INDUSTRIAL AND ENGINEERING CHEMISTRY Hardesty, J. O., and Ross, W.H., IND. ENG.CHEM.,29, 1283-90 (1937).
Hardesty, J. O., Ross, W. H., and Adams, J. R., J . Assoc. O& cial Agr. Chem., 26, 203-11 (1943). Hartford, E. P.,and Keenen, F. G., IND. ESG. CHEaf., 33, 508-12 (1941).
Hendrioks, S. B., and Hill, 7.77. L., Science, 96, No. 2489, 255 (1943).
Hendricks, S. B., Hill, W. L., Jacob, K. D., and Jefferson, M. E., IND. ENG.CHEM.,23, 1413 (1931). Hill, W. L., and Hendricks, S. B., Ibid., 2 8 , 4 4 0 (1936). Hill, W. L., Hendricks, S. B., Jefferson, M. E., and Reynolds, D. S., Ibid., 29, 1299-1304 (1937).
Hodge, H. C., Le Fevre, M. L., and Bale, W. F., IND.ENG. CHEM.,ANAL.ED.,10, 156 (1938). Hopkins, C . G . , and Whiting, A. L., Ill. Agr. Expt. Sta. Bull. 190, 395 (1916).
Keenen, F. G., IND. ENQ.CHEM.,22, 1378 (1930). Larson, H. W. E., IND. ENG.CHEM.,ANAL.ED., 7 , 4 0 1 (1935). Lorah, J. R., Tartar, H. V., and Wood, L., J . Am. Chem. Soc., 51, 1097 (1929).
MacIntire, W. H., U. S. Patent 2,095,994 (1937). MacIntire, W. H., and Hammond, J. W., IND. ENQ.CHEM.,30, 160-2 (1938).
MacIntire, W. H., and Hardin, L. J., Ibid., 32, 88-94 (1940). Ibid., 32,574-9 (1940).
MacIntire. W. H., and Hardin, L. J., J . Assoc. OAicial Agr.
,
Chem., 23, 388-98 (1940). (28) MacIntire, W, H., Hardin, L. J., Oldham, F. D., and Hammond, J. W., IND. ENQ.CHEM.,29, 758-66 (1937).
Vol. 36, No. 6
(29) MacIntire, W. H., and Hatcher, B. W., J . Am. SOC. Agron., 34, 1010-15 (1942). (30) MacIntire, R. H., and Hatcher, B. W., Soil Sci., 53, 43-54 (1942). ENG.CHEM.,24, 1401(31) MacIntire, W. H., and Shaw, W. M., IND. 9 (1932). Agron., 26, (32) MacIntire, W. H., and Shaw, W.H., J . Am. SOC. 656-61 (1934). (33) Maohtire; W. Shaw, M. hl., and Hardin, L. J., IND.ENG. CHEEM., ANAL. ED., 10, 143-53 (1938). (34) MacInCire, W. H., Shaw, W. M., and Hardin, L. J., J . A m . as so^. Agr. Chem., 21, 113-21(1938). (35) Rader. L. F., Jr., and Ross, W. H., Ibid., 22, 400-8 (1939). (36) Rindell, A,, Comp. rend., 134, 112-14 (1902). (37) Roseberry, H. H., Hastings, H. B., and Morse, H. X., J . Bid. C h m . . 90. 395 (1931). (38) Ro;s,-W: H.‘, Jacdb, K: D., and Beeson, K. C., J . Assoc. Oficial Agr. Chem., 15, 227-65 (1932). (39) Ross, W. H., Rader, L. F., Jr., and Beeson, K. C., Ibid., 21, 25868 (1938). (40) Shear; M. J., and Kramer, B., J . Biol. Chem., 79, 125-60 (1928). (41) Thornton, S. F., Ind. (Purdue) Expt. Sta., Bull. 399 (1935). ENG.CHEM.,35, 774-7 (42) Walthall, J. H., and Bridger, G. L., IND. (1943). (43) Wendt, G . L., and Clarke, ,4.H., J . Am. Chem. SOC.,45, 881 (1923) (44) Whittaker, C . W., Rader, L. F., Jr., and Zahn, K. V., Am. Fertilizer, 91, NO. 12, 5-8 (1939).
k,
PRESENTED before t h e Division of Fertilizer Chemistry a t the 106th Meeting of the AMERICAN CHEMICAL SOCIETY, Pittsburgh, Pa.
Moisture Absorptive Power of
STARCH HYDROLYZATES
T
HE absorption of moisture by various materials may be desirable or undesirable according t o the specific use of the material. Thus the use of glycerol in smoking tobacco t o keep the product moist and of invert sirup in cake and cookie icings to extend the freshness are commonplace and desirable properties from the standpoint of moisture absorption. Examples of undesirable moisture absorption are most familiar in the caking of salt, fertilizers, and sugars. This property of moisture absorption which occurs readily under normal atmospheric conditions is commonly termed “hygroscopicity”. Strictly speaking, any dry crystalline solid which is soluble in water and does not form a crystalline hydrate will, when exposed to the atmosphere, tend to absorb moisture, with the formation of a saturated solution. If surface absorption is neglected, such absorption can occur only when the vapor pressure of the saturated solution is lower than the partial pressure of the water vapor in the atmosphere t o which the solid is exposed. Since the vapor pressure of any aqueous solution is lower than that of pure water, any solid will absorb moisture when exposed to saturated aqueous water vapor and is therefore hygroscopic Lo some extent (8). This paper covers the moisture absorption of starch hydrolyantes under equilibrium conditions in atmospheres of various relative humidities. Starch hydrolyzates are here considered as the 1
Present address, Clinton Company, Clinton, Iowa.
A method of obtaining absorption and desorption moisture
equilibrium data for sugars and sirups has been developed. Starch hydrolyzates are effective materials for absorbing water. The amount of absorbed water increases with dextrose equivalent and with increasing relative humidity. Starch hydrolyxates are compared with two common materials used as humectants, invert sirup and glycerol. The water content of each material, when a t equilibrium a t any relative humidity between 20 and 7870, is defined. When, adequately dispersed, each material reaches a characteristic water content which is at equilibrium with an atmosphere of given humidity (or relative vapor pressure) a t the same temperature. Hence, precise measurement of the vapor pressure should accurately define the water content.
J. E. CLELAND AND W. R. FETZER’ Union Starch and Refining Company, Granite City, 111. products of the acid hydrolysis of starch with the usual commercial refining without removal of dextrose. This definition includes the various corn sirups and crude corn sugars. One dualconversion corn sirup (acid hydrolysis followed by enzyme hydrolysis) was included. Corn sirups (noncrystallieing starch hydrolyaates) are largely used in the confectionery and baking industries. Confectioners’ corn sirup, of 42 dextrose equivalent (D.E. = percentage of reducing sugars as dextrose on a dry basis) is used universally in the manufacture of hard candy and contributes to the moisture absorption in the finished goods. The baking industry employs the higher conversion sirups (50-55 D.E.) in the manufacture of icings and coatings, particularly in areas of low relative humidity, because the moisture absorption of these sirups is greater and products result which do not dry out so rapidly. Although these properties are well known among users, no data exist other than empirical tests, which in most cases are not generally available.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1944
In the determination of moisture m sugar pToducts (6),the dispersion of the sample was found mast essential in obtaining true moisture, particularly if the material was viscorrs and formed “surface seals” as does corn sirup. For this purpose &atomaceous silica (Johns-Manville Hyflo) was employed; it appeared that this dispersion principle might be applicable in the determination of moisture absorption equilibrium. The advantages would be as follows:
TABLE I. RESULTSON DRY POWDERED CORNSIRUP(42 D.E.) EXPOSED TO 5270 W L A T I V N HUMIDITY
Time, Hr.
40 64
168 216
288
Moisture Gain, yo of Following D r y Sample Wt.:
0.2282g. 8.81
8.76
8.20
9.64 10.03 9.73
0.7015g. 7.77 r8.33 8.58 8.87 9.19 9.48
1 . 6 1 3 0 ~ . 4,5440g. 7.53 6.93 7.95 7.29 8.21 7.48 8.76 7.90 9.02 8.24 9.39 8.45
533
6.2740g. 6.75 7.01 7.15
7.47 7.66 7.86
1. No packing or “surface sealing” mass would appear. Under these conditions, the entire mass would be available for moisture absorption. Numerous tests have shown this to be the case. I n some tests, samples of the same material were stirred a t intervals while others were not. An differences in rates of absorption were insignificant and the &a1 equilibrium values were the same. 2. Sample weights were not a factor in moisture absorption. By employing a definite ratio of solids to diatomaceous silica, approximately equal surfaces were obtained for all materials. 3. Absorption and desorption isotherms could be obtained. This method of verifyin equilibrium has been difficult to apply to water-soluble materia% which do not crystallize. 4. A method of handling noncrystallizing sirups would be provided. With previous methods, any correlation between solids and sirups had not been practical as the physical conditions of the samples had not been comparable. By reducing all sirups to a moisture-free basis on the dispersing material, it was possible to study the moisture absorption a t the initial moisture st\?* solids be reduced to a comparableabasis, In previous methods the physical size of the solid partlcles was a factor. Coarse material did not “surface seal” so readily as fine material. 6. There would be no microorganism spoilage. I n previous where long periods of time were necessary, spoilage often developed a t the surface before the test was completed. This has never been observed with the new method.
PREVIOUS WORK
Many papers (1, 2, 9, 10, IS, 16, 17-20) have been published on the moisture absorption of cane sugar, primarily t o give information on the prevention of deterioration of the product in storage. Browne (4) studied the moisture absorption of a number of carbohydrate materials, including starch, cellulose agar, and various sugars and sugar sirups. Sokolovsky (18) investigated the hygroscopic properties of sucrose, maltose, lactose, dextrose, levulose, galactose, and caramel over an extended range of relative humidities. Whittier and Gould (21) attacked the problem through vapor pressure studies and ob, tained data on lactose, sucrose, dextrose, and galactose. Dittmar (.7.) studied the moisture equilibrium of sucrose, levulose, invert sugar, and sucrose-invert -sugar mixtures a t various relative humidites. H e pointed out that liquefaction of the crystals occurred sharply a t certain moisture contents. In the above papers few data are found on corn sirups or the crude corn sugars, despite the fact that these materials are large items of commerce. This dearth of data may have resulted in Dart a t least from the nature of the materials which are extremely ;iscous and noncrystalline throughout most of the hydrolytic RELATIVE HUMIDITY CONTROL range. Such physical characteristics present difficulties in the The equipment used was basically of two general types. following technique, which was used in much of the previous The first was the well known system in which saturated solutions work: The material was weighed in shallow dishes and exposed of inorganic salts (in contact with the solid phase) are utilized to atmospheres of various relative humidities. The gain in to maintain constant humidity in a closed space. Six inverted weight was followed and weight constancy taken as the equilibrium glass bell jars with plate glass covers were used to hold the solumoisture value. Under these conditions the amount of sample tions and the samples. The bell jars were held in a constant and physical condition became dominant variables. “Surface temperature bath. The solutions used were potassium acetate, sealing” or “skin” formation stopped the flow of water vapor t o chromic acid (CrOs), potassium nitrite, sodium dichromate the bulk of the sample. Final equilibrium was dependent upon (Na&raOpHnO), sodium nitrite, and ammonium chloride. The diffusion. The slowness to reach weight constancy rendered the corresponding relative humidities are 20, 35, 45, 62, 66, and 79.2 judgment of it somewhat uncertain. For these reasons reproa t 20” C. (8, 12, 14). ducibility of data was unsatisfactory. This static method is excellent if constant temperatures can Some idea of the type of data obtained by this technique is be maintained easily, but it was found extremely difficult to mainshown in the following experiment: Different weights of dry tain temperature conpowdered corn sirup trol in the large jars (42 D.E.) were despite the bath, parweighed into alumil L ticularly when t h e num dishes of identical shape. The least jars were opened for removal of the test weight barely samples. As a result covered the bottom the test was finally of the dish, and the conducted a t room greatest represented _-_ __ - - -temperature which a depth of 3 mm. had a constant-temT h e d i s h e s were perature range beplaced in a chamFigure 1. Relative Humidity Train tween 25 ’and 30 C. ber with air a t 52% 1. Preconditioning unit 5 7. Traps This procedure is 2. 3. 4. Sulfuric acid solution 6.’ Desiccator relative humidity a t basically sound for 30”C. The data obdata expressed on t a h e d (Table I) vary relative humidity, for the relative values change very little over a with the amount of sample used. A reasonable assumption, temperature range of 5-10’ C., although the absolute values do. upon consideration of the factors of diffusion (“surface sealing” In the second method a stream of air is humidified to the deand packing), would be that the test employing the smallest sired value by passing it through a series of gas washing bottles amount of material would more nearly approach the true equilibrium value. However, data obtained with a newer technique containing sulfuric acid solution of the required concentration for the desired relative humidity. In this method as used by showed that even this value underestimates the true equilibrium Wilson ( W ) , the air was passed through a U-tube containing the by approximately 15%. O
j
INDUSTRIAL AND ENGINEERING CHEMISTRY
554
I.GL YGEROL 2.INVhRT SIRUP
170
la.-
1."70' S U G A R - 6 3 . 4 D.E. .).CORN
-
SIRUP-65.OD.E.
/'
I
CORN SIRUP-DUAL CONVERSION -64.0 D.E. &CORN S I B U P - 4 2 . 0 D.E.
IH
m 80-
*
6.CORN S I R U P - 3 2 . 8
mn I
a
2 40-
J
5
2 ao2
Vol. 36, No. 6
start the samples had approximately equal parts of water and dry substance carbohydrate. They were exposed to the highest humidity until equilibrium had been attained and then to the decreasing humidities. The determination of actual solids was left until the end in order to avoid the possibility of changes brought about by heat exerting an influence on hygroscopic properties. The agreement found in absorption and desorption results indicates that the methods of drying used had no influence on the hygroscopicity. This may be construed as evidence that the drying procedure caused no irreversible change in the materials (16). The test dishes were placed in a desiccator kept in a water bath a t 25' to 30' C., and weighings were made a t regular intervals until weight constancy was obtained. To compare the effectiveness of starch hydrolytic products with known humectants, both glycerol and invert sirup were included. The procedure for invert sirup was the same as for the starch hydrolyzates but the method for glycerol differed.
ao-
P E R C E N T RELITIVE HUYlDlTY
Figure 2.
Equilibrium Water Content of Starch Hydrolyzates and Humectants
sample, This was not practical for the products and methods used here, where the material of the sample was dispersed on diatomaceous silica. The dishes were placed in a desiccator. Since the test periods were relatively long, difficulty was experienced in maintaining the sulfuric acid at the proper density. This was overcome by placing several bottles of sulfuric acid of the same density in series and employing larger units. The train contained three bottles of 3-gallon capacity; the last was equipped with a sintered glass diffuser. The method h a l l y employed was a combination of the two (Figure 1). I n this train the first bottle (5gallon capacity) contained the saturated solution of the salt (and solid phase) for the specified relative humidity. The air from this bottle was led through three bottles of sulfuric acid of such density as t o yield air of relative humidity corresponding t o that of the first bottle. The air in turn passed through a trap into a desiccator containing the samples and finally through a seal. By this train the air was "preconditioned" before entering the sulfuric acid solutions, and a large volume was available over an extended period with little attention. The sulfuric acid solutions were adjusted to maintain relative humidities of 20,35,45, 52, 66, and 78. PROCEDURE WITH DIATOMACEOUS SILICA
A large quantity of diatomaceous silica (Hyffo) is waahed by percolation with distilled water that has been slightly acidulated with hydrochloric acid. This treatment is continued until the effluent is acid to litmus. Washing with distilled water follows until the effluent is essentially neutral, and the diatomaceous silica is then air-dried. A quantity, usually a quart, is transferred to an air oven at 105' C. and kept for use. The reparation of the sample with diatomaceous silica is identicay with the procedure for moisture employing the same material (6). Ten grams of diatomaceous silica were run into duminum dishes with tight-fitting covers and brought to constant weight in a vacuum oven at 100" C. The sample under examination was made up as a 5Oy0 solution, and a volume containing approximately 5 grams of solids was pipetted on the mass of diatomaceous silica. Dispersal into a damp homogeneous mass was effected by a small glass pestle which was left in the sample. For determination of moisture absorption, the procedure was the same as for a moisture determination up to the point of exposure in the constant-humidity chambers. The samples were dried to constancy by the methods (5) considered most reliable for the types of material and then exposed. All equilibrium values were approached. from the dry side by working upward through the series of humidities. For the desorption tests the equilibrium values were approached from the wet side. At the
I
I DEXTROSE
Figure 3.
I
I
I
80
EQUIVALENT
Equilibrium Water Content of Starch Hydrolyzates
The glycerol available was U.S.P. grade, with a specific gravity of 1.25427 at 20/20" C. (in vacuum) which corresponds to a moisture content of 3.5% from the table of Bosart and Snoody ( 3 ) . This was in close agreement with the figure obtained from the refractive index (%so = 1.4654) by the table of Hoyt (11). Samples of approximately 6 grams of glycerol were poured on the diatomaceous silica and weighed. Dispersal was then carried out exactly as with the sirups, but the drying technique used in preparation for the absorption tests was changed. The samples were dried over concentrated sulfuric acid and then over P20, until the weight loss ceased and i t was found that the moisture loss corresponded nearly to the 3.5% moisture predicted from the specific gravity and refractive index. Hence the glycerol weight was taken as 96.5y0 of the sample weighed out and this was used in the subsequent calculations. The samples were prepared for
PROPERTIES OF DIATOMACEOUS TABLE 11. HYGROSCOPIC SILICA(HYFLO) Time, Hr. 5 15 72 119 143 167
-----%
35%
0.020 0.028 0,039 0,060 0.060 0.060
Wt. Gain a t Relative Humidity of:45% 52% 66% 78% 0.031 0.036 0.041 0.075 0,041 0.048
0.071 0.071 0.071
0.041 0,048 0,079 0.079 0,079
0.058 0.063 0.096 0.096 0.096
0,085 0.056 0.12 0.13 0.18
100%
...
0.45 0.62 0.63 0.61
0.62
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1944
requires approximately twice this time. In the desorption tests, erratic results were obtained for the 90.7 D.E. corn sugar. Our explanation has been crystalli~ation,since crude sugars of this D.E. crystallize rapidly with formation of the hydrate. The curves of Figure 2 appear t o take the S-shape typical of absorption isotherms for some solids. In Figure 3 the data for the dual-conversion sirup were omitted, and a straight line best
TABLE 111. ABSORPTION AND DESORPTION EQUILIBRIUM VALUES is Rel. Hum., %
Invert sirup
90.7
83.4
.EDsE. tion Equilibdum Valuee
555
Glyo-
. K., Proc. Sugar
Tech. Assoc.
,34,403(1942).
‘,
,
; , bc rsing as hefore but were ~
,
desorption by weighing out and dis then exposed to a saturated until they had ained their Own weight Of moisture‘ The used
atmospgre Dextrose Equivalent 32.8 42.0
70 corn sugar
.
Ash.
’ %’
0.28
55.0 84.0
88.4 90..7
....
I
‘
(11) Hoyt, L.F.,IND. ENQ.CHEM.,26,329 (1934). (12) International Critical Tables, Vol. I, pp. 67-8 (1926). (13) King, R . ’ k and Suerte, D-7 Intern. Sugar J . 9 31,214 (1929). (14) Obermfiler, 2-PhYSik. Chem., 10% 145-64 (1924). (15) Owen, W. L.,Louisiana Planter, 70, 88-90, 107-8 (1922). (16) Sair, L.,and Fetser, W. R., Cereal Chem., 19,No.5,646 (1942). Cukrovar, 51,314-18 (1933). D. ENQ.CHEM.. 29,1422-3 (1937). (19) Thieme, J; G., Arch. Suikerind., 42,157-80 (1934) (20) Webster, J. H.,Dept. Agr. Brisbane, Queensland, Bur. Sugar Expt. Sta., Tech. Commun. 5, 82-90 (1940). (21) Whittier, E. 0..and Gould, S. P., IND.ENQ.CREM.,22, 77 (1930). (22) Wilson, R. E.,Ibid., 13,326 (1921). J.3
..
ual-conversion sirup, acid hydrolysis followed by enzyme hydrolyeia in Fi ure 3). (Db Made g y invertase. Wallerstein) inversion. Rotation was -19.8 at 20’ C . , indicating essentmily complete inversion.
2
The two crude sugars, 70 and 80, differed markedly in their ability to crystallize. The 70 sugar crystallizes slowly, several days being required to form a firm concrete. The 80 sugar, however, sets to a firm hard concrete in a matter of hours. ABSORPTION AND DESORPTION
The effectiveness of the procedure is based on whether the diatomaceous silica moisture absorption
Billet, “70” Corn Sugar
