Table 2.

Analysis of variance of CCD for AuNPs biosynthesis using Streptomyces flavolimosus cell-free supernatant as affected by temperature (°C), incubation period (days), HAuCl₄ concentration (µg/mL) and initial pH level.

Source of variance		Coefficient estimate	Sum of squares	Degrees of freedom	Mean square	F-value	P-value
Model	Intercept	575.71	903,800	14	64,560.43	92.17	< 0.0001*
Linear effect	X1	20	9600.34	1	9600.34	13.71	0.0021*
	X2	− 39.19	36,859.26	1	36,859.26	52.62	< 0.0001*
	X3	152.55	558,500	1	558,500	797.39	< 0.0001*
	X4	47.37	53,847.92	1	53,847.92	76.88	< 0.0001*
Interaction effect	X1 X2	17.98	5173.71	1	5173.71	7.39	0.0159*
	X1 X3	43.36	30,080.84	1	30,080.84	42.94	< 0.0001*
	X1 X4	− 19.82	6287.27	1	6287.27	8.98	0.009*
	X2 X3	− 32.95	17,370.86	1	17,370.86	24.8	0.0002*
	X2 X4	37.35	22,323.96	1	22,323.96	31.87	< 0.0001*
	X3 X4	25.46	10,370.3	1	10,370.3	14.81	0.0016*
Quadratic effect	X12	− 1.8	88.83	1	88.83	0.1268	0.7267
	X22	− 10.37	2950.84	1	2950.84	4.21	0.058
	X32	− 8.85	2150	1	2150	3.07	0.1002
	X42	− 74.24	151,200	1	151,200	215.84	< 0.0001*
Error effect	Lack of fit		9360.18	10	936.02	4.08	0.067
	Pure error		1146.64	5	229.33
R2	0.9885
Adj R2	0.9778
Pred R2	0.9392
Adeq Precision	35.3418

F Fishers’s function, P Level of significance.

*Significant values.