GB2132205A - Colouring agents - Google Patents

Abstract

A water-soluble curcumin complex suitable for use as a coloring agent in foods is prepared by dissolving and mixing a source of curcumin and gelatin in an aqueous acetic acid solution. The complex comprises up to 15% circumin by weight, and may be incorporated into a wide variety of foodstuffs in either liquid or dry form.

Description

SPECIFICATION Colouring agents This invention relatestocoloring agentsforfood- stuffs and the like and, more particularly, this invention relates to water-soluble curcumin-gelatin com plexesanda methodfor preparing the same.

Turmetic isthe dried rhizome of the plant Curcuma Longa L. It is used in foods for its coloring ability and less frquentlyfor its flavor. Curcumin is the compound in turmeric that is primarily responisble for its coloring ability. The dried turmeric rhizomes generally contain about5% curcumin.

Ground turmeric may be extracted with organic solvents to remove the curcumin and the fixed and volatile oils from the cellulose plant material ofthe rhizomes, to form oleoresins. Solvents such as isopropanol, ethanol, acetone, and ethylene dichloride and others are typically used to prepare oleoresins ofturmericwhich may typically contain about 30% curcumin, 30% volatile oils, 30% fixed oils, and 10% polysaccharides. Oleoresins are used byte food industryto colour pickles, baked goods, poultry products, and in seasoning mixtures for various other foods.

The fixed and volatile oil portions ofthe ground spice orthe oleoresin are responsible forthe characteristic flavor and bitterness of turmeric. This flavor and bitterness is sometimes undesirable in the finished food product. The fixed and volatile oils can be removed from oleoresins by extraction with an organicsolventwhich isdifferentfromthatusedinthe preparation ofthe oleoresin,from rhizomes, or by physically removing curcumin crystalsfromthe oleoresin by filtration or centrifugation. The resulting volatile oil-free product is known as "debitterized" or "deflated" turmeric.

Curcumin is substantially insoluble in water. Since most food systems contain a significant amount of water, curcumin will not colourthese systems without the aid of a synthetic chemcial emulsifier of some type.

An object of the invention is to overcome the problems described above.

Another object is to obtain a curcumin-containing substance, which gives a crystal clear yellow solution in waterwithoutthe aid of an artificial emulsifier.

According to the present invention, we propose a method of preparing curcumin-containing substances comprising dissolving a curcumin-containing substance and gelatin in a solvent comprising acetic acid, said curcumin-containing substance being present in an amount such that the said colouring agent contains a maximum of about i5weight percentcurcumin on a dry basis, based on the total weight of curcumin and gelatin,the solvent containing a maximum of about 25 weight per cent water and the dissolving operation being carried out at a temperature less than the minimum denaturing temperature of gelatin in the solvent.

The curcumin product of the invention may be prepared by dissolving a source of curcumin, typically defatted oleoresin turmeric, and gelatin in a solvent comprising up to about 25 wt.% water and the balance acetic acid, preferably at an elevated temperature less than a bout 90"C. A gelatin-curcumin complex is formed during mixing of the gelatin, curcumin source and solvent. Upon optional removal ofthe solvent by distillation, spray drying orany other convenient means, a dry water-soluble product is obtained which may be added to food products in either ground form or in admixture with a suitable dispersing agent, such as table salt or dextrose, for example.

The complex comprises up to a maximum of about 15 wt.% curcumin on a dry basis, and yields colored aqueous solutions of outstanding clarity without the aid of an artificial emulsifier.

Other characteristics and advantages of the invention will be apparent from the following specific description.

Source of Curcumin Curcumin from virtually any source may be used according to the invention. Suitable curcumin sources includeoleoresinturmeric, debitteredordefatted oleoresin turmeric, or purified curcumin.

The more purethe curcumin,the clearerwill bean aqeous solution ofthe curcumin complex, since certain oils and othermaterialsfound in oleoresin turmeric and othertypical curcumin sources tend to cause turbidity in solution.

Gelatin Complexing Agent and Choice of solvent Curcumin binds rather strongly with various proteins. However, not all protein-curcumin complexes are readily soluble in water. For example, casein, which is sparingly soluble in water, forms a watersoluble curcumin complex onlyto the extentthat casein itself is soluble, resulting in a complex which does not provide a clear aqueous solution.

Gelatin, on the other hand, is a water-soluble protein which readily binds with curcumin toform a complex which is highly soluble in water.

Gelatin, when dissolved in water, tends to absorb watertoform a gel. The strength ofthe gel is an inherent characteristic of a given gelatin and is measured as "grams bloom" or"bloom",typically varying from about 50 bloom for a weak gel to about 350 bloom for a strong gel.

Low bloom gelatins are of shorter protein chain length and are relatively polar compared to higher bloom gelatins. Hence, lower bloom gels dissolve in water more readily than do higher bloom gelatins.

While curcumin is relatively insoluble in water, it is very soluble in acetic acid. However, relatively low bloom strength gelatins, which are very soluble in water, are not readily soluble in acetic acid; high bloom gelatins are relatively soluble in acetic acid.

It has been found that, according to this invention, a solvent comprising an aqueous solution of acetic acid is a mutual solventforboth low and high bloom gelatins as well asforcurcumin.

It has been determined that, as a practical matter, an upper limit of about 25 wt.% water in the solvent is necessary in order to assure substantially complete dissolution of curcumin. As shown in the Examples, below, if the solvent contains more than about 30 wt.% water, an excessive mixing period is required in order to effect dissolution of curcumin. Atwater levels of about 33 wt.% and above, curcumin does not dissolve unless the mixing temperature is raised to an unacceptably high level.

In the method gelatin and a source ofcurcumin are dissolved by mixing in a mutual solvent comprising up to about 25 wt.% water, the balance being acetic acid.

The complexing reaction occurs substantially in stantaneouslyas gelatin is dissolved. The resulting complex is soluble in the aqueous acetic acid solvent, thus resulting in a solution ofthe complex.

Since gelatin tends to form a gel as water is absorbed, the gelatin should be added to the solvent gradually with constant stirring in orderto most efficiently effect dissolution.

Preferably, although not necessarily, the source of curcumin should be dissolved priorto the addition of gelatin, since the viscosity ofthe solution increases as gelatin is added,thereby making mixing relatively difficult.

The mixing is preferablywarried outatan eievated temperature of less than about 90"C. At about 90"C and above, with the preferred 75%/25% acetic acid: water solvent, gelatin begins two denature and loses its ability to be solubilized. A mixing temperature of about 8o0C is preferred with the preferred solvent system.

Although the mixing procedure can be carried out at lower temperatures, mixing time increases as the temperature is lowered.

Denaturing of gelatin is evidenced by the formation of an isoluble white precipitate. The initial denaturing temperature of gelatin depends primarily upon the nature of the solvent system, and may to a lesser degree depend upon the gelatin's bloom strength.

For example, gelatin dissolved in purewaterdoes not denature at a temperature at least as high as 1 00 C, while gelatin dissolved in a 75 wt.% acetic acid/25 wt.% water solvent exhibits signs of denatur ingataboveabout90"C.

Hence,the upper mixing temperature limit in this invention is determined by the minimum gelatin denaturing temperature in the selected solvent system; this temperature is readily empirically determined.

Proportions of Ingredients In a preferred solvent composition of about 75 wt.% acetic acid/25 wt.% water, up to about 1 part by weight of gelatin will dissolve in about 3 parts by weight of solvent. Further, it has been found that a maximum of about 15 wt.% curcumin can be complexed with gelatin, based on the total weight of gelatin and curcumin. Variations in the bloom strength of the gelatin have little if any effect on the proportion of curcumin that can be complexed therewith. If desired, of course, a lower proportion ofcurcumin to gelatin may be utilized.

SolventRemoval The curcumin-gelatin complex of the invention can be added to food products in solution form with the acetic acid/water solvent in which the complex is formed ifthe characteristic flavor of acetic acid is not considered objectionable in the final food product. A suitable example is use of a curcumin-gelatin complex solution in water and acetic acid, either in diluted or undiluted form, in pickled food products.

In many cases, however, it may be necessary or desirable to provide the complex in dry form, thus necessitating solvent removal. Substantially complete solvent removal can be effected by various means, including distillation, spray drying, drum drying, air drying orfreeze drying, or any other convenient means. The resulting dry product may then be ground and can be used as is or, if desired, it can be plated or mixed with a dispersing agent such as salt or dextrose.

The curcumin-gelatin complex may be incorporated into a wide variety of food products, including gelatin desserts and dry food products such as cake mixes,forexample, orin nonfood products. The complex is characterized by a strong yellow color in water, with excellent clarity. No emulsifier is required to effect complete dissolution ofthe complex in water.

Examples are now given to illustratethe present invention.

EXAMPLES Example 1 - Turmeric as a Source of Curcumin A. Preparation of Oleoresin Turmeric Oleoresin turmeric is the combination offlavor and color principles obtained from turmeric (Curcuma Longa L.) by extraction using one or more of the following solvents: acetone, ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene dichloride, or hexane.Typically,driedturmeric rhizomesaregound to U.S.A. Standard 50 mesh size and are loaded into a percolatorfor extraction with one or more ofthe above-identified solvents.

The resulting miscella isthenfiltered and solvent is removed by vacuum distillation to a residual level less than 30 ppm, as required by the FDA. The curcumin content ofthe resulting oleoresin varies with the choice ofsolventand on the curcumin content ofthe raw starting material. Commercial oleoresins are usually standardized to a desired curcumin content with a food grade diluent.

B. Preparation ofDefatted Oleoresin Turmeric 200 grams of oleoresin turmeric with a curcumin content of 37.5 wt.% was mixed with 200 grams of 0"C isopropanol and immediatelyvacuum filtered ona Buchnerfunnel fitted with #40 Whatman filter paper.

The filter cake was dried in a vacuum oven at 55"C under 29 inches Hg of vacuum for4 hoursto yeild 63 grams of defatted turmeric powder with a curcumin content of 94%.

Although all the following examples use defatted oleoresin turmeric as the source of curcumin, oleoresin turmeric may alternatively be used as the curcumin source. However, the fixed and volatile oils present in nondefatted oleoresin cause a slight cloudiness in aqueous solutions, and may impart a faintturmeric flavorto delicately flavored food colored with the curcumin complex product.

Example 2-Effect of Solvent Composition Lower bloom gelatins are relatively polar and hence are not as soluble in pure acetic acid as are higher bloom gelatins. Curcumin, on the other hand, is very soluble in pure acetic acid, but is relatively insoluble in water. In orderto determine an optimum mutual solvent composition, solvent systems ofthe following compositions were evaluated: Acetic Acid / Water (w/w) 80% I 20% 75% I 25% 70% I 30% 67% I 33% The evaluation procedure used was as follows: A. 60 grams of each ofthe solvent compositions was introduced into a respective 150 ml beaker equipped with a magnetic stirring bar and heated to 80-85"C with stirring.

B. 1 gram of defattedturmeric (94% curcumin) prepared as described in Example 1(B) was dissolved in the solvent with stirring to obtain a clearyellow solution.

C. 20 grams of 100 bloom gelatin (Davis Grade "J") was gradually added to the mixture of Step (B) with stirring until all gelatin was dissolved.

Undertheforegoing c6nditions, both the curcumin and gelatin dissolved readily in the 80%/20% and 75%/25% solvents. With the 70%/30% solvent system, it took 1.5 hours ofstirring to dissolve the curcumin. This was deemed an excessively long period of time for practical purposes. The 67%/33% solvent system would not dissolvethe curcumin unless the temperature was raised to 95-1 000C. This also is impractical, since denaturing of gelatin begins atabout90 C in such a solvent, as evidenced by the formation of a white, insoluble precipitate.

It was determined that about one part by weight of gelatin could be dissolved in three parts by weight of the75%/25% solventundertheforegoingconditions.

Example 3-Preparation of Curcumin-Gelatin Complex A series of curcumin-gelatin complex products containing from 5% to 25% of curcumin were prepared in 5% increments using 100 bloom gelatin and the 75%/25% solventsystem, as follow: A. In a 500 ml round bottom flask equipped with a magnetic stirring bar, 60 ml of solvent (75 wt.% acetic acid/25 wt.% water) was added and heated to 80-85"C with stirring.

B. An amountofdefatted oleoresinturmericwas dissolved in the heated solvent with stirring until a clearyellow solution was obtained (5-10 minutes).

One gram defatted oleoresin was used for the 5% product, 2 grams were used forthe 10% product, 3 grams were used forthe 15% product, etc. The 20% sample required heating of the solvent to 100 C in orderto completely dissolve thedefatted turmeric, and the 25% sample required heating to 105"C in order to effect complete dissolution.

C. 20 grams of 100 bloom gelatin (Davis Grade "J") was gradually added to the foregoing solutions with constant stirring. The temperature was carefully maintained at between 80"C and 85"C.

D. Solventwas removed from each solution by vacuum distillation at 20 mm pressure until a viscous orange solution was obtained.

E. Each solution was completely dried in a vacuum oven at 50-60"C under 29 inches Hg of vacuumforapproximately3 hours.

F. Each resulting product was ground in a mortar and pestle to pass through a U.S.A. Standard #170 mesh screen.

Example 4-Analysis of Curcumin Loading on Gelatin In orderto determine the maximum amount of curcumin that could be complexed with the gelatin, the absorbance of each of a series of aqueous solutions of the curcumin-gelatin products prepared in Example 3 was measured by spectroscopy as follows: A. To each of five 250 ml volumetricflasks was added 0.01 grams of a respective 5%, 10%, 15%, 20% or 25% curcumin-gelatin product of Example 3, and the volume made up with distilled water. The 20% and 25% solutions required heating to 70-80 Cto completely dissolvethe product.

B. The visible spectrum was scanned in the absorption mode from 300 nm to 600 nm. 1 cm path length cells were used, with distilled water as the reference.

The results were as follows: % Curcumin Product Absorbance Solution (420 nm) 5% 0.087 10% 0.192 15% 0.295 20% 0.330 25% 0.288 The forgoing data indicate thatthe optimum amount ofcurcumin occurred at about the 15% level, since the absorption level is fairly uniform above about 15%.

Example 5-EffectofGelatin Bloom Strength This test was performed in order to determine whethercurcumin loading varies with the bloom strength of gelatin. Four curcumin-gelatin products were prepared as previously described using gelatins with bloom strengths of 100,125, 180 and 250, with a 25% loading of curcumin, based on total gelatin plus curcumin, added to the reaction mixture. Spectroscopic analysis of each ofthe finished products indicated that only about 15% of each finished product was curcumin in each case.

Example 6 Gelatin desserts are food products wherein colors are used extensively and where clarity is an important property. The clarity and coloring ability of a 15% curcumin-gelatin complex product made according to the invention was evaluated against an uncolored gelatin. The curcumin content of the finished gelatin dessert was 5 ppm.

The colored gelatin dessert was prepared as follows: 8 grams Knox Unflavored Gelatin 50 grams Cane Sugar 0.017 grams 15% Curcumin-Gelatin Product 452 grams Water The gelatin, sugar, and curcumin complex was added to a saucepan containing the water and stirred constantly over low heat until all gelatin was dis solved. The saucepan was removed from heat and the solution was poured into a glass beaker and chilled until firm.

At usage level of 5 ppm, the colored gelatin resembled a commercial lemon Jello (Trade Mark) dessert in color, and the clarity of the chilled gelatin was identical to that of an uncolored gelatin dessert thatwas prepared in a similar fashion.

Example 7 Another application ofthe curcumin complex productofthe invention is in baked goods. In the example, a yellow cake was prepared using a commercial white cake mix and a 15% curcumingelatin productprepared asdescribed above, and compared to a cake prepa red from a commercially available yellow cake mix.

The cakes were prepared asfollows: 250 grams White Cake Mix (Loven Fresh brand -- Aldi Foods, Inc.) 31 grams Egg White 150 grams Water 0.041 grams 15% Curcumin-Gelatin Product (25 ppm, dry basis) All ingredients were beaten together at high speed for 4 minutes, and poured into a lightly greased cake pan.

The cake was baked at350 Ffor35 minutes.

The yellow cake was prepared in an identical fashion from a Loven Fresh brand yellow cake mix (Aldi Foods, Inc.), and using no curcumin complex.

The yellow cake that was prepared using the curcumin-gelatin product was identical in colortothe cake prepared from the commercially available yellow cake mix.

The dry, ground curcumin-gelatin product may be mixed with a dispersing agent such as salt or dextrose to achieve a substantially uniform distribution in dry mixes such as cake mixes or powdered soft drink mixes.

The scope of this invention is notto be limited to the foregoing description. Modifications of the specific description will be apparent to those skilled in the art.

Claims (14)

1. A method for preparing a curcumin-containing substance comprising dissolving a curcumin-containing substance and gelatin in a solvent comprising acetic acid, the curcumin-containing substance being present in an amount such that the said colouring agent contains a maximum of about 15 weight per cent curcumin on a dry basis, based on the total weight ofcurcumin and gelatin, the solvent containing a maximum of about 25 weight per cent water and the dissolving operation being carried out at a temperature less than the minimum denaturing temperature of gelatin in the solvent.

2. A method according to claim 1 wherein the solvent contains about 75 weight per cent acetic acid and about 25 weight per cent water.

3. A method according to claim 1 or 2 wherein the curcumin-containing substance is one of defatted oleoresinturmeric, oleoresin turmeric and purified curcumin.

4. Amethod according to claim 2 wherein the gelatin is present in an amount of about 1 part by weightper3 parts by weight of the solvent.

5. A method according to claim 4 wherein the admixing is carried out at a temperature less than about 90 C.

6. Amethod according to any preceding claim which includes substantially removing the solvent so as to provide the colouring agent in dry form.

7. A method according to any preceding claim wherein the curcumin-containing substance is dissolved in the solvent prior to dissolving the gelatin therein.

8. Awater-soluble curcumin-gelatin colouring agent prepared according to claim 1.

9. Awater-soluble curcumin-gelatin colouring agent according to claim 8 which is in dryform.

10. A method of imparting a yellow colour to a food product, comprising mixing the food product with a water soluble curcumin-gelatin colouring agent prepared according to claim 1.

11. A method according to claim 10 wherein the food product is in uniform and the colouring agent is dispersed on a dispersing agent.

12. A method according to claim 10 wherein the water-soluble curcumin-gelatin colouring agent is in dry form.

13. A method of preparing awater-solublecurcumin-containing substance substantially as herein described with reference to any of the examples.

14. A method of preparing a water-soluble curcumin-gelatincolouring agentforfoods substantially as herein described with reference to any ofthe examples.