Table 3.

Analysis of variance for the second-order polynomial model of biomass synthesis by C. necator NSDG-GG in batch fermentation at 30 °C for 48 h

Source	Polynomial coefficient	Sum of squares	df	Mean squares	F value	Prob > F
Model		178.95	9	19.88	43.82	< 0.0001**
Intercept	10.64
X 1	1.94	37.71	1	37.71	83.11	< 0.0001**
X 2	2.01	40.20	1	40.20	88.59	< 0.0001**
X 3	− 0.12	0.15	1	0.15	0.33	0.5764
$X_1^2$	− 3.31	30.16	1	30.16	66.47	< 0.0001**
$X_2^2$	− 0.43	0.50	1	0.50	1.10	0.3181
$X_3^2$	0.11	0.035	1	0.035	0.078	0.7862
X 1 X 2	2.2	38.81	1	38.81	85.52	< 0.0001**
X 1 X 3	0.05	0.02	1	0.02	0.044	0.8379
X 2 X 3	0.19	0.30	1	0.30	0.65	0.4377
Residual		4.54	10	0.45
Lack of fit		1.45	5	0.29	0.47	0.7858
Pure error		3.08	5	0.62

X ₁: glucose (g/L); X₂: urea (g/L); X₃: agitation (rpm); $X_1^2$, $X_2^2$, $X_3^2$: the quadratic terms; X₁X₂, X₁X₃, X₂X₃: the interaction terms. R² = 0.9753

**Statistically significant at 99% probability level