Tannase can be produced either constitutively or under
induction, depending on the strain and fermentation
conditions. The enzyme production by Aspergillus sp.
GM4 was induced in the presence of 2% (w/v) tannic
acid, methyl gallate and gallic acid. However, a basal
level of tannase production was observed when glucose
was used as a carbon source. According to Bradoo et al.
[19], the fungus A. japonicus produced tannase constitutively
in culture medium containing simple or complex
sugars, but the production is increased when tannic acid
is the sole carbon source [19]. There is some controversy
regarding the tannase regulation mechanism and the specific
roles of some compounds in the induction and repression
of tannase expression. Tannic acid cannot act
directly as an inducer because tannic acid is a large molecule
that cannot cross the cell membrane, and there is
no known tannic acid transporter. Therefore, the basal
levels of tannase synthesis are important for initiating
tannic acid hydrolysis to release the intermediary compounds
that can act as true inducers [3]. In addition,
some studies have shown that up to 0.2% (w/v) glucose
concentration may favor the production of tannase, but