The method is suitable for the determination of water vapor volatile aroma compounds in beer.
Volatile aroma compounds are driven out of the sample through steam distillation. The ethanolic distillate is saturated with NaCl. Potassium hydrogen sulfite is added to separate carbonyl groups that might interfere with the analysis. The extraction of the aroma compounds is performed by shaking out with dichloromethane and the phases separated by centrifuging.
The method is suitable for beer brewed to any original gravity or to any alcohol content.
Volatile compounds in beer are concentrated through distillation and extracted with dichloromethane. The solvent phase is analyzed with a gas chromatograph. The linearity of the detector and the determination of the concentrations of analytes in the sample are achieved by using multiple concentration levels within the relevant range and through evaluation of the relative area under the peaks.
Determination of organic acids by means of reversed phase chromatography/ion chromatography
This method is suitable for wine, fruit juice and other non-alcoholic beverages.
The organic acids are separated using two combined columns, reversed-phase HPLC and an ion exchange column and are then determined using a UV detector.
Determination of acetic acid by enzymatic means.
This analysis is suitable for wort, beer, malt-based drinks, nutritional beer, beer-based mixed drinks, non-alcoholic soft drinks, NAB, fruit juice, soft drinks, juices, drinks.
Acetic acid (acetate) is converted to acetyl-CoA in the presence of the enzyme acetyl-CoA synthetase (ACS) by adenosine-5'-triphosphate (ATP) and coenzyme A (CoA).
\(\text{(1) Acetate + ATP + CoA }\space ^{\underrightarrow{\text{ACS}}} \space \space\text{Acetyl-CoA + AMP + Pyrophosphate}\)
Acetyl-CoA reacts with oxaloacetate in the presence of citrate synthase (CS) to form citrate.
\(\text{(2) Acetyl-CoA + Oxalacetate + H}_2\text{O }\space ^{\underrightarrow{\text{CS}}} \space \space\text{Citrate + CoA}\)
The oxaloacetic acid required for reaction (2) is produced from malic acid and nicotinamide adenine dinucleotide (NAD) in the presence of malate dehydrogenase (MDH). In doing so, NAD is reduced to NADH:
\(\text{(3) L-Malate + NAD}^+ \space ^{\underrightarrow{\text{L-MDH}}} \space \text{Oxalacetate + NADH + H}^+\)
The formation of NADH+H+ forms the basis of this analysis, which is measured as an increase in the absorbance at 340 nm. Since this concerns a previous indicator reaction, the quantity of NADH+H+ is not linearly proportional to the acetic acid concentration.
Qualitative detection of harmful osmophilic and osmotolerant yeasts, moulds and bacteria in NAB raw material samples.
Raw material samples (e.g. fruit juice concentrates, sugar syrup, etc.) in the non-alcoholic beverage section.
Detection of harmful osmophilic and osmotolerant yeasts, moulds and bacteria by means of liquid pre-enrichment.
Determination of formic acid by enzymatic means.
This analysis is suitable for wort, beer, malt-based drinks, nutritional beer, beer-based mixed drinks, non-alcoholic soft drinks, NAB, fruit juice, soft drinks, juices, drinks.
Formic acid can be found in beer in small quantities, and it is also formed by contaminating bacteria, for example, by lactic acid bacteria (rods).
In the presence of the enzyme formate dehydrogenase (FDH), the formic acid created in this reaction is quantitatively oxidized to bicarbonate by nicotinamide adenine dinucleotide (NAD):
\(\text{Formic acide (HCOO}^- \text{) + NAD}^+ \space\text{+ H}{_2}\text{O }\space ^{\underrightarrow{\text{FDH}}} \space \text{CO}{_2}\text{ + NADH + H}^+\)
The amount of NADH+H+ formed during the reaction is equivalent to the amount of formic acid and can be determined photometrically based on its absorbance at 340 nm.