic acid concentration of 0.8 milligrams stearic acid per square centimeter of hydroxypropyl methyl cellulose layer.

A food prepared in accordance with the present invention could include a plurality of components having different vapor pressures, such as pizza or filled pie crusts. Preferably, an edible film prepared in accordance with the present invention would be pre-formed and then positioned so as to ^' separate the individual components. Such edible films would include a hydrophilic polymer layer, and a lipid layer -adhered to the hydrophilic polymer layer such that the film, comprising the

hydrophilic polymer layer and the lipid layer, has a thickness "in the range of 0.035 millimeters to 0.150 milliliters. The lipid layer preferably has a .concentration of at least approximately 0.8 milligrams lipid per ^' square centimeter of hydrophilic polymer layer. The exposed surface of the lipid layer is nydrophobic and should be oriented towards the food component having a higher vapor pressure, such as pizza sauce or pie fillings. Therefore, the hydrophilic polymer layer would be oriented next to the food component having the lower vapor pressure, such as a pizza crust or pie crust. With this orientation, the film can maintain the existing food component vapor pressure gradient for substantial periods of time, thereby retarding, moisture transfer from the component having a higher vapor pressure to the component having a lower vapor pressure. The film would be absorbed into the component layers upon heating or other cooking preparation in the range of 45 to 75°C during preparation of multicomponent foods such as a pizza or a filled pie ^CrUSt -

It is to be understood that modification of the above-described edible film, method for making ^' an edible film, food product, or method of making a food product, is possible within the spirit of the present invention and thus the present invention should not be limited to the above-described specification but should be interpreted in accordance with the following claims.