Biomedical Engineering Reference
In-Depth Information
nutrients of the substrate, low degree of swelling and high water tension (Zadrazil &
Brunnert, 1981). These facts explain the presence of the positive interaction between the
variables
M
and
TS
in model (3). In fact, the positive effect of variable
M
was more clearly
observed for high values of
TS
and similarly, the positive effect of variable
TS
on
TAA
production was higher for high values of
M
(Figure 7A, B and C).
Inoculum size is other important factor that influences the production of metabolites
under solid state fermentation (Pandey, 2003; Barrios-González et al., 1993; Mazutti et al.,
2007; Balkan & Ertan, 2007). Increase in inoculum size leads to an increase in the moisture
content in the solid substrate or support material, which could represent an additional
diffusional barrier together with that imposed by the solid particles of the substrate or support
material. In addition, a higher inoculum size may produce too much biomass and rapidly
deplete the nutrients necessary for growth and product synthesis (Selvakumar & Pandey,
1999). This limits the growth and enzyme production (Baysal et al., 2003). On the other hand,
lower inoculum levels may give insufficient biomass and allow the growth of undesirable
organisms in the production medium. This increases the necessary time to grow to an
optimum number to consume the substrate and synthesise the desired product (Kashyap et al.,
2002; Balkan and Ertan, 2007).
From the comparison between the results obtained in submerged (Figures 1 and 2) and
solid state fermentation (Figure 7), it can be noted that the levels of
TAA
ceased to increase
from a starch concentration of 30 g/L in the submerged cultures (Figure 8A), while in SSF
this effect was not observed (Figure 8B). In fact, the empirical model (3) predicted a linear
increase in the concentration of
TAA
when the
TS
concentrations increased from 9.5 to 70.5 g
TS
/gds, for different combinations of the variables
IS
and
M
(Figure 8B). The same trend was
observed for amylase production by
A. oryzae
CBS 125-59 by SSF on polyurethane foams
(Murado et al., 1997).
Thus, the inhibition by substrate in SSF, similar to that described for the production of
gibberellic acid by
Gibberella fujikuroi
(Kumar & Lonsane, 1987) was not observed for
TAA
production by
A. oryzae
FQB-01 in SSF on sugar cane bagasse.
120
600
A
B
500
100
400
80
300
60
200
40
100
0 0 0 0 0
0 0 0 0 0
TS (mg TS/gds)
TS (g/L)
Figure 8. Effect of
TS
concentration on the production of total amylolytic activity (
TAA
) in submerged
fermentation (A) on BW (□) and MPW (Ο) and in solid state fermentation (B) when the levels of the
other independent variables are:
M
= 0.44,
IS
= 0.42 (□);
M
= +1.0,
IS
= +1.0 (Ο);
M
= +1.0,
IS
= -1.0
(
◊
);
M
= -1.0,
IS
= +1.0 (∆) and
M
= -1.0,
IS
= -1.0 (
2
).
