Effect of Independent Variables on the Responses
The significance of each term was determined using the F ratio and P
value as shown in Table 3. The significant and magnitude of the
coefficients indicated the effect of the variables on the response and
the negative coefficient means a decrease in response when the level of
variable increased while a positive coefficient signifies an increase in
the response [14]. Furthermore, a significant interaction indicates
that the level of one interactive variable may increase while the other
may decrease for a constant value of the response [15]. Tables 3 and
4 showed that all linear terms, two quadratic terms (fermentation time
and temperature and all interactive terms had significant (P <
0.05) effect on the pH and TTA. In Figure 1, the 3D response surface
plot of pH and fermentation time displayed a linear effect on the
response where pH decreases with increase in fermentation time. This was
evident in the regression equation where fermentation time had a
negative coefficient which indicated a decrease in the response. The 3D
response surface plots of TTA during fermentation are shown in Figure 2.
The TTA increased to an optimum level when the fermentation time and
mass of root individually increased to 105 h and 3kg respectively,
followed by a decline with further increase in each of these variables
(Figure 1). The decrease in TTA as fermentation increased above 30oC could be due to the fact that the optimum
fermentation time have exceeded for maximum TTA. It could be that
microorganism was not active enough to produce more acid. This is in
accordance within the range reported by Oyewole and Ogundele [11]
for fufu (0.08 – 0.22)% lactic acid.