Bhat et al.

CH ₃ CH ₂ OH+ O 2

CH ₃ COOH +H ₂ O + 493 kJ

Ethanol

Oxygen

Acetic acid

Water

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 .

RasporȱandȱGoranovicȱ(2008)ȱreportedȱthatȱethanolȱcontentȱaffectsȱAABȱ

both in beginning and at the end of fermentation. High initial ethanol

concentrationȱdecreasedȱbacterialȱvitalityȱdueȱtoȱtheȱantimicrobialȱeffectȱ

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

apricotȱspoilageȱtoȱaȱbeneficiaryȱproduct.

Chemical Reaction and Formulation

Theȱproductionȱofȱaceticȱacidȱ(vinegar)ȱisȱpresentedȱinȱfigureȱ1.ȱInitially,ȱ

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.

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