Prof. S. V. LEBEDEV

ON THE QUESTION

OF CHANGES

IN FROZEN

CLAMP-STORED SUGAR BEET

DURING ITS WINTER STORAGE

UNDER THE CONDITIONS

OF THE SIBERIAN CLIMATE

Tomsk

1930

Prof. S. V. Lebedev.

On the Question of Changes in Frozen, Clamped Sugar Beet During Its Storage in Winter Under the Conditions of the Siberian Climate

The severe and distinctive climatic conditions of the winter period in Siberia make it necessary to raise the question of the possibility of processing frozen beet at Siberian sugar factories. Clarifying how prolonged frosts are reflected in the composition of beet, or what changes they cause in it, on the one hand, and, on the other, whether a long period of storing beet in frost can serve as an obstacle to its factory processing, must have great significance for the practice of the sugar industry in Siberia, which has grounds for its development.

A portion of the experimentally obtained material on this question is offered by the present work to the reader’s attention.

The study of the influence of Siberian climatic conditions on changes in sugar beet during prolonged—up to 5 months—storage in the frozen state was preceded by analyses of beet taken in bulk at the corresponding time of beet digging. The results of these investigations are presented in Tables I and I-a. They characterize the initial material, by which one may judge the changes that occurred in beet during its storage under the conditions of the Siberian frosts of the winter period of 1928–29 in the Barnaul District. We shall touch on the analysis of the cited data later, in the comparative evaluation of frozen and unfrozen beet. Here we shall proceed directly to the characterization of the beet obtained by the laboratory in Tomsk during the period from October 16, 1928, to April 1, 1929. The beet was sent in separate lots from the Aleisk District of the Barnaul District. The time of dispatch of the first lot corresponded to the moment when the beet digging had already been completed and light frosts were beginning, i.e., October 16, 1928.

Regarding the beet samples received, let us note the following: the beet was sent in samples (lots) weighing about three poods each, in wooden boxes, the walls of which had been bored through in several places—holes 3 cm in diameter; inside, the boxes were lined on all sides with hay; the initial weight of the samples, their weight when dispatched from the place of storage, the conditions of beet growth, the time of digging, and the conditions of storage prior to dispatch were not reported when the beet samples obtained were sent; there were no clamps in the usual sense of the word, and no nets with beet samples, as had been necessary and planned in order to determine changes in beet weight during its storage in clamps, despite the agreement that had taken place with Sibsakhstroi on this matter; the individual beet samples sent at different times differed in the heterogeneity of the forms of the roots: the number of large, small, and medium roots did not always correspond quantitatively with one another—in some samples there were only large and medium roots in the absence of small ones, in others the reverse, etc.; individual lots mo—

TABLE 1.

Results of the study of beets of the “Ordinary Selection.”

ANALYSES OF BEETS

TABLE 1-a.

Percentage content of the various forms of nitrogen in fresh beets at the time of their clamping, relative to the total nitrogen of the juice and beet shavings, taken as 100.

frozen beets sent for investigation; before the analysis of their average samples and thereafter, together with other average beet samples taken to check the change in weight during further storage, they were kept in a plank shed at the temperature of the outside air, i.e., they were protected from winds and snow, but were exposed to the action of natural frosts.

Some of the above-mentioned conditions, of course, made it difficult to resolve the question of determining the changes in frozen beets during their storage in clamps; nevertheless, as a result of the present work, a number of conclusions were obtained that still have a definite significance.

It is also worthwhile to dwell on the individual characterization of the separate lots of beets sent during the above-mentioned period to Tomsk, to the Siberian Technological Institute, for investigation.

LOT—1: Sent from the sowing site on 16 October 1928. Received by the laboratory on 25 October 1928 and analyzed on 2 November 1928; the sample was in transit for about 10 days; it was received in two boxes, weighing about 6 poods each. The beets in one box had been gathered from a field fertilized with manure ash, and those in the other—with superphosphate. The beets in both boxes arrived in a frozen state—the freezing occurred en route, since at the time the samples were dispatched there had not yet been frosts in Aleisk. In section the beets appeared completely normal, white in color, firm, without cracks, and frozen through.

LOT—2: Sent on 5 December and received on 10 December 1928, analyzed on 12 December. Shipment took about 5 days. The sample was received in two boxes in frozen form. A characteristic feature of this lot is its low juice content. Apparently, even before dispatch the beet sample had been under conditions conducive to its drying.

BATCHES 3 and 4: Received during the period of frosts, and from their appearance it was impossible to draw conclusions about any abnormalities. In section the beet appeared white, and upon thawing became yellowish-white. One circumstance must be noted: if, for the preceding batches, the beet in section presented a continuous surface, then for batches 3 and 4, on the cut surface of the root, before thawing, one could see in the mass of beet pieces of ice up to two mm across and up to four mm long, and after thawing, in the corresponding places where ice had been deposited—cracks.

It is not superfluous to note that this phenomenon pertained to the month of January.

BATCH—5: Dispatched on February 28, 1929, and received on March 20; it was therefore in transit for about one month, including the beginning of the spring thaw. Its appearance was normal. Only a certain darkening was noticeable from the surface inward into the root by 2–3 mm; in the remaining part, in the frozen state, it appeared white, without any external signs of changes.

Thawing of samples of frozen beet stored in Tomsk began on March 5, 1920.

BATCHES 6 and 7: according to the time at which the samples were taken, they corresponded to March 13 and April 1, 1929; that is, their dispatch from the place of sowing corresponded to the beginning of spring. And if batch 6 was received partially thawed, then batch 7 arrived in Tomsk completely thawed. In connection with this, naturally, there was considerable drying, an increase in the concentration of the juices, and an increase in invert content. Already by April 8 all the stored frozen beet appeared thawed, and the area of blackening of the beet from the periphery inward into the root was considerable, corresponding to 1–2 cm and more.

Thus, from observations of changes in the external appearance of beet stored for a long time under the conditions of the Siberian winter, with temperatures down to 35° C, one may already conclude the following: during the period from the beginning of the digging of sugar beet to the beginning of the spring thaws, the beet remains normal in external appearance, if one does not take into account that, under the influence of prolonged cold, beet roots in their mass undergo numerous ruptures of their tissue. Repeated thawings of beet, in connection with subsequent freezings, contribute to a change in the color of the beet in general and, in particular, to its darkening from the periphery of the root inward. The intensity of this darkening depends on the frequency and degree of thawing of the beet.

We shall now turn to the question of the change in the weight of beet when it is stored in frost, on the one hand, and to clarifying whether the darkening of beet during prolonged and repeated thawings is an indicator of its spoilage with respect to a decrease in sugar content.

To clarify the first question, several experiments were set up, the essence of which was that small samples, about 25 roots each, were selected from the batches of beet sent in; initially the samples were weighed, and thereafter the weighing was repeated systematically during each month until the end of the storage period, i.e., until April 13, 1928. The samples were stored in the same plank shed, in sacks. The results of the observations are summarized in Table II.

TABLE II.

Note to Table II: “−” denotes a decrease, “+” an increase in weight.

Analyzing the data of Table II, we arrive at the conclusion that when beets are stored in frost, under low-temperature conditions from −10 to −35°C, their weight changes very little; thawing of the beets and their further remaining under conditions of elevated air temperature, up to −8°C and higher, is accompanied by considerable drying out, causing a rapid decrease in weight.

In order to reveal the course of this process most clearly, an experiment was carried out with frozen beets and their subsequent placement under room-temperature conditions (from +14 to +20°C).

For the experiment, 10 frozen roots of various weights were taken. The roots were brought into the room and placed on trays, where they remained throughout the entire experiment. Each root was weighed separately every day. The data from these observations are summarized in Table III below.

The experiment was carried out over three days, after which the beets noticeably began to spoil. By the end of the experiment, the beet roots, together with a considerable decrease in their mass, had acquired a completely black color.

From the above it is evident that frozen beets, when transferred from air at a low temperature below zero into a room, because of the processes developing in them, up to spoilage, cannot remain in good condition under the latter conditions for a long time.

It follows from this that, in practice, under conditions of work with frozen beets, such beets must be processed immediately after they have been transferred from frost into warmth, while placing the beets under conditions of rapid thawing.

With regard to whether the blackening of beets during storage under the storage conditions known to us indicates their spoilage, we present the data of the corresponding experiments. For the experiment, beets stored under different temperature conditions were taken, with each sample con—

the black layer and the light layer were separately examined for their sugar content. Each beet sample consisted of 5 roots of identical size; the thickness of the outer layer cut off was the same for all samples, so that in one sample—namely the cellar sample, stored at a temperature of from −5° to −7°C—some light tissue was also partly mixed in with the black mass. Cutting was done only along the periphery, in the form of a truncated cone, to a depth of 1¼ cm.

The black and light masses were weighed separately, and sugar was determined separately in each by the method of hot aqueous digestion at a temperature of 85°C, for a duration of 45 minutes. The results of the experiments are presented in Table IV.

It is evident from Table IV that the blackened outer layer contains more sugar than the inner light layer. Such a distribution of sugar in the mass of frozen and then thawed beets corresponds to the topography of sugar in normal fresh beets and, thus, the phenomenon of blackening does not affect the change in the distribution of sugar zones in the beet; consequently, there are no grounds for saying that with blackening in the first moments after the thawing of beets, sugar is being consumed.

On the basis of the foregoing, with respect to the question of changes in the weight of beets during storage in the frost and the darkening of beets following thawing, we arrive at the following conclusions. Beets stored in the frost within temperature limits from −10° to −35°C during the winter until the beginning of the spring thaw (March 1) undergo a very slight decrease in weight; thawing of beets is always accompanied by a considerable decrease in weight, caused not so much by evaporation of water as by the mechanical loss from the beet of liquid formed in the beet mass under the influence of the melting of pieces of ice that appeared as a result of freezing of the beet; darkening of the beet is not an indication of beet spoilage with respect to a decrease in its sugar content.

We now turn to elucidating the changes in frozen beets, when stored in that state, with respect to sugar, good quality, and nitrogenous substances.

The research procedure was reduced to the following: before analysis, the frozen beet was first subjected to natural thawing at a temperature of 20°C, which required 3–4 hours. Then the roots of the sample were grated halfway with an ordinary coarse kitchen grater. From the resulting pulp a sample was taken for determination of sugar and nitrogen, and the other part was pressed, and the normal juice was examined in the same respect; this also included determination of acidity.

Sugar in the beet was determined by the method of hot digestion; invert was determined from the digestion juice with prior neutralization of the natural acids with chalk, clarification with lead acetate, and subsequent precipitation with soda of the excess of this reagent; in the prepared solution the invert was determined by Bertrand’s method; for determining nitrogen, the Kjeldahl method was used, with a 20 g sample; protein nitrogen was determined by Stutzer’s method, and amide and ammoniacal nitrogen with a 100 g sample by Schulze’s method; distillation of ammonia in the latter case was carried out with magnesia. Harmful nitrogen is taken as the difference between total nitrogen and the sum of protein, ammoniacal, and amide nitrogen. All determinations were carried out in three parallel samples. The acidity of normal juice was expressed in cubic centimeters of ¼ N NaOH solution; \(P_h\) was established by...

TABLE III.

by the electrometric method with quinhydrone. The results of the investigations are summarized in Tables V, VI, and VII. Table V gives a summary of systematic analyses of samples of frozen beet sent in batches during the period from October 16, 1928, to April 11, 1929; here, too, are presented data on the study of changes occurring in frozen beet in parallel samples, the analyses of which were carried out at different intervals of time (see batches 3 and 4).

TABLE IV.

TABLE V

Analyses of sea-clamp beets from the Artik region for the period from October 16–28 to April 11–29.

TABLE VI.

Changes that occurred in frozen beets during the period from 16/X-28 to 11/IV-29.

TABLE VII

Changes that occurred in frozen beets of consignments 3 and 4 during the period from 8.I.29 to 11/IV.29 and from 6/II to 11/IV.29.

Tables VI and VII characterize the beets of all lots with respect to the content in them of various forms of nitrogen, expressed as a percentage of the total nitrogen of the beet and of the nitrogen of the normal juice from it.

On the basis of the data presented in Tables I-a, VI, and VII concerning the question of quantitative changes in the various forms of nitrogen in frozen beets, the following may be noted: the amount of total nitrogen in the beet and in the normal juice proves, as a result of storage of the beet, to be relatively increased in comparison with its amount in beet just lifted—the increase for the beet is about 1.8% (see Tables I-a and VI).

This circumstance must be explained as a consequence of a decrease in the weight of the beet, mainly before the frosts and at the end of storage during its thawing, owing to drying out. The amount of protein nitrogen in the beet decreases during the storage period, and this decrease does not fall in the period of frosts, but chiefly in the period of the spring thaw (see Table VI). If the data of the analyses of beet lots 6 and 7, which had dried out considerably, are not taken into account, and only the data from the investigation of the lots up to the sixth lot, i.e. up to March 20, are taken, then, in comparison with fresh beets (see Table I-a), the amount of protein nitrogen in the frozen and thawed beet proves to be decreased.

The amount of harmful nitrogen in the stored beet also increases, but this increase is characteristic of the period of thawing of the beet. There becomes more harmful nitrogen.

Thus, the good quality of the juice decreases especially sharply during the period of thawing of the beet, as is also evident from Table V (see analyses Nos. 8-b, 9-a). From Table I we observe that the good quality of the juices of normal beet when stored in a clamp averages 86.9, whereas for frozen beet, already in the initial period after freezing, it drops sharply to 81–83, while the former sugar content is retained.

This phenomenon is undoubtedly interesting. During the period of subsequent prolonged frosts, about 4 months, the good quality changes hardly at all, and only with the onset of thawing of the beet does a rapid downward jump occur again.

The noted phenomenon is confirmed by individual references in the literature concerning the freezing of plants in general, which explain it by the dissolution of the dry matter of the cellular tissue (Maksimov et al.). To what extent this applies to frozen beet, it seems desirable in the future to verify and clarify.

As for sucrose, it turns out that the amount of it during the period of frosts, up to March 1, from the beginning of storage in the frozen state, quantitatively changes almost not at all. Only after a month, approximately from the beginning of the spring thaw, does the amount of sucrose decrease on average by about 1%, and at the same time, in a definite dependence, the amount of invert also increases simultaneously with an increase in the acidity of the juices.

Conclusions

In drawing a general conclusion from all the foregoing, and taking into account that the lots of frozen beet sent for investigation differed by a certain heterogeneity, and, on the other hand, that no cutting-up into clamps on site, as such, was carried out in 1928, nevertheless, on the basis of the—

From the results obtained in investigations during the storage of frozen beet under the natural conditions of the Siberian winter in the Altai district, it is possible to draw the following conclusions:

1) In the nearest period after freezing, sugar beet, although it does not lose its sugar content, considerably lowers its technological quality, which, apparently, is connected with the transition of part of the beet pulp into a soluble state.

2) The weight of beet during storage in the frosty winter period decreases only very slightly.

3) During the period of frost, until the onset of the spring thaws, the beet remains normal in external appearance. Its darkening develops only from the period of thawing and spreads in the root from its periphery toward the middle.

4) The darkening of beet indicated in point 3 does not affect the decrease in its sugar content.

5) The amount of sucrose in frozen beet after 4–5 months of storage remains almost unchanged until the beginning of the thaws, and only with the thaw does a rapid decrease in sugar content set in.

6) The technological quality of sugar beet that has deteriorated after freezing remains unchanged during the subsequent period of storage in the frozen state at temperatures below minus 6–8° C.

7) The amount of harmful nitrogen in frozen beet over the period during which the beet remains in the frost increases insignificantly.

In conclusion, it should be noted, on the basis of the investigations carried out during the 1928–29 season on clamp-stored beet kept under the conditions of the Siberian climate, that freezing is a rational means of preserving beet for the purposes of processing it at the sugar factories of Siberia. Freezing of beet contributes to an extended period of factory operation.

The campaign involving the processing of frozen beet may continue, for the Barnaul district, for about five months, counting September 15 as the beginning of production and March 1 as its end.

All the highly interesting propositions presented above should nevertheless be regarded as the results of a first survey undertaken toward the study of the various complex changes occurring in frozen, clamp-stored sugar beet during the winter period of the Siberian—more precisely, the Barnaul—climate.

Since in the period considered, 1928–29, the clamping of beet, as understood in the usual sense, was not carried out in the proper form, it is therefore necessary in 1929–30 to conduct the same investigations once again, broadening and deepening the work of the preceding year. The importance and necessity of the latter, in a production sense, for the future Siberian sugar industry are obvious and require no further explanation.

Tomsk.

Laboratory of Nutritional Substances
Siberian Technological Institute.