**3.4. Model validation**

The optimum values of the three factors selected for the fermentation process were obtained by solving Eq. (2) using the Design-Expert software package (version 10.0). The optimal condition was statistically predicted as glucose concentration of 78.40 g/L, CSL of 15.00% w/v, and inoculum size of 2.70% v/v. Under this condition, the AC concentration predicted was 10.73 g/L. In order to validate the model, the optimal condition values were applied to three independent experimental replicates and the average value of AC produced was 10.70 ± 0.1 g/L. The correlations between predicted and experimental values after optimization infer the validity of the response model and the existence of an optimum point [40]. The bar chart (**Figure 6**) is a graphical view for each optimal solution showing the desirability of every dependent and independent factor with combined value. Independent factors are shown with red bars, while the dependent response and combined values are displayed in blue. The desirability result is accurate as it falls within the acceptable value ranging between 0.8 and 1 [41]. In **Table 4**, variance inflation factor (VIF) obtained showed that the center points are orthogonal to all other factors in the model. The 95% confidence interval (CI) bounds showing high and low help to hypothesize that there is 95% probability of including the right predicted responses by the model, and there is only 5% chance that the observed value lies either below or above the level of confidence limits. The coefficient estimate shows the confidence interval

around the model coefficient and the standard error less than 1 shows the statistical accuracy

**Factor Coefficient estimate df Standard error 95% CI low 95% CI high VIF**

Statistical Optimization of Acetoin Production Using Corn Steep Liquor as a Low-Cost Nitrogen…

http://dx.doi.org/10.5772/intechopen.79353

95

(Glucose) −1.37 1 0.34 −2.17 −0.57 1.00

(Corn steep liquor) 2.56 1 0.32 1.80 3.32 1.02

(Inoculum size) −0.61 1 0.34 −1.41 0.19 1.00

X<sup>2</sup> −0.17 1 0.48 −1.30 0.96 1.00

X3 −0.57 1 0.48 −1.69 0.56 1.00

X3 −1.02 1 0.48 −2.14 0.11 1.00

<sup>2</sup> −1.25 1 0.47 −2.35 −0.15 1.01

<sup>2</sup> −0.50 1 0.47 −1.60 0.60 1.01

<sup>2</sup> −1.09 1 0.47 −2.19 0.011 1.01

Intercept 7.81 1 0.47 6.71 8.91

The feasibility of corn steep liquor to replace yeast extract and beef extract, which is an expensive nutrient source in acetoin fermentation, was investigated. Corn steep liquor—a low-cost nitrogen

of the predicted responses (**Table 4**).

df: degree of freedom; VIF: variance inflation factor; CI: confidence interval.

**Table 4.** Regression coefficients and significance of response surface quadratic.

**Figure 6.** Numerical optimization bar graph of AC production.

**4. Conclusion**

X1

X2

X3

X1

X1

X2

X1

X2

X3

**Figure 6.** Numerical optimization bar graph of AC production.


df: degree of freedom; VIF: variance inflation factor; CI: confidence interval.

**Table 4.** Regression coefficients and significance of response surface quadratic.

around the model coefficient and the standard error less than 1 shows the statistical accuracy of the predicted responses (**Table 4**).
