Starch, acid conversion properties

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. 

STADEX Dextrins are partially hydrolyzed starches that are prepared by heating or dry roasting starch in the presence of an acid catalyst. The conversion process - the change from starch to dextrin - changes the properties of the parent starch in several ways. Notably, the dextrin exhibits a thinner cooked-paste viscosity, an increased cold water solubility, and a color change from white to off-white or yellow. 

The biocatalytic conversion of starch to fructose syrup is a well-established process and provides a good example of a biotechnological application. In this bioprocess the consecutive use of several enzymes is necessary, which is not desirable in a biotechnological application. The first step in the process is the conversion of starch to oligomaltodextrins by the action of a-amylase.The concomitant injection of steam leads to extreme demands on the thermostability of the enzyme. Using traditional a-amylases, the pH has to be adjusted to an undesirably high level and calcium must be added to stabilize the enzyme in the system. New a-amylases with optimized properties, such as enhanced thermal stability, acid tolerance and ability to function without the addition of calcium, have recently been developed and successfully applied in the hydrolysis of starch. i° Engineering approaches have also been undertaken to develop the hydrolysis process. ... 

Treatment of starch with acids, enzymes or oxidizing agents (such as sodium hypochlorite) are commonly used to reduce the molecular weight of starch and thus decrease the viscosity and modify the gelling properties of aqueous starch dispersions. Starches that have been partially depolymerized by acids or enzymes are commonly referred to as dextrins. Conversely, the swelling and solubility of starch granules can be reduced by cross-linking. 

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