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washing with alcohol and ether. The specific conductivity of a 2.3 per cent gelatin solution, which had been de-ashed by the above method, was found t o be 1.5 X lob4 mho and the pH, 4.84. 3-The gelatin should have a constant isoelectric point, pH 4.74.9, tolerance to be fixed. 4-The gelatin should have a viscosity in the region of 4 centipoises a t 5 per cent concentration or 6 centipoises a t 7 per cent concentration, the measurements t o be taken at 40 O C. &The jelly strength should be in the region of 300 Bloom grams for a 7 per cent concentration, chilled by melting ice for 16 to 24 hours. 6-The gelatin should be nearly colorless, having a minimum absorption of blue light a t a definite thickness of 5 per cent concentration. 6
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7-The gelatin should be free from grease, fats, or heatcoagulable protein.
These specifications are quite tentative, and are intended to invite criticism. I n order to establish final specifications to which the standard material should conform, it is recommended that selected gelatins be completely tested by all laboratories concerned. Then, with definite figures, it will be possible to decide how precise will be the limits for the various properties, what methods are most accurate, etc. I n this way a scale of values may be established which will make the term “standard gelatin” one of definite significance for all laboratories.
Food Gelatin Values Relative to Concentrations’ M. Briefer a n d J. H. Cohen ATLANTIC GELATINE COMPANY, WOBURN, MASS.
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H E production of gelatin for all purposes has increased rapidly within recent years with corresponding improvement in methods of manufacture and the distribution of its use. By far the largest consumption is in the food industry, which includes such products as ice cream, confections, fancy cakes, biscuits, and so on. For these different uses food gelatin functions in various ways. One or another or several of its physical properties contribute to the quality of the product of which it is a part. This study is limited to the jelly phase of food gelatin with respect t o its behavior a t different concentrations in water, and is intended t o show the values of gelatins of different initial jelly strengths as related to their concentration, so that one mag find from the curves the approximate weight required of any one grade to equal the je& strength of any other grade. The term “grade” refers t o the initial jelly strength as determined by a standard method.2 F u n c t i o n s of Gelatin Properties in Different Foods
I n order to appreciate the limiting value of any one or several of the physical properties of gelatin we should consider briefly the functions of those properties. Naturally, the jelly phase is useful only when in the jelly state. The value of a gelatin, as expressed by the jelly strength, applies only to such products as are used, in their final form, as a chilled jelly. Gelatin jelly desserts and ice cream are examples of products depending on the jelly phase of food gelatin. On the other hand, soft marshmallow confections, because they are not in the state of a chilled jelly, depend more on the viscosity of the gelatin. Here we require a condition capable of supporting a network of foam walls and a high degree of moisture retention. Still another type of product is the hard candy or gum candies, in which the ’ gelatin is in a dry or semi-dry state. Neither jelly strength nor viscosity I alone plays the important role. Very likely “jelly consistency,”3 which is a compound property of jelly strength and viscosity, as well as solubility and i t s c o - r e l a t i v e property, water abIO
1 Presented under the title “Relations of Gelatin Concentration t o Jelly Strength” before the Division of Leather and Gelatin Chemistry a t the 76th Meeting of the Arnericdn Chemical Society, Swampscott, Mass., September 10 t o 14, 1928. * IND. END.CHEM., 16, 310 (1924). 8 Briefer and Cohen, Zbid., 20, 408 (1928).
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sorption, all combine to contribute to the quality of these candies. As a protective colloid, gelatin functions in a special way. I n this case the question of total solids is to be considered. With respect to “jelly consistency” a high-grade food gelatin may require only 3 per cent solid gelatin t o be equivalent to as much as 8 per cent of a low-grade gelatin but the protective colloid value is decidedly better with the gelatin having the larger quantity of total solids because of the increased dispersity possible in the denser medium. From these considerations it follows that the choice of gelatin for any particular use is a proposition, not simply of high or low grade, but of its power to function in a special way suitable to the purpose in hand. Experimental Procedure
The experimental work was done with a Bloom gelometer,2 using two different sized plungers. Solutions were made up of air-dry gelatin of grades from 60 to 250 Bloom grams2andiarying in-concentration from 1to 10 per cent, or in any case to the lowest concentration limit of the testing apparatus. The pH was noted and it was found that above a certain minimum concentration, varying somewhat with the grade, the pH had no appreciable effect on the jelly strength. The various samples were tested a t different times against known standards, and finally the entire group in each case was prepared a t one time and chilled all together, in the same water bath, a t 10” C., controlled to a differential of ‘F 0.1” C. The entire work is in good agreement and the curves (Figures 1 and 2) represent fairly the characteristics
I N D U S T R I A L AND ENGINEERING CHEMISTRY
March, 1929 of each grade examined. was adjusted to 6.3.
The p H of one group (Figure 2) Discussion
The curves show that within a certain range the jelly strength is a linear function of the concentration; but since few, if any, commercial products contain food gelatin in these concentrations, the results are of no value unless they can be related to the useful concentrations. That this is unlikely is evident from the fact that within the useful concentration range (up t o about 3 per cent) the curve is not linear. The straight-line portion of the curves begins a t different concentrations, varying with the grade. The higher the grade the lower the concentration included in the straightline part of the curve.
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is, the angles formed by an extension of the straight-line periods with the base line or X axis-shows the weight increments of the different grades, relative to the concentration, against jelly test expressed in Bloom grams. Concentrations from 1 to 2 per cent show no numerical agreement, which is to be expected since this region is affected, not only by the pH, but also by the viscosity and the quantity of hydrolyzed gelatin. This hydrolysis is measurable from the volume of the precipitate, in the form of a turbid suspension, formed when a 1per cent gelatin solution is adjusted precisely to the isoelectric point. The adjustment is made by addition of acid or alkali, depending on the original pH of the gelatin. Under the conditions mentioned the maximum turbidity is attained a t the isoelectric point and the intensity of turbidity may be measured ph~tometrically.~The quantity of incident light stopped by the particles in suspension, in unit volume, is a measure of the relative volumes of the precipitate. It has not been determined what constituents of the gelatin combine t o form the precipitate nor what percentage of the original weight is precipitated. It has, however, been found possible to separate the precipitate by filtration after the substance has aged sufficiently t o coagulate. This should serve as another means for measuring the volume of the precipitate and also for an analysis of the separate component^.^ The resultant pH of the ingredients compounded with gelatin in any product will modify the pH of the gelatin. This accounts for some peculiar results. It explains why some obviously poor quality gelatin often gives as good or better results than a higher grade and yet, if the p H of the manufactured products is controlled, the best results must inevitably obtain from the better grades. This is especially true of the keeping quality of the product provided, as previously pointed out, that the physical properties of the gelatin are suitable for the manufactured commodity. The solid lines in the figures are the curves obtained from the measurements. The dotted lines in Figure 1 are extensions of the straight-line portions of the curves, showing the deDarture from this linear Deriod a t the lower concentrations. In-Figure 2 it is shown &at as the initial jelly strength increases in value the curves tend to converge as the concentrations are reduced. This is especially noticeable with the highest grades.
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The relative values of the several grades are not proportional to the concentrations, but a t about 3 per cent the values are roughly proportional to their average commercial value as proved by experience. This indicates that gelatin graded on a 3 per cent concentration basis, instead of the present practice of 6.67 per cent, would result in a better approximation of gelatin values. For gelctin concentrations of 3 per cent and less the pH effect is very marked. At 1 to 1.5 per cent it is critical in the region of its isoelectric point. The slope or tangent of the linear portions of curves-that
Conclusion
From a study of this work it can be realized that the present methods for testing gelatin should be so modified as to bring all grades either within the straight-line period or entirely out of it. When using a 16-mm. plunger and 3 t o 4 per cent concentrations the relative values of all grades closely approximate the actual values assigned to them by experience and practical application. 4
See also page 266, this issue
Development of Agricultural By-products Fifty years ago the production of cottonseed oil, a by-product ofjthe cotton crop, was just beginning. The farmers of the South were often in a quandary as how best to get rid of the cottonseed. In 1927, the value of cottonseed products, including oil, meal, cake, hulls, and linters, was $240,000,000. Corn has always found its greatest use as food for livestock, but during the last half-century science and research have found other important uses for it. Glucose, one of corn’s products, is now used in the manufacture of various kinds of jams, jellies, candies, chewing gums, and sirups. Starch is finding an expanding use both for food and in the textile industries, in laun-
dries, in the manufacture of baking powder, and in certain cosmetics. Since 1878 corn oil has been developed, and it is used to an important extent in the manufacture of soaps and certain machine oils, as well as for human food. The growth of factory canning and the introduction of prepared breakfast foods have done much toward increasing the value of the corn crop. Fifty years ago no one would have thought of corn cobs, stalks, and husks as of value, apart from the very minor purposes to which the farmer himself could put them. Yet recent research has developed what promise to be important industrial uses for these products, but much more is yet to be accomplished.
