Starch, acid conversion

It is interesting to note that a similar scheme for making synthetic rubber was put forward many years ago. This Heinemann synthetic rubber process was essentially the production of levulinic acid from starch, its conversion with phosphorus pentasulfide into methylthiophene (XXXVII), which is reduced to 1,3-pentadiene. 

In the presence of MCM-41, acidic Mordenites and Beta zeolites with different Si/Al ratios, it has been shown by Abbadi et al 111 that maltose (lg in 50 ml of water, batch reactor, 0.5g of catalyst) was also selectively hydrolysed into glucose at 130°C. For other polysaccharides, such as amylose and starch, the conversion and... 

Maltodextrins may be manufactured either by acid or by acid-enzyme processes. Maltodextrins produced by acid conversion of starch from dent com contain a high percentage of linear fragments, which may slowly reassociate into insoluble compounds causing haze in certain applications. 

The quantity of acid used is usually in the neighborhood of 16 lbs of hydrogen chloride per 2,500 gallons (0.77 g per liter) of starch slurry, producing a pH of 1.80 for the suspension. The time required to attain a desired, exact degree of conversion depends on the pH attained in the converter, which, in turn, is affected by small variations in the impurities in the starch. It is difficult to judge this effect precisely by measurement of the pH of the starch-acid mixture before it enters the converters. 

Acid conversions when starch is treated with an acid such as HCI or H2SO4 at 40-60°C (commonly a starch slurry with 35-40% solids is treated with 0.2-0.5 N HCI for a few hours). Following the acid conversion, the acid is neutralized. In this process, the DP value decreases (and several physical properties are modified). Although chemical studies show that the a-D-(1- 4) links are more sensitive to hydrolysis than a-D-(1->6) links, it was determined that due to starch crystallinity more a-D-(1->6) links are hydrolyzed [55]. This happens because the a-D-(1 6) links are in the amorphous regions and they are more accessible to the reagent (less hydrogen bonds). This explains why the DP of amylose is reduced less than that of the amylopectin component. 

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 of Wort.—In harmony with greater efficiency in the distillation, patent still operators have introduced modifications in the method of saccharification of their cereal grains, usually by some application of the acid-conversion process. This process has as its object partial conversion of the starch of the grains into fermentable sugars by the use of acid rather than the diastase of malt and depends on the latter only for the final completion of the conversion. 

Many products made by fermentation are also based on the conversion of starch. Some examples of the use of enzymatically hydrolyzed starches are the production of alcohol, ascorbic acid, enzymes, lysine, and penicillin. 

Application of ion exchange refining to the process for the manufacture of dextrose may be understood from the following description of such a process. Triple-washed starch is diluted with ion-free water to the desired concentration and is acidified with a definite quantity of mineral acid such as hydrochloric or sulfuric. It is desirable that the acidified starch slurry be held for at least thirty minutes in order to permit an effective equilibrium acidity to be reached. The starch slurry may contain a quantity of soft water salts which consume acid, and since this consumption is variable, the acidity is checked and adjusted to the desired level following the holding period. The conversion is then carried out at elevated temperature and under pressure for a period sufficient to yield maximum dextrose. The conversion may be carried out batchwise in an autoclave, or continuously. 

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