Fermentation harvest time (72 h) was optimized in SSF
with 10% spent yeast as inoculum. A specific enzyme activity
of 430 U/mg was reported at the end of 72 h of cultivation
(Table 2). Alegre et al. (2009) have also reported
72 h as the optimum time for the production of extracellularinvertase
at 30°C by Aspergillus caespitosus. Similar
incubation period (3 days) for both intra and extracellular
A. niger invertase was reported by Sirisansaneeyakul et al.
(2000), Ashokkumar et al. (2001) and Mamma et al.
(2008), found that the highest invertase activity produced
by A. niger cultivated on dry orange peels was 72.5 U/g
drysubstrate at 72 h, while the highest activity produce by
N. crassa was 74.0 U/g dry substrate under the same conditions.
Rashad and Nooman (2009) had found out the
highest productivity of invertase was 272.5 U/g dry substrate
in 96 h in red carrot residue by SSF using Saccharomyses
cerevisiae. Similar behaviour was reported for
extracellular invertase production from A. niger (Park and
Pastores 2003), from S. cerevisiae (Rashad et al., 2006) and
from A. flavus (Uma et al., 2010). The enhancement in
peak invertase activity reported in Table 2 when compared
with that in Table 1 is due to the open tray cultivation
adapted as SSF for the experimentation dealt in Table 1