Table 3. The second polynomial equations for quality prediction of peony root

	The second polynomial equations	R2	Significance	Stationary point
TPC	−35.347188 + 2.230000(X1) + 3.3018750(X2) + 0.985875(X3) − 0.017009(X12) − 0.011125(X1 × X2 – 0.026363(X22) + 0.000062500(X1 × X3) − 0.00575(X2 × X3) − 0.013612(X32)	0.8213	0.0932	Maximum
ABTS	−11.811875 + 0.504938(X1) + 0.614125(X2) + 0.221062(X3) − 0.004869(X12) + 0.001106(X1 × X2) − 0.007500(X22) − 0.001781(X1 × X3) + 0.003263(X2 × X3) − 0.003262(X32)	0.9289	0.008**	Maximum
Paeoniflor	11.776875 + 1.076313(X1) + 1.410250(X2) − 1.643063(X3) − 0.004922(X12) − 0.019269(X1 × X2) − 0.011750(X22) + 0.011244(X1 × X3) + 0.022963(X2 × X3) − 0.003313(X32)	0.8508	0.059	Saddle point
Myricetin	153.653125 + 3.431875(X1) − 1.838750(X2) − 4.273750(X3) − 0.047781(X12) + 0.032500(X1 × X2) − 0.035625(X22) − 0.002500(X1 × X3) + 0.131750(X2 × X3) − 0.010125(X32)	0.9018	0.0195*	Saddle point

^* p⟨0.05, ^**p⟨0.01.