Table 2.
Corresponding F-values and p-values for each obtained coefficient and second-order polynomial models were used to express the content in total phenolics (TPC) and flavonoids (FC), as well as the ABTS, DPPH, and FRAP-based antioxidant and reducing activities as a function of independent variables in grape pomace.
| Variable | Statistic | X1 | X2 | X3 | X1,2 | X1,3 | X2,3 | X12 | X22 | X32 | Model F-Value |
|---|---|---|---|---|---|---|---|---|---|---|---|
| TPC | p-value | 0.851 | *** | *** | 0.358 | 0.205 | * | ** | * | *** | 0.16 |
| F-value | 0.04 | 39.58 | 569.91 | 0.89 | 1.74 | 8.32 | 11.26 | 6.31 | 33.61 | ||
| FC | p-value | 0.41 | * | * | 0.49 | 0.40 | 0.25 | 0.66 | 0.79 | *** | 0.20 |
| F-value | 0.71 | 7.41 | 209.99 | 0.51 | 0.76 | 1.45 | 0.20 | 0.08 | 27.46 | ||
| ABTS | p-value | ** | *** | *** | * | 0.652 | 0.063 | 0.070 | 0.078 | *** | 0.59 |
| F-value | 8.86 | 73.93 | 858.08 | 12.73 | 0.21 | 3.94 | 3.74 | 3.52 | 59.27 | ||
| DPPH | p-value | *** | *** | *** | 0.539 | * | 0.088 | 0.121 | 0.287 | ** | 0.89 |
| F-value | 32.34 | 208.97 | 270.04 | 0.40 | 6.79 | 3.36 | 2.72 | 1.23 | 15.82 | ||
| FRAP | p-value | * | *** | *** | 0.428 | 0.998 | ** | 0.072 | 0.141 | *** | 0.05 |
| F-value | 6.17 | 30.14 | 384.69 | 0.66 | 0.01 | 10.75 | 3.68 | 2.38 | 23.94 | ||
| Polynomial model | R2 | MAE | |||||||||
| TPC = 23.1678 + 0.0988027X1 + 3.33974X2 + 12.6736X3 − 3.21974X12 + 0.591537X1X2 − 0.825963X1X3 − 2.29359X22 + 1.88461X2X3 + 5.29474X32 | 0.962 | 0.010 | |||||||||
| FC = 9.38469 + 0.333288X1 + 1.12598X2 + 5.99543X3 − 0.305237X12 − 0.355901X1X2 − 0.435901X1X3 + 0.184871X22 + 0.636473X2X3 + 3.5232X32 | 0.909 | 0.989 | |||||||||
| ABTS = 0.161795 − 0.00761641X1 + 0.0226204X2 + 0.0770648X3 − 0.0092011X12 + 0.0110754X1X2 − 0.00142462X1X3 − 0.00849074X22 + 0.00643056X2X3 + 0.0348426X32 | 0.975 | 0.008 | |||||||||
| DPPH = 0.2413529 − 0.0218333X1 + 0.0690476X2 + 0.0784921X3 + 0.010625X12 + 0.00308333X1X2 − 0.01275X1X3 − 0.00761905X22 + 0.0119048X2X3 + 0.027381X32 | 0.958 | 0.100 | |||||||||
| FRAP = 0.178926 − 0.0105464X1 + 0.0239717X2 + 0.0856384X3 − 0.0151381X12 + 0.0041814X1X2 + 0.0000137318X1X3 − 0.0115839X22 + 0.0176242X2X3 + 0.0367495X32 | 0.945 | 0.010 | |||||||||
Significant at p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***). X1: Ethanol concentration (%), X2: pH (%HCl), and X3: Temperature (°C). MAE: Mean absolute error; R2, regression coefficient.