Table 2.

Independent variables and their levels in CCD

Variables	Symbol	Code level
		−α	−1	0	+1	+α
Glucose	A	0.97	12.00	20.00	28.00	39.03
NaNO3	B	0.10	1.20	2.00	2.80	3.90
KH2PO4	C	0.05	0.60	1.00	1.40	1.95
MgSO4	D	0.02	0.30	0.50	0.70	0.98
pH	E	1.93	4.00	5.50	7.00	9.07