THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Dec., 1922
1131
The Determination of Gums in Sugar Products’ By H. T.Ruff and James R. Withrow LABORATORY OF INDUSTRIAL CHEMISTRY, OHIOSTATE UNIVERSITY, COLUMBUS, OHIO
Sugar boilers and others responsible for the production of refined from raw sugar recognize that different yields and rates of crystallization may be obtained from two raw sugars of similar sucrose, invert sugar and ash content, that haoe had the same treatment. I t is generally conceded that this difference is due to the gums. The gums are presumed lo be the strongest molasses formers among ihe organic nonsugars. This situation is also encountered i n the manufacture of raw sugar from the cane. The problem with which this work is concerned is the selection of a method for determining these gums that could be used for control work or to classify sugar products further than the usual Sugar and ash determinations. Our work indicates:
I-Of the various methods proposed for gum determination, the precipitation by ethyl alcohol with hydrochloric acid acidification was found to be the most suitable for a rapid method adapted to control work. 2-The concentration of hydrochloric acid can be oaried within rather wide limits without materially aflecting the results, but the concentration of the alcohol must be kept within close limits. 3-With suitable precautions, denatured or methyl alcohol can be substituted for the ethyl alcohol. 4-The technic of the method can be simplified, so that its use is not prohibitioe for control wbrk.
HE METHODS for determining gum in sugar products may be classified into four groups, according to the precipitant used: 1-Hydrochloric acid-ethyl alcohol methods.2 2-Calcium chloride-ethyl alcohol m e t h ~ d s . ~ 3-Ferric chloride followed by reprecipitation with alcoh01.~ 4-Lead acetate in alcohol methods.5 In addition to these there are methods involving dialysis, but they could not be considered as control methods. We checked representative methods from each group, using black strap molasses for the tests. Both ethyl and methyl alcohol were used. The following average results were obtained.
much as three times the alcohol used in an HC1-alcohol precipitation. Compared with the other methods, this method gives abnormally low results. The Pb(CzHaO&alcohol method has the very obvious dissdvartage that it precipitates many other organic nonsugars in addition to the alcohol-insoluble gums, when a p plied to a product like black strap. This mcthod involves a lend correction and washing with alcohol and ether. It is slower than the HCI-alcohol method.
T
METHYL ALCOHOL Per cent
2.27 . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. 7.38 0.68 . . . . . . . ...... ...... .. ...... 15.9
HCl-Alcohol (Weichmann) , CaClz-Alcohol (Bellier) . . FezC!le-(Auguet) ... Pb(CaHB0z)z-Alcohol (Chauvin) ,
. ...
ETHYL
ALCOHOL Per cent
2.53 5.74 1.00 19.1
In the literature the HCI-alcohol method is generally conceded to give the most reliable results. Some of the methods are proposed only on a basis of their results on solutions of gums in water or pure sugar solution. This may help to account for the large variation that we have €ound. For our purpose the CaClz-alcohol method is objectionable because the precipitation requires 24 hrs. The filtration and washing require more time than the HCI-alcohol method. This is the only case in which the methyl alcohol gives higher results than the ethyl. Possibly CaCI2.(CHaOH), is formed. Auguet’s Fed.& method from a manipulative viewpoint is the most unsatisfactory of the four. It has these disadvantages: two precipitations and filtrations are involved. The first filtration requires longer than an entire HCI-alcohol gum determination. The gums from the FezCle precipitation dissolve with difficulty in hot water, and this requires a comparatively large amount of water, which requires as Presented before t h e Division of Sugar Chemistry a t the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 3 to 7,1922. L. B.Langguth, Steuerwald, and T. Van der Linden, Arch. Suikevind , 22 (1914), 1033 [C. A , , 8 (1914).35111;J. J. Hazewinkel, I b i d . , 18 (1910), 746 [C. A . , 6 (1911), 18501;I b i d . , 19 (1911),313 [C. A , , 6 (1911),244]; Weichmimn, “Sugar Analysis,” 3rd ed., p. 134, John Wiley & Sons, Inc., N. Y.;Noel Deerr, “Cane Sugar,” 1911,p. 482. 8 Bellier, Ann.fuZs., 8 (1910),528 [C. A., 6 (1911),9281. 4 A. Auguet, Ibid., 2 (1909), 136 [Chem. Zentr., 11 (1909).loll]. 6 A. C. Chauvin, Mon. x i . , [5]1 (lgll), 1, 317 IC. A , , 5 (1911),33531; Ann.fuZs., 6 (1912),27 [C. A . , 6 (1911).10741. X.Rocques and G. Sellier, A n n . chcm. anal., 16 (1911),218 IC. A . , 6 (1911),36351. 1
REQUIREMENTS
OF A
METHOD FOR GUM DETERMINATION
FOR
CONTROL WORK
1-For control work a gum determination should be easily made and should be as rapid as possible. 2-The precipitate obtained in the case of a product which has been defecated probably does not represent entirely the true cane gum present in the cane. This precipitate is thus a more or less indirect measure of the gum or substances that retard crystallization, and only comparative results are obtained. In view of this inability to obtain absolute results, almost any method that will give consistent comparative results and is adapted to rapid and convenient manipulation is justifiable. 3-It is our opinion that no method should be used that throws out large amounts of organic nonsugars other than gums. Since the pure cane gum cannot be isolated by any simple procedure, the alcohol concentration should be such that dextrin will be precipitated. Dextrin is also a gum and retards crystallization.
The most suitable method for control work has been shown to be the HCI-alcohol method. This was studied for the purpose of obtaining such alcohol and acid concentrations that slight changes in the concentration would have little effect on the gum precipitate. Ethyl alcohol is frequently hard to procure, and for this reason substitutes like methyl and denatured alcohol are desirable. Throughout this work we have compared these with ethyl alcohol,
EFFECT OF SODIUM BENZOATE AS PRESERVATIVE Five g. of sodium benzoate were added to the stock simple using 10-cc. sirup samples. Analysis before and after addition of the preservative showed the following average results: Before sodium benzoate 0.0296 g. gums
After sodium benzoate 0.0302 g. gums
There is a slight increase in the gum content after adding the sodium benzoate, but this may be an analytical variation. 8 Used in all following determinations except as expressly noted otherwise. 1000 g. 96O raw sugar (gums, 0.14 per cent) and 200 g. black strap molasses (gums 2.53 per cent), with water t o 2000 cc. This makes a sirup of 47 t o 48 per cent solids.
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THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
The sirup can be thus kept 4 wks. a t ordinary temperatures before any evidences of fermentation appear. Even when bubbles appear there is no perceptible change in the gum content.
Vol. 14, No. 12
necessary where the filtration is on filter paper. The ash was determined here only as a matter of information.'
EFFECT OF VARYING ALCOHOLCONCENTRATION WITH ACIDITY CONSTANT EFFECT OF HCl CONCENTRATION O N THE GUM PRECIPITATE The acidity used in these experiments is 1 cc. of concenThe alcohol concentration was kept constant in these trated HCl per determination for 100 cc. of alcohol. This tests while the acid concentration was varied. Ten cc. stock Concentration permits a considerable variation in the acid sirup were taken and varying amounts of acid added, but measurement without affecting the results. This is a conwater was added with the acid to make the total added volume 2.5 cc. Then 50 cc. of alcohol (94.5 per cent by volume for the ethyl and 92.7 per cent by weight, for the methyl alcohol) were added, and after 30 min. the precipitate was filtered in alundum crucibles, dried 1 hr. at 100' C., weighed, ashed, and reweighed. The gum column in the table represents the net gum content after deducting the ash.
-
_____ Ethyl Alcohol HCI Gums Ash in Gums Pptd.
Expt.
G.
No.
G.
G.
1 2
Methyl Alcohol HCl Gums G.
0.00 0.02 0.05 0.10 0.20 0.30 0.40 0.60 1.00
a
4 5 6 7 8 9
G.
0.0987 0.0809 0.0386 0.0283 0.0285 0.0271 0.0264 0.0262 0.0261
10
These results are shown in Curves I, 11, and IV of Fig. 1. The first portion of the gum curve has a very sharp slope, which breaks off sharply. Calcium salts of the various organic acids can be precipitated by alcohol of this concentration, while the free acids cannot. As soon as sufficient HCl has been added to liberate all these acids, the gum precipitate becomes practically constant. After this point is reached the acid concentration may be varied over quite a range without materially affecting the amount of gums obtained. The concentration recommended by Noel Deerr and by Weichmann falls on the flat portion of this curve. It corresponds to a concentration of about 0.27 g. HCl, as plotted on this curve.
EFFECT OF HCI CONCENTRATION
ON GUMS 0.0
I E+byl Alcohol lTMeShyl Alcohol
Grams Akohol per lOOcc. Mixture FIQ. 2
venient concentration and is the same as is recommended by Noel Deerr and by Weichmann. Ten cc. of sirup were used and 0.5 cc. of concentrated HC1 added, and then the desired quantity of alcohol in a volume of 50 cc. Filtration was in alundum crucibles for the ethyl alcohol experiments, and in an asbestos mat Gooch for the methyl alcohol experiments. The precipitate was dried 1 hr. at 100" C., weighed, ashed, and reweighed. I n the ethyl alcohol runs, Expts. 9 and 10 filtered so slowly that the washing was imperfect. I n general, the methyl alcohol precipitates settle faster and filter faster than those of the ethyl alcohol. Expt.
No. 1 2 3
4 5 6
7 8 9 10
G . Alcohol per 100 Cc. Mixture Gums ETHYL ALCOHOI, 65.4 0.0307 63.7 0.0290 60.5 0.0289 57.3 0.0242 51.0 0.0190 44.6 0.0159 38.2 0.0154 31.8 0.0154 19.1 0.0175 6.4 0.0172 METHYLALCOHOL 62.2 59.2 56.1 49.6 31.1 12.4
Ash in Gum Pptd.
...... ...... ...... ...... ...... ......
These data are represented by Curves 111 and V of Fig. 2. The higher alcohol concentrations are on a rather steep part of the curves. This abrupt drop in the gums is appar-
FIG.1
The combustible matter present in the gum precipitate, and not the ash, determines the amount of gum. It is not necessary to determine this ash to obtain the gums, as is
7 The fact that Ioss on ignition without actual determination of ash is all that is necessary to determine gums is made possible by our use of alundum crucible in place of filter paper commonly recommended. For still more rapid, less precise, work even the loss on ignition might be omitted, if a series of gum determinations were being made on a product with uniform ash character, by taking advantage of the fact, shown on the curves, that above 0.4 g. of HCI per determination, the ash is low and constant. I n such a case the ash constancy should be checked occasionally by determining loss on ignition.
Dee., 1922
T H E JOURNAL OF I N D USXRML A N D BNGINEERTNQ CHEMISTRY
ently a dextrin loss. If the alcohol concentrakions were carried much higher, there would be danger of throwing out much organic nonsugar and possible sugar. It is evident that the alcohol concentration should be kept within close limits, and as high as the higher concentrations used in these tests.
Expt. No. 30
5 6
and Washinn -
Gums btained Grams
4 hrs. 8 min. 18 min. 14 min. 14 min. 15 min.
0.0288
e for Filterin
1 2 3 4
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mln.
I
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For filtering through asbestos mat crucibles, 15 min. COMP.4RISON O F ETHYL, METHYL,AND DENATURED ALCOHOLS standing is all that is necessary. No serious error is introd TEBTSON 94" MOLASSES-HOUSE SUGAR-This sugar was duced by different times of standing. TEMPERATURE OF DRYINGAND TIMEREQUIRED TO REACH made into a 50 per cent sirup and filtered by suction through in 30-min. periods asbesios. 20 cc. of sirup, 1 cc. of HC1, and 100 cc. of alcohol CONSTANT WEIGHT-Drying a t 90' comes to constant weight in 90 min. The precipitate goes were used for each determination. froin 0.0290 to 0.0280 g. from first to last period. AVERAGEPERCENTAGE OF GUMS Drying at looo C .constant weight in 60 min.; 0.0282 to 0.0286 g. A a B C
c.
0.252 0.252 0.247 A--Pure ethyl alcohol 94 er cent b y volume. B--90 per cent ethyl akohofand 10 per cent methyl alcohol, 92 per cent b y weight. C--Methyl alcohol (commercial), 92 per cent by weight.
These results indicate that for this sugar these alcohols give results that are practically identical. Another sample of sugar was checked against completely denatured alcohol and the following average results obtained : Ethyl Alcohol (94 per cent) 0 . 2 6 6 per cent gums
Denatured Alcohol
Drying at 1 0 5 O C:: constant weight in 30 min. Drying at 110' C.; constant weight in 30 min.
Using the same gum precipitate, the drying was carried constant a t 90" C., then constant a t 95" C . , etc., with the following results: 90' C.constant at 0.0282 g.; 90 min. required 95' C. constant at 0.0281 g . ; 90 min. required loOD C constant at 0 0277 g * 60 min. required 105O C' constarit at 0'0271 g': 30 min. required
110' C:constant at 0:0269 g:f 30 min. required
These results show that even a 5" change in drying temperature will cause but little error. The time required to This alcohol was denatured by the following formula reach constant weight will also vary somewhat with the weight (parts by volume): 100, ethyl alcohol; 2, methyl alcohol; of the precipitate. For this reason it is desirable to dry a t 0.25, pyridin; and 0.50, benzine. This denatured alcohol least 1 hr. a t a temperature of 100" to 105" C. showed 94 per cent by volume. RECOMMENDED METHODFOR GUMDETERMINATION The results show a slight increase in the case of the deSAMPLE-If the sample is a sirup or juice, dilute to or natured alcohol, but the agreement for most purposes is concentrate to about 50 per cent solids. For work in which quite satisfactory. TESTSO N STOCKSIRUP, USING ALCOHOLSDESCRIBED only comparative results are desired on products of nearly the ABovE-Ten cc. of sirup, 0.5 cc. of concentrated HCI, and 50 same density, this is not necessary but it is desirable. The cc. oE alcohol were used. Series 2 was run with twicethe sample should be free from suspended matter. We find acid concentration used above. The following average filtering through asbestos or centrifuging fairly satisfactory. Care must be taken that no clarification that has a tendency results were obtained: to remove gums is used. If the gum content is low, use a Grams of Gums 20-cc. sample; if high, use a 10-cc. sample. If the density of Series Ethyl Alcohol Denatured Alcohol Methyl Alcohol the sample is not accurately known, it should be weighed to 1 0.0304 0.0301 0.0259 2 0.0301 0.0280 0.0267 the nearest 0.1 g. A sugar can be dissolved in an equal weight of water and The methyl alcohol gives results that are quite low on a product like black strap. The denatured alcohol is more should usually be filtered. Sodium benzoate satisfactorily sensitive to change in acid concentration than either the ethyl keeps sirups for gum analysis. ACIDITY-use 0.5 cc. of concentrated HC1 for the 10-cc. or methyl alcohol. sample and 1.0 cc. for the 20-cc. sample. Add the acid to THETECHNIC O F GUMDETERMINATIONS the sirup; otherwise, in the case of very low-grade products FILTRATION OF Gum-All the methods found in the litera- an unfilterable precipitate may be obtained. ture, with the exception of that recommended by Noel Deerr ALCOHOL-Use alcohol a t about 93 to 96 per cent by voland by Weichmann, are foreign methods, and none of the ume. In case methyl or denatured alcohol is used, a large foreign methods suggest the use of a Gooch crucible. Since supply should be kept so that the results will be comparable. the ash in the gums need not be known, only two weighings This old supply should not be estirely used before checking are necessary when the Gooch crucible is used. This saves against the new supply on the products usually analyzed. two vieighings over tared filters, and has the further advan- With ethyl alcohol it is only necessary to see that the density tages of greater accuracy and ease of manipulation. is the same. For some products methyl or denatured alcohol Asbestos mat Gooch crucibles are to be preferred to alun- will give results nearly the same as the ethyl alcohol, but on dum crucibles chiefly because of the better filtration obtained other products the results may be lower. Denatured alcohol with the former. Alundum crucibles are also rather difficult especially should be watched, as the nature of the substance to wash properly. Since there is no filtration between weigh- used for denaturing may be a factor in its behavior as a gum ings, the asbestos mat need not be washed free from fine fibers, precipitant. Alcohol denatured with methyl alcohol alone thus making mat preparation very simple. There is a loss is preferable for gum precipitation. All alcohol should be of only 0.0010 g. between drying and ignition, owing to as- filtered before use. bestos and crucible losses for a mat weighing 0.20 to 0.26g. PRECIPITATION-The precipitation is preferably conducted dry. The corresponding loss for an alundum crucible is a t in 120-cc. Erlenmeyer flasks or in beakers. The alcohol least 0.0020 g. should be added from a rather slow delivery pipet, and the EFFECTOF TIMEOF STANDINGAFTER PRECIPITATION ON mixture should be well agitated during the precipitation. RATE OF FILTRATION AND WEIGHTOF GUMSOBTAINED- Use 50 cc. of alcohol for the 10-cc. sample and 100 cc. for the These results were obtained from 10 cc. of stock sirup, 0.5 cc. 20-cc. sample. To avoid slow filtration allow the precipitate of concentrated HCl, and 50 cc. of 94 per cent alcohol. to stand 15 min. before filtering. 0.281 per cent
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