Determination of the density of a liquid by means of an oscillating U-tube device
wort, beer, beer-based beverages, non-alcoholic beverages, beverages, liquids
Determining the density with a digital density measuring device is performed by the electric excitation of a measurement cell (oscillating U-tube) filled with the solution to be analyzed. As the solution increases in density (corresponding to an increase in mass at the same volume in the measurement cell), this has an effect on the oscillation period (resonance frequency) in the measurement cell. The density can then be calculated from the oscillation period and from this value, the other quantities, e.g., extract content, can be extrapolated [1, 2, 3].
Determination of glucose, fructose, sucrose by enzymatic means
Suitable for wort, beer, malt beverages, nutritive beer, beer-based beverages, NAB, juices and beverages
The D-glucose content is determined before and after enzymatic hydrolysis of sucrose. D-fructose is measured following D-glucose determination.
D-glucose determination before inversion:
Glucose is phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P):
\(\text{Glucose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{G-6-P + ADP}\)
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:
\(\text{G-6-P + NADP} \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{gluconate-6-phosphate + NADP + H}^+\)
The amount of NADPH formed during the reaction is equivalent to the amount of glucose. NADPH is measurand and is determined based on its absorbance at 334, 340 or 365 nm.
D-fructose determination:
Hexokinase catalyzes the phosphorylation of D-fructose with ATP to D-fructose-6-phosphate.
\(\text{Fructose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{F-6-P + ADP}\)
After the reaction is complete, F-6-P is converted to G-6-P by phosphoglucose isomerase (PGI):
\(\text{F-6-P} \space ^{\underrightarrow{\text{PGI}}} \space \text{G-6-P}\)
G-6-P reacts in turn with NADP to form gluconate-6-phosphate and NADPH. The additional amount of NADPH formed is equivalent to the amount of fructose and is determined photometrically based on its absorbance at 334, 340 or 365 nm.
Enzymatic inversion:
Sucrose is hydrolyzed to glucose and fructose by the enzyme β-fructosidase (invertase) at pH 4.6:
\(\text{Sucrose}+H_2O\hspace{0.8em} ^{\underrightarrow{\text{B-fructosidase}}} \hspace{0.8em} \text{glucose + fructose}\)
The D-glucose determination after inversion (total D-glucose) is carried out as described above.
The sucrose content is calculated from the difference between the glucose concentration before and after enzymatic inversion.
Determination of sucrose by enzymatic means
Suitable for wort, beer, malt beverages, nutrient beer, mixed beer beverages, NAB, juices and beverages
Sucrose is important as a fermentable sugar for the technology of wort and beer production. Sucrose also plays a role in the evaluation and assessment of malt beverages and nutritional beers.
D-glucose content is determined before and after enzymatic hydrolysis of sucrose.
Sucrose is hydrolyzed by the enzyme β-fructosidase (invertase) at pH 4.6 to glucose and fructose:
\(\text{Sucrose + } H_2O \space {\xrightarrow{β-fructosidase}} \space \text{D-glucose + D-fructose}\)
Glucose is phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P):
\(\text{Glucose}+\text{ATP} \space \xrightarrow{HK} \space \text{G-6-P + ADP}\)
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:
\(\text{G-6-P + NADP} \hspace{0.8em} \xrightarrow{G6P-DH} \hspace{0.8em} \text{gluconate-6-phosphate + NADP + H}^+\)
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 absorbance at 334, 340 or 365 nm.
The sucrose content is calculated from the difference between the glucose concentration before and after enzymatic inversion.
Determination of maltose and maltotriose by enzymatic means
Suitable for wort, beer, malt beverages, nutrient beer, mixed beer beverages, NAB, juices and beverages.
Maltose is the main component of beer wort or wort extract.
Maltose and sucrose are cleaved by the enzyme α-glucosidase (maltase) at pH 6.6 into two molecules of D-glucose and D-fructose, respectively:
\(\text{Maltose}+H_2O \hspace{0.8em} \xrightarrow{α–glucosidase} \hspace{0.8em} {2 \hspace{0.2em} \text{D–glucose}}\)
\(\text{Sucrose}+H_2O \hspace{0.8em} \xrightarrow{α–glucosidase} \hspace{0.8em} {\text{D–glucose}+\text{D–fructose}}\)
The D-glucose formed is phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P):
\(\text{Glucose}+\text{ATP} \hspace{0.8em} \xrightarrow{HK} \hspace{0.8em} \text{G-6-P} \hspace{0.2em} + \hspace{0.2em} \text{ADP}\)
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:
\(\text{G-6-P} \hspace{0.2em} + \hspace{0.2em} \text{NADP}^+ \hspace{0.8em} \xrightarrow{G6P-DH} \hspace{0.8em} \text{gluconate-6-phosphate} \hspace{0.2em} + \hspace{0.2em} \text{NADP}^+ \hspace{0.2em} + \hspace{0.2em} \text{H}^+\)
The amount of NADPH formed during the reaction is equivalent to the amount of glucose. NADPH is measurand and is determined based on its absorbance at 334, 340 or 365 nm.
The enzyme α-glucosidase is group specific, i.e., the specificity is directed to the type of glycosidic bond.
Only α-1,4 bonds, i.e., in addition to maltose, sucrose and maltotriose, but not maltotetraose, are cleaved under the given conditions. Therefore, the sucrose content must be taken into account in the maltose calculation (the maltose approach records the glucose formed from maltose and sucrose and the free glucose, the sucrose approach records the glucose formed from sucrose and the free glucose).
Determination/calculation of the apparent extract content from the SGA20/20 or the density of a liquid
wort, beer, beer-based beverage, NAB, beverage
Determine the SGA20/20 obtained from pycnometry or the density measured with a precision hydrometer or another device for measuring the density. Using the value from the SGA20/20 measurement or the density from the sugar, alcohol, original gravity and correction table according to GOLDINER/KLEMANN, BLOCK, KÄMPF or a polynomial, determine the apparent extract content of the sample.
Determination/calculation of original gravity, alcohol and real extract content after distillation of beer, beer-based beverages or beverages.
Beer, beer-based beverages, beverages
After distillation of the sample, the original gravity, alcohol and real extract content of the beer in beer-based beverages or other beverages can be determined from the densities of the distillate and residue.