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 formic acid by enzymatic means
This analysis is suitable for wort, beer, beer-based beverages and NAB.
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):
HCOO- + NAD+ + H2O \(^{\underrightarrow{FDH}}\) HCO3- + NADH + H+
The amount of NADH formed during the reaction is equivalent to the amount of formic acid and can be determined photometrically based on its absorbance at 334, 340 or 365 nm.
Oxalic acid (oxalate) is transformed into formic acid and CO2 in this reaction catalyzed by the enzyme oxalate decarboxylase (Ox-DC):
Oxalic acid \(^{\underrightarrow{Ox-DC}}\) formic acid + CO2
The quantity of NADH produced during the reaction is equivalent to the amount of formic acid and is determined photometrically owing to its absorption at 334, 340 or 365 nm. In preparation for this test, the free formic acid present in the solution is determined along with the oxalic acid. Each are accounted for in the blank.