Dextrose, starch degradation

Dextrose is the partially degraded breakdown products of starch. 

Eurther conversion (saccharification) to dextrose can be done using glucoamylase. Starch consists of polymeric linear a-1,4 linked dextrose units (amylose, 25 % of the starch) and polymeric mixed a-l,4/a-l,6 linked dextrose units (amylopectin, 75 % of the starch). Eor enzymatic degradation besides a-1,4 specific amylases also a-1,6 specific amylases (pullulanases) are required. A portion of the dextrose can be converted into fructose with a glucose isomerase yielding a high fructose com symp (MFCS). 

The enzymatic degradation of starch is applied on an industrial scale to the production of corn syrup (a solution of oligomers) and dextrose (glucose) by utilizing thermally stable endoenzymes that can operate in an aqueous medium at temperatures up to 70-90 ° [14]. These temperatures are desired because the starch granules rupture in water at about 60 °C. The use of enzymatic hydrolysis for the conversion of starch to sugars is a much cleaner (more selective) process than is an acid-catalyzed hydrolysis. 

Maize juice produced from com starch, which has received considerable attention as a sucrose source, has been snccessfully deionized by conventional treatment with the result that improved sugar recoveries are possible. In the manufacture of dextrose, the organic acids and colored substances produced as degradation products during starch hydrolysis were eliminated economically by the use of the ion-exchange process to produce a high-quality sugar. 

Iodine Test Iodine forms a dark blue complex with starch molecules made up of at least six dextrose residues. Amylolytic activity is assayed by incubating starch with the enzyme under specific conditions. Iodine is then added to the reaction medium. The loss of color intensity due to the degradation is related to the extent of starch digestion and thus to the enzyme concentration. The method is rapid and inexpensive, but not accurate [32]. The KNU is the amount of enzyme that breaks down 5.26 g starch [47] per hour, at 37°C and pH 5.6, in the presence of 3 X 10 mol Ca /L. 

---