Search: dextrins

High molecular weight dextrins and starch present in the wort extracted from brewery spent grain are precipitated through the addition of ethanol, centrifuged and dissolved in phosphate buffer, followed by the addition of an iodine solution. Depending on the molecular weight and degree of branching, a red to blue color forms, the intensity of which is measured spectrophotometrically at 578 nm.

The dextrin content is calculated through multiplication of the difference between the total glucose content and the fermentable extract by a factor of 0.915.

Starch, the main carbohydrate in malt, is hydrolyzed during the mashing process partly to fermentable sugars and partly to (iodine-normal) dextrins. The determination of starch is therefore of interest for brewing technology.

In the beverage industry, maltodextrins are used in sports and energy drinks

Starch is cleaved to glucose by the enzyme amyloglucosidase at pH 4.6:

Starch + (n–1) H₂O \(\xrightarrow{amyloglucosidase}\) n D-glucose

The D-glucose formed is phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P):

Glucose + ATP \(\xrightarrow{HK}\) D-G-6-P + ADP

In the presence of the enzyme glucose-6-phosphate dehydrogenase (G6P-DH), G-6-P is oxidized from nicotinamide adenine dinucleotide phosphate (NADP) to gluconate-6-phosphate. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is formed:

G-6-P + NADP⁺ \(\xrightarrow{G6P-DH}\) D-gluconate-6-phosphate + NADPH + H⁺

The amount of NADPH formed during the reaction is equivalent to the amount of glucose. NADPH is a measurand and is determined on the basis of its absorption at 334, 340 or 365 nm.

It is not possible to distinguish enzymatically between high-polymer and low-molecular starch.