Table 2. Central composite design for ultrasound extraction from peony root and the total polyphenolic content, ABTS, Paeoniflorin, Myricetin of the extracts
| Independent variables | Dependent variables |
| Ethanol concentration (%) X1 | Extraction temperature (°C) X2 | Extraction time (min) X3 | TPC (mg GAE/g) | ABTS (%) | Paeoniflorin (mg/g) | Myricetin (mg/g) |
| 1 | 40(−1) | 40(−1) | 25(−1) | 103.32 | 19.32 | 44.11 | 147.1 |
| 2 | 40(−1) | 40(−1) | 45(1) | 103.32 | 20.13 | 31.42 | 145.4 |
| 3 | 40(−1) | 60(1) | 25(−1) | 108.25 | 20.1 | 45.61 | 115.9 |
| 4 | 40(−1) | 60(1) | 45(1) | 107.48 | 22.86 | 44.71 | 179.2 |
| 5 | 80(1) | 40(−1) | 25(−1) | 94.72 | 16.42 | 45.39 | 118 |
| 6 | 80(1) | 40(−1) | 45(1) | 94.23 | 16.45 | 44.30 | 126.6 |
| 7 | 80(1) | 60(1) | 25(−1) | 90.21 | 18.73 | 34.08 | 125.1 |
| 8 | 80(1) | 60(1) | 45(1) | 90.03 | 19.42 | 39.57 | 174.1 |
| 9 | 60(0) | 50(0) | 35(0) | 102.31 | 21.89 | 42.79 | 172.3 |
| 10 | 60(0) | 50(0) | 35(0) | 101.52 | 21.47 | 44.76 | 167 |
| 11 | 20(−2) | 50(0) | 35(0) | 90.62 | 17.95 | 42.01 | 143.4 |
| 12 | 100(−2) | 50(0) | 35(0) | 58.78 | 9.83 | 29.79 | 43 |
| 13 | 60(0) | 30(−2) | 35(0) | 103.67 | 19.09 | 43.45 | 123.3 |
| 14 | 60(0) | 70(−2) | 35(0) | 79.07 | 18.27 | 34.70 | 187.5 |
| 15 | 60(0) | 50(0) | 15(−2) | 95.79 | 19.49 | 42.24 | 137.2 |
| 16 | 60(0) | 50(0) | 55(−2) | 97.15 | 21.26 | 42.66 | 194 |