Table 1.

Experimental range and levels of the independent variables.

Independent Variables	Symbols	Units	Code Levels
			−2	−1	0	+1	+2
Substrate concentration	S	g/L	7.0	13.0	20.0	27.0	34.0
pH			4.0	4.5	5.0	5.5	6.0
Hydrolysis temperature	T	°C	45	50	55	60	65
Papain amount	M	g/L	0.3	0.4	0.5	0.6	0.7