SMOKE- AND WATER VAPOUR-PERMEABLE FOOD CASING WITH OPTIMIZED BONDING PROPERTIES

Abstract

A tubular, seamless, water vapour permeable, smokable, biaxially draw-oriented and partially or completely heat-set food casing is provided having at least two layers based on thermoplastic polymers. At least one layer A, which does not form the inside layer, comprises a blend of aliphatic (co)polyamide and at least one hydrophilic polymer, while the inside layer I comprises a blend of aliphatic or isocyclic (co)poly amide and a block copolymer selected from polyether-amide, polyether-ester and polyether-urethane. The casing is produced by a tubular-film blowing process or a process with biaxial tubular-film draw-orientation. The casing is envisaged more particularly as synthetic sausage casing, especially for smoked raw sausage, such as salami.

Claims

1. Tubular, seamless, water vapour permeable, smokable, biaxially draw-oriented and partially or completely heat-set food casing having at least two layers based on thermoplastic polymers comprising (i) at least one layer A which does not form the inside layer and comprises a blend of aliphatic (co)polyamide and at least one hydrophilic polymer and (ii) an inside layer I comprising a blend of aliphatic or isocyclic (co)polyamide and a block copolymer selected from polyether-amide, polyether-ester and polyether-urethane.

2. Food casing according to claim 1, wherein the hydrophilic polymer is polyvinylpyrrolidone, polyvinyl alcohol or a partially hydrolysed polyvinyl acetate, a copolymer having vinyl alcohol units, a polyalkylene glycol or a copolymer having alkylene glycol units, a polymer of N-vinylalkylamides or a homopolymer comprised of or a copolymer having units of ,-unsaturated carboxylic acids or ,-unsaturated carboxamides.

3. Food casing according to claim 1, wherein the aliphatic or isocyclic (co)polyamide is a polyamide 6, a copolyamide of -caprolactam and -laurolactam (PA 6/12), a copolyamide of -caprolactam, hexamethylenediamine and adipic acid (PA 6/66) or a copolyamide of -caprolactam, 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine) and isophthalic acid.

4. Food casing according to claim 1, wherein the layer A comprises a blend of 60 to 95% by weight of one or more aliphatic (co)polyamides and 5 to 40% by weight of one or more hydrophilic polymers.

5. Food casing according to claim 1, wherein the layer I comprises a blend with 40 to 90% by weight of one or more aliphatic (co)polyamides and 60 to 10% by weight of a block copolymer of the polyether-amide, polyether-ester or polyether-urethane type.

6. Food casing according to claim 1, wherein said food casing consists of the layer I and two layers A having different compositions.

7. Food casing according to claim 1, wherein said food casing has a diameter (calibre) of 28 to 90 mm and a wall thickness of 15 to 80 m.

8. Food casing according to claim 7, wherein said food casing has a diameter (calibre) of 34 to 60 mm.

9. Food casing according to claim 1, wherein the inside layer I has a thickness of 2 to 12 m.

10. Food casing according to claim 1, wherein said food casing exhibits a shrinkage of less than 25% in longitudinal and transverse directions, when placed for one minute into water having a temperature of 90 C.

11. Food casing according to claim 1, wherein said food casing exhibits a shrinkage of 5 to 15% in longitudinal and transverse directions, when placed for one minute into water having a temperature of 90 C.

12. Food casing according to claim 1, wherein said food casing has a water vapour permeability of 80 to 220 g/m.sup.2 d, measured according to DIN ISO 15106-3 with a moisture gradient from 85 to 0% and at a temperature of 23 C.

13. Method of producing a food casing according to claim 1 comprising coextruding in combination with either a tubular-film blowing process or a biaxial tubular-film draw-orientation process.

14. Method according to claim 13, wherein the method further comprises processing the food casing either into sections tied off at one end or into shirred sticks.

15. Synthetic sausage casing comprising the food casing according to claim 1.

16. Synthetic sausage casing as claimed in claim 15, wherein the sausage is air-dried and optionally smoked raw sausage.

17. Synthetic sausage casing as claimed in claim 1, wherein the sausage is salami.

Description

INVENTIVE EXAMPLE 1

Production of a Compound of Polyamide and Polyvinylpyrrolidone

[0053] PA1 and PVP were metered in a mass ratio of 35% to 15% into a commercial twin-screw extruder (barrel diameter 25 mm, L/D ratio 36, 12 barrels, feed points for pellets in barrel 1 and for powders in barrel 7, with two-hole extrusion die, manufacturer: Coperion GmbH). At a screw speed of 200 rpm and with heating in the range from 120 C. to 210 C., the polyamide was melted and was blended with the PVP to form a plastic compound. The transparent extrudate emerging from the die was cooled by immersion in a water bath and, after having solidified, was chopped with a strand chopper to form granular pellets. The pellets were dried in a forced air dryer at about 100 C. The pellets are referred to below as Camp. 1.

INVENTIVE EXAMPLE 2

Production of a Triple-Layer, Biaxially Oriented Casing

[0054] The components according to Table 1 below were supplied to the three extruders of a commercial coextrusion and tubular film drawing unit (double bubble unit with 3-layer coextrusion annular die). In the extruders, the components were melted, homogenized to form blends, and conveyed in the direction of the die. In the die, the melt flows were pressed axially through annular channels and brought together concentrically. The melt film emerging from the annular gap was shaped by means of a calibrator to form a primary tubular film with a diameter of 13 mm, which was cooled to room temperature. The primary tubular film was then heated again to about 80 C. and drawn in the transverse and longitudinal directions by means of an introduced cushion of air. The draw ratios were 3.30 in transverse direction and 1.95 in longitudinal direction. After drawing, the tubular film was passed through pinch rolls, then subjected to a second cushion of air, and guided through a setting tunnel equipped with IR emitters. Here, the tubular film attained a surface temperature of about 150 C. Lastly, the tubular film was pinched off again, cooled in the flat state and wound up. The casing formed had a diameter of 43 mm and a film thickness of 28 to 32 m.

TABLE-US-00001 TABLE 1 Components Proportional supplied % by layer Extruder Designation weight thickness [%] A Comp. 1 85 10 PA2 10 PA-AB 5 B Comp. 1 100 80 C .fwdarw. inner PA2 80 10 layer PEA 15 PA-AB 5

INVENTIVE EXAMPLE 3

[0055] Inventive Example 2 was repeated, except that extruder C was charged with components according to Table 2 below.

TABLE-US-00002 TABLE 2 Components supplied % by Extruder Designation weight C .fwdarw. inner PA2 65 layer PEA 30 PA-AB 5

INVENTIVE EXAMPLE 4

[0056] Inventive Example 2 was repeated, except that extruder C was charged with components according to Table 3 below.

TABLE-US-00003 TABLE 3 Components supplied % by Extruder Designation weight C .fwdarw. inner PA2 75 layer PEE 20 PA-AB 5

INVENTIVE EXAMPLE 5

[0057] Inventive Example 2 was repeated, except that extruder C was charged with components according to Table 4 below.

TABLE-US-00004 TABLE 4 Components supplied % by Extruder Designation weight C .fwdarw. inner PA2 55 layer PEE 40 PA-AB 5

COMPARATIVE EXAMPLE 1 (C1)

[0058] Inventive Example 2 was repeated, except that extruder C was charged with components according to Table 5 below.

TABLE-US-00005 TABLE 5 Components supplied % by Extruder Designation weight C .fwdarw. inner PA2 65 layer Comp. 1 30 PA-AB 5

COMPARATIVE EXAMPLE 2 (C2)

[0059] Inventive Example 2 was repeated, except that extruder C was charged with components according to Table 6 below.

TABLE-US-00006 TABLE 6 Components supplied % by Extruder Designation weight C .fwdarw. inner PA2 95 layer PA-AB 5

COMPARATIVE EXAMPLE 3 (C3)

[0060] Production of a single-layer, biaxially oriented casing The components according to Table 7 below were supplied to the extruder of an extrusion and tubular film drawing unit (double bubble unit with 1-layer extrusion annular die). In the extruder, the components were melted, homogenized, and conveyed in the direction of the die. In the die, the melt flow was pressed axially through an annular channel. The melt film emerging from the annular gap was shaped by means of a calibrator to form a primary tubular film with a diameter of 14 mm, which was cooled to room temperature. The primary tubular film was then heated again to about 80 C. and drawn in the transverse and longitudinal directions by means of an introduced cushion of air. The draw ratios were 3.07 in transverse direction and 2.15 in longitudinal direction. The further steps took place in analogy to Inventive Example 2. The seamless casing formed had a diameter of 43 mm and a film thickness of 23 to 28 m.

TABLE-US-00007 TABLE 7 Components supplied % by Extruder Designation weight A .fwdarw. total PA2 10 layer Comp. 1 85 PA-AB 5

[0061] To assess the casings, measurements were made of the water vapour permeability under laboratory conditions, and application-related testing was performed. The latter provided information on the permeability of the casings under real-life conditions and about the adhesion to the filling. The filling was raw sausage (salami). The results are compiled in Table 8.

[0062] The procedure for the application-related testing was as follows:

[0063] Sections of casing were filled, at constant filling pressure, with commercial salami sausage filling, then sealed at the ends with metal clips and weighed. The filled casings were hung in a conditioning chamber and brought to fermentation, maturation and drying, using a temperature and humidity profile customary for salami. The total residence time in the conditioning chamber was 14 days. Subsequently, measurements were made of the change in weight of each sausage. To test the adhesion of the casings to the sausage surface, the sausages were divided into slices with a thickness of about 2 cm. The casing lying on the slices was severed axially. At the point of separation, the casing was lifted and peeled off manually in the circumferential direction. An assessment was made according to a scale of ratings from 1 to 10: [0064] 1=no adhesion at all; casing can be peeled off without force, no adhesions to meat [0065] 5=distinct adhesion: casing can be peeled off with moderate application of force, minimal adhesions to meat [0066] 10=very strong adhesion: peeling requires high force, and relatively large pieces of meat are torn out at the same time

TABLE-US-00008 TABLE 8 Test results Water vapour Weight loss Rating for Exam- permeability.sup.1) of filled peeling ple [g/m.sup.2 d] sausage behaviour I2 142 21 3 I3 175 22 1 I4 118 17 4 I5 138 20 2 C1 181 23 9 C2 19 6 6 C3 219 25 10 .sup.1)measured according to ISO 15106-3 with a moisture gradient of 85% to 0% relative humidity and at 23 C.

[0067] The above data confirm that the casings with an inside layer comprised in accordance with the invention have only low to moderate adhesion to the salami filling. For the casings where the layer on the inside has a prior-art composition, in contrast, the adhesion is at a medium to high level. The data further demonstrate that the moisture permeability of the casings of the Invention is at approximately the same level as for prior-art casings (C3).