## 3 Results and Discussion  
### Total Phenolic Content and Antioxidant Activity  
#### 3.1.1 Pineapple Shell  
According to Figure 1, the wound had no effect on the content of phenolic content (TPC) in the pineapple shell, showing only a slight increase when combined with the treatment temperature. The wounded samples showed a significant (_p_ < 0.05) reduction in TPC compared to the raw material (95.89 \(\pm\) 0.84 mg CAE\(\cdot\)g\({}^{-1}\) dry matter), with losses between 10 and 17% depending on the storage time. The wound samples with heat treatment at 30 \({}^{\circ}\)C and without storage time (0 h) showed (97.86 \(\pm\) 0.67 mg CAE\(\cdot\)g\({}^{-1}\) dry matter) an increase of 2% compared to the raw material (95.89 \(\pm\) 0.84 mg CAE\(\cdot\)g\({}^{-1}\) dry matter). The wounded samples had the lowest TPC values, regardless of the storage time. In the case of no wound samples, the storage time of 24 h (104.08 \(\pm\) 0.84 mg CAE\(\cdot\)g\({}^{-1}\) dry matter) showed a 9% increase in TPC values (_p_ < 0.05) compared to the raw material (95.89 \(\pm\) 0.84 mg CAE\(\cdot\)g\({}^{-1}\) dry matter). The abiotic stress conditions that increase significantly TPC are whole samples (_p_ < 0.05), subjected to heat treatment of 30 \({}^{\circ}\)C and with a storage time of 48 h. These samples (Figure 1) showed an increase (109.40 \(\pm\) 0.70 mg CAE\(\cdot\)g\({}^{-1}\) dry matter) of 14% compared to the raw material (95.89 \(\pm\) 0.84 mg CAE\(\cdot\)g\({}^{-1}\) dry matter). The samples with heat treatment at 30 \({}^{\circ}\)C showed an increase of 8% with an increase in the storage time between 0 h (101.63 \(\pm\) 0.82 mg CAE\(\cdot\)g\({}^{-1}\) dry matter) and 48 h (109.40 \(\pm\) 0.70 mg CAE\(\cdot\)g\({}^{-1}\) dry matter). Heat treatments with a temperature of 40 \({}^{\circ}\)C (87.46-95.49 mg CAE\(\cdot\)g\({}^{-1}\) dry matter) are not beneficial for TPC, when compared to treatments at a temperature of 30 \({}^{\circ}\)C (93.17-109.40 mg CAE\(\cdot\)g\({}^{-1}\) dry matter). In general, wounding has a negative effect on the antioxidant activity when compared to the values obtained for the raw material (Figure 2). By the DPPH method, the storage time that seems to maximize the antioxidant activity is 48 h, with an increase of 45% in the whole sample with heat treatment at 30 \({}^{\circ}\)C (37.40 \(\pm\) 0.67 umol Trolox\(\cdot\)g\({}^{-1}\) dry matter) and an increase of 53% in the whole sample heat treated with 40 \({}^{\circ}\)C (39.36 \(\pm\) 0.71 umol Trolox\(\cdot\)g\({}^{-1}\) dry matter), when compared to raw material (25.73 \(\pm\) 0.97 umol Trolox\(\cdot\)g\({}^{-1}\) dry matter). The samples also showed an increase in the antioxidant activity values by both FRAP and ABTS methods. For the storage time of 48 h, the samples with heat treatment at 30 \({}^{\circ}\)C increased their antioxidant activity in 40% as evaluated by FRAP (35.80 \(\pm\) 0.77 umol Trolox\(\cdot\)g\({}^{-1}\) dry matter) and in 38% as evaluated by ABTS, while the corresponding increases in the antioxidant activity of the samples with thermal treatment at 40 \({}^{\circ}\)C were of 75% (44.77 \(\pm\) 0.85 umol Trolox\(\cdot\)g\({}^{-1}\) dry matter) and 56% (45.17 \(\pm\) 0.94 umol  
Figure 1: Effect of abiotic stresses, heat treatment and wounding, on total phenolic content of pineapple shell. Error bars stand for \(\pm\) standard deviation (_n_ = 9). Different letters express significant differences between samples. Trolox g\({}^{-1}\) dry matter), respectively, compared to the raw material (FRAP: 25.59 \(\pm\) 0.76 \(\mu\)mol Trolox g\({}^{-1}\) dry matter; ABTS: 29.05 \(\pm\) 0.83 \(\mu\)mol Trolox g\({}^{-1}\) dry matter).