Corn Sirups of High
Fermentability RALPH W. KERR, HARRY MEISEL, NORBERT SCHINK Corn Products Refining Company, Argo, 111.
AND
Three methods are given for producing 8 corn sirup relatively stable to crystallization and of exceptionally high fermentability: (a)by blending in the proper proportions the end products of a limit malt conversion with those from a n acid conversion, ( b ) by applying a controlled a-glucosidase conversion to the products of a limit malt diastase conversion, and (c) by a diastatic conversion of cornstarch below its gelatinization point. The second method is instructive i n pointing out certain differences between the action of a-glucosidase o n the resistant configurations i n starch and the action of acid. The third method substantiates the theory that there is a considerable portion of cornstarch more readily soluble and more simply constituted than the remainder.
I
N A PRECEDIXG paper (1) the fundamentals involved in the production of a highly fermentable corn sirup were discussed. Theoretical evidence was presented to support the view previously given (d, 3) that cornstach is composed of two or more diverse units, one of which contains configurations resistant to the action of acid, amylases, and certain other enzymes involved in fermentation, It was found inadvisable to attempt a more complete disruption of these configurations after a malt conversion with acid or with the amylases to produce the product under discussion. On the other hand, the gradual reduction in weight of these resistant limit dextrins by the use of enzyme preparations containing a-glucosidase was again pointed out. On the practical side the creation of high fermentability by agents which do so principally by the creation of dextrosefor example, extensive acid treatment or treatment of limited acid conversions with a-glucosidase-containing preparations-was pointed out to lead t o solid products or unstable sirups which crystallize on standing. Both of these types of products are unsuited for certain users because of the economics of handling. More specifically it was shown (1) that a comparatively extensive acid conversion of a limit malt conversion, increasing its dextrose equivalent (D. E.) from 46 t o 69 per cent, left the fermentability of the product unaltered. Conversely, applying a limit malt conversion to an acid conver-
sion a t 58 per cent D. E. resulted in a fermentability no higher than the two sirups first mentioned. On the other hand, while the use of a fungus-type enzyme in the latter case apparently increases the fermentability indefinitely, the solution soon becomes overbalanced in dextrose content and, upon concentration by evaporation, crystallizes. “Limit malt conversion” means the hydrolysis of starch with malt diastase into the maximum percentage of sugars obtainable, using what might be deemed practical quantities of enzyme. Such a sirup will analyze about 46 to 48 per cent D. E. Three methods to increase materially the fermentability of corn sirup are indicated from considerations already given; all of them are conditioned, however, by an empirical theory that stability in a sirup, concentrated as far as 82 per cent, solids content, is possible provided 15 per cent, or preferably 20 per cent, of the solids present are nonreducing dextrins of higher molecular weight and that not much more than half the reducing sugars present are dextrose. The first and more obvious method is a simple combination in the proper proportions of the highly fermentlzble end products of acid conversion which contain only traces of dextrins and maltose with the end product of a malt conversion which, although comparatively high in fermentability, contains little dextrose. This method deserves only passing notice. It is, however, one practical solution to the problem. Sirup 1 listed in Table I is a limit malt diastase conversion of cornstarch, the preparation of which has been described (1). To 100 parts of this sirup, on a dry solids basis, 40 parts of a dextrose refinery liquor (known industrially as refinery C liquor) was added to produce sirup 2. Refinery C liquor is the mother liquor obtained in the recrystallization of dextrose and is 90f per cent dextrose. The two other methods offer considerations worth discussing for their bearing on general starch chemistry. They are treated separately in the two following sections. Combination of Malt Diastase and a-Glucosidase Conversions It has been pointed out ( I ) that a-glucosidase-containing preparations split dextrose from the configurations in that part of cornstarch which is more resistant both to the hydrolytic action of acid and of malt diastase. Hence, we may increase the fermentability of a corn Firup almost to 100 per cent by the use of such preparations; the limit in the problem under discussion is determined by the total amount of dextrose that can be tolerated and still produce a stable sirup. However, applying this latter type of conversion to a product of acid conversion shows its use to be very limited. Acid conversions, particularly those extensive enough to show a fair initial fermentability, are already high in dextrose con-
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tent. For example, sirup 3 (Table I) made by conversion with acid to a fermentability of 68.7 per cent already contaills 44.85 per cent dextrose. Obviously, little can be done to increase the fermentability with an a-glucosidase preparation without crystallization resulting in the final product due to an overbalance of dextrose.
The results for sirup 6 show little advantage for extending the conversion beyond the limits given for sirup 5. Another important conclusion is to be drawn from this experiment. Since it wm found impossible to accomplish a similar result by acid converting a limit malt diastase conversion ( I ) , it may be concluded that the action of the acid on the limit dextrin in the latter case is indiscriminate in respect to the point of attack; i. e., the dextrin TABLE I. ANALYSISAND FERMBNTABILITY OF CORNSTARCH SIRUPS molecule is broken into fragments of Nonreducing % Solids Sirup Method of % Maltose Dextrose Dextrin Fermentable assorted sizes, - - each f r a e e n t retainDextroso Equivalent Equivalent No. Manufacture 7.80 65.8 26.3 73.5 mg most of the resistant configura1 8traight malt conversion 47.7 2 100 pnrta ,Nn. 1 -!- 40 tions, whereas the enzyme used acts 62.5 38.0 40.2 22.8 78.3 parts C 11 uor 3 ~traigiitacia 64.7 44.85 32.5 22.65 68.7 only on terminal dextrose units of these 4 Acid to 53 D. E., then 64.2 39.0 40.36 20.05 08.4 dextrins. fungus eneyrne 5 Malt
0
Malt
++ fungus en~yme firngus enzyme
7 Low-temperature malt 8 No. 7 fungus enzyme
+
04.3 68.1 53.8 56.9
32.95 40.7 11.4 16.3
51.3 44.9 69.2 66.5
The use of acid conversions as substrates, substantially more limited than sirup 3, discloses several features which are economically unattractive. The quantity of enzyme required or the conversion time necessary, or both, are excessive; and if the acid conversion is not sufficiently advanced so that the residual resistant configurations are in a high ratio to the maltose configurations, the added enzyme produces the dextrose quota principally from maltose and its lower homologs. Therefore when the total allowable dextrose has been produced, the fermentability is still low as the result of the large quantities of limit dextrins present. An acid conversion to a dextrose equivalent of about 53 per cent appears to be the lower limit desirable in this connection. Converting such a sirup with a-glucosidase-containing enzymes to 40 per cent dextrose and 20 per cent nonreducing dextrins results in only 68.7 per cent fermentability for the product, sirup 4. This type of sirup has found a well-defined market as a sweetening agent and has been used in the brewing trade because of its percentage of fermentable dry solids. A limit malt conversion, sirup 1, shows an initial fermentability of the same order of magnitude as the last sirup mentioned, although it still contains 25 to 30 per cent nonreducing dextrins and, what is most important for this discussion, only about 8 per cent dextrose. Thus, in spite of the fact that an a-glucosidase might be expected to produce dextrose a t faster rates from the reducing sugars grouped as "maltose equivalent", there is in this case such a quantity of dextrose t o be produced before the product becomes overbalanced in this constituent that it is likely a substantial weight of nonreducing dextrin would be converted to dextrose during this interval as well. EXPEIRIMENTAL. A sirup was made by converting starch to a D. E. of 47.2 per cent, dextrose content of 8.54 per cent, maltose equivalent of 63.4 per cent, and dextrin content of 28.1 per cent by procedures already detailed (1). This was concentrated to 27" BB., and 0.1 per cent enzyme (dry solids basis) was added. A commercial fungus enzyme was used, Clarase-700 (Takamine). Conversionwas made at 130-135'F. (54-57" C.) a t a pH of 5.4 for 48 hours. The analysis is given under sirup 5 in Table I. A part of the batch was converted for an additional 48 hours; this is sirup 6. The results for sirup 5 show that our anticipation was correct-that it is possible to treat a limit malt diftstase conversion with a fungus enzyme and increase the amount fermentable to 80.4 per cent before the dextrose content exceeds 40 per cent. The limit dextrins are reduced in weight during this period to 15.7 per cent. Such a sirup has been found to be stable over a 9-month aging period at room temperature with occasional agitation.
15.7 14.4 19.4 17.2
80.4 80.7 81.8 83.7
Conversions Involving LowTemperature Diastase Treatment
The third method follows from two premises: Starch is heterogeneous, and certain fractions of starch are converted in a different manner with hydrolytic agents than are others. The justification for these views was given previously (3). It was shown that a hot water extract of cornstarch (an amylose fraction prepared according to procedures suggested by Meyer, 4) is converted to a definitely higher limit with pamylase than is parent starch. Therefore, malt conversions were attempted a t temperatures below the gelatinization point of starch to avoid disorganizing the granule, but at temperatures high enough to favor a solution of this more readily soluble and apparently more simple amylose fraction. The details of this conversion follow. EXPERIMENT 1. Thoroughly washed cornstarch was suspended in water to a concentration of 22' RB. One per cent of a commercial malt diastase preparation (Pabst's Exsize) was added, based on the weight of starch treated; the pH was adjusted to 5.0 and the slurry stirred a t 120" F. (49" C.) for 24 hours. The residual starch, still ungelatinized, was readily filtered off, washed by resuspension in fresh water, and refiltered. The liquors, sparkling clear and light in color, were evaporated to a concentrated sirup; the pH was adjusted during this operation to approximately 4.8. Yields of sirup solids are approximately 15 to 20 per cent of the weight of starch treated. By our method of inspection ( 1 ) the sirup shows a nonreducing dextrin content of only 19.4 per cent. The solids of this sirup, No. 7, are 81.8 per cent fermentable. While overbalanced on maltose equivalent, this sirup is rather stable, due to a lesser tendency of the component saccharides to crystallize, as compared with dextrose. However, this minor fault may be corrected, and at the same time additional fermentability can be s ed by superimposing on this low-temperature malt dias conversion (sirup 7) a limited conversion using an a-glucosidase-containing preparation, such as certain fungus enzymes. EXPERIMENT 2. Sirup 8 was made by converting a lowtemperature diastase conversion (after filtration and concentration to 27" BO.) with 0.05 per cent (dry solids basis) of a commercial fungus enzyme for 48 hours a t 5.4 pH and 130-135" F. As shown in Table I, this sirup has the exoeptionally high fermentability of 83.7 per cent. To make this process comme:cially attractive, some use must be found for the 80 per cent unconverted starch, preferably a use where the residual starch will show an advantage over starch which has not been treated. One such use has been found. In spite of the fact that as expected (3) the
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residue starch shows a 5 per cent lower “conversion limit” with &amylase than the parent starch, by our method of calculation (1) the residual starch liquefies at a faster rate in malt diastase conversions similar to those used in practice to produce thin-boiling starch pastes for the sizing of such products as textiles and paper. EXPERIMENT 3. Such a conversion is described as follows: 28.35 grams of starch are suspended in 280 cc. of water t o which are added 0.4 gram of a commercial diastase preparation known as Diastase E (Rohm & Haas Company). The water is so preadjusted that the final mixture for conversion will have a pH of 6.0 to 6.2. The conversion mixture is brought to 78” C. in 10 minutes with stirring, and held a t this temperature for 30 minutes. It is then transferred to a metal beaker, immersed in boiling water immediately, and cooked for 15 minutes in the boiling water bath. The
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viscosity of the paste is determined by a method used in industrial practice, known as the Scott test. Two hundred cubic centimeters of the paste are transferred to a metal cup provided with an orifice standardized for starch pastes, and the time in seconds is noted for the first 100 cc. of paste to run through the orifice a t the temperature of boiling water. This specific Scott viscosity after conversion, for the residual starch mentioned above, was 43.5 seconds; for a sample of cornstarch not pretreated but simply converted as above, 51.5 seconds. Literature Cited (1) Kerr, R.W., and Schink, N. F., IND.ENQ.CREM., 33,1418(1941). (2) Kerr, R. W., and Trubell, 0. R., Cereal Chem., 18, 530 (1941). (3) Kerr, R.W., Trubell, 0. R., and Severson, G. M., Ibid., in press. (4) Meyer, K., Bretano. W.,and Bernfeld, P., Helv. Chirn. Acta, 23, 845 (1940).
Supersaturation in Sugar Boiling Operations CONTINUOUS AUTOMATIC MEASUREMENT ALFRED L. HOLVEN California and Hawaiian Sugar Refining Corporation, Limited,
Crockett, Calif.
HE desirability of securing a continuous and automatic measurement of supersaturation during sugar boiling operations has long been recognized in the sugar industry. Claassen’s work ( I ) on beet sugar and later Thieme’s adaptations (16) to cane sugar have served to emphasize the need for further developments in this field. However, practical application of graining and boiling procedures in accordance with fundamental principles of supersaturation has been handicapped in both the cane and beet sugar industry by lack of a suitable method of automatically and continuously measuring the supersaturation of sugar solutions. Recognition of the need for what might be termed a “supersaturation meter” was expressed by Kukharenko ( 1 2 ) over twenty years ago: “In order to solve the problem of continuous crystallization in sugar manufacture, one must invent a device for the direct, accurate, and instantaneous determination of the coefficient of supersaturation of the mother liquor boiling in the vacuum pan.” Lack of an instrument for direct measurement of supersaturation was also commented upon by Webre (17’) in referring to the control of sugar boiling in which he stated: “The difficult part of this work lies in the fact that to date no one has been able to devise a n instrument that would show supersaturation directly.” Such references are typical of the opinions of many investigators involved in the development of sugar boiling operations. Because of this well recognized need of some means for measuring and controlling supersaturation of sugar solutions during crystallizing operations, many investigators have
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attempted to develop an instrument which would meet the rather exacting requirements. One of the earliest instruments to be employed in sugar boiling was the Brasmoscope originally devised by Curin (3) and later developed by Claassen ( 2 ) . This instrument consisted merely of a mercury vacuum gage and a thermometer by means of which vacuum and boiling temperatures could be determined. From such measurements boiling point elevations could be calculated, and by reference to tables these, in turn, could be expressed as concentrations. A direct determination of the elevation of the boiling point without the necessity of calculations involving vacuum became the subject of a patent issued to Langen (12) in 1909. I n Langen’s device two opposing thermocouples were employed; one was in the boiling massecuite while the other was in a pilot boiler in which water was boiled under the same pressure as that prevailing in the vacuum pan. Ho-ivever, all that was achieved by either the Brasmoscope or Langen’s apparatus was a measure of the concentration of the mother liquor and not its supersaturation. To convert concentration into coefficient of supersaturation required calculation-, in which the effect of absolute pressure also had to be taken into account. Several other investigators have described devices m hich will measure the boiling point elevation of sugar solutions. However, like the Langen apparatus, these instruments indicate only concentration of the mother liquor and not supersaturation. A measure of sucrose concentration cannot be used by itself as a means of sugar hoiling control because con-
