Table 2. Analysis of variance of RSM

Source	Tannin concentration (g/g)
	Constants	F-value	p-value
Model		307.09	0.000
Linear	−14.52	615.88	0.000
X1	0.08926	1,096.98	0.000
X2	−1.426	134.78	0.000
Square		70.96	0.000
X 1 2	−0.00014	115.35	0.000
X 2 2	−1.071	26.58	0.000
Two-way interaction		27.56	0.000
X1×X2	0.00636	27.56	0.000
R-square		0.9884

RSM: response surface methodology.