DEXTRINS from CORN SIRUP Effect of Dextrose Equivalent of Sirup on Properties HE term “dextrin” designates the degradation
T
J. W. EVANS AND W. R. FETZER Union Starch & Refining Company, Granite City, Ill.
dextrins prepared by the action of diastase on starch; only one discusses acid hvdrolvsis involving different digrees of conversion. The more recent papers have dealt almost entirely withdextrinsformedby enzymatic hydrolysis of starch.
nroducts of starch. regardliss of whether they are formed by acid or by enzymatic The reducing power* rotation* and iodine hydrolysis. These degradation Of dextrins precipitated from products are soluble in hot and cold water, insoluble in aicohol, Corn having dextrose from 30 to dextrorotatory, and copper re65 by 80 per cent methanol have been determined. HISTORICAL Nine precipitations are necessary to obtain a prodducing, and give either a blue, red, or no coloration with iodine. uct of constant reducing Power. Since 1812 it has been known In this dextrose equivalent range the reducing that dextrins are formed when I n the industrial sense the term is used to denote the power Of the dextrins passes through a minimum starch is heated with dilute products obtained by roasting while the specific rotation gradually decreases. acids; Vogel(18) reported that The data give Some indication of the Course of acid a gumlike substance as well starch either alone or with a Of starch. as sugar was produced when small quantity of acid or other catalyst. These commercial starch was heated with dilute dextrins are almost completely acids. A few years later Biot soluble in hot water and, in addition to dextrins, contain and Persoz (4) studied this gumlike material and called it “dextrin” because its solutions rotated the plane of polarized soluble starch and sugar. This paper covers dextrins in the light to the right. These workers heated potato starch with former s e n s e i . e,, as they occur in acid hydrolysis of starch. Methods for the identification and particularly the dilute sulfuric acid at 85O, 95”, and 100’ C., and added alcohol estimation of dextrins in starch hydrolyzates are far from to the filtered hydrolysates. White precipitates were obsatisfactory. I n 1906 Browne (7) proposed a method tained from the material heated at 85” and 95” C. These whereby the sample in question was dissolved in a small precipitates were soluble in cold water, were reprecipitated by amount of water to which was added absolute ethanol to alcohol or lead acetate, gave a red coloration with iodine, and effect a final concentration of approximately 90 per cent. were converted to starch sugars on heating with acids. Bondonneau (6) examined the dextrins formed in the The precipitate so formed was decanted and washed with 95 per cent alcohol. The weighed precipitate was termed course of acid saccharification of starch a t different stages of the reaction. The dextrins were separated from the other “dextrin”. Known as Browne’s method, i t is described by Leach (14) and in the A. 0. A. C. methods (2) under “honey”. substances in the hydrolyzate by precipitation with alcohol. While working reasonably well for the residual dextrins in I n the early stages of the reaction, a dextrin (called CY) was malt sirup and the small amount in honey, Browne’s method obtained that gave a red coloration with iodine. After the encounters difficulty when applied to starch hydrolyzates, saccharification had been carried on further, another dextrin particularly in corn sirup where the amount of dextrins in (called 0) was isolated, which did not color iodine and was some grades may run as high as 50 per cent. The precipitate stated to be identical with the dextrin formed by the action of obtained is a gummy stringy mass which gives every evidence diastase on starch paste. On removal of this dextrin a third of occlusion. As a result data on the dextrins in corn sirup (called y) was isolated from the mother liquor; it gave no are meager, and workers have attempted to apply data on coloration with iodine. Bondonneau (6) determined the specific rotation of these dextrins. These data served the dextrins from other sources to corn sirup. Also it has led to t h e erroneous impression that the dextrins are the same, purpose for which they were obtained (namely, to show that, regardless of the degree of conversion of the sirup. Conon the saccharification of starch, dextrins and dextrose were siderable confusion has resulted, and the purpose of this formed simultaneously), but the work was qualitative in that paper is to define more clearly dextrins obtained from corn neither the degree of hydrolysis was reported nor were the sirups of different degrees of hydrolysis. concentrations of alcohol used to precipitate the dextrins Corn sirup is the thick viscous substance obtained, after given. refining and concentrating, from the incomplete acid hyLintner and Dull (16) hydrolyzed potato starch suspensions drolysis of starch or dual conversion (acid hydrolysis followed with oxalic acid (0.04 to 0.33 per cent) a t pressures of 1.5 to by enzymic treatment). The sirup is noncrystallizing and 3 atmospheres for 30 to 60 minutes. The hydrolyzates contains dextrins, higher sugars, maltose, and dextrose, the were neutralized with calcium carbonate and filtered, and proportions depending upon the degree of hydrolysis (9). the dextrins and sugars were separated by cooling to 0” C. The degree of hydrolysis is defined by the term “dextrose or by precipitating with alcohol. The iodine colorations of equivalent” or “D. E.”, the percentage of reducing sugars all the dextrins were observed, and the reducing powers and calculated as dextrose on a dry substance basis. The D. E. specific rotations were determined on all but the amyloof commercia1 corn sirups run from 25 to 70. dextrin or the dextrin obtained from the hydrolyzate of the Numerous articles (8,8, 12, 16, 17) have appeared on the lowest conversion. iodine color, specific rotation, and reducing power of dextrins. The data of this earlier work are interesting because the Most of these papers deal with either commercial dextrins or degree of hydrolysis was expressed as i t is today, although 439
INDUSTRIAL AND ENGINEERING CHEMISTRY
440
amount of water was poured in to thin the sirup, and sufficient absolute methanol was added to obtain the alcohol concentration desired in the final mixture. The methanol was delivered from a buret at the rate of 100 ml. per minute, and the mixtures were rapidly stirred during the addition. The percentages (by volume) of methanol used were 70, 75, 80, 85, and 90, calculated on the basis of water and methanol contained in the final mixture. Precipitations were carried out at 10, 31, 32, 34 and 60" C., and the mixtures were kept a t these temperatures for 10 to 18 hours in all cases except at 60" C. where the mixture was allowed to cool t o 32" C. The amounts of corn sirup,, water, and methanol used in the first precipitations are given in Table 11. The 70 per cent methanol procedure produced too small an amount of precipitate to be purified. After standing for 10 to 18 hours, .the filtrates were decanted and the precipitates were taken up with water and reprecipitated with methanol. The procedure for the addition of methanol was the same as before. The precipitations were carried out from five to fifteen times, 4 hours being allowed for the dextrins t o precipitate and settle after each alcohol addition. After the filtrate was decanted from the final precipitate, the precipitated dextrins were placed on a watch glass and dried in a vacuum oven at 100" C. for 2 hours. A t the end of this period the dextrins were scraped from the watch glass, ground in a mortar, and either dried further or stored in a sealed bottle. The data for the purifying procedure are given in Table I11 with the reduring power (calculated as dextrose) and specific rotation of the purified dextrins.
TABLEI. SUMMARY OF EARLY WORK Hydrolyiate
D.E. (or)= Murky suspension
Alcohol Used, %
D . E.
Dextrins Obtained (a')= Iodine coloration
...
..
36" 10-14 183-190 70 2 14-18 180-185 75-80 5 46.9 142 82-85 7 46.9 142 90 14 a Dextrin separated out on cooling t o C.
196 194 192 180
Vol. 35, No. 4
Blue Red-violet Red-brown Brown Brown
only one sirup falls within present commercial corn sirup ranges. No temperature was given for the specific rotation, and the concentration of alcohol was variable. The data are summarized in Table I. More recently E x o n ( I S ) studied the physical properties of dextrins isolated from corn sirup, and found that they were not homogeneous but were a mixture of dextrins of different chain lengths. The alcohol concentration necessary to precipitate dextrins depends on the type of dextrins present, on the concentration of electrolytes, and on the concentration of other carbohydrates. Alcohol concentrations of 35 to 95 per cent have been used; with the lower strength, amylodextrin is obtained in a purified condition, and with the higher, the short-chained achroodextrin is precipitated. From the quantitative viewpoint, the quantity of dextrin precipitated varies directly with alcohol concentration. Fetzer, Evans, and Longenecker (11) found on precipitating dextrins from a corn sirup (46 D. E.) with alcohol of 70 to 90 per cent strength that the amount of precipitate varied from 1.4 per cent for the lower concentration to 19.8 for the higher. The concentration of the carbohydrate in the above precipitations was 2 per cent. I n the present work the aim was to secure dextrins typical for a sirup of a given D. E. and to have these dextrins as free from other carbohydrates as possible. The dextrins were precipitated from a large quantity of sirup in the lowest alcohol concentration practical and were then reprecipitated until their reducing powers and specific rotations were constant; absence of occluded material was thus indicated.
RESULTS. The data show that the reducing power and specific rotation of dextrins precipitated by methanol from corn sirup vary with the number of precipitations, the percentage of methanol, and the temperature of precipitation. With methanol concentrations less than 80 per cent, the amount of dextrins precipitated was too small to work with. Dextrins with a constant minimum reducing power and a constant maximum specific rotation can be obtained from a 42 D. E. corn sirup by precipitating with 80 per cent methanol a t 31' C. and purifying with nine reprecipitations. The sirup solids in the precipitation mixture for the first precipitation varied from 10 to 32 per cent, the lowest solids concentration being necessarily in the highest concentration of methanol. A nonreducing dextrin was not obtained from the corn sirup by methanol precipitation, the lowest reducing power being 2.7 per cent (calculated as dextrose).
DEXTRINS FROM 42 D. E. CORN SIRUP DEXTRINS FROM 29.9 TO 63.4 D. E. CORN SIRUPS
The purpose of this work was to ascertain the concentration of alcohol, the number of precipitations, and the temperaThe sirups used were produced by straight acid hydrolysis tures necessary to obtain dextrins with the lowest constant of cornstarch; the 42 and 54 D. E. sirups were commercial reducing power and the highest constant specific rotation. products, and the others were prepared in the laboratory These constant values apply to dextrins from a sirup of a pilot plant. The dextrins were precipitated with 80 per cent methanol at 30' C., nine reprecipitations being used for given dextrose equivalent. purification purposes. The procedure for this work was the REDUCING POWER.The Munsen-Walker method ( 1 ) was same as described above. The iodine coloration of the dexused to determine the reducing power of the dextrins; it was extrins was determined by adding 0.2 ml. of 0.1 N iodine solupressed as dextrose on a dry substance basis. Fehling solutions A and B were mixed immediately before each determination to urevent high results due to autoprecipitation of- cuprous &de. A blank determination was run on each mixture of Fehling TABLE11. PRECIPITATION OF DEXTRINS FROM 42 D. E. CORN SIRUP solution. 800 800 800 800 500 500 500 DRY SUBSTANCE. Each dextrin sample was Sirup, grams 500 600 Dry substance, grama 400 400 640 640 640 400 640 400 400 dispersed on Filter-Cel and dried to a constant Water, grams 100 100 160 160 160 160 100 100 100 weight in a vacuum oven at 100" c. (10). To Water added, ml. 300 300 240 240 240 320 300 300 300 400 480 400 400 400 400 400 400 400 disperse on Filter-Cel, 5 to 7 grams of the dexTotal water, ml. Methanol added ml. 935 1200 1600 1600 1600 2720 3600 3600 3600 trins were dissolved in 14 ml. of water. Final methanol "I, 70 75 80 SO 80 85 90 90 90 SPECIFICROTATION.Two t o Pptn. temp., %. 31 31 10 31 60 32 34 32 32 five grams of the material were dissolved in sufficient water to make 100 ml. at 20" C. The TABLE 111. PURIFICATION OF DEXTRINS FROM 42 D. E. CORN SIRUP angular rotation was read in a 2Water added t o p p t ml. 200 240 240 240 240 240 250 300 300 300 decimeter tube a t 20' C. using Methanol added, mi.' 600 960 960 960 960 960 1417 2700 2700 2700 Final % ' m e t h y o l 75 80 80 SO 80 80 85 90 90 90 sodium D light. Care was taken Temperature C. 31 10 31 31 60 60 32 34 32 32 that the solutions should be at No. times p&d. 10 10 5 10 10 15 5 5 10 15 equilibrium when the final readReducing power as dextrose (% d r y substance) 5.1 3.5 2.9 2.7 2.8 4.3 7.8 5.0 4.8 ings were made. Sp. rotation (a)?&' 193.5 196.0 198.0 197.5 198.0 194.6 186.5 191.6 191.9 PRECIPITATION AND PURIFICAReduced Fehling solution; sample too small for quantitative determination. TION. The corn sirup was weighed into a wide-mouth bottle, a small 0
5
(I
Q
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1943
tion to 5 ml. of a 2 per cent dextrin solution. Data for these precipitations and the analysis of the purified dextrins are given in Table IV.
TABLE IV. DEXTRINS FROM CORNSIRUPSPRECIPITATED WITH 80 PERCENTMETHANOL AND PURIFIED BY NINE,REPRECIPITATIONS Sirup D. E. S i r u p , grams D r y substance, grams Water i n sirup rams Water added, Total water, ml. Methanol added, ml.
&f.
Precipitate Water added, ml. Methanoladded, ml. Reducing power as dextrose, Yo s p . rotation Iodine coloration
29.9 1000 761 239 301 540 2160
33.9 1000 790 210 330 540 2160
640 160 240 400 1600
1760
63.4 1000 818 182 200 382 1528
200 800
200 800
240 960
120 480
120 480
6.1 204.7 Violet
6.3 201.0 Deep red
42.0 800
2.8 198.0 Red
54.0 1200 860 240 200 440
3.6 196.0 Red-brown
5.5 192.5 Brown
A probable explanation for the phenomenon that occurs with the reducing power of the dextrins lies in the various theoretical ways a starch or dextrin molecule may be split on hydrolysis and also in the rate of hydrolysis of the dextrins and higher sugars so formed. From the above results it appears that, on acid hydrolysis, parts of the starch m o l e cule are split more easily than others, resulting in the simultaneous formation of low- and high-molecular-weight dextrins which are insoluble in 80 per cent methanol. The lowmolecular-weight dextrins are hydrolyzed to sugars more rapidly than the larger dextrin molecules are split to lowmolecular-weight dextrins. This will result in a decrease in the reducing power of the dextrin fraction during certain stages of hydrolysis. From this it can be reasoned that the low D. E. (29.9 and 33.9) sirups contain alarger amount of low-molecularweight dextrin or a high-molecular-weight sugar which is insoluble in 80 per cent methanol than does the 42 D. E. sirup. Then if these smaller dextrin molecules are the size to be just insoluble in alcohol, only a slight degree of hydrolysis will make them soluble and thus remove them from the dextrin fraction. There would be a correspondingly small change in the larger dextrin molecules which would not be sufficient to bring the reducing power of the precipitated dextrins back to the initial value. I n other words, the smaller dextrin or higher sugar molecules would be removed more rapidly than they are formed in going from a 33.9 to a 42 D. E. sirup. As the hydrolysis proceeded beyond 42 D. E., the dextrin molecules would be shortened which would result in a greater reducing power for the precipitated dextrins. The reducing power of the dextrins would continue to increase with further hydrolysis until the molecules became too small to be precipitated with 80 per cent methanol. This latter statement is borne out by the facts that, as the D. E. increases beyond 42, the reducing power of the dextrins increases and that an 82 D. E. corn sugar does not contain any dextrins which can be precipitated with 80 per cent methanol. Proof must await further research on the composition of starch hydrolyzates. DEXTRINS FROM A DUAL CONVERSION SIRUP
The sample of dual conversion sirup (D. E. 64.8) was taken from a commercial batch which was made by superimposing an enzymatic hydrolysis on an acid hydrolysis. The methods for dextrin separation and analyses are the same as were used for the other corn sirups. The dextrins precipitated with 80 per cent methanol and purified by nine reprecipitations had the following properties:
Reducing power a8 dextrose, % Specifie rotation, (a)%o Iodine coloration
441 5 0 177.5 Brown
The dextrins from the dual conversion sirup had a reducing power slightly lower and a specific rotation much lower than the dextrins from an acid-converted sirup of approximately the same D. E. SUMMARY
Dextrins precipitated with 90 per cent methanol showed a constant reducing power and specific rotation after nine reprecipitations, but these values were not the same as those for the purified dextrins obtained with 80 per cent methanol. I n the former case, the reducing power was higher and the specific rotation was lower, indicating that more low molecular weight fragments were precipitated by the higher alcohol concentration. Dextrins with a constant minimum reducing power and a constant maximum specific rotation were obtained from a corn sirup by precipitating with 80 per cent methanol a t 31O C. and purifying with nine reprecipitations. A nonreducing dextrin was not obtained from corn sirups with D. E. values between 29.9 and 64.8 by precipitating and purifying with 80 per cent methanol. The lowest reducing power (as dextrose) was 2.7 per cent and was for the dextrins from a 42 D. E. sirup. Dextrins were precipitated with 80 per cent methanol from acid-converted corn sirups with D. E. values varying from 29.9 to 63.4 and from a dual-conversion sirup (acid enzyme) with a D. E. of 64.8. The dextrins were purified by reprecipitating nine times with 80 per cent methanol, and the reducing power, specific rotation, and iodine-coloration were determined on each sample. The fact that the reducing power of the dextrins passes through a minimum indicates that, on acid hydrolysis, parts of the starch molecule are split more easily than others; the result is the simultaneous formation of low- and highmolecular weight dextrins which are insoluble in 80 per cent methanol. Apparently these low-molecular-weight dextrins are hydrolyzed to sugars more rapidly than the larger dextrin molecules are split to low-molecular-weight dextrins. The reducing power, specific rotation, and iodine coloration of dextrins precipitated from corn sirups with 80 per cent methanol are dependent on the D. E. values of the sirups from which the dextrins are obtained. LITERATURE CITED
(1) Assoc. 0 5 c i a l Am. Chem., Official and Tentative Methods of Analysis, p. 500 (1940). (2) Ibid., p. 510 (1940). (3) Bauer, H. F., Orig. Com. 8th Intern. Congr. Appl. chem., 13, 9 (1912). (4) Biot, M., and Persoz, J., Ann. chim. phys., 52, 72 (1833). (5) Bondonneau, L., Compt. rend., 81,972 (1875). (6) Ibid., 81, 1210 (1875). (7) Browne, C. A., J. Am. Chem. SOC.,28, 446 (1906). (8) Browne, C. A., and Zerban, F. W., “Physical and Chemical Methods of Sugar Analysis”, p. 1135,New York, John Wiley & Sons, 1941. (9) Cantor, S.M., and Moyer, W. W., Div. of Sugar Chem., A. C. 8. meeting, Buffalo, 1942. (10) Cleland, J. E.,and Fetzer, W. R., IND.ENQ.CEFIM.,ANAL.ED., 13,858 (1941). (11) Fetser, W. R.,Evans, J. W., and Longenecker, J. B., Ibid., 5 , 81 (1933). (12) Glabe, E.F.,Cereal Chem., 19,442 (1942). (13) Hixon, R. M.,Rept. Agr. Research 1940,Pt. 11, Iowa Corn Research Inst., 6th Ann. Rept., 67. (14) Leach, A. E.,“Food Inspection and Analysis”, 4th ed., p. 672, New York, John Wiley & Sons, 1920. (15) Lintner, C. J., and Dull, George, Ber., 28, 1622 (1895). (16) Pringsheim, Hans, “Chemistry of the Saccharides”, p. 272, New York, McGraw-Hill Book Co., 1932. (17) Samec, M.,“Kolloidchemie der Starke”, pp. 466-9, Dresden and Leipzig, Theodor Steinkopff, 1927. (18) Vogel, A., Ann. chim., 82, 148 (1812).
