Bhat et al.
CH 3 CH 2 OH+ O 2
CH 3 COOH +H 2 O + 493 kJ
Acetic acid
The studies revealed that there were two steps in the oxidation of ethanol
to acetic acid, driven by the enzymes alcohol dehydrogenase (ADH)
andȱ aldehydeȱ dehydrogenaseȱ (ALDH).ȱ Theȱ firstȱ stepȱ wasȱ oxidationȱ toȱ
acetaldehyde by ADH, which was further oxidised to acetic acid by
ALDH. The reaction was exothermic, thus increased the temperature in the
medium. The acetic acid could be further oxidised to carbon dioxide in the
tricarboxylic cycle, that was an unwanted process in vinegar production
but it could occur when the ethanol concentration was limited and leads
to the process, called over-oxidation, caused by bacteria belonging to
Acetobacter, because two of the key enzymes required for oxidation were
non-functional in species of Gluconobacter .
both in beginning and at the end of fermentation. High initial ethanol
of ethanol. And if instead, initial concentration was too low, (0.1-0.2%), the
risk for over-oxidation increased. When acetic acid concentration increased
during fermentation, the pH decreased and reduced the bacterial activity,
and set a limit for the concentration of acetic acid.
Maal et al., (2010) reported production of Apricot Vinegar using an isolated
Acetobacter strain from Iranian apricot. They reported that the isolation
andȱidentificationȱofȱanȱ Acetobacter strain from Iranian apricot had a very
good tolerance against high ethanol concentrations as well as high acetic
acid productivity in an acceptable incubation period of time industrially.
Furthermore this strain could be used in vinegar industry to convert
Chemical Reaction and Formulation
alcohol is hydrogenated to form acetaldehyde and two hydrogen ions and
two electrons are released. In the second step, two hydrogen ions bind
with oxygen to form water that hydrates acetaldehyde to form aldehyde.
During third step, aldehyde dehydrogenase converts acetaldehyde to
acetic acid and releases 2 hydrogen ions and 2 electrons.