A simple Koji fermentation process was followed which is quite
similar to solid-state fermentation. The collected fresh peels were
washed twice with sterile distilled water to remove adhering dust.
Then their finger stalk and black base regions were removed.
Thereafter, one kg of peels was steamed with one liter of water
in order to get the desired moisture content. The steamed peels
were homogenized for five minutes under aseptic conditions. After
homogenization, the pH of the steamed peels was 5.12. It was adjusted
to different pH ranges using 1 N HCl/NaOH. From the pasty
fibrous material, 2 cm thick Koji beds were prepared in a clean
sterilized glass trough having 30 cm diameter. The glass trough
was used as a fermentation vessel. After inoculation with A. niger
the Koji bed was covered with cheesecloth. The cloth cover allowed
adequate gas exchange. The troughs were placed in a sterile chamber
and fermented at different experimental conditions. Citric acid
was measured by a spectrophotometric method using pyridine and
acetic anhydride reagents