US2398004A - Controlling the isoelectric point of gelatin - Google Patents

Description

April 9, 1946.

R. C. HOUCK ET AL CONTROLLiNG THE ISOELEC'I'RIC POINT OF GELATIN Filed July 20, 1943 I I m l I EFFECT OF TIME OF REACTION OF ALKAL/ ON THE ISOELECTH'IC POINT OF GELATIN P IZZ I Z 3 4 I 5 6 7 8 TIME (IN HOURS) 'AT 52C. 55mm? ADDING A'clo ROBERT c. HOUCK JOHN RUSSELL SAMUEL E. SHEPPARD INVENTORS BY W. M

(c? sawzJmM ATTORNEYS tracted by the acid process.

Patented Apr. 9, 1946 CONTROLLING THE ISOELECTRIC POINT OF GELATIN Robert C. Houok, John Russell, and Samuel E.

Sheppard, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application July 20, 1943, Serial No. 495,454

6 Claims.

This invention relates to the manufacture of gelatin and particularly to a method for controlling the isoelectric point of gelatin.

It is known that the properties of gelatin can be changed markedly by the method of manugelatin, the isoelectric point is thepH at which it is equally dissociated as an acid and as a base. The isoelectric point of gelatin depends upon the method by which the gelatin has been made. Gelatins made by the lime process of plumping of hides have an isoelectric point of from 4.7 to 5.0 and their physical properties usually exhibit a sharp minimum somewhere in.this region. Gelatins extracted by the acid process have an isoelectric point varying from pH 7 to pH 9 and their physical properties usually do not exhibit a sharp minimum but a flat region as shown, for example, in Sheppard and Hudson U. S. Patent 2,101,877, granted December 14, 1937.

It is desirable in certain processes to have a gelatin having an isoelectric point below the values usually obtained when the material is ex- The pH of the isoelectric point of the .gelatin is not readily controlled by varying the method of extraction from the hides and the gelatin obtained does not always have an isoelectric point in the desired region.

It is, therefore, an object of the present invention to provide a method for controlling theisoelectric point of gelatin. A further object is to provide a method for obtaining gelatin of any desired isoelectric point. A still further object is to provide a method for lowering the isoelectric point of gelatin and thereby controlling its physical properties such as swelling and viscosity. Other objects will appear from the following description of our invention.

These objects are accomplished by heating gelatin in the presence of any material which raises the pH of the gelatin solution, such as an alkaline hydroxide, for a definite period of time and then stopping the action of the alkali and washing it from the gelatin.

The accompanying drawing shows a series of graphs illustrating the change in isoelectric point obtained by treating an acid process gelatin for varying periods of time at various degrees of alkalinity.

'Our method consists in treating gelatin, preferably gelatin of high isoelectric point, with any material which raises the pH of the solution, such as an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali carbonate, triethanolamine, or pyridine for a definite period of time. The time required depends upon the temperature and the pH at which the gelatin is heated or aged. The speed of the drop in isoelectric point at a given pHis affected by the temperature which can be varied from 5 C. to C. The pH can be varied from 8 to 12.5, the rate change at a given temperature increasing with increase in pH from 8 to 12.5. At the end of the desired time, the action of the alkali is stopped by adding acid to neutralize the alkali. The resulting gelatin is chilled, noodled and washed. It will then have an isoelectric point which depends upon the time, temperature and pH of treatment as stated above.

According to our method a solution of gelatin is made in the usual manner and the desired amount of an aqueous solution of an alkalinematerial, such as alkali metal hydroxide or alkaline earth metal hydroxide added to it to bring the pH to the desired point as explained below. The solution is then heated for a definite period of time and at the end of this time the reaction is stopped by adding suflicient acid such as hydrochloric acid to neutralize the alkali which was added to the gelatin. The resulting gelatin is then chilled, noodled and Washed for about 48 hours with colddistilled water.

We have treated both acid-process gelatin and lime-process gelatin by our method but find it preferable to treat the acid-process gelatin. Re-

sults obtained by treating the various types of mined and are given in the following tables.

The effect of pH on the isoelectric point of an acid process gelatin treated at 52 C. for various lengths of time is recorded in the following table. I

to 8 and the higher values at which portions of" the gelatin were treated. The results of this treatment were as follows:

pH of isoelec'tricpoint Time of treatment (hours) pH 9.6 pH 10.6

These data were plotted as shown in the accompanying drawing 'to-indic'atethe change in DHlof the isoelectric point for various times of treatment. A study of the table and the curves shows thatthe decrease in'isoelectric point is regulated at a giv'en'temperature by the pH of the solution and the time of heating. As shown, for exampleyin the curve for treatment of the gelatin at pH 10.6, the isoelectric point was reduced after two hours treatment at 52 C. from 9.17 to 7.04. After five hours treatment the iso-, electric point of this sample had dropped to 6.46 and, after 28 hours treatment it had dropped to 5.4. As the pH of treatment increased, the rate of decrease in isoelectric point showed an increase; For example, at a, pH of treatment of 12.2 the isoelectric point dropped to 5.15 after one hour whereas at a pH of treatment of 10.6 it had dropped only to 7.64 after the same length of time. v I

' In order to illustrate the effect of temperature on the lowering of the isoelectric point of acidprocess gelatin, a sampled the same gelatin having an original isoelectricpoint at pH 9.17 was treated with a sufficient quantity of sodium hydroxide solution to bringthe pH of the gelatin to 9.6. At this pH the gelatin was treated at temperatures of from 35 C. to 52 C. and the results recorded as follows:

- Time of PH Temperature a electric heatin point r 7 Hours 35 C 96 6. 52

C i 72 5. 77 7 52 C O 4. 91

point is about this pH. In spite of these difierences in times of'heating the results indicate that the reaction is slowed up by lowering the temperature as was to be expected.

In order to study the eiiect of variation in the alkali employed, we have used alkali metal hydroxides such as sodiumflhydroxide, {potassium hydroxide and ammonium hydroxide and alkaw .line earth metal hydroxides such as calcium hy- 'method employed to raise the pH does not afiect droxide. Results of these tests show that the the result appreciably. v

The swelling of gelatin is one physical property whose minimum range includes the isoelectrlc point.-

ing as compared to lime-process gelatin with a sharp minimum at the isoelectric point, Swelling measurements were made on gelatin having an isoelectric point of 6.5 after treatment of-an original gelatin having an-isoelectric point'at'pI-I 8.4. Swelling measurements were made at 15 C. using a sodium acetate-acetic acid buffer andthe regionof minimum swelling was'found to extend from pH 4.5to pH 10. This indicated that the gelatin had a region of minimum swelling in-the same region as that of the isoelectric point. In using our method for the treatment of limeprocess gelatin, we employed a deashedli'me process gelatin having anfis'oelectric point of 4.78. On heating a sample of this'gelatin at 52 C. for

' five hoursat pH'12. 2,fthe isoelectrie point' d'ecreased slightly from pH 4.78 to ;pH'4. 5. The gelatin thus obtained had been seriously degraded by this treatment'which was rather harsh. Aging at pH 12.2'for one monthat 5 C. did not decrease the isoelectric point. Under similar conditions the isoelectric point of acid-processgelatin would have been markedly reduced. J

This result with lime process gelatin, differing from the result obtained with'acid process gelatin is explained by the fact that the hide has lost most of its amide nitrogen during the liming process, Consequently the resulting gelatin has a relatively low isoelectric point andis' not atfected appreciably by further alkaline treatment. The use of gelatine of a definite isoelectric point isof value in those cases where standardization of properties, such as swelling, is concerned. In the use of only gelatine of a specific isoelectric point, all external conditions must be regulated by the isoelectric point of the gelatin. If gelatins of all isoelectric points are obtainable then the most desirable conditions with respect j '1. The method of reducing the isoelectric point of gelatin havingan isoelectric point above pH 5',

which comprises treating said gelatin at a temperature of from about 30 C. to about 60 C. for a period of time from about 1 minute to about 50 hours with an alkaline hydroxide at a pH greater I than about 8, then neutralizing the alkali and washing the gelatin, thereby effecting a reduction in the isoelectric point of the gelatin.

2. The method of reducing-the isoelectric point 'of-gelatin having an isoelectric point above pH- 5, which comprises treating said gelatin at a temperature of from about 30 C. to about 60 C. for a period of time from about 1 minute to about 50 hours with an alkali metal hydroxide at a pH greater. than about 8, then neutralizing the alkali and washing the gelatin, thereby effecting a reduction in the isoelectric point of the gelatin.

3. The method of reducing the isoelectric point of acid-process gelatin, which comprises adding sodium hydroxide to a solution of said gelatin in suificient amount to bring the pH to about 8, heating the mixture at a temperature of from about 30 C. to about 60 C. for a period of time from about one minute to about 50 hours, neutralizing the alkali with acid, and washing the gelatin with cold water.

4. The method of reducing the isoelectric point of acid-process gelatin, which comprises adding sodium hydroxide to a solution of said gelatin in sufiicient amount to bring the pH to about 8, heating the mixture at a temperature of from about 30 C. to about 60 C. for a period oftime from about 1 minute to about 50 hours, neutralizing the alkali with hydrochloric acid, and washing the gelatin with cold water.

5. The method of treating gelatin having an isoelectric point above pH 5, to lower the pH of its isoelectric point, which comprises mixing an alkali metal hydroxide with a solution of gelatin.

at a pH above about 8, heating the mixture at a temperature of approximately 50 C. for a period of time from about one minute to about 50 hours, neutralizing the alkali metal hydroxide with acid, and washing the gelatin with water.

6. The method of reducing the isoelectric point of gelatin having an isoeleotric point above pH 5, which comprises treating said gelatin with an alkaline material at a temperature of from about 5 C. to about 60 C. at a pH greater than about pH 8 and for a length 01 time sufficient to efiect a reduction in the isoelectric point of the gelatin without appreciably degrading it, then neutralizing the alkaline material and washing the gelatin, thereby effecting a reduction in the isoelectric point of the gelatin,

ROBERT C. HOUCK. JOHN RUSSELL. SAMUEL E. SHEPPARD.

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