Malt intended for use in beer brewing or elsewhere in the food industry
The substrate for the limit dextrins is prepared by adding excess β-amylase to a standard solution of starch. An extract of malt is added, and the α-amylase present in the malt brings about the degradation of the limit dextrins. With the addition of an iodine solution, the time required for the standard color of the starch-iodine complex to be reached is known as a “dextrinizing unit” [1].
Spectrophotometric determination of the iodine value of brewery spent grain
Brewery spent grain, wet spent grain, dry spent grain
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.
This is a mathematical method for calculating the dextrin content as a difference between the total glucose content and the fermentable extract as determined through analytical methods.
Suitable for beer
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.
Determination of maltose and maltotriose by enzymatic means
Suitable for malt, beer, NAB, sports drinks, energy drinks.
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.
This method describes how to determine whether kernels in a lot of barley are cracked by means of the iodine-starch reaction.
Barley intended for the production of malt is to be evaluated on the basis of the characteristics described below.
Detection of cracked kernels is based upon the reaction of iodine with starch. Unprotected starch grains located in the cracks are dyed with iodine, thereby producing a vivid shade of blue, making the cracks easily discernible.
Malt intended for use in beer brewing or elsewhere in the food industry
Using a buffer solution, malt extract is produced, and then under defined conditions the extract is incubated on an azo-barley glucan substrate. The substrate is coupled with an azo dye, which is degraded by the β-glucanase activity to form low-molecular weight fragments. After addition of the precipitating agent, these fragments stay in solution and can be spectrophotometrically determined in the supernatant after centrifugation. The absorbance in the supernatant depends directly upon the activity of the β-glucanase in the analyzed malt.