Table 6. Regression coefficients and their significance for response surface model.

Term	Coef	Standard Error	P
Intercept	120.62	2.63	<0.0001
X1 a	−5.54	1.75	0.0099
X2	12.04	1.75	<0.0001
X3	15.40	1.75	<0.0001
X1*X1	−1.64	1.70	0.3576
X2*X2	−2.48	1.70	0.1749
X3*X3	−16.43	1.70	<0.0001
X1*X2	6.62	2.28	0.0159
X1*X3	5.30	2.28	0.0427
X2*X3	−4.95	2.28	0.0554

^a X₁, X₂ and X₃ represent Sucrose, NH₄NO₃ and NaH₂PO₄•2H₂O, respectively.