Coded and actual values of the experimental variables used for the CCD matrix.

Variable	Variable code	Levels
		−2	−1	0	1	2
Initial pH level	X 1	4.7	5.7	6.7	7.7	8.7
AgNO3 concentration (mM)	X 2	0.1	0.2	0.3	0.4	0.5
O. limnetica extract concentration (mL)	X 3	1	2.25	3.50	4.75	6
Incubation period (h)	X 4	48	37.5	27	16.5	6