Hemicellulosic ethanol production by immobilized cells of Scheffersomyces stipitis: Effect of cell concentration and stirring

Figures & data

Figure 1. Process showing the immobilization of S. stipitis in Ca-alginate gel carrier.

Table 1 Matrix of 2² full factorial design with 4 replicates at the central point to evaluate the influence of immobilized cell concentration (X₁) and stirring (X₂) on different response variables

	Coded Values		Real Values
Experiment	X1	X2	X1 (g/L)	X2 (rpm)
1	−1	−1	3.0	100
2	+1	−1	10.0	100
3	−1	+1	3.0	300
4	+1	+1	10.0	300
5	0	0	6.5	200
6	0	0	6.5	200
7	0	0	6.5	200
8	0	0	6.5	200

Table 2 Response variables of 2² full factorial design with 4 replications at the central point to evaluate the influence of immobilized cell concentration (X₁) and stirring (X₂) on ethanol production after 48 hours of process

	Response Variables
Experiment number	Ethanol (g/L)	Yp/s (g/g)	Qp (g/L.h)
1	5.30	0.21	0.110
2	8.90	0.33	0.185
3	5.04	0.18	0.105
4	4.77	0.15	0.099
5	5.67	0.18	0.118
6	5.99	0.21	0.125
7	4.62	0.20	0.096
8	5.24	0.16	0.109

Table 3 Estimated effects of cell concentration (X₁) and stirring (X₂) on the response Variables

	Estimated effect
Factor	Ethanol	Yp/s	Qp
X1	1.660	0.046	0.035
X2	−2.197	−0.102	−0.046
X1^*X2	−1.935	−0.079	−0.040

* X₁*X₂ is the interaction between the investigated factor

Table 4 Analysis of variance and significance of the process variables- cell concentration (X₁) and stirring (X₂) for response variables (Ethanol production, ethanol yield, ethanol productivity and xylose consumption)

Ethanol production (g/l)
Source	Sum of Squares	df	Mean Square	F-Ratio	p-value
Model	11.33	3	3.78	8.23	0.0347*
X1	2.76	1	2.75	6.01	0.0704
X2	4.83	1	4.83	10.52	0.0316*
X1*X2	3.74	1	3.74	8.16	0.0461*
Curvature	0.79	1	0.79	2.26	0.2295
Total error	1.05	3	0.35
Total (corr.)	13.16	7
Yp/s
Source	Sum of Squares	df	Mean Square	F-Ratio	p-value
Model	0.019	3	0.006	7.28	0.0425*
X1	0.002	1	0.002	2.46	0.1916
X2	0.010	1	0.010	12.07	0.0255*
X1*X2	0.006	1	0.006	7.31	0.0539
Curvature	0.002	1	0.002	3.90	0.1428
Total error	0.001	3	0.0005
Total (corr.)	0.022	7
Qp
Source	Sum of Squares	df	Mean Square	F-Ratio	p-value
Model	0.0049	3	0.0016	8.23	0.0347*
X1	0.0012	1	0.0012	6.01	0.0704
X2	000021	1	0.0021	10.52	0.0316*
X1*X2	0.0016	1	0.0016	8.16	0.0461*
Curvature	0.0003	1	0.0003	2.26	0.2295
Total error	0.0005	3	0.0002
Total (corr.)	0.0057	7

Figure 2. Pareto charts of independent variables and their interactions on each response variable (ethanol production, ethanol yield and ethanol productivity).

Figure 3. Response surface plots and corresponding contour lines showing the relationship between responsive variables (ethanol production, ethanol yield and ethanol productivity) and process variables (immobilized cell concentration and stirring).

Figure 4. Microscope picture of a ca-alginate bead containing cells of immobilized S. stipites (400x).