Biomedical Engineering Reference
In-Depth Information
where
TAA
is the total amylolytic activity,
M
is the moisture content,
IS
is the inoculum size
and
TS
is the total sugars concentration. Among the most notable characteristics of the system
studied, it should be stated that for enzyme production, all the independent variables (
M
,
IS
and
TS
) and the binary interaction between
M
and
TS
had positive coefficients. In contrast,
the coefficients of the quadratic terms
M
2
and
IS
2
had negative sign and the quadratic term
TS
2
as well as the binary interactions
M
·
IS
and
IS
·
TS
were found to be non significant (Table
8). The significant coefficients for the quadratic terms (
M
2
and
IS
2
) implied the existence of
optimum values of
M
and
IS
inside the experimental domain. Since the quadratic term
TS
2
was
found to be non-significant and the linear term
T
had a positive coefficient, the optimum
value for this variable corresponds to its highest value.
Table 9. Significance analysis of the model (3) obtained for production of TAA in
function of the variables M, IS and TS
SS
fd
QM
Model
189619.7
6
31603.3
Error
6087.2
13
468.2
Exp. error
885.6
5
177.1
Lack of fitting
5201.6
8
650.2
Total
195707.4
19
32071.5
QME/QMEe = 2.64
F
13
5
(α = 0.05) = 4.66
QMLF/QMEe
=
3.67
F
8
5
(α = 0.05)
=
4.82
r
2
= 0.969 adj
r
2
= 0.955
SS: Sum of Squares; df: degrees of freedom; QM: Quadratic Means; E: total error; Ee: Experimental error;
LF: Lack of Fitting.
The response surfaces curves generated according to model (3) show the relative effect of
two variables on
TAA
production, when the coded value of the third variable is kept at a
constant level of +1 or -1 (Figures 7A, B and C). For example, Figure 7A illustrates the effect
of inoculum size and moisture content on
TAA
production at constant starch levels. As it can
be observed, the
TAA
concentration increased (for low and high values of
TS
) with the
increase in moisture content
and inoculum size in the range of -1.267 to 0.44 and -1.267 to
0.42, respectively. Any further increase in the levels of
M
and
IS
led to a sharp decline in
TAA
production. At constant levels of
M
(Figure 7B), a quadratic effect of
IS
on
TAA
production
was observed in contrast with the linear effect produced by
TS
on the response. Similarly,
Figure 7C shows a quadratic effect of
M
as well as a linear effect of
TS
on
TAA
production for
low (-1) and high (+1) values of
IS
.
Thus, a moisture content of 75% (coded value = 0.44), an inoculum size of 1.4 × 10
7
spores/gds (coded value = 0.42) and starch concentration of 70.5 mg/gds (coded value =
1.525) were the best conditions to produce the high amounts of enzyme (539 EU/gds) with
A.
oryzae
FQB-01 on sugar can bagasse.
The effect of initial moisture content on enzyme production in SSF has usually been
related to the interference that this variable produces on the physical properties of the solid
particles (Ellaiah et al., 2002). Higher moisture content could reduce the porosity of the solid
substrate or support material, thus interfering with the oxygen transfer (Feniksova et al., 1960;
Lonsane et al., 1985). Lower moisture levels can lead to a reduction in the solubility of
