Hops and hop products intended for use in beer brewing or elsewhere in the food industry
Hop constituents are distributed between an aqueous acidic methanolic phase and diethyl ether. Hop bitter substances extracted with ether are subsequently separated according to their different solubility properties in cold methanol and hexane into fractions: total resins, soft resins and hard resins. The soft resins are further separated according to their capacity to form complexes with lead salts into α-acids (conductometer value) and a β-fraction.
Hop extract intended for use in beer brewing or elsewhere in the food industry
Determination of glucose by enzymatic means.
Suitable for wort, beer, malt-based drinks, nutritional beer, beer-based mixed drinks, non-alcoholic soft drinks, NAB, fruit juice, soft drinks, juices, drinks.
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 by nicotinamide adenine dinucleotide phosphate (NADP+) to gluconate-6-phosphate. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is formed:
\(\text{G-6-P + NADP}^+ \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{gluconate-6-phosphate + NADPH + H}^+\)
The amount of NADPH+H+ formed during the reaction is equivalent to the amount of glucose. NADPH+H+ is determined based upon its absorbance at 340 nm.
Note:
Alternatively, NAD+/NADH + H+ can be used instead of NADP+/NADPH+ H+:
\(\text{G-6-P + NAD}^+ \space ^{\underrightarrow{\text{G6P-DH}}} \space \text{Gluconate-6-Phosphate + NAD + H}^+\)
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.
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.
Determination of L-malic acid by enzymatic means.
This method is suitable for malt, wort, beer, malt-based drinks, nutritional beer, beer-based mixed drinks, non-alcoholic soft drinks, NAB, fruit juice, soft drinks, juices, drinks
L-Malic acid (L-malate) is oxidized by nicotinamide adenine dinucleotide (NAD) in the presence of L-malate dehydrogenase (L-MDH) to oxaloacetic acid:
\(\text{L-Malic acid + NAD}^+ \space ^{\underrightarrow{\text{L-MDH}}} \space \text{Oxaloacetic acid}\text{ + NADH + H}^+\)
The equilibrium of this reaction disproportionately favors malic acid. However, the oxaloacetic acid can be captured with the help of a downstream reaction involving the enzyme glutamate-oxaloacetate-transaminase (GOT) in the presence of L-glutamic acid, shifting the reaction in favor of oxaloacetic acid and NADH + H+:
\(\text{Oxaloacetic acid + L-Glutamate} \space ^{\underrightarrow{\text{GOT}}} \space \text{L-Aspartate + 2-Oxoglutarate}\)
The amount of NADH+H+ produced during the reaction is equivalent to the quantity of L-malic acid and its absorption is determined photometrically at 340 nm.