August, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
calculated from the tabulated data to be 7640 calories. From the plot in Figure 3, the slope of the 10 mole per cent ammonia line is 0.733. This slope is obtained as the tangent of the measured angle between the 10 per cent line and the horizontal, or from the measured lengths of the legs of the right triangle formed by the 10 per cent line, the abscissa, and the ordinate. The molar latent heat of the reference substance, water, at 18’ C. is 10,555 calories. The partial heat of solution of ammonia gas in a 10 mole per cent ammonia solution is the product of the slope and the molar latent heat of water 0.733 X 10,555 or 7720 calories. This value checks that obtained from the tabular data within 1 per cent. While this value is called the “partial heat of solution” of ammonia gas, it is redly the latent heat of ammonia gas on condensation, plus the heat of solution. The latent heat of ammonia a t 18” C. is 5120 calories per gram mole. Thus, the actual chemical partial heat of solution without the physical heat of condensation is only 7720 - 5120, or 2600 calories per gram mole. The partial molar heat of solution of hydrochloric acid gas in a 10 mole per cent solution of the gas in water is calculated from thermal data to be 14,750 calories. The corresponding value determined from the slope of the 10 mole per cent (18.2 weight per cent) hydrochloric acid gas line in Figure 1 is 15,800 calories. The difference in values obtained by the two methods is about 7 per cent, and probably within the limits of accuracy of the various data involved. Figure 11 is a plot of the slopes.of the lines of partial pressures of ammonia out of aqueous solutions. It must be noted that this plot permits direct calculation of the partial molar heats of solution at any concentration (i. e., the heat involved
959
in dissolving a mole of ammonia gas in such a large amount of solution of the given concentration that the concentration of the solution is not affected). The integral heats of solution may, of course, also be related to this plot. They would refer t o the heats involved in going from one concentration to another by removing or adding ammonia gas or a solution of different strength (as would be done, for example, in a rectifying column fed with a given strength of solution), taking off an overhead product of higher strength of ammonia, and discharging water from the base. Normally, distilling-column calculations neglect these heats; but suitable corrections may be incorporated, if desired, from values found in this manner.
Literature Cited (1) Glasstone, Samuel, “Textbook of Physical Chemistry”, p. 691, New York, D. Van Nostrand Co., 1940. ENG.CHEM.,25, 528 (1933). (2) Harte, Baker, and Purcell, IND. (3) Haslam, R. T., Hershey, R. L., and Keen, R. H., Ibid., 16, 1224 (1924). (4) International Critical Tables, Vol. 111, New York, McGrawHill Book Go., 1929. (5) Markham, A. E., and Kobe, K. A., Chem. Rev., 28, 519 (1941). (6) Miller, P., and Dodge, B. F., IND. ENQ.CHEM.,3 2 , 4 3 4 (1940). (7) Othmer, D. F., Chem. & Met. Eng., 47, 551 (1940). (8) Othmer, D. F., IND.ENQ.CHEM.,32, 841 (1940). (9) Perry, J. H., Chemical Engineers’ Handbook, 2nd ed., New York, McGraw-Hill Book Co., 1941. (10) Perry, J. H., and Smith, E. R., IND.ENQ. CHEM.,25, 195 (1933). (11) Sherwood, T. K., Ibid., 17, 745 (1925). (12) Wan, S., and Dodge, B. F., Ibid., 32, 95 (1940). (13) Wiebe and Gaddy, J. Am. Chem. SOC.,61, 315 (1939); 62, 815 (1940). PRES~NTED before the Division of Industrial and Engineering Chemistry CHEMICAL SOCIETY, Memphis, Tenn. at the 103rd Meeting of the AMERICAN
Waxy Starch of Maize and Other Cereals J
R. M. HIXON Iowa Agricultural Experiment Station, Am=, Iowa
G. F. SPRAGUE
A POSSIBLE COMPETITOR FOR TAPIOCA
Bureau of Plant Industry, U. S. Department of Agriculture, Washington, D. C .
The properties of starch from waxy corn are discussed. This starch has high viscosity, low gelling characteristics, and slight tendency to retrograde. These qualities suggest the utilization of this starch as a replacement for tapioca in many commercial products. Indicated uses are as a remoistening glue, in paper sizes, and as a minute-tapioca substitute. Starch has been milled from waxy rice, waxy sorghum, and waxy barley. That from waxy barley differs from the others in having both red- and blue-staining granules.
OR the past six years duty-free imported starches, consisting chiefly of tapioca, have made up about one fourth the total United States supply of starches as shown in Figure 1 (14). The annual consumption of 350 million pounds of tapioca in the world’s largest cornstarchproducing country may be attributed to two factors, price differential and the properties of the starch itself. Most tapioca has been imported from the Netherlands Indies, where labor is cheap and cassava produces large yields. Since 1930 the price of tapioca has been consistently about 0.5 cent less per pound than that of cornstarch ( I S , 29). The present emergency, however, has made tapioca difficult to obtain. The estimates of the quantities of tapioca required for purposes which cannot be readily replaced by other starches vary greatly. Some place the figure as low as 15 million pounds, if tapioca is considered indispensable only in the production of remoistening glues and certain food products.
F
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Other estimates place the figure as high as 200 million pounds. The analysis by Hosking ( I S ) of tapioca and sago importations as a function of price indicates that these starches supplied a market of approximately 100 million pounds in the period I I I I I I I. TOTAL U. S. SUPPLY OF STARCHES 1200 2. DOMESTIC SUPPLY OF CORNSTARCH 3, DUTY-FREE IMPORTED STARCHES
1
1322
24
FIGURE 1.
26
28
30 Year
32
34
36
38
40
RELATIONOF IMPORTED TO DOMESTIC STARCHES
1925-32 when price was about equal to cornstarch. Substitution of domestically produced cornstarch for the quantities of imported tapioca shown in Figure 1 would offer a potential market for over 10 million bushels of corn. The purpose of this paper is to call attention to the unique properties of the starches from waxy corn and certain other cereals which stain red-brown with iodine rather than blue. The existence of such starches has been known for many years but they have not been commercially available. The fact is emphasized that such starches possess the physical properties ordinarily associated with tuber starches as contrasted with cereal starches, and that they can be used in products for which tapioca has been considered indispensable.
TABLEI. SOURCES OF WAXYSTARCHES Cereal Rice Corn Sorghum Barley
Classification
Place Grown
Oryza glutinosa (Asahi moohi) Zea m a y s (Hybrid)
Biggs Rice Field Station, Calif. Madison, Wis.; Ames, Iowa
Sorghum vulgare (Sagrain, Leoti) Arlington, Va. Hordeum vulgare coe2este (Murasaki mochi) Aberdeen, Idaho”
Citations (11, 16, 20,
$1, ZB, 9s) (6, 6, 7 , 9, 19, 16#94)
(16)
...
Obtained originally from S. Kashiwada, Plant Breeding Laboratory, Kyushu Imperial University, Fukuoka, Japan, in 1931. a
Sources of Waxy Starch Waxy starch, most easily recognized by the reddish-brown color it stains with iodine, is found in certain varieties of maize, rice, sorghum, millet, and barley. (The term “waxy” has become established in the genetic literature on corn and the term “glutinous” in the literature on rice, millet, and sorghum. Although “glutinous” and “waxy” are equally unsatisfactory in a chemical sense, the latter term has been used in this manuscript for lack of a better one.) Gris in 1860 (II), as reported by Brink and Abegg (6), obtained a “redstaining starch from glutinous rice”, and Tanaka (23) in 1912 showed that erythrodextrin was not present in sufficient
Vol. 34, No. 8
quantity to account for the iodine color. But strangely enough, when a red-staining starch was discovered in corn, it was erroneously considered t o be an erythrodextrin (24)as late as 1924. The term “waxy” was applied to this type of corn because the endosperm when cut appeared smooth and opaque and resembled a hard wax in texture (9). Table I shows the sources of the waxy cereals milled in this laboratory and literature references concerning them. Of the several glutinous or waxy cereals, corn appears to offer the best possibilities as a commercial source of waxy starch because its other characters are not essentially different from those of ordinary hybrid corn which is already milled on a large scale. However, probably not less than 50,000 acres of waxy sorghum are being grown in the United States a t present. lgronomic Problems Collins (9), vho first reported the presence of waxy endosperm in corn, carried out a limited number of crossing experiments which showed that this character is completely recessive to the horny and starchy condition in the endosperm of common varieties of corn. Kempton (15) later confirmed this observation on a larger scale and emphasized the lack of any condition intermediate between starchy and waxy. It is evident, then, that waxy corn, millet, or sorghum must be grown in isolated plots to prevent cross pollination with ordinary varieties. For self-pollinated crops such as rice and barley, this precaution is unnecessary. Soon after the observation appeared that waxy cornstarch stains red with iodine ( 2 4 , it was found that the waxy gene also expresses itself in the pollen (7, 1 0 ) ; thus in a plant bearing genes for both the starchy and waxy condition (heterozygous), half of the pollen grains would be blue staining and half red staining. This fact has been of tremendous importance in facilitating breeding operations, since plants heterozygous for the waxy gene can be identified a t the time of pollination. If this were not possible, each plant used in the breeding operation would have to be self-fertilized to determine whether it carried the waxy gene. This would involve either a loss in time or the handling of much larger numbers of plants. The plants and ears of the original Chinese waxy corn were too small to provide competition with commonly grown varieties of starchy corn. Using the ordinary backcross technique of breeding, in which an improved inbred line of starchy corn is used as the recurrent parent in crosses with waxy corn, it has been possible to develop numerous waxy inbreds. Any four of these may now be combined in a double cross to produce waxy hybrids in the same manner that ordinary commercial hybrids are developed. As a result of the cooperative corn-breeding program carried on by the Iowa Agricultural Experiment Station and the Division of Cereal Crops and Diseases, Bureau of Plant Industry, largely under the direction of AI. T. Jenkins, the late A. A. Bryan, and G. F. Sprague, hybrids containing waxy starch are being produced which compare favorably with the corresponding starchy hybrids. By 1943 enough seed will be available to grow 1500 or more acres of this corn.
,Milling of Waxy Cereals A small-scale laboratory unit which handles from 5 t o 20 pounds of grain per batch was constructed for milling small batches of widely differing cereal types (Figure 2). It duplicates industrial wet-milling practices ( I ) as nearly as possible and permits experimental variations to be made in each step of the process. The separation of starch from gluten is facilitated by substituting a solid basket centrifuge for the long starch tables used in the commercial process. In the case of corn, an average run requires 2 days for steeping add from 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1942
FIGURE 2. STARCH MILLINGPLANT 1.
2. 3.
Steeping unit Attrition mill Reel
4.
5. 6.
961
granules, as shown in a photograph by Brink and Abegg (6). Both have crystalline x-ray patterns of the A type (2); both have a chain length of approximately 25-30 glucose units as determined by methylation and end-group assay ( I d ) . /3Amylase digestion follows nearly the same course ( I @ , and the limit dextrins so produced exhibit a close chemical similarity (8). I n a study of pasting characteristics of various starches, Morgan (1'7) found that gelatinization of ordinary cornstarch pastes (as measured by translucence of the pastes recorded by a photoelectric cell) begins a t about 64" C. and continues irregularly over a range of 30"; that of waxy pastes, although beginning a t a slightly higher temperature (70" C.), progresses uniformly and completely within the narrow range of 8". The shape of the gelatinization curve resembles that of tapioca rather than cornstarch. The photomicrographs of Figure 4 compare the behavior of ordinary and waxy starches upon swelling. The latter are distinguished by the multinucleate appearance of the granules upon incipient swelling, after which they become extremely shriveled. Freshly prepared pastes of tapioca and of waxy starch are similar in their glutinous viscous character and translucent appearance.
Germ separator Basket centrifuge Shaker (corner only visible)
0.60 to 16 hours for milling, purification, and drying of products. The wooden steeping unit shown in Figure 2 was later replaced by a Knight stoneware jar in which the metal heating coils do not make direct contact with the steep. An average yield of products fSom a yellow dent corn is as follows: starch (0.29 per cent protein), 46 per cent; germ, 6; fine fiber, 3; coarse fiber, 5. Waxy cereals may be milled in the same manner as the starchy varieties. The protein content of starches milled by this procedure is shown as a criterion of purity: Source of Waxy Starch Corn Barley Sorghum Rice
yo Protein in Starch 0 2 0.3 0.6 1.2
The somewhat greater difficulty encountered in separating rice starch from gluten is typical of ordinary rice as well. After purification by alcohol-alkali treatment, the protein content of the rice starch sample dropped to 0.46 per cent. The glumes of Sagrain waxy sorghum contain a purple pigment with a high affinity for starch. Preliminary milling tests yielded a light chocolate-colored starch due to the presence of this pigment. It was almost impossible to remove the color without degrading the starch. However, this difficulty was not encountered with Leoti sorghum, a variety with light red glumes. Ten samples of waxy starch milled in an identical manner from the same batch of corn were characterized by viscosity measurements (3) in order to check the duplicability of the milling procedure. There was close agreement among the samples, the average viscosity being represented by curve 3, Figure 3. When the conditions of preparation were altered to shorten the period of contact with sulfur dioxide-water, it was possible to produce an equally pure starch with considerably higher viscosity (curve 1, Figure 3). The evidence indicates that waxy starch is more susceptible to modification by changing the milling procedure than is ordinary starch.
.
Properties of W a x y Starch
In some respects waxy and ordinary cornstarch are much alike. There is little difference in the size and shape of the
UJ
0.45
B
2
L
0.30 Y 0
?> 0.15
0
I
I
0
/O
I
I
20 30 P R r s s U R E CCM. HpO)
5.
I
40
3
FIGURE 3. VISCOSITIESOF WAXYSTARCHES(2 PER CENT PASTES AT 90" C.) 1. Waxy corn (short SO2 contact) 2. Waxy sorghum (Leoti) 3. Waxy corn (longer 90%contact) 4. Waxy barley a n d waxy rice 6. Ordinary aorn
The hot viscosity of waxy cornstarch is appreciably above that of tapioca throughout thk temperature range from 75" to 90" C. If not violently agitated, waxy pastes may be kept a t 90' for an hour without decreasing in viscosity. However, they are less resistant to disruption by heat or mechanical treatment than are tapioca pastes. The high hot viscosity of waxy as compared with ordinary cornstarches (Figure 3) is not the only outstanding physical difference between them. When pastes of each are cooled, ordinary cornstarch soon becomes opaque and sets to a stiff gel, while waxy pastes, even in concentrations of 20 per cent, do not increase a great deal in consistency and remain gummy and viscous for days. Quantitative measurements reported in a previous publication (4) revealed a conspicuous lack of rigidity in waxy pastes. Other properties associated with the waxy character are the difficulty with which its pastes retrograde and the red-violet
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Vol. 34, No. 8
pears purple. The properties of this starch are intermediate between a pure waxy and an ordinary type; e. g.? the viscosity (Figure 3, curve 4) is lower than would be expected of a true waxy starch with granules larger than those of cornstarch. Investigations on barley have not progressed to the stage where a discussion of the genetic significance of its unique waxy endosperm is warranted. Other starches, such as sweet potato (18A),have been found suitable for replacing cassava starch in some products. As yet no starch other than the waxy starches has been found that can be used to make food products similar to minute tapioca. The limiting factor in such uses is probably the relative amounts of straight-chain component which is responsible for retrogradation.
Applications Samples of waxy starch were submitted to several industrial laboratories which use large quantities of tapioca in the manufacture of adhesives, gums, paper sizes, and puddings. Results of their tests indicate that, after minor adjustments in cooking time, temperature, moisture content, etc., are made, products can be obtained from waxy cornstarch which practically duplicate those from tapioca.
Literature Cited
70’ C.
FICURE4.
800
c.
SWELLIKC CHARACTERISTICS OF VARIOUS STARCHES ( X 200) 1. Ordinary corn 2 . Waxy corn 3. Waxy sorghum 4. Tapioca 5 . Potato
iodine reaction. A colored reproduction of the latter along with the ordinary blue starch-iodine color is given by Brink and ilbegg ( 6 ) . A possible explanation of these properties in terms of molecular structure lies in the concept of branching of starch chains. If the molecules of waxy starch had a moderate number of branches, they would have difficulty in orienting into insoluble groups of parallel chains, which is characteristic of retrogradation. They would have difficulty in forming regular helices with hydrogen atoms oriented toward the center, thought to be a prerequisite for production of a blue iodine color. I n such behavior waxy starch is intermediate between cornstarch with relatively few branches (blue iodine color, strong tendency to retrograde) and glycogen which is highly branched (red iodine color, does not retrograde). The relation between waxy and ordinary starches from sorghum and rice appears to be the same as that shown by the corresponding cornstarches. The small granule size of rice starch accounts for its relatively lower viscosity (Figure 3, curve 4.) Waxy barley presents an interesting variation in the character of its starch. When stained with iodine, some of the granules appear deep blue and some reddish broxn; many of them contain both brown- and blue-staining portions. Viewed without a microscope, therefore, the iodine color ap-
(1) Bartling, F. W., Am. Miller, 67,KO.12, 26 (1939); 68,No. 2, 24; No.3,42; No.4, 24; No. 8, 40; No. 9, 46; No. 10, 28; No. 12,25 (1940); 69,No. 2,32; No. 3, 48; KO.5, 34; KO. 6, 38; No. 8, 40; No. 10, 46; No. 11, 32; No. 12, 34 (1941); 70, No. 2, 38; No. 3, 80 (1942). (2) Bear, R. S., and French, D., J . Am. Chem. Soc., 63,2298-305 (1941). (3) Brimhall, B., and Hixon, R. M.,Cereal Chem., 19, in press (1942). ENC.CHEM., ANAL.ED., (4) Brimhall, B., and Hixon, R. M., IND. 11, 358-61 (1939). (5) Brink, R. A., Biochem. J . , 22, 1349-61 (1928). (6) Brink, R. A,, and Abegg, F. C., Genetics, 11, 163-99 (1926). (7) Brink, R. A., and MacGillivray, J. H., Am. J . Botany, 11, 46569 (1924). (8) Caldwell, C. G., and Hixon, R. M., J . Am. Chem. Soc., 63, 2876-305 (1941). (9) Collins, G. N., U. S. Dept. Agr., Bur. Plant Ind., Bull. 161 (1909). (10) Demerec, M., Am. J . Botany, 11, 461-4 (1924). (11) Gris, A., B u l l . soc. botan. France, 7, 876-7 (1860) ; as reported by Brink and Abegg (6). (12) Haworth, W. N., Hirst, E L., and Woolgar, M.D., J. Chem. SOC., 1935,177-81. (13) Hosking, F. J., Contrib. Iowa Corn Research Inst., I, No. 2, 182 ( 1 989). \ _ _ _ _
(14) Hosking, F. J., “Statistics of Imported Starches”, p. 1 (1941). (15) Kempton, J. H., U. S. Dept. Agr., B u l l . 754 (1919). (16) Meyer, Arthur, Ber. deut. botan. Ges., 4, 337-62 (1886); as reported by Brink and Abegg ( 6 ) . (17) Morgan, W. L., IND.ENG. CHEIM.,AXIL. ED.,12, 313-17 (1940). (18) Newton. J. M..Farlev, F. F., and Naylor. N. M., Cereal Chem., 17,342-55 (1940). (HA) Paine, H. S., Thurber, F. H., Balch. R. T., and Richee, W.R., IND. Exo. CHEM.,30,1331-48 (1938). (19) Staley, A. E., and Eakin, F., Contrib. Iowa Corn Research Inst., I, No. 2, 243 (1939). (20) . . Tadokoro, T., J . Coll. Agr. Holckaido I m p . Univ., 16, 90-123 (1926). (21) Tadokoro, T., J . Faculty Sci. Hokkaido Imp. Univ.,111,2, 59-79 (1934). (22) Tadokoro, T., and Sato, S., J . Coll. Agr. Hokkaido I m p . Univ., 13, 1-65 (1923). (23) Tpnaka, Y., J. IND.ENG.CaEM., 4, 578-81 (1912). (24) T.T.eatherwax, Paul, Genetics, 7, 568-72 (1922). .
I
PRDBENTED in part before the Division of Agriculture and Food Chemistry a t t h e 103rd Meeting of the AMERICAN CK~MICA SocmrY, L Memphis. Tenn. Journal Paper 5-987 of the Iowa Agricultural Experiment Station, Projeot 616, in cooperation with the Division of Cereal Crops and Diseases, Bureau of Plant Induscry, U. S. Department of Agriculture, Supported in part by a grant from t h e Corn Industries Research Foundation.
