Moisture Content of Soybean Oil Meals A. C. BECKEL AND T. H. HOPPER U. S. Regional Soybean Industrial Products Laboratory', Urbana, 111.
Soybean oil meal resulting from oil processing does not absorb so much moisture as unprocessed meal when both have been allowed to come to equilibrium under the same conditions of temperatures and humidity. The changes in moisture-absorbing ability brought about by processing may be stepwise. Certain oil meals undergo oxidation when heated at 130' C. in an air oven, while some others undergo decomposition. The moisture in soybean oil meals may be satisfactorily determined by heating for 5 to 7 hours at 105' C. under a vacuum of less than 5 mm.
STUDY of the moisture content of soybean oil meals is desirable in view of their commercial importance and
A
the fact that the applicability to these meals of the official methods for the determination of moisture in cereal foods and grains has not been determined. I n a previous publication on the moisture content of ground whole soybeans (8), a comparison of the several oven methods for the determination of moisture was made, utilizing the apparatus (8) which had been developed in this laboratory for the continual observation of changes in weight a t oven temperatures. I n that work the 130' C. air-oven method and the 105" vacuum-oven method gave identical results in the period from 2 to 6 hours; subsequent to this period the 130" method showed an appreciable and continuing loss, whereas the 105' method showed a very slight additional loss. This and several other considerations emphasized the reliability of the oven methods for the determination of moisture in whole soybeans. On extending the study to the oil meals remaining after most of the oil had been removed from the bean, the situation was found to be different owing, apparently, to changes brought about in the meal by the method of processing. The soybean oil meal samples studied were commercial products resulting from the current methods of processing-namely, hydraulic meal, solvent-extracted meal, expeller meal, and toasted solvent-extracted meal. These were studied a t 105" and at 130' C. in the vacuum oven and a t 130" C. in air and in nitrogen. The drying curves for toasted solvent-extracted 1 A oooperative organization participated in by the Bureaus of Agricultural Chemistry and Engineering and of Plant Industry, U. 9. Department of Agriaulture, and the Agrioultural Experiment Stations of the North Central States of Illinois. Indiana Iowa, Kansas, Michigan, Minneaota, Missouri. Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
meal were also determined a t 80", go", and a t 100" C. in the vacuum oven. I n addition] drying curves were obtained in the 130" air oven and a t 105" in the vacuum oven for hydraulic linseed meal which yielded oil of high iodine number, for hydraulic linseed meal which yielded oil of low iodine number, for cottonseed meal, and for peanut meal.
Treatment of Samples The samples were ground in a Wiley mill through a 1mm. screen and were then conditioned for at least 3 weeks in a room maintained a t constant temperature of 25" C. and constant relative humiditv of 50 Der cent. The handling of the samples has been described (2; 3). The results for the soybean IO samples are shown in Figures 9 1 to 5 and in Table I; those a for t h e other meals are given in Figure 6. All 7 of the results are expressed on the oil-free basis. The analyses of 1 5 the samples are m given in Table 11. 9 It is necessary to discuss the ef83 f e c t s of t h e method of ob2 taining the results along with the effects of the I method of processing the meal 0 0 3 6 12 since the one is TlME IN HOURS influenced by the other. Certain FIGUE~E 1. Loss IN WEIGHTAT 105' C. of the methods UNDER VACUUM were used in 1. Solvent-extracted meal 2. Hydraulio meal order t o study 3. Toasted extraoted meal the differences 4. Expeller meal resulting, apA . around whole soybeans parently, from the method of processing. The effects due t o processingappear as (u) a decrease in the moisture-holding capacity due to the denaturation of the proteins or the degradation of the carbohydrates or both, ( b ) a tendency t o increase in weight due to oxidation resulting after a partial removal of antioxidants] and ( c ) a decomposition into volatile materials probably caused by hydrolysis a t the elevated temperatures used in processing.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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that the two meals which have been subjected to less heat absorb more moisture than do the other two. The agreement between the members of each pair is astonishing. Curve A is the average of the 105’ C. (vacuum) values for the five varieties of whole soybeans previously reported (2). These samples were conditioned in the game room as the meal samples and at the same temperature and relative humidity. They too showed remarkable agreement, having lost a t the 24-hour period 9.87, 9.98, 9.98, 9.99,and 10.00 per cent, respectively. These agreements at the several levels were unexpected, and they would seem to indicate that the differences in composition have only a small effect on the moisture values and that the changes induced by the,methods of processing brought about stepwise changes. Both of these points are being investigated more fully. Incidentally, Boyer (6) indicated that the essential difference in his method of extracting the oil from meal to be used in preparing protein for soybean wool is the maintaining of “a much lower temperature” than is usually employed during the processing. He also pointed out that this procedure enabled him to prepare solutions containing 20 per cent protein, whereas it is usually difficult to prepare solutions having more than 12 per cent solids. Both of these statements indicate the preparation of a protein which is denatured as little as possible since denaturation is caused by heating in the presence of moisture and is measured in terms of solubility. These points are brought out in connection with this work since it is here shown that treatment in processing is discernible in the moisture content of conditioned samples. It is possible that the latter fact supplies a method for evaluating the proteins to be used in making soybean wool and other industrial products dependent on the condition of the protein. No method for this purpose has been developed. Nutritional studies have shown (4, 6) that the digestibility and palatability of the soybean oil meals are improved by FIGURE 2 (Above). SOLVENT-EXTBACTED SOYB~A MEAL N FIQTJRE 3 (Below). HYDRAULIC SOYBEAN MEAL 0 130° C., vaouum oven ,& 130’ C., in sir 8
130° C., in nitrogen
105’
C., vsouum oven
TABLE I. SIGNIFICANT HOURLY VALUESFOR MOISTURE ON THE OIL-FEEE BASISFOR SOYBEAN SAMPLES Line Oil Meal Sample
Decrease in Moisture-Holding Capacity The hydraulic and the solvent-extracted meals were not subjected to so much heating in the presence of moisture as the expeller and the toasted solvent-extracted meals. Heat and moisture promote denaturation and also hydrolysis. The curves of Figure 1 and lines 1, 5, 9, and 13 of Table I, which give the values for the loss in weight a t 105’ C. in uucuo, show
1 2 3 4
Hydraulio
5 6 7 8
Solvent-extd.
Temp., 105 130 130
C.
Atmosphere
Per Cent Moisture after: 1 hr. 2 hr. 4 hr. 6 hr. 24 hr.
Vacuum Air Nitrogen Vacuum
8.85 8.98 8.88 9.10
9.00 9 09 9.05 9.29
9.10 9.20 9.15 9.42
9.15 9.29 9.30 9.56
9.28 10.18 9.95 10.12
Vacuum
105 130 130 130
Air
Nitrogen Vacuum
9.03 5.73 8.98 9.16
9.10 8.86 9.15 9.27
9.11 9.01 9.38 9.38
9.15 9.09 9.52 9.44
9.28 9.78 10.10 10.02
9 10 11 12
Expeller
105 130 130 130
Vacuum Air Nitrogen Vaouum
8.33 8.54 8.47 8.64
8.47 5.60 8.h7 8.85
8.52 8.68 8.68 9.00
8.54 8.70 8.73 9.12
8 82 9.18 9.85 9.58
13 14 15 16
Toasted solventextd.
105 130 130 130
Vaouum Air Nitrogen Vacuum
8.04 8.41 8.48 8.60
8.35 8.64 8.64 8.75
8.47 8.71 8 77 8.95
8.60 8.85 8 85 9.03
8.86 9.56 9.50 9.57
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INDUSTRIAL AND ENGINEERING CHEMISTRY
heating to the proper temperature during certain stages of the processing. The equivalence in the moisture-absorbing ability of conditioned samples of toasted solvent-extracted meal and expeller meal suggests the possibility of developing this method as a rapid means of determining the relative nutritive value of the soybean meals.
Vol. 33, No. 11
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Oxidation The effect of atmospheric oxidation is apparent in the results obtained from the solvent-extracted meal a t 130" C. in the air oven where an actual gain in weight appears a t the 80-minute period, as shown in Figure 2. This phenomenon has been observed in this laboratory before. The net effect of this gain in weight is to make the apparent loss less than it actually is. This is the only case among the soybean samples where a curve obtained a t 130" C. is lower than the corresponding curve obtained a t 105" C. in vacuo. The actual values are shown in line 6, Table I. In order to confirm the explanation as an
I
SOLVENT-EXTRACTED SOYBEAN MEAL IN VACUUM OVEN 4. TOASTED 0 130" C., 105O C., €3100' C., BOo C., 0 80" C.
' TABLE 11. AKALYSISOF MEALSAMPLES Nitrogen, Oil Neal Sample Soybean Hydraulic Solvent-extd. Expeller Toasted extd. Linseed Highiodine No. Low iodine No. Cottonseed Peanut
%
Oil, %
Iodine No.
Refractive Index
Moisture, %
7.41 7.73 7.33 7.88
4.33 0.38 4.53 0.37
124.5 99.5 127.0 85.7
1.47325 1.48568 1.47349 1.48550
9.15 9.15 8.54 8.67
5.21 5.88 6.75 6.86
4.39 4.50 5.22 1.92
173.9 166.6 103.4 91.8
1.47717 1.47777 1.47088 1.46819
11 .os 10.72 9.30 8.84
oxidation, a drying curve was obtained a t 130' C. in an atmosphere of nitrogen; from Figure 2 and Table I the increaied "loss" is readily apparent: This explanation is also corroborated by the fact that t h e determination a t 130' C. in vacuo is nearly identical with the 130' C. nitrogen curve stt .all points beyond the 3-hour period (lines 7 .and 8, Table I). In the cases of the toasted solvent-extracted meal and that of the expeller meal, both of which were heated in processing, the small amount of oxidation has already taken place, apparently, and hence does not Gfi appear during the analysis. In the case of the s hydraulic meal, the explanation of the absence of oxidation would seem to be that less antioxidant 2 5 material has been removed from theoil meal than Lo IA in the case of the solvent-extracted meal. This 94 may also be the explanation for the expeller meal. + w The oxidation, a t 130" C. in the air oven, of z 3 meals other than soybean (Figure 6) is most n. evident in the case of the linseed meals, and 2 a n actual gain in weight for both samples appeared at about the SO-minute period. A much greater spread between the two curves I for the meal which yielded oil of high iodine number is evident and was to be expected. 0 The 130' C. air-oven curve for the cottonseed meal is also below that obtained a t 105" C. in the vacuum oven, but no gain in weight 0 is anywhere observable. The two curves for 3 . C
the peanut meal are close together a t all points beyond the 60-minute period, but an acceleration in the loss in weight appears a t about the 120-minute period. It would seem that decomposition is an important factor a t both temperatures.
Decomposition The evident decomposition of the four soybean oil meal samples by all methods a t 130" C. is completely a t variance with the results obtained with the ground whole beans (2) where, as indicated, the 130" C. air-oven determination corresponded exactly with the 105" C. vacuum determination at all points from 2 to 6 hours. The figures show that in this respect the hydraulic meal is more nearly like the whole meal than are the other meals.
TIME IN MINUTES
FIGURE 5. EXPELLER SOYBEAN MEAL 130* C., vacuum oven 130" C., in nitrogen
8
130' C., in air 105' C., vacuum oven
I N D U S T R 1.A L A N D E N 0 I N E E R I N G C H E M I S T R Y
November, 1941
0 20 40
ec
I 80 100
1%
I
I
I
I
I
I
200
250
320
350
400
450
TIME IN MINUTES
FIGURE 6. OIL MEALSOTHERTHANSOYBXYAN 0
Linseed meal which yielded oil of low iodine number, 130' 0 Linseed meal which yielded oil of low iodine number, lO5O Linseed meal which yielded oil of high iodine number, 130' 0 Linseed meal which yielded oil of high iodine number, 105' @ Cottonseed meal, 105' C., vaouum oven €3 Cottonseed meal, 130° C., air oven e Peanut meal, 130° C., air oven 0 Peanut meal, 105O C., vaouum oven
C., air oven C., vaouum oven C., air oven C., vaouum oven
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oven at 130" C. or in a vacuum oven under less than25mm.pressurefor5hoursat9S0to 100°C. The methods recommended for grain and stock feeds call for heating of the sample for 2 hours in an air oven a t 135" C. or for 5 hours in a vacuum oven under less than 100 mm. pressure a t 95" to 100' C. For the oil meals studied in this paper, the values corresponding to the above methods appear in Table IV. The soybean meals produce a satisfactory correspondence between the methods with the exception of the solvent-extracted meal in which oxidation took place in the air oven. None of the oil meals other than soybean showed satisfactory correspondence between the several methods because of oxidation and, in the case of the peanut meal, because of decomposition. While the curves for the peanut meal are close together (Figure 6), the differences in the values obtained by the usual methods are due to the differences in the time used for the determination. Undoubtedly the vacuum-oven methods are the most reliable for meal samples since they do not suffer from the oxidative complicstions arising in the air oven and, if used at temperatures in the neighborhood of 105" C., are not unduly complicated by decompositions. It remains, then, to examine the length of time which would lead more nearly to the true moisture content and still not be too lengthy for praotical use. A consideration of Table I11 seems to indicate that the most probable value for the
I n order to examine more closely ON OIL-FREBBASISCORRESPONDING TO THAT DETERMINED TABLEIV. MOISTURE the effect of temperature on the deBY OFFICIALMETHODS composition, the drying curves for the P -er Cent Moisture toasted solvent-extracted meal were Soybean --LinseedLow High obtained a t SO", go", loo", 105", and SolventToasted iodine iodine Cotton130" C., under less than 5 mm. presMethod Hydraulic extd. Expeller extd. No. No. seed Peanut 1 hr 130° C 8.98 8.73 8.54 8.41 10.1110.19 8.63 8.16 sure. The results are shown in Figure 5 hi', 1050 C.,less 4 where the relative rates of decomposithan 25 mm. 9.11 3.52 8.53 1 0 . 6 5 11.01 9.22 8.77 pressure tion are shown by the slopes of the 9.10 Difference 0.12 0.38 0.02 0.12 0.54 0.82 0.69 0.61 curves. Significant hourly values are 2 hr 130' C 9.09 8.86 8.60 8.64 10.12 10.19 8.80 8.35 given in Table I11 where the 24- and 485 hi.', 105O 6.. less than 100 mm. hour values show that there is no conpressure 9.10 __ 9.11 8.52 8.53 w 5 11.01 9.22 8.77 tinuing decompositiona t 90" C., a very Differenoe 0.01 0.25 0.08 0.11 0.53 0.82 0.42 0.42 small amount a t loo", and a small amount at 105" which is insignificant when translated into an effect on a demoisture content of the toasted solvent-extracted soybean termination up to 7 or 8 hours. The decomposition at 130" C. meal is 8.70 per cent on the oil-free basis. It may be observed is considerable and has been shown to continue indefinitely. that a t 90" C. the rate of loss per hour before reaching 8.70 per Determination of Moisture cent is 0.021 per cent, and that in the ensuing 24 hours there was no loss; a t 100" the rate of loss preceding the value The official methods (1) for determining moisture in cereal of 8.73 per cent is 0.014 per cent, and after that point foods call for the heating of the sample for 1 hour in an air it is 0.003 per cent; at 105" the rate preced. ing 8.67 per cent is 0.09 per cent, and after that point, 0.011 per cent. It is also significant OF TEMPERATURE ON DECOMPOSITION OF TOASTED TABLE111. EFFECT that, in spite of increasing temperature levels, SOLVENT-EXTRACTED SOYBEAN MEALIN VACUUM OVEN in the interval from 7 to 24 hours the sample Per Cent Decomposition* after: Temp, 7hr. 6hr. A 5hr. A OC. 4hr. A A 24hr. A 48G. lOst0.36per Cent a t 9ooc.,0.24 a t loo", and 80 8 . 0 5 0.09 8.14 0.06 8.20 0 . 0 2 8 . 2 2 0.019 8.55 0.003 8 . 6 2 0.19 at 105". The first two losses signify the 90 8.17 0 . 1 1 8.28 0.06 8 . 3 3 0.01 8.34 0.021 8.70 0.000 8 . 7 0 relative proximity to the 8.70 per cent level, 100 8 . 3 8 0.07 8 . 4 5 0.03 8 . 4 8 0.01 8.49 0.014 8 . 7 3 0.003 8.80 105 8 . 4 7 0.06 8 . 5 3 0 . 0 5 8 . 6 8 0.09 8.67 0.011 8.86 0.008 9 . 0 6 and the last figure shows the passing of that 130 8.95 0 . 0 5 9 . 0 0 0.03 9 . 0 3 0 . 0 2 9.06 0.030 9 . 5 7 ... .. value. No other value in all the data on this A rate per hour. sample has any consistent significance. L
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-
0
-
-.
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TABLEV.
SIGNIFICANT HOURLYVALUESAND RATESON ALL SAMPLES AT 105' C. in vacuo c
Oil Meal Sample Soybean Hydraulic Solvent-extd. Expeller Toasted extd. Linseed High.iodineNo. Low iodine No. Cottonseed Peanut 0 A rate per hour.
-
b 9.13 9.13 8.53 8.53 11.02 10.66 9.22 8.77
A
Per Cent Moisture" after: 6 A 7 A
0.02 0.02 0.01 0.07
9.15 9.15 8.54 8.60
0.04 11.06 0 . 0 4 10.69 0.02 9.24 0.07 8.84
0.00 0.00 0.00 0.07
9.15 9.15 8.54 8.67
2
0.007 0.007 0.016
0.011
4 9.28 9.28 8.82 8.86
0.02 11.08 0.015 11.33 0.03 10.72 0,009 10.87 0.06 9.30 0.006 9.40 0.00 8.84 0.008 8.98
Vol. 33, No. 11
period. The selection of one or the other of these times as the proper time for a moisture determination at 105" C. in a vacuum oven is dependent on the accuracy desired and/or the type of product to be analyzed. I n any case, it would be profitable to examine a number of meal samples a t the two periods. Each of the meal samples other than soybean lost 0.08 per cent or less in the 2-hour period following 5 hours, and the limited number of samples gives no indication that it would be desirable to lengthen the 5-hour analysis at 105" C. in a vacuum oven.
Literature Cited
In Table V all of the meal samples exhibit the same behavior with respect to undergoing a drop in the rate of loss a t or before the 7-hour period. With the exception of the toasted solvent-extracted meal discussed above, which lost 0.14 per cent in the interval between 5 and 7 hours, the other soybean meals lost an insignificant amount during the same
Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., Chap. XXVII, pp. 2, 7 (1940). Beckel, A. C., and Earle, F. R.,IND.ENG.CHEM.,ANAL.ED., 13. 40 (1941). Beckel, A. C . , and Sharp, A . G., Ibid., 12, 45 (1940). Bohstedt, G.,Flour and Feed, 37 (6), 18 (1936). , ED.,12, 1549 (1940). Boyer, R. A., IND.ENG.C H E M .ANAL. Wilgus, H.S., Jr., Norris, L. C., and Heuser, G. F., IND.ENG. CHEM.,28,586-8 (1936).
COMMERCIAL INSECTICIDAL SULFURS Average Particle Diameters as Determined by Air Permeation ERNEST L. GOODEN Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C .
A survey of commercial insecticidal powdered sulfurs with regard to average diameters (surface mean diameters) has been made by means of the self-calculating airpermeation apparatus. In the fifty-four samples tested, the average diameters range from 5 to 25 microns. The plain sulfurs occupy mainly the upper half of the range, and the wettable and conditioned sulfurs, the lower half.
HE particle-size distributions of commercial insecticidal sulfurs were investigated by Goodhue (6) through sedimentation aiialysis. Subsequently a self-calculating apparatus was developed for determining the average particle diameter of a powder as deduced from its permeability to air when compacted (4). Because of the promise given by air permeation as a convenient means of evaluating powder fineness, a survey of commercial insecticidal sulfurs was made with the new apparatus. The material used in the survey comprised fifty-four samples. Most of them were obtained directly from a dozen manufacturers in various parts of the United States. The other samples were obtained through miscellaneous channels.
T
'
The survey was limited to dry powders consisting essentially of sulfur, not combined or mixed with any other material, except for slight impurities and small percentages of conditioning and wetting agents.
Procedure The weight, in grams, of a sample required for a determination is numerically equal to the density of the material in grams per cc. It is well known that crude mined sulfur ordinarily possesses a remarkably high degree of purity. Goodhue's study (6) indicates that the densities of the commercial insecticidal sulfurs, which in many cases contain small amounts of added impurities as aids to dusting or wetting, usually depart by less than 1 per cent from that of pure rhombic sulfur. For the sake of simplicity this density (2.07 grams per cc.) was assumed throughout the experiments here reported. The weighed sample was spread on a sheet of paper, and a glass rod was rolled over it t o break up any lumps present. The powder was then transferred to the sample tube and compacted by a new pressure device described elsewhere (8). Otherwise the procedure was the same as that outlined previously (4). Two permeation machines were used on every sample. The differencein results by the two machines was in most cases not more than 1 micron. Since the second apparatus had been constructed with greater care than the first, the results by it alone were adopted for the report.
