Prof. S. V. LEBEDEV and N. G. ZABEGALOV

EFFECT OF THE DRYING TEMPERATURE OF SUGAR BEET COSSETTES ON THE DEGREE OF TRANSFER OF NON-SUGAR SUBSTANCES FROM THEM INTO JUICE

Prof. S. V. Lebedev and N. G. Zabegalov

Effect of the Drying Temperature of Sugar Beet on the Degree of Transfer of Non-Sugar Substances from It into Juice.

The processing of dried beet in the sugar industry is at present acquiring ever greater significance, not only as an idea but also as a possibility being carried out in practice. In connection with this, especially in recent years, many works have appeared by prominent theoreticians and practitioners of the sugar industry. The result of these investigations has been the clarification of a whole series of questions connected with the economic and technical possibilities of processing dried beet. Thus, the most favorable temperatures for drying beet cossettes have been established with respect to extracting sugar from them with minimal losses; it is being determined to what extent an increase in drying temperature promotes caramelization and the formation of invert sugar; it is also known that, when dry beet cossettes are processed, juices of higher purity are obtained than when the same beet is processed in its raw state.

In connection with the latter, there naturally arises the question of the purifying significance of drying beet, in the sense of the influence of the latter on the transfer into diffusion juice of various kinds of non-sugars. In the indicated direction the literature has not yet provided an exhaustive answer. In view of the breadth of this question, the task of the present work was to elucidate only a part of it, namely to determine the influence of the drying process and its temperatures on the degree of transfer into digestion juice of nitrogen-containing substances, which in the process of sugar manufacture have significance as harmful molasses-formers, of ash constituents, and of pentosans under conditions of work with dried cossettes.

The methodology and technique of conducting the experiments amount to the following: beet, previously cleaned and wiped dry, was cut with the knife of a factory beet slicer and converted into grooved cossettes 3–4 mm thick. The resulting cossettes were thoroughly mixed, and from this combined sample were taken: a sample for determining sugar and nitrogen, and five samples of equal weight for drying them at various temperatures. Subsequently it is assumed that all these samples were identical in their composition. The samples were placed on metal plates, 300 grams on each. The latter were placed on the five shelves of an electric drying cabinet, arranged one above another. Drying was carried out by a current of hot air. To each shelf correspond—

maintained its own quite definite constant temperature. Thus, one sample was dried at 65°C, another at 75°C, the third at 80°C, the fourth at 85°C, and the fifth at 95–97°C. These temperatures are the least threatening with respect to the development of decomposition processes in the beet being dried. Under the indicated conditions, drying of the beet was carried out until its weight no longer changed at the given temperature over the course of one hour. Thus, as a result of drying, five samples of dry cossettes were obtained—fractions I, II, etc. The material for the investigation consisted of a batch of beets from the Barnaul experimental field (A) and a batch of beets from the Aleisk district of the Barnaul okrug (B). The conditions and results of drying are presented in Table 1 below.

TABLE 1.

In characterizing the initial material, it should be noted that beet batch A was richer in water content than beet batch B. This was taken into account subsequently when recalculating the weighed portions of dry cossettes to the raw substance of the beet. Each fraction of dry cossettes was stored in a separate jar with a ground-glass stopper.

The essence of the research procedure was as follows: sugar was determined both in the raw beet and in the corresponding dry beet by the method of hot aqueous digestion at a temperature of 85°C and a duration of 45 minutes; polarization was carried out in 400 mm tubes. These digestion conditions, as is known (see the work “On the Dynamics

drying of sugar beet” — S. V. Lebedev and N. G. Zabegalov, and vol. I of the works of TsINS*) are satisfactory in the sense of maximum extraction of sugar from dried beet. In all sugar determinations the sample weight corresponded to the normal one—26 grams. For dry cossettes the sample weights were reduced, for each beet fraction, according to the percentage of water removed, and, recalculated to the raw substance of the beet, were equivalent to the normal sample weight.

In determining the various forms of nitrogen, the sample weight in all cases corresponded to 20 g of the raw substance of the beet.

Total nitrogen was determined by the Kjeldahl method, protein nitrogen by Bernstein, and amide and ammonia nitrogen by Schulze. Ash was determined in the dry cossettes of the separate fractions and in the juices evaporated from them on a water bath by ignition in a muffle, with preliminary slow charring under gentle heating. The sample weights corresponded to quantities of about 1.5 grams of dry beet substance. The ash determinations concerned only batch B. We shall discuss the method used for investigating pentosans later.

We now turn to the presentation of the results of the work and first consider the characterization of the raw beet taken for investigation.

Table 2 gives a summary of the results of the investigation of the raw beet. Nitrogen in the cossettes and in the digestion juices obtained from them is shown as percentages by weight of the raw substance of the beet (columns 4, 6, 9, 11); columns 5, 7, 10, 12 show how much of the various forms of nitrogen passes into the digestion juice, as a percentage of the total nitrogen of the cossettes; column 8 indicates how much protein nitrogen passes into the digestion juice as a percentage of its total content in the cossettes; column 3 presents the results of the sugar determination (see Table 2).

TABLE 2.

In analyzing the results of the study of dried beet, we shall touch also on the data set out in Table 2. We shall dwell on the main part of our work, namely the study of fractions of dried beet and juices from them. The results of the observations with respect to nitrogen-containing substances are reduced to Tables Nos. 3, 4, 5.

Tables 3 and 4 (pp. 5 and 6) present data from determinations of total, protein, amide, and ammonia nitrogen, and of harmful nitrogen, the latter being taken as the difference between total nitrogen, on the one hand, and the sum of protein, amide, and ammonia nitrogen, on the other. Table 3 corresponds to beet lot A, Table 4 to beet lot B. Columns 3, 5, 7, 9, 11 show the content of the various forms of nitrogen in dried cossettes and in the diffusion juices from individual fractions thereof as percentages of the weight of the raw substance of the cossettes; columns 4, 6, 8, 10, 12 express, as percentages, the content of all types of nitrogen in the cossettes and in the diffusion juices relative to the total nitrogen content of the cossettes, taken as 100 percent.

Table 5 gives the percentage content of protein nitrogen in the diffusion juice from dried beet relative to its total content in the cossettes, taken as 100 percent.

TABLE 5.

Percentage content of protein nitrogen in the diffusion juice from dried cossettes relative to its total content in the cossettes, taken as 100 percent.

Considering the data of the above tables, we can draw the following conclusion. For all fractions of dried beet, both for beet lot A and for lot B, the quantities of total nitrogen in the dried cossettes remain almost constant, if one does not take into account the results given in Table 3 that correspond to fractions IV and V. Here there is, as it were, a certain decrease in total nitrogen in the cossettes in connection with an increase in the drying temperature. But this apparent decrease is more likely due to possible nonuniformity of the raw material. There are no grounds for saying that drying can affect a decrease in total nitrogen.

With respect to the transfer from the dried cossettes into the diffusion juice of total nitrogen, the influence of the drying temperatures is apparent, namely: the percentage of total nitrogen in the diffusion juice relative to its total content in the cossettes, taken as 100 percent, proves to be lowest for beet fractions dried at 75 and 80°C (see Table 3) and for fractions dried at 80, 85°C (see Table 4).

This circumstance is directly connected with the way in which the protein nitro-

TABLE 3.

Percentage content of nitrogenous substances in dry cossettes and in the diffusion juice from them, per 100 parts of dry matter.

Variant A.

TABLE 1.

Percentage content of nitrogenous substances in dry beet cossettes and in the juice from them, recalculated per 100 parts of raw beet.

substances present in it. Resolving this question was the main objective of the present work. The most important point for this question is the effect of the drying temperatures of beet cossettes on the degree of transfer of protein nitrogenous substances into diffusion juice. From consideration of the data in Tables 3 and 4 it is evident that, as a percentage of the total nitrogen of the cossettes, the amount of protein substances passing into the diffusion juice proves to be smaller for beet fractions dried at temperatures of 75, 80, and 85°C for lot A, and for beet fractions—temperatures of 80 and 85°C—for lot B.

For beet fractions dried below 75°, the percentage of protein substances passing into the diffusion juice, relative to the total nitrogen of the cossettes, proves to be elevated for beet lot A and reduced for lot B in comparison with the subsequent temperature fractions, which apparently is connected with certain individual features of the beet lots studied. For the beet fractions (see Tables 3 and 4) dried at a temperature of 97°C, however, the percentage of protein substances, relative to the total nitrogen of the cossettes, passing into the diffusion juice is always elevated.

The same thing can be clearly seen from consideration of the data in Table 5, the explanation of which was given above. Within the range of temperatures from 65° to 85°C at which the corresponding fractions were dried, the percentage of protein substances, relative to their total content in the cossettes, passing into the diffusion juice decreases with increasing temperature. But for beet fractions dried at 97°C there is a sharp jump—in these conditions more protein substances pass into the diffusion juice than under the preceding conditions. It would perhaps be difficult to explain the reason for this if one did not take into account the circumstance that, with the gradual process of dehydration of the cossettes at high temperatures, relatively favorable conditions are created for the hydrolysis of proteins.

As regards the transfer of other forms of nitrogen, we note that, with respect to the influence of drying temperatures on the transfer of amide and ammonia nitrogen from dry cossettes into diffusion juice, it is not possible to draw any conclusions.

Finally, let us note that, with respect to nitrogen-containing substances, the drying process acts in the sense of an effect of juice purification, somewhat increasing it in comparison with raw cossettes. Thus (see Table 2), from raw cossettes into diffusion juice there passes from 23.6 to 24.7 percent of protein substances from their total content in the cossettes, whereas under the same conditions, but already from dry cossettes of the same beet, dried at temperatures of 75°, 80–85°C, from 22.1 to 23.5 and from 17.8 to 20.3 passes into the diffusion juice (see Table 5).

Let us briefly dwell on the influence of the drying temperature of beet on the degree of transfer of ash substances from dry cossettes into juice. The data are given in the following Table 7. Ash is shown as a percentage by weight of dry matter, both in the cossettes and in the juices from them, according to the dried temperature fractions. From consideration of the data presented it becomes clear that the beet fractions dried at a temperature of 85°C are under more favorable conditions with respect to purification of the juice from inorganic constituent parts of the beet than the other fractions. This is in complete agreement

and also by the fact that for this fraction a smaller percentage of protein substances is obtained in the digestion juice. The latter accounts for the known retention of ash in the masses of cossettes, and therefore part of the ash is not subjected to digestion.

TABLE 6.

It remains to discuss the influence of beet drying and of the temperature conditions of drying on the degree of extraction, in the digestion method of obtaining sugar, of substances determined in ordinary analyses by the concept of the so-called “pentosans,” by which in the present case is meant the totality of nitrogen-free extractive substances of the beet that yield furfural on boiling with hydrochloric acid. The products of hydrolysis of such substances, which are constituents of sugar beet, are also harmful molasses-forming substances. Consequently, posing the question indicated above is quite natural, and if a reduction in the transfer of beet “pentosans” into juices from dried cossettes occurs, this would be a favorable factor for dried beet in the purification of the juices obtained from it. This part of the work was carried out by S. V. Lebedev and S. N. Loskutova with beet already characterized above, while observing the same conditions of beet drying and digestion as were adopted in elucidating the questions relating to the nitrogen-containing substances of the same sugar beet. Pentosans were determined both in the raw and in the dry beet by Tollens’ method.

The results of the experiments are summarized in Table 7, where the percentage contents of pentosans in the raw beet and in the same beet dried, as well as in their digestion juices, are shown; in the last columns are given data on the transfer of pentosans into the digestion juice as percentages of their total amount and the reduction in the transfer of pentosans into the juice as percentages of their total amount in the beet.

When comparing the results of the analysis of raw and dried cossettes and the corresponding digestion juices, it is found that the degree of extraction of pentosans during digestion from dried beet cossettes is lower than during digestion from raw cossettes.

TABLE 7.

Summing up the foregoing, we arrive at the following conclusions:

1. The process of drying beet cossettes and the temperatures at which it is carried out affect the degree of transfer of nitrogen-containing substances into the juice, tending to reduce it.

2. The most favorable temperatures for this are drying temperatures of beet within the range of 75 to 85°C—precisely those temperatures which at the same time also promote the greatest degree of extraction of sugar from dried beet.

3. The significance of the indicated drying temperatures for enhancing the effect of juice purification consists in their direct connection with the coagulation of proteins under the influence of one or another degree of heating.

4. A drying temperature for beet cossettes of 85°C also favors a reduction in the degree of transfer of ash elements from the dried cossettes into the diffusion juice.

5. Drying beet cossettes affects the degree of extraction of pectin substances (pentosans), more precisely, pentosan derivatives, reducing the content of the latter in the diffusion juice.

All that has been said above provides grounds for the general conclusion that drying beet cossettes, for the purpose of processing them in the sugar industry, is expedient from the standpoint of increasing the effect of purifying juices from non-sugar substances. The numerical values of the purification effect of juices from dried beet may evidently vary depending on the individual characteristics of the dried sugar beet under investigation.

Tomsk.

Laboratory of Nutrient Substances
Siberian Technological
Institute.