On the Causes of the Viscosity of Rye Mashes

Graduation thesis of A. M. Okorokov, student of the Chemical Department of the Tomsk Technological Institute.

Of all the grain materials used in distilling, rye has long attracted the attention of distillers by its particular property: rye mashes are stringy and viscous, owing to which a rye mash is less mobile than mashes made from other materials, for example wheat or millet.

Because of their immobility, rye mashes also give larger shortfalls.

The latter circumstance gave rise to the fact that, in the laboratory of nutritive substances of the Tomsk Technological Institute, at the suggestion and under the direction of Professor E. L. Zubashev, the author of the present article carried out an investigation into the causes of the viscosity of rye mashes.

The fact of the viscosity of rye mashes was noted by Ritthausen in his work: “Die Eiweisskörper der Getreidearten, Hülsenfrüchte und Ölsamen”.

Ritthausen finds the cause of the viscosity of rye mash in a certain adhesive substance—camede, or its mixture with vegetable mucilage.

According to Ritthausen, the composition of this substance is expressed by the chemical formula—\((C_6H_{10}O_5)_n\). Dried at \(110^\circ C\), it dissolves in water, though not completely, and after inversion gives dextrorotation.

Using the data of the above-named work, the author attempted to investigate this substance more precisely, and also to determine its content in rye and to establish the nature of the substances forming it. The investigation was preceded by a chemical analysis of the grain intended for the experiments.

To determine the starch content in the rye taken, the latter was boiled under a pressure of three atmospheres for two and a half hours, after which the amount of starch was established by the inversion method using Fehling’s solution. In doing so, of course, a correction was introduced for the amount of pentosans that had passed, during boiling, into the soluble state and had undergone hydrolysis during the inversion of the starch.

The determination of protein was carried out on the basis of the total nitrogen content, which was established by the Kjeldahl method.

The determination of ash was carried out in the form of sulfuric-acid salts; the result was multiplied by 0.9.

Fiber was determined by the Henneberg method.

Composition of rye:

Viscosity of mashes. Comparative experiments established that rye mashes possess greater viscosity in comparison with wheat mashes.

The mashes were prepared from flour and from grain after treating it in an autoclave under a pressure of three and a half atmospheres for two and a half hours.

The preparation of the mashes was carried out in the proportion accepted in practice, with malt extract being taken instead of malt.

The saccharification of mashes made from flour ended approximately after two hours, while that of mashes made from grain, after its treatment in an autoclave, ended after an hour and a half; in the latter case the mass was liquid, and therefore saccharification proceeded more successfully.

The end of saccharification was determined by the reaction with iodine.

The degree of viscosity of the filtered mash was established by the rate of outflow of a definite quantity of liquid from a viscometer.

The following results were obtained:

From the table given it is clear that, under the condition of identical treatment of bread materials, mashes from rye possess greater viscosity in comparison with mashes from wheat.

As stated above, Rittausen believes that the cause of this viscosity is the gum contained in rye.

Now, of course, it would be interesting to isolate this substance from rye and, having prepared a mash from such rye, again to test its viscosity.

The corresponding experiments that were carried out showed that a mash prepared from rye freed from gum by the method described below, in its outward appearance, resembled a mash from wheat flour: it was fairly mobile and filtered much more easily than a mash from rye without preliminary removal of the gum.

100 cubic cm of the mash thus prepared and filtered flowed out of the viscosimeter in 55 sec.

Thus:

100 cubic cm of mash from rye flour flowed out in 63 sec.
100 cubic cm of “ wheat ” “ ” “ 52 sec.
100 cubic cm of rye after removal of the gum from it . . . . . . . 55 sec.

These results clearly show that in rye there really is some substance which imparts viscosity to the mash made from it, and that after removal of this substance the viscosity of the mash decreases, and such a mash approaches wheat mash in viscosity.

Isolation and study of the substance. After this an attempt was made to isolate this substance and to determine quantitatively its content in rye.

For this purpose 100 g of rye flour were infused with 400 cubic cm of 50% aqueous alcohol.

After a week’s infusion, the clear dark-yellow liquid was carefully separated from the sediment by decantation. The liquid was allowed to stand, and again separated from the settled particles of entrained starch, after which the liquid filtered more easily.

After very careful and slow evaporation on a water bath to one third of its volume, a liquid was obtained that filtered with difficulty. The latter was treated with a large amount of 96% alcohol, whereupon there appeared a slightly colored white, mucilaginous and voluminous precipitate, which at first collected on the surface of the liquid in the form of a lump and then gradually settled to the bottom of the vessel. After long standing, when the liquid had become completely clear, the precipitate was carefully filtered off and washed with alcohol.

After drying in a desiccator over strong sulfuric acid, a white, slightly yellowish-colored substance was obtained, fairly readily soluble in hot water, although the solution did have a slight turbidity.

The reaction of the solution is acid.

This substance gives no coloration with iodine, does not reduce Fehling’s solution, and gives no compound with acetic-acid phenylhydrazine. The angle of rotation is \([\alpha]_{\mathrm{D}}^{20} = -88,^{\circ}32\).

In testing the substance for nitrogen, an insignificant amount of ammonia is obtained, probably owing to a small admixture of protein substances.

For determining the content of the substance in rye quantitatively, the precipitate, washed with alcohol, was dried at 110 degrees for two hours and weighed. It was thereby found that the investigated rye gum contains about 1.23%.

Dried at 110 degrees, this substance has a yellowish color and changes its properties: it becomes sparingly soluble in water. When 30 parts of water are used for one part of the substance, an incompletely clear, gluey solution is formed, which filters with great difficulty.

Copper sulfate with caustic potash, added to an aqueous solution, gives a voluminous precipitate of light-blue color, insoluble in excess caustic potash and stable upon heating.

Lead acetate, lead sugar, and a nitric-acid solution of mercurous oxide give no precipitate.

Basic lead acetate and ammonium oxalate give a white precipitate. Caustic and carbonated alkalies dissolve the substance, though not completely.

Thus, all the reactions give grounds for supposing that this substance resembles gum. Some confirmation of this supposition is the high content of pentosans, the amount of which was determined to be within the range of 86.38–86.72% by weight of the substance.

Upon hydrolysis with weak \(H_2SO_4\) (1:20), a new substance is formed, and the solution already possesses right rotation; at the same time it was established that the amount of the newly formed substance depends on the duration of hydrolysis.

1 g of the substance, when heated with 100 cu. cm. of dilute (1:20) sulfuric acid while boiling for 3 hours, gives 0.87 g of substances reducing Fehling’s solution, calculated as dextrose; and when boiled for 4 hours, gives 0.77 g.

Thus, the sugar solution obtained, after neutralization with chalk and decolorization with charcoal, possesses right rotation: at first \([\alpha]_{\mathrm{D}}^{20} = +148.7^\circ\), and then \([\alpha]_{\mathrm{D}}^{20} = +98.4^\circ\).

On long standing, small crystals of unclear and indefinite form separate from the solution.

Taking into account all the described properties of the substances, it may be supposed that, after hydrolysis in the case under consideration, arabinose should predominate as the substance in the solution; nevertheless, the solution was examined for galactose, arabinose, and glucose.

In view of the absence of galactose in the solution, it must be supposed that the substance cannot be assigned to the class of plant mucilages, as Rittausen assumed.

Substances belonging to the class of mucilages give, with iodine, a blue coloration, and when heated with acids, being hydrolyzed, they give galactose; the latter, when oxidized with nitric acid, gives mucic acid, very characteristic of galactose.

Meanwhile, the solution of the substance gives no coloration with iodine, and after hydrolysis and oxidation with nitric acid no signs of mucic acid were obtained.

The presence here of arabinose could certainly be suspected. On the basis of all the analytical data it may be assumed that the principal constituent of the substance is araban, which on heating passes into a compound difficultly soluble in water—metaraban, which on hydrolysis gives arabinose as the final product of the action of the acid (according to O’Sullivan ¹).

The presence of arabinose was proved by the formation of the benzoylhydrazine of arabinose ²).

After boiling with benzoylhydrazine and cooling, a compound separated in the form of thin plates of a white silky color. The melting point of these plates was \(+182^\circ\).

In view of the fact that in the literature there are statements by Professor Zubashev ³) and Davidis ⁴) concerning the melting point of arabinose benzohydrazide, differing from one another, the author checked these data with a preparation of pure arabinose obtained from Kahlbaum in Berlin. In this case the melting point of the derivative obtained from arabinose with benzohydrazine proved to be \(183—184^\circ\mathrm{C}\), i.e., lying within the limits indicated by Prof. Zubashev. Meanwhile, according to Davidis the corresponding value is \(212^\circ\mathrm{C}\).

On this basis it must be supposed that the substance obtained, as having a melting point of 182, is arabinose benzohydrazide.

The presence of glucose was established by the formation of saccharic acid under the action of nitric acid. A fairly considerable amount of silver saccharate was obtained in the precipitate, in the form of a small white precipitate.

With phenylhydrazine, on heating, a compound was obtained that was almost completely soluble in a large quantity of boiling water.

¹) See Prof. Zubashev’s “Carbohydrates,” p. 86, ed. 1897.

²) Ibid., p. 96, and also Die Chemie der Zuckerarten, Lippmann I, p. 90.

³) See Subaschow, “Ueber eine neue Trennungsmethode der Galaktose und Arabinose,” Zeitschrift d. Ver. f. die Rübenzucker-Industrie des deutschen Reiches, 1896, II, p. 270.

⁴) Ber. d. deutsch. chem. Gesellsch. 29, p. 2310.

Upon cooling, fine yellow crystals of osazone again separate. The melting temperature of such a compound is \(162.5^\circ\).

After artificial separation of the osazone by dissolving it in a large quantity of boiling water, a small amount of a compound was obtained that did not dissolve in water; the other part, dissolving in water, upon cooling again separates in the form of yellow crystals.

The melting point of the first osazone is \(204^\circ\), of the second—\(159^\circ\).

Thus, it may be said that the isolated substance of the gum, containing chiefly pentosans in its composition (\(86.68\)—\(86.72\%\) by weight of the substance) and having a left-handed specific rotation—\(88.32^\circ\), in its chemical reactions resembles araban.

Upon hydrolysis there is formed a mixture of glycoses, the predominant one of which is arabinose, and in an insignificant amount glucose.

The presence of the latter is not taken to be the result of hydrolysis of an impurity (starch), since the substance was undoubtedly free from starch, because in the iodine test it gave no traces of starch.

The presence of a third glycose—galactose—was not established with complete certainty.

Tomsk, lith.-typ. Sib. Association of Printing Business.