## 2 Materials and Methods
### Analytical Tests
#### 2.3.2 Determination of Total Flavonoid Content  
The TF was quantified by aluminum chloride assay following a previously reported procedure [17]. Briefly, 1 mL of sample properly diluted was added into a 10 mL volumetric flask containing 4 mL of milli-Q water. A total of 0.3 mL of 5% NaNO\({}_{2}\) (Sigma-Aldrich, Milan, Italy) was added at time zero and, after 5 min, 0.3 mL of 10% AlCl\({}_{3}\) (Sigma-Aldrich, Milan, Italy). After 6 min, 2 mL of 1 M NaOH ([PERSON], Milan, Italy) was added to the mixture. Finally, the solution was adjusted to 10 mL with milli-Q water and carefully mixed. Absorbance of the complex flavonoid-aluminum mixture was determined at 510 nm. Quantification was carried using a catechin (C) (Sigma-Aldrich, Milan, Italy) calibration curve (2.5-20 ug mL\({}^{-1}\), r\({}^{2}\) = 0.995). The same procedure was applied for standard solutions of C. Results were expressed as mg of catechin equivalent (CE) \(\times\) g\({}^{-1}\) of dried matter (mg CE g\({}^{-1}\) DM). Samples were analyzed in triplicate. Determination of Proanthocyanidins Content  
The acidified vanillin method was used to quantify the extractable PA content, according to [17]. Briefly, 4 mL of diluted samples were mixed in a 10 mL volumetric flask containing 2 mL of ethanol ([PERSON], Milan, Italy) and 4 mL of vanillin (Sigma-Aldrich, Milan, Italy) solution (1% vanillin in 70% sulfuric acid ([PERSON], Milan, Italy)). The samples were compared to a blank with 4 mL of 70% sulfuric acid instead of vanillin solution. The absorbance of vanillin-tannin adducts was spectrophotometrically detected at 500 nm. Concentrations were calculated referring to a C calibration curve (1-6 ug mL\({}^{-1}\), r\({}^{2}\) = 0.998). The same procedure was applied for standard solutions of C. Results were expressed as mg CE g\({}^{-1}\) DM. Samples were analyzed in triplicate. Determination of Antioxidant Capacity  
The antioxidant capacity of CP extracts was evaluated by DPPH and ABTS (Sigma-Aldrich, Milan, Italy) assays, according to the procedures reported in [42]. Briefly, for each assay, 0.1 mL of appropriately diluted sample was mixed with 3.9 mL of 60 uM DPPH or 7 mM ABTS, and then stored in the dark for 120 or 6 min, respectively. The absorbance was spectrophotometrically detected at 515 nm for DPPH and at 734 nm for ABTS. Concentrations were calculated referring to a Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, Sigma-Aldrich, Milan, Italy) calibration curve (2-12 umol L\({}^{-1}\) of trolox; r\({}^{2}\) = 0.997 for the DPPH assay and r\({}^{2}\) = 0.998 for the ABTS assay). The same procedure was applied for Trolox standard solutions. The results were expressed in terms of Trolox equivalent antioxidant capacity (TEAC), as mmol trolox equivalents-100 g\({}^{-1}\) dry matter (mmol TEAC-100 g\({}^{-1}\) DM). Samples were analyzed in triplicate. The radical scavenging activity (RSA) was determined as a percentage of DPPH and ABTS discoloration, according to [19]. EC\({}_{50}\), (mg mL\({}^{-1}\)) is the extract concentration necessary to achieve a 50% radical DPPH or ABTS inhibition, calculated from the graph of RSA percentage against the extract concentration (from 0.01 to 0.1 mg mL\({}^{-1}\)) (Figures S3 and S4 in Supplementary Materials). The FRAP assay was carried out according to [19]. An aliquot (100 uL) of each extract was transferred to a test tube and 3.0 mL of freshly prepared FRAP reagent (25 mL of 300 mM acetate buffer pH 3.6), 2.5 mL of 10 mM 2,4,6-tripyrid-S-triazine (TPTZ, Sigma-Aldrich, Milan, Italy) in 40 mM HCl ([PERSON], Milan, Italy) and 2.5 mL of 20 mM FeCl\({}_{3}\)\(\times\) 6H\({}_{2}\)O, (Sigma-Aldrich, Milan, Italy) was added. The absorbance was recorded after 5 min at 593 nm. The antioxidant activities were calculated from the calibration curve of L-ascorbic acid (Sigma-Aldrich, Milan, Italy) (0.1- 1 mM, r\({}^{2}\) = 0.989). The same procedure was applied for L-ascorbic acid standard solutions. The results expressed as mg of L-ascorbic acid equivalents (AAeq) g\({}^{-1}\) DM.