This method describes how to evaluate the sensory impact of lactic acid or food-grade lactic acid.
Lactic acid or food-grade lactic acid which are used in the brewing and food production industries
Food-grade lactic acid may be used to adjust the pH during mashing and wort production for products not subject to the regulations of the Reinheitsgebot or the German purity law concerning beer.
Determination of lactic acid/lactic acid by enzymatic means
This analysis is suitable for malt, wort, beer, beer-based beverages and soft drinks
Fruit juices
The positive effect of fermented beverages on the human body has been known for centuries. Current beverage trends, like kvass (Russia) and kombucha (Asia), stem from traditions with roots deep in the past. They have always been consumed as healing beverages. Non-alcoholic forms of fermentation employ microorganisms, such as lactic and acetic acid bacteria. They produce organic acids like lactic acid and gluconic acid, which promote digestion and metabolism. Due for the most part to their slightly acidic flavor, these kinds of fermented beverages are popular with consumers as a healthy natural refreshment.
Malt, fruit juice and tea serve as a base for fermented beverages.
As a rule, fermented beverages contain 0.5 – 15 g/l D-gluconic acid.
Malt, wort and beer
L- and D-lactic acid are produced during fermentation and are already present in malt and wort to some degree. The lactic acid content increases through biological acidification of the wort or through the use of acidulated malt.
L-Lactic acid (L-lactate) is oxidized to pyruvic acid by nicotinamide adenine dinucleotide (NAD) in the presence of L-lactic acid dehydrogenase (L-LDH). The enzyme D-lactate dehydrogenase (D-LDH) is required for the oxidation of D-lactic acid:
L-lactate + NAD \(^{\underrightarrow{L-LDH}}\) pyruvate + NADH + H+
D-lactate + NAD \(^{\underrightarrow{D-LDH}}\) pyruvate + NADH + H+
The equilibrium of the reaction disproportionately favors lactic acid. However, the pyruvic acid can be captured with the help of a downstream reaction involving the enzyme glutamate pyruvate transaminase (GPT) in the presence of L-glutamic acid and the reaction can be shifted in favor of pyruvic acid and NADH:
Pyruvate + L-glutamate \(^{\underleftrightarrow{GPT}}\) L-alanine + α-ketoglutarate
The quantity of NADH consumed during the reaction is equivalent to the quantity of L-lactic acid or D-lactic acid and can be determined photometrically due to its absorption at 334, 340 or 365 nm.
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.