Table 2.

F-ratio and p-value for each Independent Variable Effect in the Polynomial Response Surface Models.

Variables		Main effects			Quadratic effects			Interaction effects
		X1	X2	X3	X12	X22	X32	X1X2	X1X3	X2X3
Specific activity(Y1, U/mg)	p-value	0.000 *	0.003 *	0.187	0.000 *	0.024 *	0.001 *	0.057	0.003 *	0.016 *
	F-ratio	110.88	45.42	2.52	109.66	12.53	64.48	4.84	42.12	16.16
Temperature stability (Y2, %)	p-value	0.066	0.026 *	0.005 *	0.100	0.002 *	0.006 *	0.055	0.018 *	0.124
	F-ratio	3.24	9.79	22.94	4.04	33.64	20.88	7.18	11.83	2.56
Storage stability (Y3, %)	p-value	0.061	0.017 *	0.039 *	0.191	0.013 *	0.009*	0.454	0.103	0.047 *
	F-ratio	6.70	15.21	9.06	2.46	17.80	23.04	0.67	4.44	8.00
Surfactant agent stability (Y4, %)	p-value	0.051	0.027 *	0.002 *	0.126	0.030 *	0.008 *	0.064	0.050	0.004 *
	F-ratio	5.18	11.76	54.02	3.68	10.82	23.42	1.21	8.94	35.88

X₁, X₂ and X₃: The main effect of B/S ratio, temperature and pH of buffer, respectively. X₁², X₂² and X₃²: The quadratic effect of B/S ratio, temperature and pH of buffer, respectively. X₁X₂: The interaction effect of B/S ratio and temperature. X₁X₃: The interaction effect of B/S ratio and pH of buffer and X₂X₃: The interaction effect of temperature and pH of buffer. * Significant at (p < 0.05).