Table 1.

Experimental range and levels of independent variables

Variables	Component	Level
		−2	−1	0	+1	+2
A	Temperature (°C)	37	45	50	55	60
B	pH	4	5	6	7	8
C	Incubation time (days)	0	30	60	90	120
D	Agitation (rpm)	0	50	100	150	200