GB2036750A - Tannin complexes - Google Patents

Abstract

The precipitation of tannin with one or more other substances, including gelatine, natural and synthetic gum and synthetic derivatives of gums, collagen, milk protein, albumen, plastics materials and natural or synthetic rubber in latex form yields complexes which have the following properties; workability, before hardening, into a variety of shapes which are retained after hardening; upon exposure to air becoming hard and mechanically strong below a particular temperature; being moisture resistant; and being resistant to microbial action. The complexes may have some or all of the following applications; use as preservative coatings for foodstuffs; use as foodstuffs, including meat analogs and chewing gum; use in photography; use as industrial fibres; use in making casings. Work with and applications of the tannin-gelatine complex are described in detail. Methods of preparing and handling the complexes are described.

Description

SPECIFICATION Tannin complexes The present invention relates to complexes and mixtures of tannin (ortannic acid) and other substances, such as, for example, gelatine, gum, collagen, milk protein, albumen, plastics materials, rubbers and mixtures of plastics materials and gelatine. In the remainder of this specification and in the claims where the word "tannin" is used this should be taken to include tannic acid.

I have discovered that when liquid gelatine and a warmed solution of tannin are mixed, a precipitate is formed which can be worked or drawn into various shapes including sheets, filaments, films and needles, and that on exposure of the precipitate to air it becomes very hard, retains the shape given during drawing or working, is moisture resistant and is non-toxic.

I have also discovered that when meat is coated in a film made from such a complex it can be preserved for long periods at room or domestic refrigerator temperatures without putrefying. A considerable saving in energy may result from storing meat at room or domestic refrigerator temperatures instead of using conventional meat storage techniques.

The food preserving properties of tannin are described in the provisional and complete specifications filed in connection with my co-pending Irish Patent Application No. 2318/78, which specifications describe solutions of tannin, and preparations, including complexes and mixtures, of tannin and other substances such as gelatine, collagen, milk protein, albumen, and a range of natural and artificial gums and synthetic derivatives of gums, and describes the use of these solutions, mixtures, and complexes as food preservatives and as foodstuffs.

The present invention provides complexes formed by the precipitation of tannin and one or more other substances, which complexes have the following properties; workability, before hardening, into a variety of shapes which shapes are retained after hardening; upon exposure to air, becoming hard and mechanically strong below a particulartempera- ture; being moisture resistant; and being resistant to microbial action.

In particular the invention provides complexes as above in which the other substance is gelatine, a natural or synthetic gum, a synthetic derivative of gum, collagen, milk protein, albumen, a plastics material, or natural or synthetic rubber in latex form.

The invention also provides complexes as above in which the other substance is a mixture comprising a plastics material mixed with another substance, such as for example gelatine.

Preferred plastics materials include acrylics, methacrylates, polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinylchloride and polyethylene, and copolymers.

Some of the complexes and mixtures according to the invention are edible but others are not.

Complexes and mixtures according to the invention have many applications. They may be used as foodstuff preservatives by giving the foodstuff to be preserved a coating of the complex. Foodstuffs which may be coated include meat, eggs (in place of waterglass silicate), confectionery and sweets.

They may also be used in photography. It has been noticed in industrial uses, in developing films, that the action of the naturally derived developing materials and derivatives thereof have a "tanning" or an insolubilizing effect on the gelatine used in the photographic films or plates. Tannin/gelatine or tannin/gum complexes are useful as separation films or supports in general photographic applications.

Fine threads or filaments of certain complexes according to the invention may be used as foodstuffs, for example in the making of meat analogs, or as chewing gums. The complexes which may be used as foodstuffs may also be used as animal feedstuffs and consequently, where reference is made in the specification and claims to the use of the complexes as foodstuffs, food analogs, and the like, this should be taken to include feedstuffs.

Additionally complexes according to the invention may be used to make industrial fibres, as the filaments can later be hardened by well known chemical methods using acids, aldehydes, and various metal salts such as chrome, aluminium, iron, tungsten, molybdenum and vanadium.

Complexes according to the invention have been used to make casings. The casings were made by hand but it may be possible to made casings by extrusion methods, probably by using the solvent method described below of combining the tannin and the gelatine, gum, or other substance.

When complexes according to the invention are used as food preservatives or food substitutes, commonly used food preservatives and antioxidants may be added to or included in the complexes. Examples of such food preservatives are benzoates, sorbic acid, sorbates, sulphites, and metabisulphites, and examples of anti-oxidants are propyl gal late, ascorbic acid and butylated hydroxy anisole.

To further improve the preservative qualities of coatings obtained from complexes according to the invention, meat and foods can be cooked before coating so that an even longer life results than with uncooked materials. In addition, treatment with a mild acid or salt, for example acetic acid, tartaric acid, citric acid or sodium sulphate, may also increase the resistance of the film.

Experiments with and applications of the tannin/ gelatine complex are described in Example 1. Complexes of tannin and gums are described in Examples 2- 5, tannin and plastics materials in Example 6, tannin and rubber in Example 7 and tannin and a mixture of plastics materials and gelatine in Example 8.

Example 1 Solutions of 10% and 20% by weight of tannic acid and commercial tannins in water were prepared and were found to be very soluble. Strong gels of 5% by weight of gelatine in water were also prepared, using gelatine of high Bloom, the Bloom being about 1800to 190". On liquefying the gelatine and warming the tannin solution to the same temperature, and mixing the two together, a precipitate formed. When this precipitate was further warmed in the mother solution or in water to about 40"C or 50"C it became dense, coherent and very plastic. When warm, it was sticky, and would attach itself to the stirring rod, and could then be drawn out into filaments of varying thickness, from very fine to very thick; could be formed into various shapes; and could be cast as a sheet or a film.Upon exposure to ambient air the sheets, films, filaments and other shapes hardened.

They possessed considerable mechanical strength and retained their shape almost irrespective of the intricacy of form. In addition, they exhibited resistance to hot water. For example, filaments cast on glass were immersed in water, having a temperature between 45"C and 70"C, and retained their shape.

In addition, very fine threads were formed by filling a hypodermic needle with a tannic acid solution, immersing the point of the needle under the surface of the warmed gelatine solution and injecting the tannic acid solution into it.

Several pieces of the tannin gelatine complex were allowed to remain in a relatively damp atmosphere for several weeks, and it was found that they became remarkably hard and almost vitreous; and, even after several months, they showed no sign of microbial attack. The absence of microbial attack is believed to be due to the preservative properties of tannin which are described in the provisional and complete specifications filed in connection with my Irish Patent Application No.2318/78.

The dry tannin/gelatine complex, which is very strong and difficultto handle, was found to dissolve in some food solvents such as ethylene glycol and propylene glycol. When dissolved in ethylene glycol it formed a thick viscous solution which became thin on warming and thus convenient to handle. It was found that tannin or gelatine could be dissolved separately in ethylene glycol, and the resulting solutions mixed when convenient. Some food solvents delay the reaction of tannin with gelatine and it may be preferable to dissolve only the tannin in food solvent, while the gelatine could be dissolved in water. This delaying or inhibiting action may be useful in certain cases, reaction taking place when the materials have dried out.

Insoluble tannin complexes may also be formed without the use of solvents, such as ethylene glycol, as described above, by the addition of an alkali, which when present, prevents the precipitation of the complex. When the alkali is later neutralised or allowed to evaporate the complexes then become insoluble.

For example, 5 parts by weight of gelatine of 180" Bloom were dissolved in 100 parts by weight warm water. A dilute solution of ammonia was added to the solution to bring the pH to approximately 8. A solution of 20% tannin was then added. A clear viscous solution resulted. This was then spread on a sheet of glass and allowed to dry. When both the moisture and ammonia had evaporated off, a clear insoluble film remained on the glass. The film exhibited remarkable adherence to the glass. This method may be of importance in the formation of sheets, films, and fibres from complexes according to the invention.

Thick pieces of the complex prepared in this way withstood immersion in boiling water for several minutes, and, even though they swelled, they retained their shape on cooling. Subsequently, when stood in cold water for several days, they did not dissolve or disintegrate.

Pieces of beef were treated with a mixture of ethylene glycol and tannin/gelatine, as described above, containing about 10% by weight of tannin and 5% by weight of gelatine. The coating solidified on cooling. These pieces of treated beef were left on an uncovered plate in a domestic refrigerator at a temperature of about 8"C (46"F) for fourteen days. At the end of fourteen days the pieces of beef were inspected. They were completely devoid of any putrefactive appearance or odour and did not seem to have shrunk. Their appearance was quite dark; this may be obviated by including anti-oxidants, or by using pure tannic acid which is light coloured, or both. The pieces of beef were then stored in a plastic box at room temperature for a further fourteen days, during which period the lid was removed each day from the box for inspection.After several days a deep ripening odour developed similar to that of maturing cheese, but there was no putrefactive odour such as is normally associated with rotting meat. Fat attached to the meat appeared to be free of rancidity. At the end of this fourteen day period one of the pieces of beef was cut with a knife. The internal part of the meat had also deepened considerably in colour but was completely free from odour of any kind. When the fat was cut there appeared to be no internal rancidity. Some of the pieces of beef were than cooked in a domestic pressure cooker for about twenty minutes at a pressure of fifteen pounds per square inch (15 p.s.i.). The odour from the steam was the normal pleasant odour associated with meat cooking and was completely devoid of any putrefactive smell. When cut, it was observed that some of the red colour had been restored.The meat had probably been somewhat over-cooked and it is likeiy that ten or fifteen minutes cooking at a pressure of 20 p.s.i. would have been adequate due to the very long period of maturing at room temperature of the uncooked meat.

The tannin/gelatine complex may also be used in the pet food trade as an alternative to soya. In the food industry, including the pet food industry, large quantities of soya are used not only in meal form, but also as preformed chunks of soya. When canned, the soya chunks absorb the liquour ingredients and give the appearance of being pieces of meat. They are rich in protein, and also provide a measure of chewability to help the animals' gums and teeth. Soya chunks are, however, relatively expensive. Accordingly, lumps were made using the tannin/gelatine complex. In order to increase the nutritional character of the lumps as gelatine is deficient in some amino-acids, lumps were also made containing a significant quantity of casein. The lumps stood up to the high temperatures of the retorting process, which is necessary both to cook food and to ensure sterilization. The resistance to water of these lumps was-increased if, after drying, they were immersed for a few moments in a mild acid solution. In this case 1% to 2% acetic acid was used, equivalent to a mild vinegar. This acid treatment is not, however, essential. Despite the fact that casein is notoriously subject to microbial attack, the dried lumps showed no deterioration after standing unprotected for some weeks.

The tannin/gelatine complex also finds use as a savoury chewing gum. It softens readily in the mouth, is pleasant to chew, and breaks down under the action of saliva and thus will not stick in the intestine as some conventional chewing gums do.

Example 2 A preparation was made, using a food solvent in the manner described in Example 1, of propylene glycol alginate and tannin. Pieces of raw beef were coated with this solution. While the tannin/gelatine complex, described in Example 1, set on cooling, this coating needed to be dried in a blast of hot air from an electric fan. When dried after a few minutes the samples of treated meat were stored in a plastic box and left at room temperature. The box was opened for inspection purposes every day for fourteen days and no putrefactive odour was apparent, but the meat darkened in colour. The samples showed the appearance of some colonies of white fungus after about ten days, but the colonies evidently found it difficult to proliferate, despite condensation in the plastic box.It should be noted that the box was unsterilized, that only one coating was applied to the samples, and that the surfaces of the samples may not have been fully covered. It should also be noted that the propylene glycol alginate used in the experiment was of high viscosity and low solids content, so that its covering strength may have been low, thus allowing some fungal attack. The alginates used for these tests belong to a class known as alginic acid esters and are made by reacting alginic acid with alkylene oxides. There are several of these esters, but the common material of commerce is propylene glycol alginate, and it is widely used in foods.

Example 3 A preparation was made, using a food solvent, as before, of cellulose ether and tannin and pieces of raw beef were coated with this solution. The coating needed to be dried in a blast of hot air. When dried the samples of treated meat were stored in a plastic box and left at room temperature. The box was opened every day for fourteen days for inspection purposes. After a few days a serum fluid separated out but the samples did not putrefy. The samples darkened in colour. As in Example 2, the box was unsterilized and only one coating was applied. It should be noted that there exist several cellulose ethers, but the normal grade of commerce, used in this Example, is ethyl hydroxy ethyl cellulose which is non-toxic.

Example 4 Under slightly acidic conditions, tannin causes coagulation of Solvitose C5, a synthetic gum produced by Messrs Scholtens of the Netherlands, forming a rubbery material.

Example 5 Tannin causes coagulation of Indalca Gum produced by Cesalpinia, Italy, similar to the coagulation described in Example 4.

The effect of tannins on other gums besides those given in Examples 2- 5 was also investigated and it was found that while some had no reaction at all, other important commercial gums became insoluble including albumen, isinglass, locust bean gum, guar gum, gum karaya, and milk casein. None, however, were plastic like the tannin/gelatine complex. Despite this, several films from the gums mentioned above were cast on glass and dipped in 10% and 20% by weight tannin solutions. In every case there appeared to be a marked resistance to water both hot and cold. Water resistance appeared to increase in the presence of acids, but was much reduced in the presence of alkalis.

Example 6 Solutions of tannic acid and commercial tannins in water were prepared. Polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride, polyethylene, acrylics, methacrylates and co-polymers were obtained in their commercially available emulsion form. On mixing, a precipitate formed which had physical properties similar to those of the tannin/gelatine complex of Example 1.The mechanical strength and moisture resistance of these complexes were, however, found to be greater than those of the tannin/gelatine complex. As in Example 1, the complexes were left in a relatively damp atmosphere for a considerable length of time and they became hard and almost vitreous, and showed no sign of microbial attack. The above plastics were chosen because they are widely available commercially.

The complexes thus formed may not be suitable on their own as foodstuff preservatives due to the inedibility of the plastics material. However, meat and other food products which have already been treated with a coating of tannin, as described in the Provisional and Complete Specifications accompanying Irish Patent Application No. 2318/78, or treated with a coating or film of, for example, a tannin/gelatine complex as described in Example 1 of this Specification, may be further coated with a film of the tannin-plastics complexes described above. The tannin/plastics films have advantages over the tannin-gelatine film in that they are mechanically stronger and more moisture resistant. The tannin-plastics films are flexible, and are somewhat like a strong skin. They may be stripped away by hand when it is desired to use the meat or other food product.

In an alternative method of applying this second or outer coating to meat or other food products, the plastics material may first be applied in the form of a film, and then subsequently treated with tannin. This subsequent treatment may consist of spraying the foodstuff with tannin or of dipping the meat or other food in a bath containing tannin. Precipitation occurs on contact. The films thus formed are very strong and set rapidly.

In addition to use as food preservatives, the tannin-plastics complexes have many industrial uses including use as industrial fibres, moulding compounds, films and filling compounds. The property of resistance to microbial attack is very important in enabling such varied use.

Polyvinylpyrrolidone, which is a relatively cheap ingestible plastics material used in connection with foodstuffs, precipitates with tannin to form a complex having properties similar to those of the complexes described above. The polyvinylpyrrolidone used is not in emulsion form and dissolves in water. These complexes are especially useful for coating foodstuffs because no solvent is necessary for their preparation and because they are ingestible.

Example 7 If commercially available natural or synthetic rubber in latex form is mixed with tannin they may appear compatible in the sense that no hardening or precipitation takes place. I believe that this is due to the fact that many commercial rubbers in latex form are treated with alkali materials, frequently ammonia, to give them stability and to prevent them harding in the containers in which they are sold commercially.

I have found, however, that if the latices are spread out on a surface and the ammonia allowed to evaporate, or if the alkali is otherwise neutralized, mixtures of rubber and tannin dry out and harden, yielding a product which may be a complex or a mixture and which has the properties of resistance to water, and resistance to microbial attack.

Example 8 Complexes of tannin and gelatine are described in Example 1. Complexes of tannin and plastics material are described in Example 6. Complexes of tannin and a mixture of gelatine with plastics materials are described in this Example. The gelatine was mixed with water and the mixture warmed so that the gelatine dissolved. This mixture was mixed with plastics materials in emulsion form. The resultant mixture was then precipitated with tannin. The complex so formed has properties similar to those of the tannin-plastics complexes but it is somewhat more malleable and easier to work. It is mechanically stronger than the tannin-gelatine complex. As it contains plastics materials, it is preferably applied to foodstuffs as a secondary coating, as in Example 6.

These complexes have many applications including use in or as industrial fibres, as moulding compounds, as films and as filling compounds.

Various alcohols and solutions or organic acids, such as acetic acid in water, may be convenient solvents for complexes according to the invention or their constituents. Alternatively, when coating a foodstuff for example, tannin may be dissolved in an alcohol or other suitable organic solvent and may then be applied to the foodstuff which has already been treated with gelatine our a gum or the like.

Complexes according to the invention may be dissolved using a mild alkali, so that a film or shape may be easily removed. A solution of ammonia gas in water has been found to be a suitable alkali, particularly when used with foodstuffs, as it evaporates leaving no residue. Ammonium bicarbonate is widely used, for this reason, for "raising" biscuits during baking.

Natural and synthetic gums and plastics materials very seldom react in exact stoichiometric proportions. The same is true of tannins and tannic acids.

Consequently, only approximate proportions found from empirical trials when reacting natural and synthetic gums and emulsions of plastics materials with tannins and tannic acids are given in the specification and it is to be understood that the proportions given in the above Examples may be varied considerably.

Claims (46)

1. A complex formed by the precipitation of tannin with one or more other substances, which complex has the following properties; workability, before hardening, into a variety of shapes which shapes are retained after hardening; upon exposure to air, becoming hard and mechanically strong below a particular temperature; being moisture resistant; and being resistant to microbial action.

2. A complex according to Claim 1 in which the other substance is gelatine, a natural or synthetic gum or a synthetic derivative of a gum, collagen, milk protein or albumen.

3. A complex according to Claim 1 in which the other substance is a plastics material.

4. A complex or mixture containing tannin and natural or synthetic rubber which complex or mixture has the properties mentioned in Claim 1.

5. A complex according to Claim 1 in which the other compound or substance is a mixture of a plastics material and another compound orsubst- ance.

6. A complex according to Claim 2 wherein the gum is an alginic acid ester.

7. A complex according to Claim 6 wherein the alginic acid ester is propylene glycol alginate.

8. A complex according to Claim 2 wherein the gum is a cellulose ether.

9. A complex according to Claim 8 wherein the cellulose ether is ethyl hydroxy ethyl cellulose.

10. A complex according to Claim 2 wherein the gum is isinglass.

11. A complex according to Claim 2 wherein the gum is locust bean gum.

12. A complex according to Claim 2 wherein the gum is guar gum.

13. A complex according to Claim 2 wherein the gum is gum karaya.

14. A complex according to Claim 2 wherein the gum is the gum sold by Messrs Scholtens of the Netherlands under the trade name Solvitose C5.

15. A complex according to Claim 2 wherein the gum is Indalca gum produced by Cesalpinia of Italy.

16. A complex according to Claim 2 wherein the milk protein is casein.

17. A complex according to Claim 3 in which the plastics material is an acrylic.

18. A complex according to Claim 3 in which the plastics material is a methacrylate.

19. A complex according to Claim 3 in which the plastics material is a copolymer.

20. A complex according to Claim 3 in which the plastics material is a polymer.

21. A complex according to Claim 20 in which the polymer is polyvinyl alcohol.

22. A complex according to Claim 20 in which the polymer is polyvinyl acetate.

23. A complex according to Claim 20 in which the polymer is polyvinyl chloride.

24. A complex according to Claim 20 in which the polymer is polyethylene.

25. The preparation of a complex according to any of Claims 3 or 17-24 using plastics material in emulsion form.

26. The preparation of a complex or mixture according to Claim 4 using natural or synthetic rubber in latex form.

27. A complex according to Claim 5 containing gelatine.

28. A complex according to any of Claims 1,2 or 6-16, when used as a coating for food.

29. A complex according to any of Claims 1,3,4,5, 17-24 or 27 when used as a coating for food.

30. A complex according to Claim 28 including or treated with one or more antioxidants.

31. A complex according to Claim 29 including or treated with one or more antioxidants.

32. A complex according to Claim 30 in which the antioxidant is propylgallate, ascorbic acid or butylated hydroxy anisole.

33. A complex according to Claim 31 in which the antioxidant is propylgallate, ascorbic acid or butylated hydroxy anisole.

34. A complex according to Claim 28 including or treated with one or more known food preservatives.

35. A complex according to Claim 29 including or treated with one or more known food preservatives.

36. A complex according to Claim 34 in which the known food preservative is a benzoate, sorbic acid, a sorbate, a sulphite or a metabisulphite.

37. A complex according to Claim 35 in which the known food preservative is a benzoate, sorbic acid, a sorbate, a sulphite or a metabisulphite.

38. A complex according to any of Claims 1,2 or 6-16 when used as a casing.

39. A complex according to any of Claims 1,3,4,5, 17-24 or 27 when used as a casing.

40. A complex according to any of Claims 1,2 or 6-16 when used as an industrial fibre.

41. A complex according to any of Claims 1,3,4,5, 17-24 or 27 when used as an industrial fibre.

42. A complex according to Claim 2, containing gelatine, when used as a photographic separation film or support.

43. Complexes substantially as herein described with reference to Examples 1 to 5.

44. Complexes substantially as herein described with reference to Examples 6-8.

45. Methods of preparing and handling complexes according to any of Claims 1-24 and 28-44, substantially as herein described.

46. A complex according to claim 3 in which the plastics material is polyvinylpyrrolidone, when used as a food preservative.