I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
July, 1923
727
Starch in Sorghum Juice’ By Sidney F. Sherwood OFFICE OF SUGAR-PLANT INVESTIGATIONS, BUREAUO F P L A N T INDUSTRY, DEPARTMENT OF AGRICULTURE, WASHINGTON, D.
c.
The investigation here reStarch. sucrose, and reducing sugars contents of the expressed Ported Was conducted in juice of fifteen varieties of sorghum at time of maturity are girren. of the hundreds of samples of j ui c e The probable eflect of starch upon filtration of juice, consistency of connection with breeding experiments and varietal sirup, and crystallization of sucrose is briefly mentioned. from sweet sorghum tested tests of sweet sorghum^.^ by the writer for the presence of starch, using the ESTIMATION OF STARCH iodine test, have shown a negative reaction. In juice that samples of juice have been expressed by a small 3-roll has been preserved by the addition of mercuric chloride, the mil1 from mature stalks from which the blades and seed heads suspendetf solids separate into a more or less compact layer had been removed. Two hundred cubic centimsters of the of greenish gray material, showing in most cases a well-de- thoroughly mixed juice were placed in a bottle, preserved by fined layer or band of white starch granules. The literature the addition of a trace of mercuric chloride, and stored in an contains an occasional brief reference t o the presence Of starch icebox. Other work necessitated a delay of several months in sorghum juice, but there Seems t o be no Printed statement before the determination could be made, and during this pergiving the quantities of starch present in the expressed juice. iod the supernatant juice became perfectly clear and the sedWiley2 states that he never failed to obtain a Positive test iment formed a compact layer containing a clearlydifferenwith the iodine reaction, Sylvester3 measured the size of tiated starch layer or band. The clear portion was siphoned starch grains in sorghum juice, finding them to be extremely off and discarded; the entire residue ,was washed into a ~01small as compared ~ i t hStarch from corn and Potatoes. lodian dialyzing sack; a few drops of toluene were added, Weber and Scovel14 report 4.12 per Cent of starch in the and the inaterial was dialyzed against running tap water stalks of Orange sorghum, but do not give the quantity in until all sugars had been removed, as indicated by negative the expressed juice. tests with @-naphtholand with Seliw-anoff’stest. Ordinarily Tlii1eys refers to the Presence of starch grains in Cross they were free in 4 days (96 hrs.). As a matter of precaution, sections of the stalk. Jouliee proposed an alcohol clarifica- they then dialyzed against distilled water for 2 ,jays tion of the cold juice, claiming as a special advantage the (48 hrs.), changing the water several times each day. All elimination of starch which in hot processes of clarification is the material in tile sack was then transferred to a beaker and converted into “dextrins” that interfere with subsequent the starch was determined bs the diastase method,iO working of the juice. Willaman, West, Spriestersbach, and ting the preliminary extraction with ether and alcohol. Holm’ state that starch is always found in sorghum juice, and The dialyzing sacks TITeremade as follows: 9.5 g. dry that “as maturity approaches, the starch increases from pyroxylin (snowy) Ivere dissolved in 75 cc. of ethyl ether; about 0.7 per cent to 1.8 per cent.” They do not give de- 60 CC. of absolute alcohol were added, and the mixture tailed results of the estimation of starch in the juice. Wileya was shaken and permitted to stand until free from air gives “starch isomers” in the dry material of two samples of bubbles. The interior of a test tube, 10 1.5 in., was made sorghum blades as 21.22 and 14.49per cent. Many ~ f e r e n c e s thoroughly wet with the solution, inverted, and permitted to on the composition of sweet sorghum seed show that the air- drain for 2 min. The membrane was air-dried untilit could dried seed contains from 65 to 70 per cent starch. be handled (approximately 0.5 hr.), and removed by flowing water between it and the wall of the tube. It was carefully 1 Received March 3, 1923. examined in order t o insure absence of leaks, air bubbles, * U.5’. Dept. Agr , Dzu. Chem., Bull. 18 (1888), 116. 3 I b i d , 34 (1892), 77. etc. Yembranes that were not used at once were kept im1 “Report on t h e Manufacture of Sugar, Sirup, and Glucose from mersed in WTater.
NLY four or five out
0
Sorghum,” Illinois Industrial University, 1881, p. 11. 6 U. S. Dept. Agu., Dzv. Chem., Bull 2 (1884), 6. a “Etudes e t experiences sur le sorgho e t sucre,” Paris, 1864. 7 J. Agr. Reseavch, 18 (1919), 16, 25. 8 U S. Dept. Agr., Diu. Chem., Bull. 3 (1884). 115.
9 Project in charge of H. B. Cowgill, agronomist, under direction of C. 0 Townsend, pathologist in charge, Office of Sugar-Plant Investigations, Bureau of Plant Industry. 10 Assoc Official Agr Chem , Methods, 1920, p 95.
.......... TABLE I-STARCH I N SORGHUM JUICE Corresponding Brix Specific Sample Variety of Sorghum (171/2’ C.) Gravity Folger 1 20.85 1.08711 2 Japanese R i b b o n . . 16.35 1.06718 3 Indiana Amber.. 20.45 1.08531 Farmer Tones. .......... 17.70 1.07309 4 5 Colman, 17.55 1.07243 1.07662 6 Sugar D r i p . . 18.50 1.06653 7 Silver T o p . . 16.20 1.09004 8 Rex X.. ............... 21.50 9 Orange, 1.06718 16.35 1.08576 10 Collier. . . . . . . . . . . . . . . . . 20.55 11 Texas Seeded Ribbon.. 1.06980 16.95 Planter. ............... 1 5 . 0 0 1.06133 12 13 McLean 1.06284 15.35 1.06479 15.80 14 Early Folger, D . A.. 15 Honey.. 1.05639 13.85 Average Maximum Minimum
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Starch Per cent 0.528 0.178 0.433 0.289 0.368 0.443 0.257 0.852 0.275 0.640 0.374 0.263 0.143 0.312 0.142 0.366 0.852 0,142
Weight of Starch per 100 per Gallon Gallons G. Lbs. 21.73 4.8 1.6 7.19 17.77 3.9 2.6 11.73 14.95 3.3 4.0 18.06 2.3 10.36 7.8 35.16 2.5 11.12 5.8 26.30 15.12 3.3 10.55 2.3 1.3 5.75 12.56 2.8 1.3 5.70 14.94 3.3 35.16 7.9 5.70 1.3
Sucrose (Clerget) Per cent 15.54 8.45 14.24 11.91 11.95 11.77 9.91 15.75 10.56 14.94 10.83 9.65 7.42 10.14 6.86
Reducing Sugars (As Invert Sugar) Per cent 1.41 5.99 3.20 2.75 1.89 3.05 3.48 0.60 2.38 1.04 3.05 1.57 3.36 1.so 4.12
Ratio
’% Starch plus 0.12 0.73 0.26 0.26 0.19 0.30 0.38 0.09 0.26 0.11 0.32 0.19 0.47 0.21 0.62
I,YDUSTRIAL A N D ENGINEERIiYG CHEMISTRY
728
The sugars had been determined previously on duplicate samples of the fresh juice. The results for starch and sugars are given in Table I.
DISCUSSION The starch content shows a comparatively wide range. Referring for convenience to the column for weight of starch in pounds per 100 gal. of juice, it will be noted that the quantity varies from 1.3 to 7.8. Separating the series arbitrarily into three groups as the starch varies 1.3 to 2.2, 2.3 to 3.2, and 3.3 to 7.8, and averaging the sucrose and reducing sugars of the samples that fall within these groups give the results in Table 11.
Vol. 15, h’o. 7
I n some cases the sirup-manufacturing process involves clarification of the juice with lime, followed by settling and decantation or by filtration, but probably 85 per cent of the sirup produced is made by direct open-pan evaporation of the raw juice, with removal of scums by skimming. That portion of the starch that finds its way into the finished sirup probably has a tendency to retard crystallization. However, there are indications that starch is responsible for the wellknown “jellying” of sorghum sirup, and that juice low in starch will produce sirup which is more satisfactory from the standpoint of consistency and general appearance. Indications also point to starch as the cause of the great difficulty in filtering sorghum juice, especially after i t has been heated.
TABLE I1
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Group Number of samples in group.. Average sucrose.. Average reducing sugars.. ..............
1.3-2.2 3 7.58 4.49
2.3-3 2 5 10.43 2.40
3.3-7.8 7 13.58 2.03
These figures indicate that a high starch content is accompanied by a high sucrose content and a low reducing sugar content, and vice versa. This is also shown very plainly by the results for Samples 8 and 15 in Table I. Either starch or reducing sugar is always present in considerable quantity, and the low ratios Per cent starch plus per cent reducing sugar per cent sucrose are usually found in samples with a high sucrose content. Willaman, et u Z . , ~ ~ show that as the sorghum approaches maturity there is a rapid increase in the sucrose content and a rapid decrease in the levulose and dextrose content, the dextrose decreasing a t a more rapid rate than the levulose. They consider that the decrease in dextrose is due to a t least three causes: (a)respiration; ( b ) conversion into sucrose; and ( c ) conversion to a slight extent into starch. I n view of the fact that no analyses were made on immature samples, no information is available as to whether or not the metabolism of the plants conformed with Willaman’s observations. I n each case the juice had been obtained from plants which from appearance, hardness of seed, etc., were mature and at the stage of growth ordinarily considered suitable for the manufacture of sirup. It seems probable that the starch-sucrosereducing sugar ratios may be characteristics of the variety. Bulletins of the United States Department of Agriculture, Division of Chemistry (1884 to 1893), dealing with experimental work in connection with the attempted production of sugar from sorghum, show that “gummy” and “mucilaginous” constituents of the juice were responsible for extreme difficulty in clarification and filtration and that these constituents plus reducing sugars were responsible for unsatisfactory crystallization of sucrose. The gummy constituents were investigated but apparently no investigation was made on the quantities of starch present. The repeated failure of numerous attempts forty years ago to produce sugar commercially from sorghum showed quite conclusively that the commonly grown varieties of sorghum are not adapted to the production of sugar and that i t is not practical to attempt to produce sugar from them. The presence in the juice of the quantities of starch and reducing sugars here shown is further evidence of this. I n view of the large areas in the United States that seem to be suited to the production of sugar beets and sugar cane, there appears to be no necessity a t present to consider sorghum for sugar production. It is of great value, however, for the production of sirup, as much as 49,505,000 gal. having been produced in 1920. For this purpose, the presence of reducing sugars is desirable because it retards and, when present in sufficient amount, prevents crystallization of sucrose. 11
Lac. C i t . , p. 25.
A Stirring Device‘ By Henry W.George HARVARD MEDICAL
SCHOOL,
BOSTON,MASS.
I n carrying out a reaction in a narrow-neck, balloonshaped flask i t is difficult to introduce a stirrer with arms long enough to extend close to the walls of the flask. To overcome this difficulty the following piece of apparatus has been developed : A glass T-tube with short arms is sealed to a long glass rod, and another rod of slightly smaller diameter than the tubing is passed through the T. The rod is bent a t right angles close to the arms of the T so that the ends of the rod point in opposite directions. The rod is then flattened a t each end. To insert into the flask the movable glass rod is fixed so that the arms are vertical (Position A). After the stirrer has passed through the neck of the flask, it is jarred sharply and the movable rod falls so that the arms assume a horizontal position. When the stirrer rotates the paddles remain horizontal and cause vigorous agitation throughout the contents of the flask.
POSITION A
Evidently, such an apparatus can be used in any large flask with a small neck. Care should be taken to have the movable rod evenly balanced. 1
Received April 12, 1923.
