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The quantity of soluble dry matter is determined refractometrically. This is related to the percent by weight of sucrose in an aqueous sucrose solution, which under defined conditions possesses the same refraction index as that of the product being analyzed. The amount of soluble dry matter is expressed in g per 100 g of solution. The refraction index is not determined directly for non-alcoholic soft drinks, but rather by means of a scale based on the percentage of sucrose by weight (°Brix). Since the °Brix scale uses sucrose, correction factors for other sugars must be taken from tables for each individual type of sugar. The presence of other substances, such as organic acids, minerals and amino acids, has an effect on the refraction index of a product. Due to the high acidity of citrus juices and citrus juice concentrates, correction factors are also necessary for measuring their °Brix values.

The amount of time required for a special ball to fall while sinking through a glass tube filled with a sample liquid between two marks is measured. The precision of this method is increased if the time is measured using a photoelectric beam to an accuracy of 0.01 s, rather than manually with a stopwatch.

These devices measure the torque transferred through a cylindrical liquid layer between a stationary and a rotating disc. This method also allows changes in viscosity, which occur, e.g., through the action of α-amylase on starch, to be automatically recorded by a plotter or PC.

Capillary viscometers measure the kinematic viscosity of Newtonian fluids, unlike falling ball and the rotational viscometers, which directly measure the dynamic viscosity. However, with values for the kinematic viscosity and the density of the test liquid, the dynamic viscosity can be calculated.

The time required for a volumetrically defined amount of fluid (the volume between two marks on the tube of the viscometer) to flow through a capillary of a defined length is measured.

1 square meter per second of a homogenous fluid with a dynamic viscosity of 1 Pa × s and a density 1 kg/m³

The unit for expressing kinematic viscosity (the relationship of viscosity to density = viscoplasticity) is 1 m²/s = 10⁶ mm²/s

The kinematic viscosity is expressed as 1 square meter per second of a homogenous fluid with a dynamic viscosity of 1 Pa × s and a density 1 kg/m³.

Glucose and fructose are phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P) and fructose 6-phosphate (F-6-P):

\(\text{Glucose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{G-6-P + ADP}\)

\(\text{Fructose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{F-6-P + ADP}\)

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 (NADP + H⁺) is formed:

\(\text{G-6-P + NADP}^+ \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{Gluconate-6-phosphate + NADPH + H}^+\)

The amount of NADP + H⁺ formed during the reaction is equivalent to the amount of glucose. NADPH + H⁺ is a measurand and is determined based on its absorbance at 340 nm.

After the reaction is complete, F-6-P is converted to G-6-P by phosphoglucose isomerase (PGI):

\(\text{F-6-P} \space ^{\underrightarrow{\text{PGI}}} \space \text{G-6-P}\)

The amount of NADPH + H⁺ formed during the reaction is equivalent to the amount of fructose. NADPH + H⁺ is the parameter being measured and is determined on the basis of its absorption at 340 nm.

G-6-P reacts in turn with NADP⁺ to form gluconate-6-phosphate and NADP + H⁺. The additional amount of NADP + H⁺ formed is equivalent to the amount of fructose and is determined photometrically based on its absorption at 340 nm.

Note:

Alternatively, NAD⁺/NAD + H⁺ can be used instead of NADP⁺/NADPH + H⁺:

\(\text{G-6-P + NAD}^+ \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{Gluconate-6-Phosphate + NAD + H}^+\)

The D-glucose content is determined before and after enzymatic hydrolysis of sucrose. D-fructose is measured following D-glucose determination.

D-glucose/D-fructose determination before inversion:

Glucose and fructose are phosphorylated by the enzyme hexokinase (HK) and adenosine-5'-triphosphate (ATP) to glucose-6-phosphate (G-6-P):

\(\text{Glucose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{G-6-P + ADP}\)

\(\text{Fructose + ATP} \space ^{\underrightarrow{\text{HK}}} \space \text{F-6-P + ADP}\)

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 (NADP + H⁺) is formed:

\(\text{G-6-P + NADP}^+ \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{Gluconate-6-phosphate + NADP + H}^+\)

The amount of NADP + H⁺ formed during the reaction is equivalent to the amount of glucose. NADP + H⁺ is measurand and is determined based on its absorbance at 340 nm.

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 NADP + H⁺. The additional amount of NADP + H⁺ formed is equivalent to the amount of fructose and is determined photometrically based on its absorbance at 340 nm.

Enzymatic inversion:

Sucrose is hydrolyzed to glucose and fructose by the enzyme β-fructosidase (invertase) at pH 4.6:

\(\text{Saccharose + H}{_2}\text{O} \space ^{\underrightarrow{\text{β-Fructosidase}}} \space \text{Glucose + Fructose}\)

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.