GB2052518A

GB2052518A - Materials formed of collagen and gelatin

Info

Publication number: GB2052518A
Application number: GB8019041A
Authority: GB
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1979-06-12
Filing date: 1980-06-11
Publication date: 1981-01-28
Also published as: DE3021780A1; JPS55165999A; CA1131981A; GB2052518B; DE3021780C2; NL8003401A; FR2458224B1; FR2458224A1; AU520503B2; AU5917980A

Abstract

A material formed of collagen and gelatin may be produced by admixing gelatin with an aqueous dispersion of collagen of an isoelectric point not exceeding 6.2 in an amount of 0.05 to 2 parts by weight of gelatin per part by weight of collagen; adjusting the pH of the mixture to from 3 to 3.5 by the addition of an aqueous acid solution; and forming said material therefrom. The mechanical strength of such a material, in particular its tear strength, is higher than that of a corresponding material made from collagen only. The collagen may be prepared by first cross-linking or acetylating a hide to reduce the isoelectric point of the original collagen in said hide and then obtaining collagen fibres from the thus-treated hide. Electrodeposition and extrusion techniques can be employed to produce the material, which can be used as an outer skin for foods. The material, in aqueous dispersion, may be treated by application of an electric current.

Description

SPECIFICATION Materials formed of collagen and gelatin The present invention relates to a material formed of collagen and gelatin and to its preparation.

Hitherto, collagenous shaped materials have been prepared by slicing the skin of a mammal into a suitable size and treating it with an aqueous 0.1 to 3% alkaline solution of, for instance, calcium hydroxide, sodium hydroxide or sodium sulfide to remove hair from it. After finely cutting up the skin in a mincing machine, it is swollen in an acidic or alkaline medium. The swollen material is opened by a crushing opener and is collected as an aqueous dispersion of collagenous fibers.

Various shaped articles such as film, threads and non-woven cloths can be prepared from this dispersion of fibers.

However, in cases where finely cut mammal skin is mechanically treated by vigorously agitating or crushing it in an aqueous medium at a pH at which collagen is apt to be dissolved or swollen, the collagen fibers are broken or cut into fibrils. This dispersion has several disadvantages as regards its ability to be processed. The fibrils may also be denatured by the frictional heat caused by the mechanical agitation or crushing of the dispersion. Moreover, since the length of collagenous fibrils is not uniform and is generally short, the mechanical properties of the shaped articles prepared from such a dispersion, particularly tear strength, are unfavorable.

Accordingly, when shaping collagen fibers into, for instance, edible films, the mechanical strength of the film, particularly its tear-strength, has hitherto been improved by increasing the thickness of the film. However, the alien feeling when foods wrapped by such films are eaten is stronger because of the increase of the thickness a the film. Therefore, it is not preferable to strengthen the film by increasing its thickness.

It has now been discovered that the mechanical strength of a material incorporating collagen fibers, especially the tear strength of a film, can be improved by using collagen which has an isoelectric point not exceeding 6.2 obtained from depilated, purified and finely cut skin, and by including gelatin in the continuous phase of the dispersion of collagen fibers from which the material is produced.

Accordingly, the present invention provides a material comprising collagen with an isoelectric point not exceeding 6.2 and gelatin, the gelatin being present in an amount of from 0.05 to 2 parts by weight per part by weight of said collagen.

The present invention further provides an edible material prepared by applying an electric current to an aqueous dispersion containing collagen and gelatin.

The present invention also provides a process for preparing a shaped material formed of collagen and gelatin, wherein the shaped material has a mechanical strength higher than that of a shaped material substantially formed of collagen, the method comprising: admixing gelatin with an aqueous dispersion of collagen showing an isoelectric point of pH of not exceeding 6.2; adjusting the pH of the admixed aqueous dispersion into 3 to 3.5 with an addition of an aqueous acid solution; and forming the thus adjusted aqueous dispersion into the shaped material.

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 is 6.2 to 7.5 in pH and it is said that the pH changes to a lower value accompanying the age of the mammal, and in the case of the present invention, the isoelectric point of the collagen derived from mammal's hide is lowered by acetylation or cross-linking to less than 6.2. In cases where the isoelectric point of collagen of the hide as the raw material is lower than 6.2 in pH, the above-mentioned treatment of acetylation or cross-linking may be omitted.

The acetylation is carried out by immersing the hide into acetic anhydride or a mixture of acetic anhydride and acetic acid after finely cutting the hide into 3 to 1 5 mm square, preferably into 5 to 8 mm square. By this treatment, the isoelectric point of collagen of the hide is gradually reduced to a constant value of about 3.8 in pH. In the process according to the present invention, however, it is enough to make the isoelectric point of lower than 6.2 in pH. In the case of crosslinking, a cross-linking agent is utilized to reduce the isoelectric point lower than 6.2 in pH.The conditions of cross-linking depend on the kind of collagen of the hide, however, usually the preferable amount of the cross-linking agent for use in this case is 0.1 to 10 parts by weight of 100 parts by weight of collagen of the hide, at a preferable temperature of cross-linking of lower than 300C preferably for 3 to 24 hours of the treatment. As a cross-linking agent, an aldehyde such as formaldehyde, glyoxal, glutaraldehyde, dialdehyde-starch and dialdehyde-dextrin is utilized and a polyhydric alcohol such as ethylene glycol, glycerol, sorbitol and sugars is also utilized.

The thus treated collagen of the hide of which the isoelectric point has been adjusted to lower than 6.2 in pH is acid-swollen and opened by a 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 of pH of 2 to 6 for 5 to 30 hours to be sufficiently swollen and then it is processed by 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 molecular state.Even in the case where the thus obtained dispersion of the opened collagen fibers is shaped into a shaped material after subjecting to direct vacuum-de-bubbling, a shaped material of larger strength is obtainable as compared to a shaped material prepared from a dispersion of collagen to which the adjustment of the isoelectric point has not been carried out.

However, the strength of the shaped material is possibly 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 so 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 becomes larger not enough to keep the shape of the processed material. In addition, the gelatin added to the dispersion may be a crude gelatin obtained by roughly crushing a depilated and purified cattle-hide and keeping the crushed hide at a temperature of about 800C for more than 24 hours, 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 containing the co-existing gelatin after adjusting the concentration and the pH of the dispersion to predetermined values, respectively is remarkably improved as compared to that of the conventional product.

The present invention is explained more in detail while referring to Examples and Comparative Examples as follows: EXAMPLE 1 Stea-hide product of North America showing an isoelectrical point of 6.5 in pH was depilated and 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 two times with each one liter of de-ionized water, they were swollen in an aqueous hydrochloric acid solution at a pH of 2 for 1 5 hours. The isoelectric point of the collagen in the treated hide with the aldehyde was lowered to 5.7 in pH.

The thus acid-treated hide was dispersed into one liter of de-ionized water by using a juice-mixer and after filtration, an aqueous dispersion of collagen of a concentration of one percent was obtained.

After admixing 40 g (10 g in dry weight) of crude gelatin into the above-mentioned dispersion of the collagen, the pH of the dispersion was adjusted 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 electrophoretically deposited film in the cathode side. The thus obtained film of 5 cm x 10 cm in dimension was tested of its tearstrength in a wet state by an Elmendorf tearstrength tester. The resuit showed that the film of 1 5 microns in thickness showed a tear-strength of 40 g cm/cm in a wet state.

COMPARATIVE EXAMPLE 1 After preparing a dispersion of the collagen, not containing any additional gelatin, from the same raw material according to the same procedures in Example 1, the dispersion was subjected to electrodeposition to be a collagen film deposited on the cathode by electrophoresis of the collagen fibers. After air-drying the thus obtained collagen film of 5 cm x 10 cm in dimension, the tearstrength of the film was determined by an Elmendorf tester at a wet state. The tear-strength of the collagen film thus prepared of 15 microns in thickness was 25.5 g cm/cm.

The tear-strength of another collagen film of 14.3 microns in thickness prepared from the same raw material according to the same procedures of Example 1, however, without subjecting to the reaction with glutaraldehyde was 8.4 9 cm/cm.

EXAMPLE 2 Forty grams of a depilated and purified cattlehide (Stea-hide, product of North America), finely cut into 5 to 8 mm square showing an isoelectric point of 6.5 in pH was immersed in 100 ml of acetic anhydride at a temperature of lower than 200C 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 hydrochloric acid solution of pH of 2 for 1 5 hours.

After acetylation, the isoelectric point of the collagen in the treated hide was changed to 3.8 in pH.

The acid-swollen and acetylated hide was dispersed into one liter of de-ionized water by using a mixer and the thus obtained dispersion was filtered to be a dispersion of collagen of a concentration of 1% by weight.

After admixing 20 g (5 g in dry weight) of crude gelatin used in Example 1 into the abovementioned dispersion of collagen, adjusting the pH of the dispersion to 3 to 3.5 with the addition of an aqueous 3N hydrochloric acid solution and then de-bubbling the dispersion under vacuum, the thus treated 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 the collagen film prepared from the same raw material of and by the same procedures in Example 2, except for not admixing the crude gelatin, of a thickness of 20 microns was 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 square showing an isoeiectric point of 5.3 in pH was acidswollen in 500 ml of an aqueous hydrochloric acid solution of pH of 2 for 1 5 hours, and they were dispersed into one liter of de-ionized water by using a mixer to obtain a dispersion of collagen of 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 abovementioned 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, it was subjected to film formation by the same procedures as in Example 1. The tear-strength of the thus prepared film of 1 7.5 microns in thickness was 45 g cm/cm in a wet state.

COMPARATIVE EXAMPLE 3 The tear-strength of the film of 1 8 microns in thickness prepared from the same raw material of and by the same procedures in Example 3, except for not admixing the crude gelatin into the dispersion was 33 g cm/cm.

EXAMPLE 4 One hundred and twenty grams (30 g in dry weight) of cattle-hide from a Holstein prepared by depilation and purification and finely cut into 5 to 8 mm square showing an isoelectric point of 5.3 in pH was acid-swollen in 1.5 1 of an aqueous hydrochloric acid solution of pH of 2 for 1 5 hours, and they were dispersed into one liter of deionized water by using a mixer to obtain a dispersion of collagen of a concentration of 3% by weight.

After admixing 120 g (30 g in dry weight) of the crude gelatin used in Example 1 into the abovementioned 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 microns was obtained by extruding 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.

On this obtained film, the tear-strength of rectangular direction to the extrusion direction is 69.5 g cm/cm.

COMPARATIVE EXAMPLE 4 The tear-strength of the film of 30 microns in thickness prepared from the same raw material of and by the same procedures in Example 4, except for not admixing the crude gelatin into the dispersion was 51 g cm/cm.

Claims

1. A material comprising collagen with an isoelectric point not exceeding 6.2 and gelatin, the gelatin being present in an amount of from 0.05 to 2 parts by weight per part by weight of said collagen.

2. A material according to claim 1, wherein said collagen has an isoelectric point of lower than 6.

3. A material according to claim 1 or 2, wherein said collagen is derived from cattle hide or pig hide.

4. A material according to any one of the preceding claims, wherein said collagen is crosslinked or acetylated.

5. A material according to claim 4, wherein said cross-linking has been effected by glutaraldehyde.

6. A film of collagen and gelatin substantially as hereinbefore described in any one of Examples 1 to 4.

7. A process for the preparation of a material formed of collagen and gelatin, wherein the mechanical strength of said material is higher than the mechanical strength of material of the same dimensions but formed substantially of collagen, which process comprises mixing gelatin with an aqueous dispersion of collagen of an isoelectric point not exceeding 6.2; adjusting the pH of the mixture to from 3 to 3.5 by the addition of an aqueous acid solution; and forming said material therefrom.

8. A process for the preparation of a material comprising collagen and gelatin, which process comprises mixing gelatin with an aqueous dispersion of collagen of an isoelectric point not exceeding 6.2 in an amount of 0.05 to 2 parts by weight of gelatin per part by weight of collagen; adjusting the pH of the mixture to from 3 to 3.5 by the addition of an aqueous acid solution; and forming said material therefrom.

9. A process according to claim 7 or 8, wherein said collagen has an isoelectric point of lower than 6.

10. A process according to any one of claims 7 to 9, wherein said collagen is derived from cattle hide or pig hide.

11. A process according to any one of claims 7 to 10, wherein said collagen has been prepared by first cross-linking or acetylating a hide to reduce the isoelectric point of the original collagen in said hide and then obtaining collagen fibers from the thus-treated hide.

12. A process according to claim 11 wherein said cross-linking has been effected by glutaraldehyde.

13. A process according to any one of claims 7 to 12 wherein said material is formed by electrodeposition.

14. A process according to any one of claims 7 to 12, wherein said material is formed by extrusion.

1 5. A process for the preparation of a film of collagen and gelatin substantially as hereinbefore described in any one of Examples 1 to 4.

16. An edible material prepared by applying an electric current to an aqueous dispersion containing collagen and gelatin.

17. An edible material according to claim 16, wherein said aqueous dispersion contains 0.05 to 2 parts by weight of gelatin per part by weight of collagen of an isoelectric point not exceeding 6.2, and a suitable amount of a diluted hydrochloric acid.

18. An edible material according to claim 16 or 1 7 wherein said aqueous dispersion has a pH of from3to3.5.

19. A shaped article made using a material as claimed in any one of claims 1 to 6 or 16 to 18 or which has been prepared by a process as claimed in any one of claims 7 to 1 5.

20. A food having an outer skin which is a material as claimed in any one of claims 1 to 6 or 16 to 18 or which has been prepared by a process as claimed in any one of claims 7 to 1 5.