Table 2.

Estimated effects and variance analysis of the tested variables on keratinolytic activity, concentration of soluble protein, feather degradation, and bacterial growth using 2³ fractional factorial design to analyses the variable FeSO₄, CuSO₄, and ZnSO₄

Source	Keratinolytic activity (U/ml)				Concentration of protein (mg/ml)				Feather degradation (%)				B. subtilis AMR growth (UFC/ml)
	Effect	Std errror	F value	p value	Effect	Std error	F value	p value	Effect	Std error	F value	p value	Effect	Std error	F value	p value
Model			67.76	0.0146*			41.56	0.0237*			112.18	0.0089*			3.54E + 10	< 0.0001*
Intercept	160.46	5.18			2.53	0.065			40.18	1.01			8.52	0.736
A-FeSO4	− 0.37	5.18	5.25	0.9488	− 0.095	0.065	2.09	0.2853	− 4.82	1.01	22.63	0.0415	− 5.51	0.736	5.60E + 10	< 0.0001
B-CuSO4	− 110.21	5.18	453.43	0.0022*	− 1.08	0.065	270.68	0.0037*	27.67	1.01	745.34	0.0013*	− 7.77	0.736	1.11E + 11	< 0.0001
C-ZnSO4	4.79	5.18	0.86	0.4522	− 0.024	0.065	0.13	0.7512	− 2.87	1.01	8.03	0.1053	− 1.17	0.736	2.52E + 09	< 0.0001
AB	− 12.04	5.18	5.41	0.1455	− 0.049	0.065	0.55	0.5355	0.75	1.01	0.55	0.5358	6.26	0.736	7.22E + 10	< 0.0001
AC	− 11.96	5.18	5.34	0.1470	− 0.17	0.065	6.45	0.1264	− 1.58	1.01	2.43	0.2591	− 1.54	0.736	4.40E + 09	< 0.0001
BC	-2.04	5.18	0.16	0.7312	0.026	0.065	0.16	0.7317	2.32	1.01	5.22	0.1496	0.42	0.736	3.24E + 08	< 0.0001
ABC	15.63	5.18	9.11	0.0944	0.22	0.065	10.86	0.0810	1.05	1.01	1.07	0.4104	0.79	0.736	1.16E + 09	< 0.0001
Center point	− 122.01	9.91			− 1.1	0.13			− 25.72	1.94			− 8.52	1409
Std. dev	14.64				0.18				2.87				2.08E-03
Mean	127.18				2.23				33.16				6.2
CV %	11.51				8.29				8.64				0.034
R2	0.9958				0.9932				0.9975				0.999
Adjusted R2	0.9811				0.9693				0.9886				0.99
Adeq prec	21.133				16.852				26.469				15,293.83

Prob > F values less than 0.05 indicate that the terms are significant

"Adeq Prec" (Adequate precision) measures the signal to noise ratio. A ratio greater than 4 is desirable