Effect of Acid and Heat on Dextrose and Dextrose Polymers W. R. FETZER, E. K. CROSBY, C. E. ENGEL, AND L. C. KIRST Clinton Foods Inc., Clinton, Iowa
T
HE acid hydrolysis of starch has been used for over a century for the production of starch sirups and dextrose and as an analytical procedure for the determination of starch. This longcontinued use of the procedure would normally indicate wellestablished principles for the acid hydrolysis of starch. However, an examination of the literature on this subject indicates t h a t the basic underlying conditions of hydrolysis are still not too well understood. The lack of clarity in published research may arise from two causes:
The commercial hydrolysis of starch employs relatively high concentrations of starch and very low concentrations of acid in proportion to the starch. Published research on the reversion, polymerization, or condensation of dextrose by acid has employed high concentrations of acid in proportion t o the dextrose so treated. The condensation polymerization of dextrose in more concentrated solutions under the influence of heat and small amounts of acid has received relatively little attention. This paper reports research on hydrolysis employing the usual variables of time, temperature, and acid concentration, more particularly the pH, but it is devoted chiefly t o a study of the most neglected variable, carbohydrate concentration of the system, or the sugarwater ratio. This variable is shown to be more significant than any of the others on the final reducing sugar content. COMMERCIAL HYDROLYSIS OF STARCH
The acid hydrolysis of starch is a complex series of reactions. It is further complicated by the fact that starch is not exclusively carbohydrate ( CeHlo05),. Starch, from whatever botanical source derived, contains small amounts of noncarbohydrate substance (ash, nitrogenous and lipoid bodies, and perhaps other materials). Starch obtained through the wet milling of corn contains 0.65 to 0.80% of “crude fat,” 0.25 t o 0.50% of “crude protein” (IV X 6.25), and 100 t o 200 p.p.m. of crude fiber, in addition to ash which may be chemically combined with the starch, or may be adsorbed in the processing. These noncarbohydrate constituents have a significant effect on the course and degree of hydrolysis, as they have an acid demand, tend t o alter and buffer the p H of the acid medium, and react with the dextrose produced, resulting in color bodies and a loss in yield. The situation is still further complicated by the variation in starch varieties. Potato and waxy maize starches contain less lipoid material (42’) than cornstarch. The commercial acid hydrolysis of starch, in general, covers two types of product-starch sirups (noncrystallizing) and starch sugars (crystallizing). These two types of products require different hydrolyzing conditions and they also differ in the degree or extent of hydrolysis. The degree of hydrolysis is defined as the “percentage of reducing sugars, expressed as dextrose, calculated on a dry substance basis” or dextrose equivalent (D.E.). Starch sirup is produced by using the highest practical concentration of starch in a slurry, 40 to 43% solids, to which is added hydrochloric acid to a normality of 0.012 t o 0.014 with a corresponding pH, depending upon starch quality, of 1.7 t o I .9. The time required to produce starch sirup (42 to 55 D.E.) is 4 to 6 minutes a t 145” C. (293’ F., 45 pounds gage pressure). Starch sugar (dextrose) is produced by using a much lower
concentration of starch, for it has long been recognized t h a t in order to attain maximum reducing sugar content one must use a low concentration of starch. The concentration of the starch slurry has been a compromise between the type and character of the desired hydrolyzate and the economics of water evaporation and refining. I n general, the concentration of starch in the slurries used for hydrolysis has been between 17 and 20%. However, the effective concentration in the converter is dependent upon the amount of prime water (dilute acid used for hydrolysis), the amount of condensate produced from the steam, and the chemical gain in solids obtained in the hydrolysis of starch t o sugar. The final concentration of sugar solids in the converter at the time of discharge is 15 to 16%. The amount of hydrochloric acid employed gives a normality of 0.025 t o 0.040 with a p H range of 1.4 to 1.6, depending upon the starch quality. The time required to produce a starch hydrolyzate of 91 t o 92 D.E. is 22 t o 29 minutes at 145’ C. (293’ F., 45 pounds gage pressure). The acid hydrolysis of starch for maximum dextrose content proceeds rapidly at the start and tapers off abruptly as the maximum is approached. The color formation is slow until the maximum dextrose content is approached, and subsequently increases rapidly. The situation is further complicated by the fact that the dextrose equivalent does not give the actual or “true ”dextrose, which is usually 3 to 5% lower than the dextrose equivalent a t the maximum dextrose equivalent value. Research in the wet milling industry has been directed constantly toward obtaining the maximum conversion; for the economic gains resulting from a dextrose equivalent higher than 92 are considerable. I n theory, the hydrolysis of 100 pounds of starch should yield 111 pounds of anhydrous dextrose. B u t in current commercial practice, 100 pounds of dry substance starch produces only 95 pounds of dextrose and 14 pounds of other sugars. Cantor has discussed reversion products (6,24) and has summarized the number and types of reaction occurring during the hydrolysis of starch (6) as follows:
A. The hydrolysis of starch via intermediate products, and ultimately t o dextrose. B. The reversion or polymerization or condensation of dextrose t o sugars of higher molecular weight, probably a variety of polysaccharides. C. The destruction of dextrose. Reactions A and C are regarded as unimolecular, and B as bimolecular. A and C are independent of the carbohydrate concentration. However, B is dependent upon the carbohydrate concentration and proceeds fastest when the concentration is high. The nondextrose carbohydrates have become known as reversion products, implying t h a t at least a part is derived from the condensation polymerization of dextrose. Fetzer (IS) suggested that they were derived entirely from dextrose, as he found t h a t acid-heat treatment of dextrose solutions and of starch slurries produced similar dextrose equivalents and specific rotations when the end concentrations were similar. He suggested a method t o utilize the reversion products by adding them t o a virgin starch slurry. Ebert, Newkirk, and Moskowitz ( I O ) patented the process of 1075
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DEXTROSE EQUIVALENT
Figure 1. Dextrose Equivalent-Specific Rotation Relationship for Usual Commercial Corn Sirups and Corn Sugars
reconverting hydrol, the mother liquor obtained from the manufacture of dextrose. This reconversion duplicated the procedure employed for starch, except that more acid was used in order t o compensate for the increased acid demands of the impurities. The process increased the dextrose equivalent of the hydrol (65 to 75) to approximately that obtained from starch, if allowance %asmade for the increased ash content. The analytical determination of starch by acid hydrolysis, an accepted empirical procedure of long standing, has been the subject of constant research (11, 33). In the official methods of the Association of Official Agricultural Chemists ( 1 ) the starch quantity varies from 2.5 to 3.0 grams in 200 ml. of 0.78 N hydrochloric acid which is refluxed for 2.5 hours. Unfortunately in the method pentosans and other carbohydrate bodies that undergo hvdroly sis are also converted into reducing sugars. The reducing sugars are calculated back to starch by employing the factor of 0.9, although recent investigators (9) have suggested the factor of 0.92. The question of dextrose loss during hydrolysis has been recognized by Lampitt, Fuller, and Goldenberg ( 2 5 ) who give correction factors for the dextrose polymerization. depending upon the conditions of the test. CONDENSATION POLYMERIZATION OF DEXTROSE BY ACID
T h e literature on the reversion or condensation polymerization of dextrose is extensive and confusing. The products formed have been called a t various times gallisin (40, 4 1 ) , isomaltose (15,16), revertose (d2,23),delta dextrose(b?), and dextrinose(44). A complete bibliography o n this subject is beyond the scope of the paper and only a fevl pertinent references are given. Musculus ( S I ) , Gautier ( 1 9 ) , and Grimaux and Lefkvre ( 2 1 ) reported on dry sirup carbohydrates, produced by the action of concentrated acid on ~-glucose. Fischer (16) treated 100 grams of D-glucose with 400 grams of concentrated hydrochloric acid,
Figure 2. Effect of Acid-Heat Treatment on a Dextrose S o h tion and a Starch Slurry, at Concentrations Identical a t Equilibrium
and produced what is called isomaltose. Scheibler and Mittelmeier (39) heated a 12% solution of dextrose in 2.5% sulfuric acid on a water bat,h for 12 hours and obta.ined a sugar called gallisin, whose osazone had the same inclting point as Fischer’s isomaltose. They concluded that it resulted from the condensation polymerization of dextrose and was not an intermediate step in the starch degradation. Wohl ( 4 6 ) extensively studied the action of hydrochloric acid on sucrose, followed by similar investigations on levulose, D-glucose, and starch. His study on dextrose was carried out on an 80% D-glucose solution with concentrations of hydrochloric acid based on rhe glucose from 0.05 to 1.0%. He summarized his research by stating that the hydrolytic cleavage of di- and polysaccharides is not a simple reaction of the first order, since another reaction reforms the monoses into higher complexcs of a dextrinlike nature. Ost ( 3 4 5 5 ) treated n-glucose with 33 % sulfuric acid. Moeln-yn-Hughes (30) studied the change in rotatioii of 10 to joyc dextrose solutions in W hydrochloric acid at 60” and 70” C. and found an increase of 4.57c for the former concentration and 20.87, for the latter. Berlin ( 4 ) reported that hydrol (dextrose molasses) was approximately 70% fermentable (dry basis), largely dextrose. From the unfermentable fraction he isolated gentiobiose in amounts of 5’%) based on the original carbohydrate. Berlin showed, by a comparison of physical and chemical properties, that the “unfermentable” portion of hydrol closely resembled Fischer’s isomaltose but concluded that because it was a mixture of carbohydratee it should not be given the definitive name of isomaltose. Later workers have interpreted .Berlin’s work to imply that the gentiobiose was residual to the starch. This is not Berlin’s conclusion and is not justified by his data. Coleman ( 8 ) , continuing his work on hydrol, confirmed Berlin’s data. Taylor and Lifschitz (45) acid-heat treated starch, corn, amyloses, and dextrose under t,he conditions of acidity, temperature, and
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Figure 3. Dextrose Equivalent, True Dextrose. and Specific Rotation of Equilibrated Dextrose Solutions at Various Concentrations
time employed in the commercial hydrolysis of starch slurries to crude corn sugars. By this treatment, they obtained 1.5% of gentiobiose from dextrose, a trace from starch, a trace from a-amylose, and none from pamylose. They concluded that the gentiobiose found in starch hydrolyzates under these conditions results from a direct scission of a polysaccharide in the insoluble @-amylosefraction of cornstarch rather than from the condensation polymerization of dextrose. These papers have generated the widely accepted concept that gentiobiose is derived from the starch in the course of the hydrolysis. Farber ( l a ) disclosed reactions of hydrochloric acid on pure dextrose, anhydrous, and hydrated, wherein the sugar is “roasted,” under conditions similar to the manufacture ok dextrin from starch. The conditions require that the moisture on the “roast” be kept a t a minimum. He obtained condensation polymers of dextrose, which he believed might be reconstituted with water as noncrystallizing sirups. Silin and Sapegina (43) investigated the condensation polymerization of dextrose (8.6 to 62.9%) in 0.5 N hydrochloric acid. They determined the residual reducing sugars, a t equilibrium, iodimetrically. The values obtained were stated to be dextrose, as the authors state that contrary to published data, products of the reversion of dextrose are not oxidized by Fehling’s or iodine solutions; from these data, they developed a formula for estimating the equilibrated dextrose based on the initial dextrose used in the system. These data indicate an equilibrium value of 91.8% dextrose when an initial dextrose concentration of 20% or an initial starch concentration of 18.0% is employed. Leuck (26-29) patented a process for the condensation polymerization of dextrose, preferably in the molten state by heat and catalysts, such as dry hydrogen chloride gas or boron trioxide. Frahm (17, 18) studied the reversion of dextrose with concentrated hydrochloric acid. His conditions with respect to acid
Figure 4.
Effect of Acid and Heat on 87% Solution of C.P. Dextrose
were much more severe than those employed for the usual starch hydrolysis. Experiments were made a t 20’ C. with acid concentrations ranging from 2.67 to 40.8% and dextrose concentrations from 11.95 to 57.6y0 by weight. By using a 1 M concentration of dextrose (16.8%) in 40.8% acid and allowing the mixture to stand a t 20’ C . until equilibrium was reached, he obtained a final dextrose equivalent of 66.2. Using the same concentration of acid with 4 moles of dextrose (67.2%), a final dextrose equivalent of 33.6 was obtained. The resulting reversion products (“polycondensates”) could all be quantitatively rehydrolyzed to dextrose. He concludes that the reaction is strictly reversible and that the end state could be determined by the mass action law. Saeman (38)in studies on the hydrolysis of cellulose, investigated the decomposition of 5% dextrose solutions, acidulated with 0.4,0.8, and 1.6% sulfuric acid a t 170°, B O 0 , and 190’ C. Myrback (32) stated that if the concentrations of acid and starch are very high, higher saccharides are formed, which may be, to some degree, remnants of starch molecules but are mainly secondary products formed by the reversion of dextrose similar to the action of concentrated hydrochloric acid on dextrose alone, His statement implies that this reversion in a starch hydrolysis occurs only if the concentration of acid is high. More recently Pacsu ( 3 6 ) reported the preparation of a “poly9se” from dextrose with a specific rotation of 108”. This was produced by dissolving boy0 dextrose in 5y0 hydrochloric acid solution, and evaporating it under reduced pressure a t temperatures below 45O C. to a hard glassy product, from which the polyose was obtained by dialysis. Graefe has reviewed the status of reversion products in starch hydrolyzates (90). From many of the investigations recorded in the literature it may be concluded that much can be learnedabout theacid hydrolysis of starch by studying the effect of acid and heat on chemi-
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Figure 5. Effect of Concentration on Dextrose Equivalent and Specific Rotation of “70” Corn Sugar Sirups under Acid-Heat Treatment
Figure 6. Effect of Temperature on Dextrose Equivalent and Specific Rotation of 42.5” Baume “70” Corn Sugar Sirup at pH 1.0
cally pure dextrose, under the accepted conditions for the commercial hydrolysis of starch. Such a study should yield pertinent information on the condensation polymerization of dextrose, which must be taken into account when the hydrolytic technique is employed. All prior literature references cite experiments on either dextrose or starch. No published literature has been found on the effect of the acid-heat treatment on intermediate acid hydrolyzates of starch at concentrations higher than commercial conversion conditions, 40 to 43%. This paper, in addition to exploring the effect of concentration on dextrose systems, also includes studies of the reaction of the intermediate hydrolyzates. The work reported in this paper started in 1944 ( 1 4 ) .
ing. Samples were removed periodically and analyzed for reducing sugars, “true” dextrose, rotation, and solids.
EXPERIMENTAL METHODS
Two types of experimental procedures were used.
EQUILIBRIUM DEXTROSE EQUIVaLENT
FOR
In the condensation polymerization of dextrose, a loss of “dry substance” and a corresponding increase in water occur. Thus in the experiments with dextrose or “TO” and “SO” corn sugars, a decrease in dry substance occurs. However, when the less hydrolyzed corn sirup is used, there appears to be a chemical gain as the oligosaccharides are hydrolyzed while dextrose polymerizes. This changing solids content during the course of an experiment posed a problem. This was resolved by starting with a sirup of definite Baume (dry substance) and allowing the solids to vary with the degree of polymerization obtained. The change in solids content during a polymerization changes the boiling point of the sirup during the test. For this reason the boiling points observed were temperature ranges, largely as follows: 45’ BB. 42.5O BB. 35’ BB.
DEXTROSE UNDER
ACID-HEAT TREATMENT. Solutions of dextrose 10, 20, 30, 40, 50, 60, 70, and SO% by weight w-ere prepared and acidulated t o p H 1.4 to 1.5 with sulfuric acid. The sirup samples (150 ml.) in glass pressure bottles were autoclaved at 45 pounds gage pressure (145” C., 293” F.). Each series of sirups was heated for periods of 0.5, 1, 1.5, and 2 hours. At the end of the period, the bottles mere removed and quickly cooled, and the pH was determined. If the p H of the sirup fell within the range of 1.5 to 1.6, the sirup was neutralized to p H 5.0 by dry barium hydroxide, or oxide, and centrifuged, and reducing sugars, rotation, and solids were determined on the clear filtrate. If the pH was outside the range given, the initial acid was decreased or increased and the test repeated. POLYMERIZATION OF SUGAR SIRUPSFOR RATEAND COURSEOF REACTION. One and one half liter portions of sugar sirups (35’ 42.5 or 43’, and 45’ Be.) were acidulated with sulfuric acid t o p d 1.0 f 0.1, placed in a 5-liter flask equipped with reflux condenser, and heated by a mantle adjusted t o produce gentle boil-
116-11Q0C . 110-112” C. 103-104’ C.
(240-248’ F.) (230-234O F.) (217-219’ F.)
MATERIALS USED IN EXPERIMENTATION
The dextrose used was anhydrous C.P. dextrose manufactured by the Corn Products Refining Co. from dextrose hydrate. The sirups used in the tests were commercial products having the following analyses: Medium Conversion Corn Sirup
D.E., ash-free basis Specific rotation, ash-free basis Solids 45O BB.
42.5’ BB. 35” BB.
42.0 150 84.3 79.3 64.8
High Conversion Corn Sirup
59.5 120
85.5 80.4 65.8
70 Brewer’s Corn Sugar 83.8 68-69
87.2 82.0 66.8
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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Figure 7. Effect of pH on Dextrose Equivalent and Specific Rotation pf 45” Baumt! “70” Corn Sugar Sirup a t Boiling
Figure 8. Effect of Concentration on Dextrose Equivalent and Specific Rotation of 42 D.E. Corn Sirup under Acid-Heat Treatment
The relationship of these sirups t o the usual commercial products as defined by dextrose equivalent and specific rotation, ash-free basis, is shown in Figure 1.
EXPERIMENTAL RESULTS
TYPICAL COMMERCIAL STARCH HYDROLYSIS. The effect of the acid-heat treatment on starch and on dextrose under identical final conditions of solids, temperature, and p H as employed comREDUCING SUGARS. Lane-Eynon volumetric method (a), calmercially is shown in Figure 2. The increase in carbohydrate culated as dextrose. TRUEDEXTROSE.Zerban-Sattler modification of the Steinsolids resulting from the hydrolysis of an 18.5% starch slurry hoff method (5). (chemical gain), and the decrease in carbohydrate solids from the DRYSUBSTANCE.Filter-cel method ( 7 ) . condensation of part of the dextrose in a 2070 dextrose solution ANGULAR ROTATION.Approximately ‘10% solids basis; 2(chemical loss), result in identical final concentrations. Both dcm. tube. DEXTROSEEQUIVALENT. Percentage of reducing sugars as materials have the same dextrose equivalent a t equilibrium. dextrose, expressed on a dry substance basis. EQUILIBRIUM DEXTROSE EQUIVALENT FOR DEXTROSE, COMCOLOR. Lovibond Tintometer, BDH model, 20 Brix solution, MERCIAL BASIS. The conditions for the usual commercial hydrol1.O-inch cell, caramel series 52. ysis of starch to dextrose, employing a converter, with live steam pH. Determined on the sirup a t its own final concentration by Coleman Model 3 D p H meter; standardized against 2.0 p H as the heating medium, have been given above. The same condibuffer solution. tions of temperature (145’ C.) and acid (pH 1.4 to 1.6) have been applied to dextrose solutions in a closed system (glass pressure Despite criticism by some t h a t the p H determination is unbottle), wherek the condensation polymerization of dextrose can reliable in the ranges given, in the acid-heat treatment which be followed more readily. The initial concentrations of dextrose follows the authors have found that these measurements, though were 10, 20, 30-90% by weight. Because the condensation of they may lack accuracy, are an indispensable guide in following dextrose involves a loss of water, the equilibrium values must be and predicting the rate of possible polymerization. The apbased on the equilibrium sugar solids, which are always less than proximate amount of concentrated sulfuric acid used per liter of the initial sugar solids. From the large amount of experimental sirup is given in the following table: data obtained, only a few typical results For Regular Corn Sirup For 70 Sugar Sirup are presented in Table I. This table P H 1.0 p H 0.5 p H 1.0 p H 0.5 shows the loss in solids produced through 2.5 ml. (0.087 N ) 450 BB. 1.1 ml. (0.039 N ) 0.1 ml. (0.035 N ) 2.0 ml. (0.070 N ) the condensation polymerization of dex1.1 ml. (0.039 N ) 2.2 ml. (0.077N ) 3.4 ml. 0.119 N ) 1.4 ml. (0.049 N ) 42;s BB. 2.6 ml. (0.091 N ) trose. 3.9 ml. r0.137 N ) 1.5 ml. (0.052 N ) 35 B6. 2.0 ml. (0.070N ) Normality calculated per liter of sirup, not per liter of water. The data in Table I were plotted on large graph paper from which even values of equilibrated sugar solids have been obtained with the correAnalytical results for reducing sugars, true dextrose, and sponding figures for dextrose equivalent, true dextrose, and specific rotation were calculated on the basis of dry substance, specific rotation, which appear in Table I1 and in Figure 3. ash-f ree. ANALYTICAL METHODS
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TABLE I.
EXPERIUENTAL
(Condensation polymerization Equilibrated Dextrose Equilibrated Solids, Sugar Solids, 7% by Wt. % by W t . 29.26 30.0 49.03 00.0 60 0 37.41 70.0 66.53 75.37 80.0 84.34 90 0
TABLE11. DATAO S
DATA
of dextrose a t 143' C. and 1.5 pH)
D.E. 88.8 79.3 73.5 65.8 26.4 43.7
' h i e Dextrose. 55 by Wt.
S1i:mfic Rotation
81.1 66.6 29.6 do. 1 3 Q .6 28.1
56.8 62.6 05.9 69.9 73. 1 80 8
EQUILIBRATED SUGAR S O L I D S
(Condensation polymermation of dextrose a t 145' C. and 1.5 1111) Equilibrium Sugar Solids, True Dextrose, Specific %; by Wt. D.E. % by Wt Rotation
a
Figure 9.
5' 0
Effect of Initial Dextrose Equivalent of Corn Sirup on Course of Heaction
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Figure 10. Relationship of Dextrose Equivalent to Specific Rotation i n Systems of Varying Initial Compositions and Concentrations under Acid-Heat Treatment
Values for C.P. dextrose.
AklCID-HEAT TREATMENT O F DEXTROSE SIRUP. The effect oi' acid-heat t'reatment on 45" Baume dextrose sirup is shoxn in Figure 4 as defined by dextrose equivalent, true dextrose, and specific rotation. The fermentable sugars calculated as dextrose are greater than the dextrose content; but less than the dextrose equivalent. ACID-HEA4TT R E A T I I E X T O F 70 CORS SEq.4R SIRUP. The effect of acid-heat treatment on 70 corn sugar sirup of 83.8 D.E. is shoir-n in Figures 5, 6, and 7. Figure 5 shows the effect 011 sirups with initial Baume of 35", 42.5', and 45" as defined by dextrose equivalent a,nd specific rotation. Figure 6 shows the effect of temperature on a 42.5' Baume sirup with constant pH. Figure 7 shows :he effect of p H on the rate and degree of polymerization as defined by dextrose equivalent and specific rotation. ACID-HEAT TREATMEKT OB CORNSIRUPS. Two types of corn sirup v-ere studied: a medium conversion product of 42 D.E., and a high conversion product of 59.5 D.E. Figure 8 covers the course of the acid-heat treatment on 42 D.E. sirup at two levels of solids-35" and 45' Baume, as defined by specific rotation a i d dextroee equivalent. The 45" Baume sirup having a higher boiling temperature reacts faster than the lower boiling 35' Baume product. Figure 9 compares 42" Baume sirups of 42 and 59.5 D.E. The true dextrose content increases in the former treatment and decreases in the latter. Sc-aiarARi7 OF ACID-HEATSTUDIES. The data obtained on the acid-heat treatment of corn sirup and corn sugar sirup of heavy density are shown in Figures 10, 11, and 12. The curve to the right is a composite specific rotation curve based on average data. obtained from commercial products produced from the hydrolj-sis of starch (unpublished data). I n Figure 10 it is essentially a straight line in the corn sirup range; the dotted line is a hypothetical extension to the value for dextrose (52.7). The data are given for three densities of corn sirup and corn sugar sirups under 0.1, a t their respective boiling acid-hcat treatment (pH 1.0 =I= points) and their apparent equilibrium values. Figure 11 shows the course of the acid-heat treatment on 45" BaumO corn sirups of different dextrose equivalents, corn sugar sirup, and dextrose. The equilibrium products of this treatment as defined by specific rotation and dextrose equivalent tend t o converge in a definite area, which suggests similarity in their carbohydrate composition. Figure 12 employs the same experimental sirups as used in Figure 11, except that the plot covers true dextrose instead of dextrose equivalent. The equilibrated
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INDUSTRIAL AND ENGINEERING CHEMISTRY
products of the acid-heat treatment again tend to converge, indicating a close similarity in the carbohydrate composition of these products, The equilibrated sirups above have been analyzed for their fermentable sugar content calculated as dextrose. The data obtained are shown in Figure 13. The heavy curve is a composite curve based on the average fermentable values obtained from the commercial products, indicated by their respective dextrose equivalents. The dotted lines from these values connect to the dextrose equivalents and fermentable sugars in the same sirups after they have been acid-heat treated (45’ Baum6, p H 1.0 f 0.1). The converging of these values again indicates a similarity of their carbohydrate composition. MISCELLANEOUS STUDIESON ACID-HEATTREATMENT. The above research on the acid-heat treatment has employed sirups obtained from the acid hydrolysis of starch. Similar data were obtained on maltose sirups prepared by enzymic hydrolysis as shown in Figure 14. The maltose sirups were concentrated t o 45“ Baume and acid-treated as indicated. The progressive stages in the reaction by the acid-heat treatment are shown. The general area of the equilibrated end products from several tests is indicated by the circular areas. The various equilibrium mixtures have been analyzed according to A.O.A.C. procedures for “starch” ( I ) , with data indicating complete conversion t o dextrose when the usual conversion factor is employed. This factor of 0.9 is based on the chemical gain from the hydrolysis of starch, (C~HIOO&,to monomeric dextrose, CsH1206. The chemical gain from the hydrolysis of partially polymerized dextrose will be less. Hence if one analyzes a polymerized dextrose system, and use the starch factor 0.9, the result will be above the theoretically possible value for starch. This was found t o be the case. A large quantity of the equilibrium mixture was diluted to conditions for the A.O.A.C. procedure, hydrolyzed, concentrated,
Figure 11. Lack of Influence of Initial Dextrose Equivalent of Starting Carbohydrate upon Equilibrium Values of Dextrose Equivalent Versus Specific Rotation
X
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Figure 12. Lack of Influence of True Dextrose Content of Starting Carbohydrate upon Equilibrium Values of True Dextrose Versus Specific Rotation
1
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EQUIVALENT
Figure 13. Changes in Fermentability Resulting from Acid-Heat Treatment of Various Sirups
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tncreosing with : Concentration
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STARCH POLYSACCHARIDES (ornylose. omy1opectin.etc.l
AREA STUDIED
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OLIGOSACCHARIDES 1D.P. 3-101
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Figure 14.
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DEXTROSE EaUIVALENT
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olso. gentibbtose? 1scgentiobiose7
DESTRUCTION PRODUCTS (humins, ocids,colors, etc )
Figure 15. Schematic Mechanism for Hydrolysis of Starch and Condensation Polymerization of Dextrose
Effect of Acid-Heat Treatment on Maltose Sirup
and crystallized. The crystals so obtained have been chemically and microscopically identified as dextrose. A large quantity of the equilibrium mixture has been diluted t o the concentration employed for commercial acid hydrolysis of starch slurries for sugar production (approximately 20% solids) and hydrolyzed under these same conditions. The sirup &-as then refined, and concentrated t o 45” BaumB. Upon crystallizing, this sugar mass could not be distinguished from the sugar obtained by hydrolyzing starch. This sugar \vas then acid-heat treated, yielding a noncrystallizing sirup of approximately the same dextrose equivalent and specific rotation as the original starting equilibrium sirup. DISCUSSION
The condensation polymerization (reversion) of dextrose into di- and oligosaccharides is primarily a function of the concentration of the system (dextrose, maltose, dextrin content, etc.) and is catalyzed by heat and hydrogen ion concentration. When a carbohydrate, such as starch, dextrin, oligosaccharides, and disaccharides, composed of anhydroglucose units, glycosidically linked, is hydrolyzed, the elements of water are added to the fragments a t the points of cleavage. Hydrolysis involves a “chemical gain.” The effect on the system is more than added water. When the elements of water are combined into the carbohydrate molecules, a loss of water from the solvent phase of the system occurs and an increase in the dry substance concentration results. When C.P. dextrose solutions are similarly treated, condensation polymerization takes place and the elements of water are removed in the condensation. The dry substance is decreased and the true (solvent) water is increased. This reduction in dry substance is “chemical loss.” Because water is not only a solvent medium in a hydrolytic *system, but also a reactant, its concentration affects the equilib-
rium according t o thelaw of mass action. Most hydrolytic systems are so dilute that the change in Tvater concentration ia inconsequential. But the authors have found that in systems where the water content is low, this change in water concentiation becomes highly significant, the effect increasing as the water content is decreased. The authors have shopn that the condensation polymerization of dextrose proceeds readily under proper conditions of concentration and temperature, and a i t h amounts of acid so small that they are normally disregarded. Accordingly, research done on dextrose in aqueous acid systems should take cognizance of the condensation polymerization (reversion) and due allowance foi it must be made in the interpretation of the results. Certain data presented in this paper engender speculation as to the character of the transfoimations that occur. Theie has long been a concept in sugar chemistry that changes in reducing poa er are invariably associated with corresponding changes in specific rotation. That this does not necessarily follow is clearly shown in Figures 5 and 6. In Figure 5 , there is a large change in reducing power but very little change in rotation; in Figure 6, there is little change in reducing pol! er but a large change in rotation. In some of the older literature the effectof heat and acid on carbohydrate systems is reported either only in terms of reducing power, or only in the observed change in rotation. The authors’ findings demonstrate that neither criterion alone is sufficient to warrant specific conclusions as to the nature or extent of the change which has occurred. A schematic representation of the course of the acid hydrolysis of starch is shown in Figure 15. Others in this laboratory have investigated some of these products by column and paper chromatography. Detailed results will be published in future communications. In polymerized C.P. dextrose solutions, they have obtained maltose in amounts of 10% and gentiobiose in amounts of 5%: both sugars were identified as their octaacetates. Presumptive evidence indicates the
May 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
presence of trehalose and isogentiobiose. Part of the sample on which maltose ww obtained was sent t o another laboratory without identification &s to its origin. These workers reported maltose by paper chromatography, employing a series of dilutions and they estimated the concentration of the maltose t o be between 10 and 15%. In studies on the structure of starch, agreement has not been reached as t o whether some of the products which have been identified in starch hydrolyzates are fragments from the original starch molecule, or artifacts (reversion products). The present data show that some of the sugars found in starch hydrolyzates are produced from pure dextrose by a treatment identical with that used for the hydrolysis of starch. Thus, their presence in starch hydrolyzates is no indication that they existed in the original starch structure. CONCLUSIONS
The extended acid-heat treatment of cornstarch slurries, 42 and 60 D.E. cornstarch sirup, “70” and “80” corn sirups, or C.P. dextrose, whether the treatment is ‘hydrolysis or condensation polymerization, yields an equilibrated mixture of sugars, dependent upon the solids concentration of the sirup a t equilibrium. The composition of the sirups, based on the analytical data presented] is similar if not identical. The reaction results in a true equilibrium which can be shifted repeatedly from substantially pure dextrose to a complex mixture of monomeric and polymerized dextrose by altering the concentration of the substrate undergoing the acid-heat treatment. The rate a t which equilibrium is reached for a given solids concentration is dependent upon the temperature and pH of the sirup dndergoing the treatment. The higher the concentration of the sugar solids, the greater is the polymerization of the dextrose. The new sirups are noncrystallizing. The acid-heat treatment causes color and bitterness, the amount dependent upon the severity and extent of the treatment. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance and criticism of Geo. T. Peckham, Jr., Clinton Foods Inc., and Karl Paul Link, University of Wisconsin, in the preparation of this paper. LITERATURE CITED (1) h s o c . Official Agr. Chemists, “Official and Tentative Methods of Analysis,” 7th ed., p. 348, 22.34, 1950. (2) Ibid., p. 506, 29.32. (3) Ibid., p. 528, 29.148. (4) Berlin, H., J . Am. Chem. Soc., 48, 2627 (1926).
1083
Cantor, S. M., “Summaries of Doctoral Dissertations,” Vol. IV, p. 113, Northwestern University, 1936. Cantor, S. M., U. S. Patent 2,203,325 (June 4, 1940). . . Cleland, J. E., and Fetaer, W. R., IND. ENQ. CHEM.,ANAL. ED., 13, 858 (1941). (8) Coleman, G. H., Buchanan, M. A., and Paul, P. T., J . Am. Chem. Soc.. 57, 1119 (1935). (9) Earle, F. R., and Milner, R. T, Cereal. Chem., 21, 567-75 (1944). (10) Eberti C., Newkirk, W. B., and Moskowita, M., U. S. Patent 1,704,037 (1929). (11) Etheredge, M. P., J . Assoc. O$ic. Agr. Chemists, 27, 404-12 (1944). (12) Farber, E., U. S. Patent 2,027,904 (Jan. 14, 1936). (13) Fetaer, W. R., Zbid., 2,210,659 (Aug. 6, 1940). (14) Fetzer, W. R., U. S. Patent Application Serial 735,247 (March 17, 1947). (15) Fischer, E., Ber., 23, 3687-91 (1890). (16) Ibid., 28, 3024-8 (1895). (17) Frahm, H., Ann., 555, 187-213 (1944). (18) Frahm, H., Be?., 74B, 522-5 (1941). (19) Gautier, A., Bull. SOC. chim. France, (2) 22,145 (1874). (20) Graefe, Gerd, Sttlrke, 2, 27 (1950). (21) Grimaux, E., and LefBvre, T., Compt. rend.. 103, 146 (1886). (22) Hill, A. C., J. Chem. Soc., 1898, 634-58. (23) Zbid., 1903, 578-98. (24) Hurd, C. D., and Cantor, S. M., J . Am. Chem. Soc., 60, 2677 (1938). (25) Lampitt, L. H., Fuller, C. H. F., and Goldenberg, N. J., J . SOC. Chem. I n d . , 66, 117-21 (1947). (26) Leuck, G. J., U. S. Patent 2,375,564 (1945). (27) Ibid., 2,387,275 (1946). (28) Zbid., 2,400,423 (1946). (29) Zbid., 2,436,967 (1948). (30) Moelwyn-Hughes, E. A., Trans. Faraday Soc., 25,503 (1929). (31) Musculus, F., Bull. soc. chim. France, (2) 18, 66 (1872). (32) Myrbiick, Karl, Advances in Carbohydrate Chem., 3, 308 (1948). (33) Noyes, W. A., Crawford, G., Jumper, C. H., Flory, E. L., and Arnold, R. B., J. Am. Chem. SOC.,26,266-80 (1904). (34) Ost, H., 2. angew. Chem., 17, 1663 (1904). (35) Ost, H., and Broadkorb, Th., Chem.-Ztg., 36,1125-6 (1911). (36) Pacsu, Eugene, and Mora, P. T., J. Am. Chem. Soo., 72, 1045 (1950). (37) Roessing, A., Chem.-Ztg., 29,867-73 (1950). (38) Saeman, J. F., IND.ENQ.CREM.,37,43-52 (1945). (39) Scheibler, C., and Mittelmeier, H., Bey., 242, 301 (1891). (40) Sohmitt, C., and Cobenzl.,Ibid., 17, 1000-15 (1884). (41) Schmitt, C., and Rosenhek, J., Ibid., 17, 2456-67 (1884). (42) Schoch, T. J., J. Am. Chem. SOC.,64, 2954 (1942). (43) Silin, P.M., and Sapegina, E. A., Trudg voroflezh, K h i m . Teknol. Inst., 3-4,79 (1939). (44) Syniewski, W., Ann., 324, 212-68 (1902). (45) Taylor, T. C., and Lifschitz, D., J . Am. Chem. SOC. 54, 1054 (1932). (46) Wohl, A,, Bey., 23, 2084-110 (1890). RECEIVED for review September 11, 1952. ACCEPTEDJanuary 23, 1053. Presented before the Division of Sugar Chemistry, Memorial Program Celebrating the 100th Anniversary of the Birth of Emil Fischer and J. H. van’t Hoff, at the 122nd Meeting of the AMERICANCHEMICAL SOCIETY, Atlantic City, N. J.
Ternary System: Furfural-Me thvl Isobutyl ketone-Water at 25” C.‘ JOSEPH B. CONWAY AND JAMES B. PHILIP‘ Department of Chemical Engineering, Villanova College, Villanova, Pa.
I
N CONNECTION withthe solvent extraction of furfural from aqueous solutions Trimble and Dunlop (7) suggested the use of ethyl acetate as the extracting solvent. A research program is now under way t o obtain the necessary data to evaluate various solvents for this extraction. The System presented herein represents but a portion of this program. 1
Present addreas, Merck & Co., Ino., Rahway, N. J.
MATERIALS
Technical furfural (Quaker Oats Co.) was purified using a laboratory-type (Vigreux) fractionating column about 2 feet in height. Purification Was carried out at 15 mm. of mercury and the first and last portions (about 50 ml.) of the distillate were discarded. The furfural was purified as needed, 250 at a timel using a 1-liter distilling flask as a still pot. The purified product was clear and had a very faint straw-yellow color. Methyl isobutyl ketone (Carbide and Carbon Chemicals
