INDUSTRIAL UTILIZATION OF CARBOHYDRATES
Industrial Starch Research Fundamental knowledge is guiding efforts to improve and e x p a n d uses of starch . . . the effects of this in a commercial sense are just beginning to be felt C. G . CALDWELL, National Starch Products, Inc. 270 Madison A v e . , N e w York 76, N. Y.
X H E organic chemistry, physical c h e m istry, a n d colloidal chemistry of starch highlights the fact t h a t starch is both a carbohydrate u n d e r g o i n g organic c h e m i cal reactions a n d conversions common to all carbohydrates, and at die same time is a high polymeric material whose behavior in dispersion or solution a n d in the solid state is governed by principles applicable to all polymers. One of the most significant forward steps in starch k n o w l e d g e w a s contributed b y K. Meyer in clearly characterizing t h e material extracted from starch grains by hot w a t e r as a linear polymer, now generally called amylose, a n d indicating conversely that t h e residue w a s primarily b r a n c h e d in nature, n o w generally called amylopectin. FTOITI that t i m e , only a b o u t 10 years ago, o u r k n o w l e d g e of and techniques for studying starch h a v e grown in ever widening circles. It is impossible to mention the m a n y historic advances that h a v e been m a d e . However, it m a y b e concluded that in the period of the past 10 years w e have b e e n concerned with analyzing starches for linear and b r a n c h e d components, and with t h e chemical, physical, a n d biochemical characterization of these components. So far, the principal facts of commercial interest resulting from these studies, stated in a very simplified form, are first, that the hydroxyl groups in one molecule have a strong affinity for those in another molecule, especially if t h e y c a n get close e n o u g h together. Second, t h e y can get close enough together in straight lineax chains like amylose, b e c a u s e straight chains can line u p parallel to each other. This h a p p e n s in a starch paste—the chains line u p and* t h e hydroxyl groups b i n d t h e m fast together. If it is a very dilute solution, these b u n d l e s of chains will fall o u t as an insoluble precipitate; if it is a concentrated solution, a gel will form. This associating or b a n d i n g together of starch molecules is called rétrogradation, since it is observed in starch cooks to b e a reversal from a fluid, liquid state to a solid, gelled state. T h e third fact is t h a t not many of t h e hydroxyl groups can get close enough together with a b r a n c h e d 514
G. CALDWELL absorbed from his agricultural environs ( h e w a s b o r n in Arkansas a n d schooled in I o w a ) a lasting interest in agricultural a n d food chemistry. W h i l e a p o s t g r a d u a t e student at Ames he b e g a n h i s career a t National Starch Products as research chemist. H e later became supervisor of starch research and in 1940, after receiving his P h . D . h e was m a d e director of research. K i s fields of interest i n chemistry include t h e industrial chemistry of starch, starch modifications, adhesives, high polymers, a n d agricultural chemistry.
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chain like amylopectin, because with the branching, parallel orientation is not easily possible. Solutions of amylopectin, t h e r e fore, will not gel. As a result of the studies on starch a n d of studies m a d e on other polymers we have some u n d e r s t a n d ing and interpretation of the b e h a v i o r of starch. U n d e r s t a n d i n g is the first contribution of research to application studies. One knows w h y starch dispersions set to a gel a n d become pasty with age, so he asks himself h o w this can be overcome. One knows w h y films of starch are brittle and weak, so immediately h e asks h o w they can be m a d e flexible and strong. U n d e r standing t h e cause, one may m o r e intelligently seek t h e remedy. T h e less understanding or basic knowledge h e has, the more the applied chemist is r e d u c e d to the hit or miss, t r y every bottle on the shelf type of experimentation a n d the odds against his success become greater. Ind e e d , basic knowledge m a y be invaluable to him in t h e negative sense of making it clear that certain projects have n o chance of success and t h u s saving his time for expenditure on other more promising projects. T h e commercial importance of this knowledge is highlighted b y t h e fact that last year about t w o billion p o u n d s of corn starch w e r e p r o d u c e d a n d u s e d in this country, either as such or in t h e form of modifications b u t excluding corn sugar, syrups, or dextrose. Roughly o n e half of this, or at least one billion p o u n d s , was used in p a p e r mills, cotton and textiles, in CH E Ml
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adhesives, in c o r r u g a t i n g and laminating, and for laundry s t a r c h , uses w h e r e it serves primarily b e c a u s e of i t s film-forming properties. In foods, starch p k y s an essential n u tritional role "but i t s viscosity a n d gelling effects become of ^primary i m p o r t a n c e in confectionery, p u d d i n g s , pie fillings, salad dressings, and canr^ed foods; uses w h i c h might account for on the o r d e r of 2 0 0 million p o u n d s of corn starch per year. With this should b>e include-d a guess of about 7.5 billion p o u n d s of w h e a t starch per y e a r used as a. component of w h e a t flour i n b a k i n g . Without g o i n g f-urther it is clear t h a t starch usage i s vitally concerned w i t h t h e relation of chemical composition a n d structure t o the physical properties of its films, dispersions or solutions, and p o w d e r s . And as w e proceed to s o m e of t h e a d v a n c e s made in industrial srfcarch chemistry w e will find t h a t up t o the present, m o s t of t h e m have b e e n in t h e r i a t u r e of operations on the starch to b-eneficially modify or c h a n g e these physical properties. S u c h has r>een t h e case with all t h e well-known d e g r a d a t i v e methods of treating starches, a_s in i£he -case of acids, with heat, with o x i d i z i n g agents, a n d with enzymes. These procedures, l o n g practiced in t h e art, resulted from the necessity for reducing the viscosity of starch for application in adhesives, sizings, a n d coatings. Lower viscosities g i v e better penetration and permit higher solids dispersions w i t h resultant incre-ase i n pick-up of solids on the sized clotri or jpape>r, increased tackiA N D
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INDUSTRIAL STARCH RESEARCH ness, and reduction in drying times. It has also been known in the art, however, that there is a limit to how far degradation of starch can be carried without loss of its filming and adhesive strength. Application of the modern techniques for studying starch to these commercial products has given greater insight into the nature of the changes that take place during their manufacture. The acid hydrolyzed "thin boiling" starches have been found to have higher contents of the linear amylose and less of the branched amylopectin, explaining their exaggerated tendency to retrograde. This is objectionable in some cases since it leads to gelling or pasting in the glue pot or size bath, but is an advantage where waterresistant filnfs are desired, as in the fabrication of bag adhesives. The oxidized "thin boiling" starches are more stable to gelling. Sodium hypochlorite, the converting agent, does not preferentially destroy the branched amylopectin and furthermore, it introduces highly soluble carboxyl sodium and carbonyl groups into the chain fragments, which counteract their tendency to retrograde. Oxidized starches are desirable for the clay coating of paper, the preparation of liquid laundry starches, the warp sizing of textile yarns, and the finishing of fabrics. Roasting of starch to produce dextrins has long been known to result in products such as the yellow dextrins and British gums with surprising stability to gelling. Brimhall (1942) provided very good evidence to indicate that heating of starch under conditions of dextrinization leads to a disappearance of linear chains and an increase in the degree of branching of the molecules. The action of enzymes on starch has been the subject of a vast amount of fundamental work and has played an essential role in clarifying the structure of starch. The specificity of ß-amylase has been useful in characterizing linear starch chains and has given the initial clues to the architecture of the branching in amylopectin. /3-Amylase, producing as it does only maltose and no intermediate" molecular sizes, may be said to give conversions which resemble the original starch, but only at lower concentrations. It is not desirable for reducing the viscosity of starch for use as films or adhesives. The presence of large amounts of sugar gives rise also to nondrying films. The action of the a-amylases on starch, in contrast to ^-amylase, is in general characterized by an apparent simultaneous attack on the starch molecule at many points, the formation of fragments that are relatively homogeneous as to chain length, and the production of a minimum of the very low molecular weight sugars. From the standpoint of filming and adhesive properties, theory tells us such conversions as these should be ideal. For these reasons conversions with enzyme preparations containing both the sacchariViJO L U M E
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fying ß-amylase and the dextrinizing a-amylase have been carried out under conditions of temperature and pH such as to favor the latter, arid the producers of enzyme materials for commercial use have sought to produce them with relatively high proportions of the dextrinizing component. Conversion of starch with enzymes is used for making liquid adhesives and finds wide application in treatment of starches for the coating and sizing of paper, and for the sizing of textiles. Starch preparations more readily converted by enzymes have recently been introduced. The present commercial status of the starch from waxy corn is a very good example of the successful blending of basic and applied research. Waxy corn, from the time it was first brought to this coun-
these products are shipped and stored in the winter as well as in the summer. A starch derivative results from the treatment of starch with a chemical which reacts with hydroxyl groups to introduce into the molecule replacement or substituent groups for the hydroxyl groups. The formation of derivatives of starch in order to modify its physical and colloidal properties has been given new impetus and is being approached with new understanding as a result of our greater knowledge, not only of starch but also of other polymeric materials. It is appropriate to speak first of those derivatives of qufte low degrees of substitution, since up to the present they have had the greatest commercial significance. By low, is meant not more than one sub-
Effects of increasing amylose content on gelling. Approximate amylose content left to right is: 0, 7.5%, 1 5 % , 22.5%, and 30% for cornstarch try in 1908 from China, was a curiosity and primarily of interest to the geneticists. During the 193CTs, on the basis of the resemblance of its starch pastes to those of tapioca starch and the interest in developing a domestic source for a tapioca-like starch, work was begun by the geneticists to develop hybrid varieties suited to commercial planting in the corn belt. Let it be observed that the techniques for accomplishing this owed their existence to a broad body of knowledge accumulated through long years of research in genetics and plant breeding. By the time the agricultural production and wet milling of waxy corn had been established on a commercial basis, it was known that the resulting starch was unique in that it contained essentially only branched molecules similar to the branched component recoverable from ordinary cornstarch. Furthermore, the relationship between branched structure and resistance to rétrogradation or .gelling and pasting was well understood and suggested many applications of waxy starch. In food applications such as in thickeners for the fillings of commercial pies and in salad dressings, a very much reduced tendency to set is desired to give the most acceptable texture. In salad dressings and prepared liquid laundry starches, resistance to rétrogradation malces possible preparations which are not adversely affected by freezing, a fact of considerable economic significance when it is remembered that
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stituent group for each glucose unit, and in most cases not more than one for each 100 to 200 glucose units. Such products have capitalized on the inherent properties of starch and improved on it for the uses where it is already being used, for example as a hydrophilic, viscosity-modifying agent with moderately good film properties. One of the most important types of starch derivative is that resulting from the action of bi- or polyfunctional reagents, with bi- or polyfunctional reagents meaning those capable of reacting with more than one hydroxyl group and thus able to form cross-links or bridges from one starch molecule to another. Such cross-linking reactions carried out extensively on a starch paste lead first to an increase in viscosity and then to gelling and insolubilization. If they can be arranged to take place in a starch film, water-resistant, or water-insoluble films are the result and as such they have important commercial utility. One can mention washproof textile finishes, water-resistant adhesives, and wet strength paper. Treatment of the ungelatinized starch granules with cross-linking reagents has had particularly valuable use. What appears to take place is a cross-linking of molecules on or near the surface, with a resultant tanning or toughening of the granule. Where the degree of treatment results in an estimated cross-link to only one 515
ÎNDUSTRIAL UTILIZATION OF CARBOHYDRATES. glucose unit out of 300 or 400, the gelatin ization temperature is raised a n d a higher maximum viscosity of the cooked paste is attained. Since starch is used in many cases for its contribution to viscosity, a higher viscosity per unit of starch solids is of commercial value. Such is the case with textile printing gums, thickeners for canned foods, and strangely enough, for one adhesive application. In the starch process for manufacture of corrugated board, high speed production is made possible by utilizing the rapid gelatinization of starch as a means of setting the adhesive bond. T h e adhesive consists of a suspension of ungelatinized starch in a cooked starch paste. On application to the board, heat is applied, resulting in almost instantaneous increase in viscosity and setting of the adhesive bond. The higher viscosities of slightly cross-linked starch have recently come into widespread use for this purpose, making possible the use of less starch and giving better adhesive bonds. Another result of slight degrees of crosslinking is to increase the resistance of starch paste viscosities to the thinning effect of prolonged agitation, heat or low pITs. Apparently the swollen granules are more resistant to rupture and collapse than those of untreated starch. In many commercial applications of starch, enough is cooked at one time for a day's operation, and it becomes desirable that the cooked paste maintain a uniform viscosity throughout the day. To d o this under conditions of continual heating and pumping requires a starch resistant to thinning. One last property of slight degrees of cross-linking that shall be mentioned is the reduction of the cohesive, rubbery characteristic of starches such as potato, tapioca, and waxy maize to give smooth, creamy pastes. The texture of such products is favored for application as pie fillings, salad dressings, and puddings. As the degree ot cross-linking of ungelatinized starch granules is extended, they become more and more resistant to gelatinization and it is possible to get starches that show any degree of swelling desired. With an average degree of crosslinking corresponding to about one on even- 20th glucose unit, starches are obtained which show extremely limited ability to swell on cooking. A starch of this type has found interesting application as a dusting powder for surgeons' gloves. It can he steam-sterilized without loss of its dusting characteristics and if accidentally introduced into the body, is absorbed without ill effect. These properties make it a more desirable powder than talc, which is known to give rise to adhesions and has been held responsible for many postoperative difficulties. Without attempting to mention all of the means that can be used to get crosslinking, an idea of the possibilities may b e had from a few of the patents in this field. T h e action of formaldehyde on starch has long been known. Rowland and Bauer 516
( 1 9 3 8 ) disclosed a method for making a heavy cooking corn starch with formaldehyde; Pierson ( 1 9 4 7 ) , using greater amounts, produced a starch nongelatinizing in boiling water. Bauer and coworkers ( 1 9 4 6 ) disclosed the treatment of dextrins to reduce the swelling, dispersibility, and solubility. It may be assumed t h a t similar results can be obtained with t h e dialdehyde glyoxal. Allied to the action of formaldehyde are the results that m a y b e obtained with formaldehyde resins. Gill and McDonald (1946) revealed t h e use of urea and melamine formaldehyde, for example, to get heavy cooking starches, and of course there exists an extensive technology in the use of starch a n d formaldehyde resins to obtain water-resistant adhesive films. T h e use of dihalides and epoxyhalohydrins in the presence of caustic t o increase the viscosity of starch pastes w a s taught by Maxwell ( 1 9 3 9 ) , and application to ungelatinized starch granules b y Königsberg ( 1 9 5 0 ) . A recent interesting patent by Schoene (1950) discloses t h e use of divinyl sulfone. Caldwell ( 1949 ) reported the use of linear anhydrides of dicarboxylic acids such as adipic, azelaic, and sebasic. Phosphorus oxychloride and antimony oxychloride were used by Felton and Schopmeyer ( 1 9 4 3 ) . Presumably diesters of these inorganic acids are formed. Other inorganics which give rise to cross-linking are chromium salts (Caesar, 1 9 3 8 ) , and pyroantimonates (Griffin, Truax, and Nuttal, 1946). They appear to do so by means of stable secondary valence complexes with the starch hydroxyl groups. Kerr ( 1 9 4 9 ) in a very interesting patent, revealed the use of sodium staxmate with starch to obtain tremendous increases in viscosity. This perhaps is also a case of weak cross-links, as is suspected with borax. Newer
Knowledge
Turning now to the low substituted water-dispersible derivatives which are not cross-linked, it can be said that here particularly, the newer fundamental knowledge of starch and of other polymers finds application.* First, for example, the relation between linearity and rétrogradation suggests the introduction of a few substituent groups to îh ter fere with the parallel orientation of linear chains a n d so reduce rétrogradation and gelling. Second, the nature of the substituent groups can have a profound effect on the properties of the dispersed starch and its films. Having a better understanding of t h e effect of carboxyl, sulfate, sulfonate, amine, and amide groups when present in water-dispersible polymeric materials, it does not seem an impossibility that starch derivatives exhibiting certain of the properties of natural gums, of pectin, of proteins, and so on, will be produced. If, for example, the substituent group terminates in an acid group such as carboxylic, sulfonic, or sulfuric, a n u m b e r of interesting properties are observed. The CHEMICAL
Volume of settled granules from cook ups of corn starches with varying degrees of cross linking. T h e estimated glucose units per cross link are 2 2 0 , 100, and 20 for t h e starch which has gelled sodium or ammonium salts of the derivative have a tremendous affinity for water, giving highly viscous, clear, and nongelling dispersions which are not insolubilized by freezing. The d r y films are easily redissolved making possible, for example, their removal from sized fabrics by washing without t h e use of enzymes. If the derivative is that of an ungelatinized starch, it is found to have a lower gelatinization temperature than t h e untreated starch. T h e introduction of diese polar acidic groups confers properties of affinity and repulsion not known in ordinary starch. Adhesion or affinity to polar surfaces may be enhanced. Deflocculation of suspended soil is promoted, useful, for example, in preventing redeposition of soil in laundry wash waters. The dry films are repellent to fats and oils, making them of interest in the greaseproof coating of paper and board and possibly as soil-repellent laundry finishes. These few illustrations are enough to demonstrate the really vast possibilities that exist just in the field of modifying the physical-chemical properties of starch as a hydrophilic colloid. W a t e r soluble starch acetates resulting from treatment with acetic acid and acetic anhydride were described in 1909 by Traquair. Other forms of this procedure have been described calling for variations in temperature, use of various salt and mineral catalysts and so on. All of these products are of relatively low viscosities due to degradation of the starch under the acidic conditions of preparation and are suited for use as adhesives a n d sizes. Caldwell ( 1949 ) described a process for treating ungelatinized starch in aqueous slurry with organic acid anhydrides under conditions such that no degradation occurs. With acetic anhydride, ungelatinized corn starch derivatives containing up to about 59c acetyl groups can b e obtained. These give as viscous pastes as t h e untreated starch, but show a markedly reduced tendency to retrograde or gel. Like the acetates, the low substituted methyl and ethyl ether derivatives of starch are water soluble and stable to,gelling. Lillienfeld ( 1 9 2 0 ) , a n d Kreimeier AND
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„INDUSTRIAL STARCH RESEARCH and Maxwell ( 1 9 3 8 ) , covered t h e use of diethyl and dim ethyl sulfate respectively, to prepare derivatives suitable as adhesives and sizes. W h e n t r i e substituent g r o u p , as described earlier, terminates in a hydrophilic group, the effect of t h e substituent on stability and solubility is greatly enhanced. In. a series of three recent patents, Kessler and .lljermstad describe processes for forming in a q u e o u s slurry low substituted hydroxy e t h y l and hydroxy propyl ethers of u n gelatinized starches by means of ethylene and propylene oxides. These starches h a v e properties of solubility and stability which a r e making t h e m useful in the sizing o f textiles and paper. One of the patents in this series describes a very interesting process for introducing into thé starch granule sufficient hydrophilic groups to give cold water solubility. In the Caldwell process, th-e use of such cyclic dibasic acid anhydrides as succinic, glutaric, and citraconic lead to the formation of the sodium half-ester derivatives of the ungelatinized starch which on cooking exhibit rather amazing properties of viscosity, clarity, solubility, a n d stability, especially in view of the relatively low degrees of substitution, one to every 40 or 5 0 glucose units. Highly substituted starch derivatives, that is, those containing one or more moles of substituent per glucose unit, have had up to the present time only limited commercial importan-ce. Starch, in contrast to cellulose, is dispersible in w a t e r and in caustic to highly viscous pastes, and is more sensitive t o degradation by acids. For these reasons t h e commercial preparation of highly substituted starch derivatives presents problems of processing and recovery^ which are not encountered with cellulose a n d which can not help but add to t h e cost of manufacture. Because o f the nonlinear component, starch gives derivatives with poor film and fiber characteristics compared to cellulose, and while the starch is a few cents cheaper, this is p a r t l y offset by the fact that with highly substituted derivatives that part represented by the carbohydrate portion may be as low as 5 0 % b y weight. T h e foregoing considerations explain why starch has n o t been used as a base for synthetic films and plastics, and they reT h e rubbery, cohesive characteristics of waxy corn starch c o m p a r e d w i t h the smooth, short spoonable consistency of a slightly cross-linked waxy corn starch
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main as formidable problems to b e overcome if it is to b e used in t h e future. Research has shown that derivatives of linear starch amylose give films c o m p a r able in strength a n d flexibility to cellulose, so t h a t t h e problem h a s now been defined at least as that of obtaining amylose a n d making derivatives of it in a n economically competitive manner. Separation of amylose from the commercial -starches at a reasonable cost has n o t been possible, b u t there still exists t h e promising approach of biochemical synthesis, for example, through t h e breeding of strains of corn high in amylose content. I n addition to the interest in amylose for making derivatives, there are possibilities for unmodified amylose films in the food and pharmaceutical fields as pointed o u t in a recent paper by Wolff a n d coworkers describing their properties. By w a y of illustration, it is suggested that a food product packpged in amylose film can b e thrown right into the pot without bothering to remove t h e wrapper. F r o m t h e long r a n g e standpoint, t h e prospect for diminishing supplies of highgrade cellulose and t h e fact that starch is an annually renewable raw material would suggest more favorable conditions for starch as a starting base for making derivatives. Highly substituted starch derivatives containing one or more substituents per glucose unit, wherein the subsituent contain« a hydrophilic group, remain soluble in water. Carboxymethyl starch ethers prepared b y treating alkaline starch with monochloracetic acid were described b y Chowdhury in 1923. T h e possible applications of the carboxymethyl derivative of amylopectin were reviewed by Hoeppler ( 1943 ) who mentioned among manyothers the sizing of p a p e r and textiles, the printing of textiles and the thickening of foods. T h e latter application is precluded, however, on the basis of a recent paper by W a n g , Grossman, and Ivy reporting on the action of carboxymethyl starches in causing diarrhea. Even highly substituted carboxymethyl starch is readily degraded by amylolytic enzymes. This behavior is to b e contrasted with that of carboxymethyl cellulose, which passes through the animal body unchanged and without apparent harmful effect. Starch ethers and esters containing saturated substituents and soluble in organic solvents, particularly the acetate a n d the methyl and ethyl ethers, h a v e b e e n extensively reported on in the fundamental literature on starch chemistry, but they have been of little industrial significance, primarily for the reasons mentioned earlier. In the case of derivatives containing unsaturated substituents such as the starch allyl ether and the acrylate and m e t h a crylate esters, the nonlinearity of the an./lopectin component is not such a handicap, since these derivatives are crosslinked subsequent to application, through interaction of the unsaturated substituents. They may be used in t h e form of lacquers
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or emulsions and are cured w i t h heat a n d / or catalysts to give h a r d , infusible, insoluble, a n d resistant surfaces. Allyl starch is at present being offered in semicommercial quantities a n d is reported to look promising for t h e coating of wood a n d metal, in printing inks, and for the lamination of cloth a n d glass, for example. A significant development in t h e field of starch derivatives is the preparation b y Gaver ( 1 9 4 6 ) of a monosodium alcoholate of starch b y use of sodium hydroxide in alcohol. T h e sodium is reported to be on n u m b e r 2 carbon and may b e replaced with other metals or give rise to two-substituted ethers or esters by use of a p p r o priate reagents. M a k i n g It Easy for t h e Consumer Convenience a n d simplicity of use h a v e been -the object of several developments in the field of starch utilization. For example, an appreciable share of the laund r y starch for h o m e use is n o w precooked a n d sold in bottles. Another means of avoiding t h e cooking of starch by the consumer is to supply o n e that will disperse by merely mixing with cold water. Besides t h e convenience t o t h e user, this has the a d d e d advantage of eliminating transportation charges on t h e water in liquid starches and adhesives. A very essential characteristic of these p r o d ucts is that they mix readily into w a t e r without lumping and foaming. For t h e most p a r t they a r e m a d e b y gelatinizing a n d drying starch suspension on h e a t e d rolls. A laundry starch and several starch p u d d i n g preparations which d o not r e quire cooking a r e on t h e market at t h e present time. Cold water-soluble starchbased adhesives and pregelatinized starch for use in t h e beater sizing of paper a n d to improve the water retention of oil well muds h a v e been sold for some time. An attempt has been made to give an impression of the industrial chemistry of starch and the importance to it of fundamental research. T h e subject of starch as a raw material for the production of organic chemicals has n o t b e e n touched since this seems to be a question, for the most part, of degrading starch first to glucose, which is in reality t h e starting material. It is not inconceivable, however, that conditions m a y be found u n d e r which starch m a y b e directly converted to organic chemical materials of commercial value. However accomplished, t h e use of starch as a craw material for the production of chemicals is perhaps w h e r e important future advances in the industrial use of starch will come. While, naturally, all of t h e corn produced will never b e used for chemical purposes, it is interesting to contemplate that an a n n u a l 3-billionbushel corn c r o p is equivalent t o 100 billion pounds of starch. T H E three papers above were presented as part of a Symposium on Industrial Utilization of Carbohydrates sponsored by the Division of Sugar Chemistry at the ACS Diamond Jubilee Meeting, Sept. 4, 1 9 5 1 , in New York City.
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