## 2 Materials and Methods
### Antioxidant Capacity Assays In Vitro  
Once extracted, samples were subjected to a variety of tests to determine the antioxidant capacity. The methods applied were Folin and Ciocalteu reducing capacity (FRC), the ferric reducing antioxidant power (FRAP), radical scavenging activity by DPPH assay and ABTS cation radical all based on the electron transfer mechanism. The ABTS+ discoloration assay was employed to obtain the Trolox equivalent antioxidant capacity (TEAC). The TEAC assay was previously carried out by [PERSON] et al., 1999 and it was slightly amended for a previous work [24; 25]. Then, 200 \(\mu\)L of the extracts were combined with 3 mL of the diluted ABTS solution in a polystyrene disposable cuvette with a lid and then after that it was homogenized in a vortex for 5 s approximately. The reaction mixture was incubated at 25 \(\pm\) 2 \({}^{\circ}\)C for 30 min and afterwards the absorbance was measured at 734 nm.  
The employed FRAP assay was based on the methodology developed previously by [PERSON] and [PERSON] (1996) [26] but introducing slight modifications that were optimized in a previous work [25]. An extract volume of 200 \(\mu\)L was mixed with 3 mL of FRAP reagent in a polystyrene disposable cuvette and incubated for 40 min sheltered from the light at 25 \(\pm\) 2 \({}^{\circ}\)C. Measurements were conducted with a spectrophotometer at 593 nm.  
The DPPH methodology used was adapted from a previous study by [PERSON] et al., 2019 [25]. An aliquot of 200 \(\mu\)L of the pineapple peel or core extract was added to 2.5 mL of 24 mg a methanol solution of DPPH in a polystyrene cuvette and the kinetics of the reaction was followed monitoring the absorbance spectrophotometrically at 517 nm until the signal reached a stable value. For these samples a stable reaction time of 60 min was selected. Thereafter, all samples were measured in the spectrophotometer at the same wavelength after 60 min of incubation in the dark at ambient temperature. A standard curve was obtained similar to the one obtained in the ABTS, FRAP assays. The results of FRAP, DPPH, and ABTS were expressed as TROLOX micromodes equivalents (TE) per 100 g of pineapple fresh weight (FW).  
The FCR assay was carried out based on previous work with some modifications [27]. 300 \(\mu\)L of the methanolic extract was mixed with 100 \(\mu\)L of Folin and Ciocalteu phenol reagent (2 N) and 500 \(\mu\)L of a 7% sodium carbonate solution. The mixture was homogenized with a vortex stirrer for 10 s followed by an incubation period at room temperature for 90 min. Afterward, 5 mL of distilled water was added to each tube and the absorbance of each sample or standard solution was measured at 760 nm in a spectrophotometer using deionized water as blank. Results were expressed as mg gallic acid equivalents (GAE) per  
Figure 1: **(a)** Frozen core and peel pineapple by-products used in this study; **(b)** crushing process of the samples with the domestic blender; **(c)** crushed and homogenized pineapple by-products core samples.  
100 g of 100 g of pineapple FW. All antioxidant results obtained were presented in the form of an average of three different extracts for each sample.