Edible molded bodies, especially flat and flexible tubular films

This application is a 371 of PCT/EP97/07212, filed Dec. 19, 1997.

The invention relates to edible shaped bodies based on plastifiable biopolymers, cleavage products or derivatives thereof and/or synthetic polymers made from natural monomers. They are mainly used as packaging films, and sausage casings.

As edible sausage casings, there have proved useful, in addition to natural casings (for bockwurst especially sheep gut), only collagen films and tubes (DE-B 17 92 627 and U.S. Pat. No. 3,535,125). Edible casings based on calcium alginate (DE-B 12 13 211) have not been able to establish themselves.

Edible collagen films and tubes are produced from cattle hides by a very complex and environmentally-polluting process. The hides are digested with acids (e.g. lactic acid) until the fibrils are obtained; the high-viscosity mass is extruded and precipitated and consolidated slowly and compactly using gaseous NH 3 or with NH 4 OH. During drying, crosslinking (curing) then takes place, which strengthens the products to the extent that they withstand the scalding process without any significant loss of mechanical stability.

In contrast, it has not been possible to give the alginate-based sausage casings the necessary stability. In the case of these casings, owing to the action of the sausage emulsion and the brine, the poorly soluble calcium salt is gradually converted into the readily soluble sodium salt of alginic acid. The casings as a result lose their strength.

It was the object of the invention to provide edible shaped bodies, in particular flat and tubular films, which no longer have the abovedescribed disadvantages. In addition, they are to be able to be produced from natural raw materials in a simple, inexpensive and environmentally friendly manner. For the use as sausage casings, in addition, the tubular films are to have the required functional properties. In addition to the mechanical, swelling and shrinkage properties, these include especially sufficient heat stability, scalding stability and hydrolysis stability. This means they must also be sufficiently resistant to the hot water or superheated steam used for the scalding.

The object is achieved by providing an edible shaped body in, the form of a flat or tubular film based on plastifiable biopolymers or cleavage products or derivatives thereof and/or synthetic polymers of natural monomers which is produced by a process having the following stages:

a) mixing the biopolymers, cleavage products or derivatives thereof and/or the synthetic polymers with at least one edible plasticizer, at least one lubricant and at least one crosslinker, b) melting the resultant mixture to give a thermoplastic mass, c) extruding this mass and d) calendering and/or stretching or blowing the product obtained from the extrusion to give the edible shaped body.

In a preferred embodiment, the biopolymers, the cleavage products thereof and/or the synthetic polymers are first mixed with the plasticizer and the lubricant and processed to form a thermoplastic mass. Not until then is this mass admixed with the crosslinker and extruded.

The edible shaped body can also have a different shape than that of a flat or tubular film. Instead of stage d), or in addition to this stage, if appropriate, other shaping processes then occur, such as injection molding or thermoforming. An example of a shaped body produced in this manner is edible table utensils.

The process stages c) and d) need not follow one another directly. It is also possible to store the extruded mass in the interim, e.g. in the form of granules. If it is desirable or required for the respective application, the flat films or tubes of the invention can in addition be partly or completely heat-set.

Depending on the shape of the die (annular or slit-shaped), sheets or tubes form during the extrusion from the thermoplastic mixture, and can then be converted, by calendering and/or stretching in the longitudinal and/or transverse direction, or by blowing, into flat films or seamless tubular films. If required, the material is heated during the blowing, calendering or stretching (again). The edible flat or tubular films of the invention generally have a thickness or wall thickness of from 20 to 120 μm, preferably from 30 to 60 μm. In the case of the tubular films, the wall thickness generally increases with increasing internal diameter. By means of the stretching or blowing, the shaped body gains further mechanical strength.

The shaped body of the invention has the particular advantage that it may be produced in a particularly environmentally friendly manner without special precipitation and wash baths or any other sorts of baths. In the production process, the generally customary apparatuses for mixing and extrusion, in particular kneaders and single- or twin-screw extruders, can be used.

Preferred examples of the plastifiable biopolymers, of their likewise plastifiable cleavage products or derivatives and of plastifiable synthetic polymers are thermoplastic starch, starch derivatives (in particular starch esters, especially starch acetates and starch propionates; and in addition also starch ethers, especially starch alkyl ethers), extrudable gelatins and other natural proteins, such as maize protein, wheat protein and rapeseed protein, casein and is derivates, chitin and chitosans, alginic acids and alginates, carrageenan (a galactose polysaccharide produced from seaweed), dextran, galactomannans (from carob bean meal, guar gum), pectins (polygalacturonic acids and methyl esters thereof) and polylactic acid (=polylactides). For the shaped bodies of the invention, there is thus a broad selection of starting materials of vegetable and animal origin available. Collagen is unsuitable. It is not available in consistent quality. The content of the biopolymers or cleavage products or derivatives thereof and/or of the synthetic polymers is generally from 10 to 90% by weight, preferably from 15 to 80% by weight, in each case based on the total weight of the shaped body.

Preferably, two or more of the starting materials are used together. They are expediently uniformly mixed and plastified at relatively high temperatures by relatively long kneading in a twin-screw extruder in the presence of a plasticizer, a plasticizing aid (=lubricant), a hardener (=crosslinker) and, if appropriate, a filler.

Suitable plasticizers are glycerol, diglycerol, sorbitol, sorbitol esters, triglycol, carboxymethylcellulose and other compounds which are suitable for food contact and are preferably already officially approved. The content of the plasticizer is generally from 0.5 to 50% by weight, preferably from 2 to 25% by weight, in each case based on the total weight of the shaped body.

Suitable plasticizing aids or lubricants are, especially, vegetable oils, in particular sunflower seed oil, rapeseed oil, olive oil and poppyseed oil. In addition, compounds suitable for use in foods, such as lecithins, triethyl acetylcitrate, sucrose esters, lactones (such as 12-hydroxystearic lactone), lactams and synthetic triglycerides. The content of lubricant(s) is generally from 2 to 30% by weight, preferably from 5 to 20% by weight, in each case based on the total weight of the shaped body.

Hardeners or crosslinkers which can be used are caramel (caramelized sugar, maillose), woodsmoke condensate, sugar aldehydes, dialdehydes (especially glyoxal and glutardialdehyde), dicarboxylic acids (particularly aliphatic dicarboxylic acids, such as oxalic acid, malonic acid, adipic acid and succinic acid), dicarboxylic anhydrides (partiuclarly adipic-acetic, anhydride=diacetyl adipate), di- or triisocyanates (especially hexamethylene diisocyanate) and di- or triepoxides, polysaccharide aldehydes (particularly dialdehyde starch, dialdehyde alginic acid, dialdehyde pectic acid, dialdehyde gum tragacanth and dialdehyde gum arabic). Generally, suitable crosslinkers are those compounds which contain at least two reactive groups. The content of crosslinker(s) is generally from 0.2 to 30% by weight, preferably from 0.5 to 25% by weight, particularly preferably from 1 to 10% by weight, in each case based on the total weight of the shaped body.

For edible films, which are, for example, to be used for wrapping cooked ham, and are thus not exposed to high mechanical loading, crosslinkers of relatively weak action are sufficient, such as dicarboxylic acids, sugar aldehydes (mono- and-disaccharides) or caramel. Sausage casings which are exposed to a higher mechanical load, especially during stuffing, and must also withstand the scalding process undamaged, in contrast, should be considerably more intensively crosslinked, which can be achieved particularly well by the use of a plurality of crosslinkers. For these, in addition, use may be made of dialdehydes, such as glyoxal or glutardialdehyde, di- or triisocyanates or di- or triepoxides.

To strengthen the shaped bodies of the invention, the mixture, if appropriate, can further comprise fibers, preferably woodpulp fibers or cotton linters, and/or pigments, in particular inorganic pigments such as calcium carbonate.

Woodpulp fibers having a length of from 0.2 to 5 mm, preferably from 0.5 to 2 mm, are particularly suitable. The fiber content is expediently from 2 to 30% by weight, preferably from 5 to 20% by weight, in each case based on the total weight of the shaped body.

Although the short pulp fibers which act to strengthen are not digestible, as dietary fiber they do promote digestion. They are preferably disposed in a compact middle layer by using special dies, i.e. a layer of a fibrous polymer pulp is extruded into two fiber-free layers. It is also certainly possible to distribute the fibers over the entire cross-sectional area, i.e. to extrude only one fibrous polymer mixture. It is frequently advantageous to incorporate, in addition to the fibers, fillers, such as leather shavings.

As polymeric starting material, particular preference is given to mixtures of thermoplastic starch with an extrudable protein, particularly preferably gelatin. The ratio of starch to protein in this case is generally from 95:5 to 5:95. To improve stability to moisture and heat, in addition, chitosan or pectin can be added in an amount of from 3 to 30% by weight, preferably from 5 to 20% by weight, in each case based on the total weight of the polymer mixture. Mechnical stability can be increased still further if the thermoplastic starch is completely or partially replaced by starch acetate. By mixing in from 5 to 25% by weight, preferably from 8 to 22% by weight, of glycerol (in each case based on the total weight) and from 2 to 20% by weight, preferably from 5 to 15% by weight, of a natural oil, e.g. sunflower seed oil, the mixture is made soft and flowable, to simplify extrusion.

For hardening, in a preferred embodiment, from 0.8 to 5% by weight, preferably from 1 to 3% by weight, of caramel and, in addition, from 0.5 to 10% by weight, preferably from 1 to 5% by weight, of a dicarboxylic acid, such as oxalic acid, malonic acid or succinic acid, are mixed in.

For edible sausage casings it is expedient to add from 1 to 10% by weight, preferably from 2 to 6% by weight (based on total weight of all components) of a dialdehyde, such as glyoxal or glutardialdehyde, a diisocyanate, such as hexamethylene diisocyanate, a diketene, a diepoxide, a lactam or lactone (e.g. 6-gluconolactone). The mixture is melted and uniformly mixed by relatively long kneading at from 90 to 170° C., preferably at from 95 to 150° C. The melt can then either be immediately extruded or granulated for later processing.

The edible seamless tubes in a caliber range from 16 to 50, preferably from 18 to 30, are expediently produced by extruding through a ring die, followed by blowing. The area stretching ratio during blowing is generally from 1:5 to 1:20, preferably from 1:6 to 1:10, particularly preferably about 1:8.

The tubes can then, in a subsequent process step, be treated internally or internally and externally and thus further modified in their properties. In particular, post-hardening can be carried out here, either using ionizing radiation, e.g. with X-rays, or with the abovementioned hardeners and crosslinkers. These can then be applied in the form of solutions or dispersions. The tubes are then (as usual) dried in the inflated state between two pairs of squeeze rolls. This is followed by a generally known manufacturing step. Generally, the tubes are gathered in sections and the resultant shirred sticks are processed on conventional machines. The seamless tubular films are particularly suitable as sausage casings, in particular for small sausages. In addition, the shaped bodies of the invention are also suitable for packaging other foods, e.g. cheese.

The broad base of natural starting polymers, additives and crosslinkers in addition makes possible a very broad variation of the properties expected of food casings, so that shaped bodies may be adapted precisely to highly specific requirements, as shown by the following examples. Percentages are percentages by weight, unless stated otherwise.