Organic acids
The production of organic acids, varying with time is
shown in Tables 1–3. The concentration of acetic acid
increased slowly with time until a maximum of 9.5 g/l in
GTK on 15th day of fermentation followed by a slow
decrease. L-glucuronic acid was the other major organic
acid found in the metabolites of tea fungus and it reached
a maximum concentration of 2.3 g/l in BTK on 12th day
of fermentation. Glucuronic acid is considered to be one
of the important key components found in kombucha
tea due to its detoxifying action through conjugation
(Loncar, Petrovic, Malbasa, & Verac, 2000). Concentration
of lactic acid and citric acid was very less in all three
types of kombucha tea studied. Maximum concentration
of lactic acid was detected on 3rd day of fermentation
in GTK followed by BTK and TWK. Citric acid was
detected only on 3rd day of fermentation in GTK and
BTK, and it was not detected in TWK throughout the
fermentation period. Yeast cells hydrolyse sucrose into
glucose and fructose by yeast invertase and produce ethanol
via glycolysis with preference for fructose as substrate.
Acetic acid bacteria utilize glucose to produce gluconic
acid and ethanol to produce acetic acid. One of the possible
ways of glucose transformation is also its oxidation
at C-6 position into glucuronic acid. Lactic acid is formed
by the acetic acid bacteria from ethanol and acetic acid
(Dufresne & Farnworth, 2000). Green tea and black tea
was found to be the best substrate for acetic acid and glucuronic
acid production respectively by kombucha
culture.