WO2003063620A2

WO2003063620A2 - Moisture resistant barrier

Info

Publication number: WO2003063620A2
Application number: PCT/NL2003/000069
Authority: WO
Inventors: Govardus Adrianus Hubertus De Jong; Johannes Andreas Clyde Don; Johannes Wilhelmus Leonardus Boumans; Martijn Willem-Jan Noort; Johanna Plijter-Schuddemat; Johannes Jozef Plijter; Matheus Wilhelmus Louis Jozef Van Son
Original assignee: Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno
Priority date: 2002-02-01
Filing date: 2003-01-31
Publication date: 2003-08-07
Also published as: NL1019890C2; WO2003063620A3

Abstract

The invention relates to a method for the preparation of a food wherein components having different moisture contents are prepared separately and are then combined and wherein an edible moisture resistant barrier is applied on the separation surface of said components. The present invention also relates to a method for inhibiting moisture migration between components having different moisture contents in a food according to the invention.

Description

Title: Moisture resistant barrier

The present invention relates to a moisture resistant edible coating layer for foods.

In many cases, the preservability of foods is adversely affected by the diffusion of moisture. With cookies, pizza, rusks etc., through uptake of water from the surroundings, the products will gradually soften and no longer have the desired organoleptic properties. This also holds for composite foods such as, for instance, combined products wherein a dry product is combined with a wet filling. Examples hereof are pastry, pizzas, meat rolls, salad rolls, etc. Due to the diffusion of moisture from a wet component to a dry component, the organoleptic quality of the product diminishes.

To enhance the preservability of foods, different measures can be taken which reduce the diffusion of moisture in and through the product. In many cases, such a measure consists in providing a moisture resistant coating layer around or in the food. In this manner, the penetration of moisture into, for instance, bakery products such as cookies can be reduced and the migration of moisture through composite foods can be strongly reduced. The use of a coating layer having moisture resistant properties is particularly advantageous for composite foods in which the water contents in diverse components is different and may not alter significantly during storage. In all cases it holds that the coating layer should be edible.

To keep different components in composite foods having different moisture contents separated, moisture resistant coating layers on the basis of fats and oils (DE 3,921,454; EP 0 638 488; WO 00/78165) or shellac (US 4,874,618) are often used. Fats do not allow water migration and form impermeable barriers. However, in practice, the usability of these moisture barriers is low because they are sensitive to tearing, so that the barrier effect is undone. By embedding the fats in a biopolymer matrix (EP 0471 558) such as a matrix of carbohydrates (US 4,293,572; GB 2,015,315) or proteins (EP 0 451 491; EP 0 454 287; EP 0 465 801; US 6,066,368) the sensitivity to tearing is reduced. By contrast, through this addition of proteins and carbohydrates, the moisture resistant capacity diminishes. For this reason, a coating layer of biopolymers could additionally be coated with a moisture impermeable composition consisting of oil or wax as known from WO 92/01394, but this renders applying the coating layer time-consuming and laborious. Another drawback of certain carbohydrates or proteins is that they have the tendency to rigidify the barrier, as a result of which it may break.

US 4,689,238 describes a binder matrix for a muesli bar consisting of a baked protein-foam with gelatin. EP 0 178 074 describes the use of a thermoplastic binder matrix for a muesli bar on the basis of gelatin in glycerol from which preferably all water has been removed. Alternative compositions for impermeable moisture barriers have been described, such as coating layers consisting of polyol fatty acid polyesters (EP 0 375 240) or of a combination of fat with lactose (WO 97/15198), polyvinyl alcohol with soy lecithin (WO 96/01877) and fat with sugar alcohol polyol fatty acid polyester or sugar fatty acid polyesters (US 5,130,151). In conclusion, it can be stated that coating layers on the basis of fats have good moisture resistant properties but, for lack of structure, tear and disintegrate rapidly. By contrast, moisture resistant barriers in which carbohydrates or proteins have been processed have poor moisture resistant properties and often have a brittle structure. Also, known coating layers are poorly resistant to freezing. In many cases, tear formation will occur.

In contrast with current moisture barriers, which are used to arrest moisture by using materials which repel water or which are impermeable to water, the moisture barrier according to the present invention is based on the principle of reduction of the rate of moisture migration. Surprisingly, it has been found that a coating layer comprising a gel-forming biopolymer in gelled condition obviates many drawbacks of known moisture barriers.

The present invention relates to a moisture resistant, edible coating layer for foods, comprising a gel-forming biopolymer in gelled condition. Preferably, the moisture resistant, edible coating layer consists of one or more biopolymers, such as proteins or carbohydrates, which, in gelled condition and when in contact with moisture, are capable of absorbing this moisture. As this coating layer is indeed capable of absorbing water from the surroundings, eventually, an equilibrium is formed between the coating layer and the surroundings wherein the water activity (A_w value) of the coating layer corresponds to that of the surroundings. In addition, due to the gelling properties, the coating layer will retain the moisture and decelerate migration thereof through a food onto which the coating layer has been applied. The difference in A_w value between the food and the surroundings is the driving force in the moisture migration in and through the food. Without this driving force, no migration takes place.

A coating layer according to the present invention is especially advantageous in combined bakery products such as pizzas, custard buns, salad rolls and pastry, but also in bakery products which should remain dry, such as biscuits and other cookies, a coating layer according to the present invention can be used. Further, the invention is advantageous to deep frozen products in which conventional barriers on the basis of fats and biopolymers do not perform well as a result of crystallization processes and the associated tear formation. The present invention also relates to a food comprising a moisture resistant edible coating layer according to the invention.

A food according to the invention relates, inter alia, to a food consisting of at least two components having different moisture contents separated by an edible, moisture resistant coating layer comprising a gel- forming biopolymer in gelled condition. Examples hereof are composite foods consisting of a component having a low moisture content, such as cake, bread, Dutch rusk, biscuit, crackers or cookies and one or more components having a higher moisture content, such as fruit or vegetables mixtures, mushrooms, individual vegetables, salads, whipped cream, cream cheese, jam, pasta, sauce or a different sp readable or liquid or high moisture- containing component both in warm and cooled condition, in which a coating layer according to the invention has been processed.

Other foods to which the invention relates are dry foods provided with a coating layer according to the present invention, as a result of which they soften less rapidly under the influence of any moisture present in the surrounding atmosphere.

The present invention also relates to a method for inhibiting moisture migration in a food, wherein a coating layer according to the invention is applied onto the surface of the food such that, consequently, moisture exchange with the surroundings is prevented, at least, reduced. What could be considered here are methods for inhibiting moisture migration from wet foods to the relatively dry air as well as methods for inhibiting moisture migration from the relatively moist air to dry foods. The present invention also provides a method for inhibiting moisture migration between components having different moisture contents in a composite food consisting of dry and wet components, wherein a coating layer according to the invention is applied between the components as separation, and wherein moisture from a component having a higher moisture content is absorbed by the coating layer which prevents, at least reduces, moisture migration to a component having a lower moisture content. This method comprises steps wherein a solution or suspension of a gel-forming biopolymer is prepared, this solution or suspension is applied onto a food while forming a gel and, optionally, is dried for obtaining a coating layer according to the invention as separation between the components mentioned. Herein, a composite food is defined as a food comprising ingredients and/or components having different water or moisture contents, which ingredients and/or components having different water contents are in contact with each other such that exchange or migration of moisture from the ingredient and/or the component having a higher moisture content to the ingredient and/or the component having a lower moisture content is possible and which moisture migration is undesired.

The present invention can very advantageously be used in composite foods. Notwithstanding the great difference in water activitiy between components having different moisture contents in a composite food, it has been found that an edible, moisture resistant coating layer according to the present invention used therein provides very good results. By means of an edible, moisture resistant coating layer according to the present invention, for composite foods, therefore, a very good moisture barrier is now provided.

In the present invention a gel is understood to mean, in a general sense, a three dimensional network of a solid substance dissolved or dispersed in a liquid, so that the liquid adopts a semi-solid form. In particular, the present invention relates to gels in which the network is formed by a biopolymer.

An edible, moisture resistant coating layer according to the invention preferably comprises at least one gel-forming biopolymer. Biopolymers that can be used in an embodiment of the invention, in many cases, have the capacity to dissolve when heated or under pressure, and when they are cooled down or when the pressure is reduced, to turn into a three dimensionally, mutually stabilized network or matrix in which moisture can be captured, i.e. a gel. In a general sense, a gel-forming biopolymer is understood to mean a biopolymer which has the capacity to allow a liquid composition to gel, such as, for instance, in the case of a gelatin, or to allow to gelatinize, as in the case of, for instance, a starch. A feature of these biopolymers is that a matrix thereof can swell while absorbing moisture.

A suitable biopolymer which can be used in an embodiment according to the invention is for instance a protein, comprising a vegetable protein obtained from beans or cereals, or an animal protein, comprising milk protein such as casein and whey protein, egg protein such as ovalbumin, meat protein such as myosin and actin, blood protein such as serum albumin, and tendon protein such as gelatin and collagen. Also, biopolymers derived from or obtained from microorganisms can be used in the present invention. A protein that can preferably be used in a coating layer according to the invention is gelatin. Gelatin has as a special advantage that it can gel reversibly. This means that it can be applied onto a food or onto an ingredient of a composite food as a liquid, for instance in that it is applied at a temperature over 35°C, whereupon it gels through cooling. Other proteins could be formed into a gel, for instance by cross- linking the protein after application onto a food or onto an ingredient of a composite food, but such an operation is much more complex and less easy than the one based on the protein gelatin.

Further, the use of gelatin as biopolymer in embodiments according to the present invention is preferred, because the reversibly gelling character of gelatin, and, consequently, the possibility of applying the biopolymer in liquid form, hence prior to gelling, onto a food or ingredient thereof, has the advantage that the gel breaking upon application will not occur, or less rapidly. As a result, a moisture resistant edible coating layer on the basis of gelatin presents a reliable moisture barrier already at a relatively limited thickness. Cross linking a protein for forming a gel thereof, followed by the application of the thus formed gel onto a food or onto an ingredient of a composite food, such as a cookie or a pizza, has the drawback that the gel should not break and hence must be strong enough. Generally, this means that the gel is to be relatively thick, which is not desirable for the quality and the level of appreciation of the food by the consumer.

Other suitable polymers are, for instance, polysaccharides such as inulin, fructo-oligosaccharide, soy polysaccharide, cellulose, starch, agar- agar, alginate, carrageenan, xanthan gum, gum-arabic, locust bean gum, pectin and (arabino)xylans. Also protein carbohydrate polymers such as pectin-casein polymers can be used as biopolymer in the present invention.

Biopolymers which can be used in an embodiment of the invention can, optionally, be modified or derivatized. For instance, when using the biopolymer starch, a modified starch, comprising an oxidized starch, a cationic starch, an esterified or an etherized starch can be used. The preparation of modified biopolymers can be done by means of any method known to that end.

The biopolymers can also be used in cross-linked form. Cross- linking the biopolymers can be done enzymatically or chemically in generally known manners. The extent of cross-linking and the means with which the cross-linking is effected can enhance the action and the effect of the coating layer and, additionally, can be optimized by the skilled person. Optionally, the coating layer according to the invention can be composed wholly or partly of decomposed biopolymers for the purpose of, for instance, increasing its rate of gelling. Decomposition of a biopolymer according to the invention can be effected by oxidation, enzymatic decomposition or hydrolysis or by means of any other method known to that end. Different biopolymers can be combined in a coating layer according to the present invention while various biopolymers, such as several proteins, several polysaccharides or protein polysaccharides combinations can be used.

Such combinations of biopolymers in a coating layer according to the invention, but also modifications of individual biopolymers or, conversely, derivatives thereof can enhance the organoleptic properties of the coating layer. On the basis of such combinations, modifications or derivatives, it is also possible to arrive at coating layers with improved physical properties, among which heat resistance, density, moisture absorbing capacity or tensile strength, but also improved edibility and, conversely, a decreased cohesiveness can be achieved in this manner. On the basis of the present text, it will be clear to the skilled person how combinations of biopolymers, suitable modifications or derivatives can be identified for enhancing the organoleptic properties of a coating layer according to the invention.

Preferably, a coating layer according to the invention comprises a gel-forming biopolymer which is present in an amount of 1-100 % by weight, calculated on the basis of the dry weight of the coating layer. More preferably, a gel-forming biopolymer is present in an amount of at least 60% by weight, calculated on the basis of the dry weight of the coating layer. Still more preferably, a gel-forming biopolymer is present in an amount of at least 80% by weight, calculated on the basis of the dry weight of the coating layer.

The coating layer according to the present invention comprises a biopolymer in gelled condition which is understood to mean that a coating layer according to the invention has the form of a gel and that the matrix formed by the mutually connected network of biopolymer molecules is capable of capturing or absorbing moisture, or has already captured or absorbed moisture. Gels in which the biopolymers are interconnected by the formation of non-covalent interactions, such as hydrogen bridges, (such as, for instance, gelatin), as well as gels in which the biopolymers are interconnected by covalent bonds, such as cross-linked biopolymers, can be used in the present invention. As already stated, the use of gels on the basis of gelatin is greatly preferred. The coating layer according to the present invention comprises a biopolymer which is present in the form of a gel. What is meant by gel in the present invention is both a gel which has already captured moisture and a dried gel which is capable of still absorbing substantial amounts of moisture. A dried gel can be obtained by allowing a solution of a gel-forming biopolymer to gel and then to dry it.

Preferably, a coating layer according to the invention is applied having a low moisture content while the coating layer has the capacity of absorbing moisture. This will have a favorable effect on the moisture migration inhibiting action of the coating layer.

Preferably, the moisture content of a coating layer according to the invention, at the moment of application is at most 99% by weight on the basis of the weight of the coating layer measured at the moment of application. More preferably, the moisture content of a coating layer according to the invention is between 75% by weight and 95% by weight on the basis of the weight of the coating layer the moment of application. After application, the gel is preferably partially or substantially dried.

Generally, when taking up moisture, the coating layer will swell, and shrink when giving it off. In dried condition, a coating layer according to the invention preferably has a thickness between 0.01 mm and 3 mm. More preferably, a coating layer according to the invention has a thickness between 0.05 and 1 mm.

If desired, additives can be added to a coating layer according to the invention. These additives can be intended to improve the flavor of the coating layer. For instance, sweeteners and flavorings can be added to the coating layer. Also additives which modify the color, the texture and/or the mouthfeel of the coating layer can be added to the coating layer, and, for instance, discoloration reaction inhibitors to vegetables and fruit. Further, softeners can be added to the coating layer according to the invention. Examples thereof are glycerol and sorbitol. If an additive is used in the coating layer, the amount thereof is, preferably, between 0.001 and 20% by weight based on the dry weight of the coating layer.

The present invention also relates to a method for the preparation of a food, wherein components having different moisture contents are prepared separately and are then combined while the coating layer is applied onto the separating surface of the two components. In advance, the components having different moisture contents can be prepared separately in conventional manners such as mixing, baking, frying, cooking, steaming, roasting or poaching and, optionally, can be cooled down before being combined. According to a particularly usable aspect of the invention, a component having a low moisture content is covered with a coating layer according to the invention before it is combined with one or more components having a high moisture content.

A coating layer according to the present invention can be prepared by dissolving or suspending a biopolymer according to the invention in, for instance, water, while, optionally, heating it. Before incorporating such a composition for a coating layer in a food according to the invention, the temperature of the composition can be reduced and its moisture content can be decreased. Reduction of the moisture content of the coating layer can be effected by heating, by vacuum drying or a different, suitable method which can decrease the moisture content. A composition for a coating layer according to the invention can be applied in the form of a solution, a slurry, a paste or a film, by means of spreading, spraying, spouting, atomizing, immerging, brushing, rolling, laminating and applying an intact film.

Also after the application of a coating layer according to the invention onto a component having a low moisture content, the moisture content of the coating layer or both can, optionally, be reduced by drying. Thereupon, combination with one or more components having a high moisture content can take place. In a different preferred embodiment, a component having a high moisture content can be enrobed with a coating layer according to the invention, and then be combined with a component having a low moisture content. The order in which the different components of a composite food according to the invention and a coating layer according to the invention are combined is not essential.

The invention will now be illustrated on the basis of the following examples which should not be taken as being limitative.

Example 1. Knappertjes (dry biscuits)

Pre-dried knappertjes (10 min at 90°C) were provided with a composition for a coating layer by applying a solution of 10% gelatin in water onto the surface of the biscuit with the aid of a brush. Also, in this experiment, a commercial gelatin sheet was soaked in water for 5 minutes (room temperature) and then applied onto a knappertje. The applied layer was dried by heating the knappertjes for 10 minutes at 90°C and then allowing them to cool down for 30 minutes.

The knappertjes thus provided with a coating layer were cast in bees wax (100 °C casting temperature, solidification at room temperature) in the manner as represented in Fig. 1, so that it became possible to expose only the covered surface of the knappertje to moist air. The knappertjes were stored in a climate chamber at 20°C with a relative air humidity of 80% and the weight was measured on a regular basis for determining the increase in weight resulting from moisture uptake of the cookie. The measuring results are represented in Fig. 2. The knappertjes provided with a gelatin coating layer exhibit a clear reduction of the rate of moisture migration relative to the non-treated (blank) biscuits.

Example 2. Knappertjes covered with moisture containing composition. The knappertjes provided with a gelatin coating layer and cast in bees wax as described in Example 1 were provided with moisture containing composition by applying jam and a yellow (pastry) cream onto the entire gelatin coating layer, which was exposed to air in Example 1. The moisture migration from the covering to the biscuits was observed by visual inspection of the moisture penetration into the biscuit for a period of some hours to some days. For the purpose of testing, biscuits were used which were not provided with a gelatin coating layer.

It was determined that the moisture migration as a result of the presence of the gelatin coating layer was greatly inhibited and that the biscuits which were provided with the gelatin coating layer remained dry much longer than the control biscuits.

Claims

1. A moisture resistant edible coating layer for composite foods comprising a gel-forming biopolymer in gelled condition.

2. A moisture resistant edible coating layer according to claim 1, wherein the biopolymer is present in an amount of at least 80% by weight based on the dry weight of the coating layer.

3. A moisture resistant edible coating layer according to claim 1 or 2, wherein the biopolymer is a protein or a carbohydrate.

4. A moisture resistant edible coating layer according to any one of the preceding claims, wherein the polymer is selected from the group consisting of optionally modified or derivatized casein, whey protein, ovalbumin, myosin, actin, albumin, gelatin, collagen, inulin, fructo- oligosaccaride, soy polysaccharide, cellulose, starch, agar-agar, alginate, carrageenan, xanthan gum, gum-arabic, locust bean gum, pectin, (arabino)xylanes, and pectin-casein polymers.

5. A moisture resistant edible coating layer according to any one of the preceding claims, wherein the biopolymer is gelatin or starch.

6. A moisture resistant coating layer according to any one of the preceding claims, wherein the coating layer has a thickness between 0.01 mm and 3 mm.

7. A food consisting of at least two components having different moisture contents separated by a coating layer according to any one of claims 1 — 6.

8. A method for the preparation of a food according to claim 7, wherein components having different moisture contents are prepared separately and thereupon are combined, and wherein said coating layer is applied onto the separation surface of components.

9. A method for the preparation of a food according to claim 7, wherein the coating layer is applied by means of spreading, spraying, spouting, atomizing, immerging, brushing or rolling.

10. A method for inhibiting moisture migration between components having different moisture contents in a food according to claim 7, wherein the coating layer is applied as separation between said components and wherein moisture from a component having a higher moisture content is absorbed by the coating layer which prevents, at least reduces, moisture migration to a component having a lower moisture content.