## 2 Materials and Methods
### Phytochemical Profile of Red and Yellow Bell Pepper By-Products
#### 2.3.5 Antioxidant Activity  
The antioxidant activity of the samples was assessed based on a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay as well as the ferric reducing antioxidant power (FRAP) assay.  
DPPH Assay  
The free radical scavenging activity of investigated samples was evaluated using a 0.03 mM 1,1-diphenyl-2-picrylhydryl (DPPH, Sigma-Aldrich, Taufkirchen, Germany) ethanolic solution according to the method described by [PERSON] et al. [13] with slight modifications. This method is commonly used to evaluate a food's ability to act as an antioxidant, especially for fruits and vegetables. Thus, from each extract prepared as described in Section 2.3.1, 1 mL was taken to which 2.5 mL of DPPH solution (Sigma-Aldrich, Taufkirchen, Germany) was added. The obtained mixture was shaken energetically and then incubated in the dark for 30 min at room temperature. The absorbance was read using a UV-VIS spectrophotometer (Specord 205; Analytik Jena AG, Jena, Germany) at 518 nm against a 70% (_v/v_) ethyl alcohol control sample. Each sample was analysed in triplicate, and their mean value was reported.  
The radical scavenging activity of the Investigated samples was expressed as a percentage of DPPH free radical inhibition relative to the control using the Equation (1):  
\[\text{DPPH~inhibition}(\%)=\frac{\text{A}_{\text{control}}-\text{A}_{\text{sample }}}{\text{A}_{\text{control}}}\times 100 \tag{1}\]  
where Acontrol is the absorbance value of control and Asample is the absorbance value of the tested sample.  
The ferric reducing ability of yellow bell pepper pulp and corresponding processing by-products, both fresh and dried, was evaluated with the FRAP assay according to the protocol described by [PERSON] and [PERSON] [15]. This assay is based on the ability of antioxidant compounds contained in the investigated samples to reduce Fe\({}^{3+}\) to Fe\({}^{2+}\) in the presence of tripyridyltriazine (TPTZ) at a temperature of 37 \({}^{\circ}\)C in a sodium acetate buffer solution with pH of 3.6. As a result, the Fe\({}^{2+}\)-TPTZ complex is formed, which has a deep blue color and a maximum absorption at a wavelength of 593 nm [16].  
Prior to analysis, the alcohol extracts prepared in Section 2.3.1 from RBPP, YBPP, RBPB, and YBPB were diluted 1:5 (_v/v_) with distilled water, while those obtained from DRBPP, DYBPP, DRBPB, and DYBPB were diluted 1:50 (_v/v_) with distilled water. Then, 2.5 mL of the FRAP reagent was added to a 0.5 mL aliquot of the diluted extracts, and the resulting mixtures were incubated for 30 min at 37 \({}^{\circ}\)C. The absorbance was then measured at 595 nm against a blank sample obtained under the same conditions using a UV-VIS spectrophotometer (Specord 205; Analytik Jena AG, Jena, Germany). The FRAP value of the analyzed samples was reported as uM Fe\({}^{2+}\) equivalents/g dry substance (d.s) based on a calibration curve prepared using standard Fe\({}^{2+}\) solutions with concentrations in the range 0.1-1.0 uM Fe\({}^{2+}\)/mL. The analyses were performed in triplicate, and the results were reported as mean value \(\pm\) standard deviation (SD).