The Acid Hydrolysis of Starch

If a dilute solution of starch is treated at a suitable temperature with dilute mineral acid and the degree of hydrolysis a is calculated from the number of reducing groups set free, we find that the values of 

Acid hydrolysis Action of 0-amylase Action of malt a-amylase 

As mentioned before, the number of o-glucosidic linkages split by malt a-amylase in the dextrinization period decreases with the degree of acid hydrolysis and when a is about 0.6 (60%) there is no further dextrinization (Table XXVIII). This is due to the fact mentioned before that the enzyme attacks chains with less than about eight members only with very low velocity. When the number of chain molecules with longer chains is calculated for different degrees of hydrolysis, values for the extent of the dextrinization are found which agree fairly well with those found in the experiment. 

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The electrolysis of glucose syrup from the acidic hydrolysis of starch yields pure D-glucose. Symp is placed in a chamber with a lead cathode surrounded by diaphragm.321 Starch was similarly electrolyzed, with an energy consumption of 0.05-0.1 kWh/kg of starch. The degradation of starch in alkali is less selective and faster than in acidic medium, as shown in Fig. 38. 

A great advantage that enzymic-catalysis systems have over acid-catalysis methods lies in the much wider range of compositions attainable, as may be seen in the ternary-composition diagram17 depicted in Fig. 4. It illustrates the compositions attainable by (a) the acid hydrolysis of starch and (b) the use of beta-amylase and glucoamylase, or (c) combinations of them. 

Such reversion-type reactions are observed, e. g., in the acidic hydrolysis of starch. 

The acid hydrolysis of starch granules from potato, waxy maize, and amylo-maize-7 was studied in different ratios of mixtures of two of the four alcohols, from 100/0 to 0/100% in 10% (v/v) intervals [53]. Again, a series of soluble limit dextrins was obtained in 48-72 hr of reaction. The average d.p. of the limit dextrins decreased as the content of the higher alcohol was increased. Plots of the d.p. of the limit dextrins vs. the ratio of each alcohol mixture produced curves that resembled titration curves, with different plateau regions in which the d.p. of the limit dextrins changed very slowly or not at all. These plateau regions were characteristic and dependent on the types of alcohols, the volume ratios of the two alcohols in the mixture, and the type of starch. It was proposed that the formation of... 

G. is formed as one of the reversion products during the acid - hydrolysis of starch. It is found enriched in the mother liquor - hydrol of dextrose crystallization, together with - isomaltose, - panose and other oligosaccharides. G. cannot be split by a-glucosidases (- amylases) it develops a strong bitter taste. It lowers the crystallization yield of dextrose in starch hydrolysates after acid hydrolysis. 

I. is a-D-glucopyranosyl-l,4-D-glucopyranosyl-1,6-a-D-glucopyranose, which is formed as a component in - branched oligosaccharide syrups by action of transglucosidase (ot-glucosidase) on - maltose. It may also be found as a reversion product of the acid hydrolysis of starch, which is enriched in the mother liquor of glucose crystallization (->hydrol). 

Glucose syrups, also known as com syrups in the United States, are defined by the European Commission (EC) as a refined, concentrated aqueous solution of D(+)-glucose, maltose and other polymers of D-glucose obtained by the controlled partial hydrolysis of starch (Howling, 1984). Glucose syrups were fust manufactured industrially in the nineteenth century by acid hydrolysis of starch. Hydrochloric acid was normally used, because sulphuric acid caused haze in syrups due to insoluble sulphates. The source of starch can vary in the United States corn is widely used, whereas in other parts of the world wheat, potato and cassava starch are also employed. Acid hydrolysis of starch is still used today. The method is non-specific, but if conditions are tightly controlled, it is possible to make products with a reasonably consistent carbohydrate profile. 

The enzymatic hydrolysis of starch to glucose is commercially preferred to the acid hydrolysis route using hydrochloric acid. The enzymatic process produces fewer sideprod-ucts, does not involve a corrosive acid, and allows the use of less pure starch products whose protein contaminants would, upon acid hydrolysis, give amino acids and browning reactions. 

Acid hydrolysis of starch is conducted with hydrochloric acid or sulfuric acid, mainly in a continuous process, yielding syrups with 20 to 68 DE. The process consists of the acidification of a starch slurry with hydrochloric acid to a pH of about 1.8 to 1.9, and pumping the suspension into a converter (autoclave) where live steam is gradually admitted to a pressure of 30 to 45 psi. Converted liquids are neutralized with sodium carbonate to a pH of 5 to 7. Proteins, lipids, and colloidal matter are separated as sludge. Pigments are eliminated with activated carbon and minerals with ion exchangers. The raw juice, thus obtained, is evaporated under a vacuum (falling-film evaporator) up to a solids content of 70 to 85 percent. 

Dextrin is prepared by the incomplete hydrolysis of starch by heating in the dry state with or without the aid of suitable acids and buffers moisture may be added during heating. The PhEur 2005 specifies that dextrin is derived from maize (com) or potato starch. A specification for cassava is included in the USPNF 23. 

Early work on the hydrolysis of starch was reviewed by Rolfe and Defren, who made the first, systematic investigation (following the report by Kirchoffi in 1811 that acid hydrolysis of starch yields a sugarlike sub-... 

It should be pointed out that Holl6 and Szejtli concluded that the acid hydrolysis of glycosidic linkages in starch is bimolecular (A-2) on the basis of thermodynamic data, but that this is not a universally accepted conclusion. 

Acid Conversion.—The theory of the acid conversion of starch into sugars was discussed in Chapter I. Practically, this method finds some use in the preparation of cereal raw materials prior to fermentation although probably less in this country than abroad. In the United States the hydrolysis of starch for fermentation is almost invariably accomplished by the diastatic action of malts. These malts are mixed with unmalted grain (the starch of which has been pastified by prior cooking) and the conversion to fermentable sugar carried to completion by a subsequent operation called mashing. ... 

Preparation. D-Glucose (often called dextrose commercially, because of its dextrorotation) is manufactured on a large scale by acid hydrolysis of starch, usually potato starch in Europe and com starch in the United States.96... 

Mandels et al. (22) found that glucose manufactured commercially by acid hydrolysis of starch contained sophorose as an impurity which is a powerful inducer of cellulase in Trichoderma viride. In the studies... 

Maltose, C12H22O11.H2O, is formed as the result of the action upon starch of the diastase in malt, the ptyalin in saliva, and other ferments, and in the partial hydrolysis of starch and dextrin by acids. It is present in commercial glucose, in beer, and probably in bread. It is manufactured on the large scale in the preparation of alcohol and alcoholic beverages (59). Maltose crystallizes from water, in which it is readily soluble, in plates, which contain one molecule of water of crystallization. It is obtained from alcohol in wart-like aggregates which are anhydrous. Maltose is dextrorotatory, and shows mutarota-tion for the anhydrous form [a]jy = 137°. 

The products from the acid hydrolysis of 0-(2-hydroxyethyl) starch contain, in addition to the expected 2-0-, 3-0-, and 6-0-(2-hydroxyethyl)-D-glucoses, three isomeric derivatives of 2-0-(2-hydroxyethyl)-D-glu-coses that have been identified as l,2-0-ethylene- -D-glucofuranose,... 

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