The positive effects of fermented beverages on human health have been known for hundreds for years. For this reason, the cult drinks kvass (Russia) and kombucha (Asia) can be traced over a long history and have been consumed for their healing powers through time. Microorganisms such as lactic acid and acetic acid bacteria are used for non-alcoholic fermentation. The products of fermentation include organic acids such as lactic acid and gluconic acid, which facilitate digestion and metabolic processes. Fermented beverages are especially favored by consumers as healthy, natural refreshments due to their slightly sour flavor.
In addition to other criteria, the acid spectrum typical for certain types of fruit serves as the tool for evaluating whether a fruit juice is pure, and its composition has not been altered. Generally, tartaric acid, citric acid and L-malic acid are analyzed. These are the primary acids, with a few exceptions, that are responsible for the total acid in fruits.
Determination of pyruvic acid by enzymatic means
This analysis is suitable for wort, beer, beer-based beverages and NAB.
Pyruvic acid is produced during the fermentation of wort.
Pyruvic acid (pyruvate) is reduced to L-lactic acid by reduced nicotinamide adenine dinucleotide (NADH) in the presence of the enzyme L-lactate dehydrogenase (L-LDH):
Pyruvate + NADH + H+ \(^{\underrightarrow{D-LDH}}\) D-lactate + NAD+
The quantity of NADH consumed during the reaction is equivalent to the quantity of pyruvic acid and its absorption can be determined photometrically at 340 nm.