GB2036535A

GB2036535A - Foodstuff preservatives comprising tannin

Info

Publication number: GB2036535A
Application number: GB7940255A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-11-23
Filing date: 1979-11-21
Publication date: 1980-07-02
Also published as: IE782318L

Abstract

Tannin (including tannic acid) has been found to possess food preserving qualities. The invention provides the use of tannin as, or as a constituent of, a foodstuff preservative. A preservative may comprise tannin in powdered form, a solution of tannin in water, or may be a preparation containing tannin. Such preparations include complexes formed by the precipitation of tannin with certain non-toxic substances including gums, proteins, collagen, albumen, and, in particular, gelatine. The preparations also include mixtures of tannin and certain gums. These complexes and mixtures may be applied to foodstuffs, and in particular meat, in the form of a film or coating and may preserve meat at room temperatures thus enabling considerable energy savings to be achieved. The complexes, in addition to having preserving properties are hard and moisture resistant. The tannin-gelatine complex has been used as a meat analog and as a savoury chewing gum.

Description

SPECIFICATION Foodstuff preservatives and footstuffs The present invention relates to foodstuff preservatives and foodstuff substitutes.

I have discovered that tannin (and tannic acid) has hitherto undisclosed properties which are particularly useful in preserving foodstuffs. In the remainder of this specification and in the claims "tannin" should be taken to include tannic acid.

An experiment was carried out to test the preserving action of tanning. Several pieces of raw lean beef of about one inch cube in size were immersed cold in a 10% weight solution of tannin in water. No particular care was taken in sterilizing the tannin solution, the container, or the knife for cutting the meat.

Over a four week period it was noticed that the meat absorbed the tannin solution, but no putrefaction whatever appeared to take place. A rather pleasant but heavy odourwas apparent; the colour of the solution lightened, and a very slight bubbling took place atthe bottom of the liquid. Afterthisfourweek period, the meat was cut and it was found to be devoid of any putrefactive odour. When cut the internal meat fibres could be seen very clearly and appeared to have become light in colour, while the outside of the meat had become a brown red colour.

I have also found that powdered tannin may be used as a preservative by direct sprinkling on food.

When sprinkled on meat, the meat juices dissolve the tannin, and the film thus formed preserves the meat.

In addition, 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, films, filaments 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 used this complex as a savoury chewing gum. I have also prepared meat analogs from this complex. Furthermore I have used this complex as a preservative coating for various foodstuffs.

I have also discovered that tannin precipitates with other substances such as gums or derivatives of gums, collagen, albumen and milk proteins, in particular, casein, to form complexes having properties similar to those above.

Accordingly, the present invention provides the use of tannin as, or as a constituent of, a foodstuff preservative. The invention provides the use of powdered tannin and solutions of tannin in water as food preservatives. In addition the invention provides preparations containing, and in particular complexes formed by the precipitation of tannin and, certain non-toxic substances, which preparations may be used as foodstuff preservatives. The complexes may also be used as foodstuffs.

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.

Experiments with an applications of the tannin/gelatine complex will now be described in Example 1. Other preparations will then be described in subsequent Examples.

Example 1 Solutions of 10% and 20% by weight 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 1800 to 1900. On liquefying the gelatine, and warming the tannin solution to the same temperature, and mixing the two together, a precipitate was formed.

When this precipitate was further warmed in the mother solution or in water to about 40 or 50"C it became dense, coherent and very plastic. When warm, it became 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. The sheets, films, filaments and other shapes all 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 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 atmos phere 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 dry tannin/gelatine complex, which is very strong and difficult to 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 either ingredient could be dissolved separately in the ethylene glycol, and the resulting solutions mixed when convenient. Some 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 visc ous 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 exhi bited 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 tanning 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 the maturing of 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.

Atthe 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 cutthere appeared to be no internal rancidity. Some of the pieces of beef were then cooked in a domestic pressure cooker for about twenty minutes at fifteen pounds per square inch pressure. 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 was pleasant to eat but a certain fullness was absent in the flavour; the fat portion tasted normal. The meat had probably been somewhat overcooked and it is likely that ten or fifteen minutes cooking at twenty pounds per square inch pressure would have been adequate due to the very long period of maturing at room temperature of the uncooked meat. It will be obvious that considerable energy savings may be achieved by storing meat at room temperatures instead of using conventional meat storage techniques.

The tannin gelatine complex may also be used in the pet food trade as an alternative to soya. In the food industry, including the petfood industry, large quantities of soya are used not only in meal form, but also as preformed chunks of soya. When can ned, 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 very expensive. Accordingly, lumps were made using the tannin/gelatine mixture. In order to increase the nutritional character of the lumps, as gelatine is deficient in some amino-acids, lumps were atso made containing a significant quantity of casein. The lumps stood up to the high temp eratures of the retorting process, which is necessary both to cookthefood 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 factthatcasein is notoriously subject to microbial attack, the dried lumps showed no deterioration after standing unprotected for some weeks.

The tanninlgelatine 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 solvent, of propylene glycol alginate and tannin. Pieces of raw beef were coated with this solution. While the tannin/gelatine mixtures set on cooling, this coating needed to be dried in a blast of hot airfrom 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 dayforfourteen 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 their surfaces 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 materiat of commerce is propylene glycol alginate, and it is widely used in foods.

Example 3 A preparation was made, using solvent, 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 the Example, is ethyl hydroxyl ethyl cellulose which is non-toxic.

Various alcohols and solutions of organic acids such as acetic acid in water, may be convenient solvents for complexes according to the invention or the constituents. Alternatively, the tannin may dissolve in an alcohol or other suitable organic solvent and be applied to a food already treated with a suitable gum. 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, as it evaporates leaving no residue.

Ammonium bicarbonate is widely used, for this reason, for "raising" biscuits during baking.

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.

Fine threads or filaments of complexes according to the invention, formed as described in Example 1, may be used to make meat analogs. Complexes according to the invention have been used to make casings. The casings were made by hand but it may be possible to make casings by extrusion methods, probably using the solvent method of combining the tannin and the gelatine, gum, or other substance.

Complexes according to the invention may also be used for coating eggs (in place of waterglass silicate), confectionary and sweets.

The tannin in the above description complexes in addition to being non-toxic and causing precipitation of gelatin or gums to form hard water-resistant complexes, has itself some preservative or antimicrobial action as previously mentioned. It is possible that the high tannin content, as well as the hardness of the complex, renders the protein unassimilable to the micro-organisms, and may even affect the protein constituents of the bacterial cells so that they cannot function.

Consequently, mixtures of tannin and those gums, which do not precipitate with tannin, such as gum acacia, gum tragacanth, sodium alginates and carageenin may also be used as coatings for food provided they are further wrapped or packaged so that the soft coating is held in place. For example, chunks of meat coated in such a mixture could be further wrapped in tin foil.

Commonly used food preservatives and antioxidants may be added to or included in the complexes, mixtures or solutions of the invention, examples of such food preservatives including ben zoates, sorbic acid, sorbates, sulphites, and metabisulphites and examples of anti-oxidants including propyl gallate, ascorbic acid and butylated hydroxy anisole.

Natural and synthetic gums 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 gelatine and natural and synthetic gums, with tannins are given in the specification and it is to be understood that the proportions given in the above Examples may be varied considerably.

Example 4 Polyvinylpyrrolidone, which is a relative cheap ingestible plastics material used in connection with foodstuffs and which dissolves in water, precipitates with tannin to form a complex having properties similar to those of the tannin-gelatine complex but being mechanically stronger and more moisture resistant and being flexible like a strong skin. These complexes are especially useful for coating foodstuffs because no solvent is necessary for their prep aration and because of their mechanical strength and moisture resistance.

Claims

1. Tannin when used as or as a constituent of a foodstuff preservative.

2. Tannin in powdered form when used as or as a constituent of a foodstuff preservative.

3. A solution of tannin in water when used as or as a constituent of a foodstuff preservative.

4. A preparation containing tannin when used as a foodstuff preservative.

5. A complex formed by the precipitation of tannin with one or more non-toxic substances, when used as a foodstuff preservative.

6. A complex according to Claim 5 wherein the non-toxic substance is gelatine.

7. A complex according to Claim 5 wherein the non-toxic substance is a natural or artificial gum or synthetic derivative of a gum.

8. A complex according to Claim 7 wherein the gum is an alginic acid ester.

9. A complex according to Claim 8 wherein the alginic acid ester is propylene glycol alginate.

10. A complex according to Claim 7 wherein the gum is a cellulose ether.

11. A complex according to Claim 10 wherein the cellulose ether is ethyl hydroxy ethyl cellulose.

12. A complex according to Claim 5 wherein the non-toxic substance is a milk protein.

13. A complex according to Claim 12 wherein the milk protein is casein.

14. A complex according to Claim 5 wherein the non-toxic substance is collagen.

15. A complex according to Claim 5 wherein the non-toxic substance is albumen.

16. A mixture of tannin and a natural or synthetic gum or a synthetic derivative of a gum when used as a food preservative.

17. A mixture according to Claim 16 containing gum acacia.

18. A mixture according to Claim 16 containing gum tragacanth.

19. A mixture according to Claim 16 containing a sodium alginate.

20. A mixture according to Claim 16 containing carageenin.

21. A complex according to any of Claims 5-15 when applied, in the form of a film or coating, to the foodstuff to be preserved.

22. A mixture according to any of Claims 16-20 when applied, in the form of a film or coating, to the foodstuff to be preserved.

23. A mixture according to Claim 22 when the foodstuff is further wrapped, packaged or coated to retain the coating or film in place.

24. Tannin, alone or as part of a preparation, sol ution, complex or mixture according to any preced ing claim, when used to preserve meat.

25. Tannin according to Claim 25 when used to preserve red meat.

26. Tannin according to Claim 25 when used to preserve beef.

27. A complex according to any of Claims 5-15 when used to preserve eggs by coating the eggs with the complex.

28. A complex according to any of Claims 5-15 when used to preserve sweets or confectionary by coating the sweets or confectionary with the complex.

29. A food preservative comprising tannin or a preparation, solution, mixture or complex according to any preceding claim, and one or more preservative compounds in addition to tannin.

30. A food preservative according to Claim 29 in which the preservative is a benzoate, sorbic acid, sorbate, a sulphite or a metabisulphite.

31. Afood preservative comprising tannin our a preparation, solution, mixture or complex according to any preceding claim and one or more antioxidants.

32. Afood preservative according to Claim 31 in which the anti-oxidant is propyl gal late, ascorbic acid, or butylated hydroxy anisole.

33. A complex formed bythe precipitation of tannin and one or more non-toxic substances, when used as a food or food substitute.

34. A complex according to Claim 33 in which the non-toxic substance is gelatine.

35. A complex according to Claim 33 or 34, treated to raise the amino acid content.

36. A complex according to Claim 33 or 34 which includes casein.

37. A complex according to any of Claims 5-15, 21,27 or 28, which has been treated with a mild acid or salt, such as acetic acid, tartaric acid, citric acid, or sodium sulphate.

38. A complex according to Claim 33 or 34 when used as, or as the principal constituent of, a chewing gum.

39. The use, substantially as herein described, of known food solvents in preparing, dissolving and otherwise handling complexes as claimed herein.

40. The use, substantially as herein described of an alkali in preparing, dissolving and otherwise handling complexes as claimed herein.

41. The use, substantially as herein described, of an alcohol or a solution of organic acid, in preparing, dissolving or otherwise handling complexes as claimed herein.

42. A foodstuff when coated with a solution, preparation, complex or mixture as claimed herein.

43. Afoodstuffwhen cooked and subsequently coated with a solution, preparation, complex or mixture as claimed herein.

44. Meat analogs when made from fibres formed from complexes as claimed herein.

45. The preparation, substantially as herein described, of complexes as claimed herein.

46. A complex according to claim 5 wherein the non-toxic substance is polyvinylpyrrolidone.