2.6. Bioconversion by solid state fermentation and acid
protease activity
The major factors for a successful SSF process are the
selection of micro-organisms, the substrate, process optimization,
product isolation and purification (Gupta et al.,
2002). Therefore, preliminary experiments were conducted
with modification as per Murthy and Naidu (2010) to select
a suitable nitrogen source (either a 10% yeast extract (w/w)
or 10% polypeptone (w/w) or both mixed 1:1) to supplement
the PPP in the SSF. A suitable medium that synergized PPP
was used in further investigations of fermentation with moisture
modulation using mineral solutions containing trace salts
CuSO4·5H2O, ZnSO4·7H2O and FeSO4·7H2O that had been sterilized
at 121 ◦C for 20min. The cooled sterilized solid substrate
(10 g) was placed in a 250ml conical flask, inoculated with 10%
of inoculum containing 2.6 × 106 conidia/ml, mixed uniformly
and incubated at 30 ◦C for 96h. Protease was extracted by suspending
the fermented substrate in distilled water (1:5) using