CA1131981A

CA1131981A - Shaped material formed of collagen and gelatin

Info

Publication number: CA1131981A
Application number: CA353,742A
Authority: CA
Inventors: Tadaaki Kato; Naohiro Murayama
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1979-06-12
Filing date: 1980-06-11
Publication date: 1982-09-21
Also published as: FR2458224A1; NL8003401A; AU520503B2; DE3021780C2; JPS55165999A; GB2052518B; FR2458224B1; GB2052518A; AU5917980A; DE3021780A1

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention related to a shaped material prepared from one part by weight of collagen showing an isoelectric point of not exceeding pH
6.2 and 0.05 to 2 parts by weight of gelatin. The shaped material is usually an edible film used to wrap food, e.g., meats and the like. The film has increased tear strength without the usual increased film thickness.

Description

BACKGROUND AND DETAILED DESCCRIPTION OF THE INVENTION:
The present invention relates to a shaped material formed of collagen and gelatin.
Hitherto, collagenous shaped materials have been prepared as follows:
the skin of a mammal is sliced into a suitable size and is treated with an aqueous 0.1 to 3% alkaline solution of, for instance, calcium hydroxide, sodium hydroxide or sodium sulfide to depilate it. After finely cutting the depilated skin by a mincing machine, it is swollen in an acidic or alkaline medium. The swollen material is then crushed by a crushing opener, and there-after collected as an aqueous dispersion of collagenous fibers. In the nextstep various shaped materials such as films, threads, non-woven cloths are prepared from the aqueous dispersion of collagenous fibers.
However, in cases where the finely cut skin of the mammal is mechanically treated by agitation or crushing vigorously in an aqueous medium of a range of pH at which collagen is apt to be dissolved or swollen, the collagenous fibers of the skin are broken or cut into fibrils. The thus obtained dispersion of collagenous fibrils has many defects in processability and of thermal denaturation due to friction heat when mechanically agitated or crushed. Moreover, since the length of collagenous fibrils is not uniform and short, the mechanical properties of the shaped material prepared from such a collagenous dispersion, partioularly the tear strength is unfavorable.
AcoordinKly, where oollagen fibers are shaped lnto, for instance, edible film, the improvement of the meohanioal strength of the film, parti-cularly of the tear-strength has hitherto been effected by increasing the thickness of the film.
However, with this method, the alien funotional feeling when food wrapped by the film is taken into the mouth inoreases as the thiokness of the -.
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113~981 film increases. Therefore, it is not preferable to strengthen the film by increasing its thickness, and there is a necessity for a thin film having greater strength without the undesirable thickness.
The inventors of the present invention, after having studied the de-pilating step and the shaping step of the previous processes, especially those used to produce films of great tear-strength, have found that the mechanical strength of the shaped material is remarkably improved by adjusting the iso-electric point of collagen of depilated, purified and finely cut skin to a pH
value lower than 6.2, and adding gelatin to the dispersive liquid in which lQ collagen fiber is dispersed.
Thus the present invention provides a shaped material comprising one part by weight of collagen having an isoelectric point designated by a pH
value not exceeding 6.2, and from 0.05 to 2 parts by weight of gelatin.
In another aspect of this invention provides an edible shaped material prepared by applying an electric current to an aqueous dispersion containing collagen and gelatin. A further aspect of this invention provides a method for preparing the shaped material which comprises admixing gelatin with an aqueous dispersion of collagen having an isoelectric point designated by a pH
value not exceeding 6.2; adjusting the pH value of the admixed aqueous dis-persion so that it ranges from 3 to 3.5 by addition of an aqueous acidic solution; and subjecting the pH adjusted aqueous dispersion to a shape-formation step to obtain the shaped material. The shaped material produced by thls method has a mechanlcal strength whlch is greater than that oP a shaped materlal formed substantially oP collagen.
The collagen for use in the process and material according to the present invention is prepared as follows.
Usually the isoelectric point of collagen derived from a mammal's hide

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is designated by a pH value in the range of from 6.2 to 7.5 and it is said that the pH changes to a lower value depending on the age of the mammal. In the case of the present invention, the isoelectric point of the collagen derived from mammal's hide is preferably lowered by acetylation or cross-linking to a pH value less than 6.2. In cases where the isoelectric point of collagen of the hide as the raw material is lower than pH 6.2, the above-mentioned treatment of acetylation or cross-linking may be omitted.
The acetylation is carried out by immersing the hide into acetic an-hydride or a mixture of acetic anhydride and acetic acid after finely cutting the hide into 3 to 15 mm squares, preferably into 5 to 8 mm squares. By this treatment, the isoelectric point of collagen of the hide is gradually reduced to a constant value of about pH 3.8. In the process according to the present invention, however, it is enough to lower the isoelectric point to a pH of 6.2. In the case of cross-linking, a cross-linking agent is utilized to lower the isoelectric point to less than pH 6.2. The conditions of cross- linking depend on the kind of collagen of the hide. However, usually the preferred amount of the cross-linking agent for use in this case is O.l to lO parts by weight per lO0 parts by weight of collgen of the hide. The preferred temperature for cross-linking is lower than 30 C, preferably for 3 to 24 hours of treatment. As a cross-linking agent, an aldehyde such as formaldehyde, glyoxal, glutaraldehyde, dialdehyde-staroh and dialdehyde-dextrin is utlllzed and a polyhydrlo alcohol suoh as ethyle~e glyool, glycerol, sorbltol and sugars is also utilized.
The thus treated collagen of the hide of which the isoelectric point has been adjusted to less than pH 6.2 is acid-swollen and opened by a well known method to be an aqueous dispersion for use in the preparation of the ':

shaped material~ That is, the collagen of the hide of which the isoelectric point has been adjusted is immersed into an aqueous hydrochloric acid solution, having a pH of 2 to 6 for 5 to 30 hours to render it sufficiently swollen and then it is subjected to the treatments of loosening, mashing and squashing to be opened. In this treatment, the collagen of the hide of which the isoelectric point has been adjusted is opened to long fibers without being more finely divided into fibrils or a molecular state. Even in the case where the thus obtained dispersion of the opened collagen fibers is shaped into a shaped material by subjecting it to direct vacuum-de-bubbling, a shaped material of greater strength is obtainable as compared to a shaped material prepared from a dispersion of collagen in which the pH adjustment has not been made. However, the strength of the shaped material is believed to be improved by adding and mixing gelatin into the above-mentioned dispersion before shaping. The amount of gelatin admixed with the dispersion is 0.05 to 2, preferably 0.2 to 1.5 parts by weight per 1 part by weight of the amount of collagen fibers in the dispersion.
In cases~where the additional amount of gelatin is less than 0.05 part by weight, the strength of the shaped material prepared from the dispersion is not 90 much improved, and on the other hand, in cases where the amount is larger than 2 parts by weight, the water-content of the shaped material is too great to keep the shape of the processed material. In addition, the gelatin added to the dlsperslon may be a crude ~elatin obtained by roughly arushin~ a depilated and purified aattle-hide and keeping the crushed hide at a temper-ature of about ~0 C for more than 24 hours, and thus other than a commercial gelatin.
` The strength, particularly the tear-strength of the shaped product prepared by extruding or electrodepositing the dispersion of the collagen - ' ' .

1~31981 containing the co-existing gelatin after adjusting the concentration and the pH of the dispersion to predetermined values, respectively is remarkably im-proved as compared to that of a conventional product.
The present invention is illustrated in more detail in the following Examples and Comparative Examples.
EXAMPLE 1:
A steer-hide product of North America having an isoelectrical point of pH 6.5 was depilated, purified and finely cut into pieces of 5 to 8 mm square. Forty grams (10 g in dry weight) of the pieces of the hide was immersed into 500 ml of an aqueous 0.25~ glutaraldehyde solution for 3 hours and then after washing the pieces of the hide twice with one liter of de-ionized water, they were swollen in an aqueous hydrochloric acid solution at pH 2 for 15 hours. The isoelectric point of the collagen in the treated hide with the aldehyde was lowered to pH 5.7.
The acid-treated hide was then dispersed into one liter of de-ionized water by using a juice-mixer and after filtration, an aqueous dispersion of collagen having a concentration of one percent was obtained.
After admixing 40 g (10 g in dry weight) of crude gelatin into the above dispersion of the collagen, the pH of the dispersion was adju-sted to 3 to 3.5 by using an aqueous 3N hydrochloric acid solution and after de-bubbling ~; the dispersion under vacuum, it was subjected to film formation by electro-deposition in the form of an eleatrophoretiaally depasited film on the oathode side. The thus obtained fllm of S cm x 10 am in dimension was tested for its tear-strength in a wet state by an Elemendorf tear-strength tester. The re~ult showed that the film of 15 microns in thiakness had a tear-strength of 40 g./am/am in a wet state.
COMPARATIVE EXAMPLE 1:
After preparing a dispersion of the collagen, not containing any addi-tional gelatin, from the same raw material according to the same procedures in Example 1, the dispersion was subjected to electrodeposition to form a collagen film deposited on the cathode by electrophoresis of the collagen fibers. After air-drying the tar strength of the thus obtained collagen film of dimension 5 cm x 10 cm was determined by an Elemendorf tester at a wet state. The tear-strength of the coll~gen film, which had a 15 micron thick-ness, was 25.5 g.cm/cm.
The tear-strength of another collagen film of 14.3 micron thickness prepared from the same raw material according to the same procedures of Example 1, however, without the step of reaction with glutaraldehyde, was 8.4 g.cm/cm.
EXAMPLE 2:
Forty grams of a depilated and purified cattle-hide (steer-hide, pro-duct of North America), finely cut into 5 to 8 mm square showing an iso-electric point of pH 6.5, was immersed in 100 ml of acetic anhydride at a temperature of lower than 20 C for 8 hours to effect acetylation.
The thus obtained acetylated hide was washed with flowing de-ionized water for 6 hours, and then it was acid-swollen in 500 ml of an aqueous hydro-chloric acid solution having a pH of 2 for 15 hours.
After acetylation, the isoelectric point of the collagen in the treated hide was changed to pH 3.8.
The acid-swollen and acetylated hide was dispersed into one llter o~
de-ionized water by using a mixer and the thus obtained dispersion was filtered to provide a dispersion of collagen having a concentration of 1% by weight.
After admixing 20 g (5 g in dry weight) of crude gelatin used in Example 1 into the above dispersion oP collagen, ad~usting the pH of the dis-persion to 3 to 3.5 with the addition of an aqueous 3N hydrochloric acid sol-ution and then de-bubbling the dispersion under vacuum, the thus treated , . . .
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dispersion is subjected to film formation according to the procedures as in Example 1. The tear-strength of the thus obtained film in a wet state was 50 g.cm/cm, the thickness of the film being 20 microns.
COMPARATIVE EXAMPLE 2:
The tear-strength of a collagen film prepared from the same raw material and by the same procedures as in Example 2, except for the absence of the crude gelatin, having a thickness of 20 microns was tested and found to be 34.5 g.cm/cm in a wet state.
EXAMPLE 3:
Forty grams (10 g in dry weight) of cattle-hide from a Holstein treated by depilation and purification and finely cut into 5 to 8 mm squares having isoelectric point of pH 5.3 was acid-swollen in 500 ml of an aqueous hydrochloric acid solution of pH 2 for 15 hours. They were dispersed into one liter of de-ionized water by using a mixer to obtain a dispersion of collagen having a concentration of 1% by weight.
After admixing 12 g (3 g in dry weight) of the crude gelatin used in Example 1 into the above-mentioned dispersion, adjusting the pH of the mixture to 3 to 3.5 by adding an aqueous 3N hydrochloric acid solution and then de-bubbling the resultant ~ispersion, it was subjected to film formation by the same procedures as in Example 1. The-tear-strength of the thus prepared film of 17.5 micron thickness was 45 g.am/cm in a wet state.

The tear-Qtrength of a film of 18 micron thickness prepared from the same raw material and by the same procedures in Example 3, except for the absence of the crude gelatin in the dispersion, was 33 g.cm/cm.
EXAMPLE 4:
One hundred and twenty grams (30 g in dry weight) of cattle-hide from a ; Hol~tein prepared by depilation and purification and finely out into 5 to 8 mm - `'' , -.
squares having an isoelectric point of pH 5.3 was acid-swollen in 1.5 of an aqueous hydrochloric acid solution, pH 2 for 15 hours. They were dispersed into one liter of de-ionized water by using a mixer to obtain a dispersion of collagen of concentration 3% by weight.
After admixing 120 g (30 g in dry weight) of the crude gelatin used in Example 1 into the above dispersion, adjusting the pH of the mixture to 3 to

3.5 by adding an aqueous 3N hydrochloric acid solution and then de-bubbling the resultant dispersion, a film of 29 micron thiclcness was obtained by ex-truding the resultant dispersion from a slit of 10 cm length and 0.3 mm width into 0.06N aqueous ammonium hydroxide solution, neutralizing and then air-drying.
With this film, the tear-strength of the rectangular direction to the extrusion direction is 69.5 g.cm/cm.
GOMPARATIVE EXAMPLE 4:
The tear-strength of a film of 30 micron thickness prepared from the same raw material and by the same procedures as in Example 4, except for the absence of the crude gelatin in the dispersion, was 51 g.cm/cm.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a shaped material formed of collagen and gelatin, wherein the mechanical strength of said shaped material is higher than the mechanical strength of a shaped material formed substantially of collagen, said method comprising:
admixing (a) 0.05 to 2 parts by weight of gelatin with (b) an aqueous dispersion of one part by weight of collagen, which has an isoelectric point of pH not exceeding 6.2;
adjusting the pH of the admixed aqueous dispersion to from 3 to 3.5 with the addition of an aqueous acid solution; and subjecting the pH adjusted aqueous dispersion to shape-formation to obtain said shaped material.

2. The method according to claim l, wherein said collagen shows an isoelectric point of pH of less than 6 and is prepared from cattle hide or pig hide.

3. The method according to claim 2, wherein said collagen is prepared by first cross-linking or acetylating said hide thereby to reduce the isoelectric point of the original collagen in said hide and then finely dividing said hide into fibers of collagen.

4. The method according to claim 3, wherein said cross-linking is effected by reaction with glutaraldehyde.

5. The method according to claim 1, wherein said shaped material is formed by electrodeposition.

6. The method according to claim 5, wherein said aqueous solution contains one part by weight of collagen having an isoelectic point of pH not exceeding 6.2, from 0.05 to 2 parts by weight of gelatin and a suitable amount of a diluted hydrochloric acid solution.

7. The method according to claim 1, wherein said shaped material is formed by an extrusion process.

8. A shaped material comprising:
one part by weight of collagen of an isoelectric point of pH of not exceeding 6.2, and 0.05 to 2 parts by weight of gelatin whenever prepared by the process of claim 1 or an obvious chemical equivalent thereof.

9. A shaped material comprising:
one part by weight of collagen of an isoelectric point of pH of not exceeding 6.2, and 0.05 to 2 parts by weight of gelatin whenever prepared by the process of claim 5 or an obvious chemical equivalent thereof.