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.
Malt, fruit juice and tea serve as the base for fermented beverages.
As a rule, fermented beverages typically contain 0.5–15 g/l D-gluconic acid.
Determination of D-gluconic acid by enzymatic means
This analysis is suitable for non-alcoholic beverages and for those containing alcohol.
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.
D-gluconic acid is phosphorylated by adenosine 5'-triphosphate (ATP) in the presence of gluconate kinase to gluconate-6-phosphate
D-Gluconate + ATP \(^{\underrightarrow{\text{gluconate kinase}}}\) D-gluconate-6-P + ADP
The enzyme 6-phosphogluconate dehydrogenase (6-PGDH) catalyzes the oxidation of gluconate-6-phosphate to ribulose-5-phosphate with nicotinamide adenine dinucleotide phosphate (NADP):
D-Gluconate-6-phosphate + NADP+ \(^{\underrightarrow{6-PGDH}}\) ribulose-5-phosphate + NADPH + H+ + CO2
The amount of NADPH formed during the reaction is proportional to the amount of D-gluconic acid.