## 3 Results and Discussion
### Enzymatic Activity
#### 3.2.2 Pineapple Core
The greater increase in PAL activity promoted a greater increase in total phenolic compounds concentration in purple-flesh potatoes. The correlation between antioxidant capacity and phenolic content is evident through the results obtained for the purple-fleshed potatoes which were wounded. The phenolic content showed increases of 65% and 51% in flesh and peel, and the antioxidant capacity increased 107% and 49% in flesh and peel, respectively. [PERSON] et al. (2018) [34] carried out a work with fresh strawberries to study the changes in bioactive compounds, enzymatic activity in phenylpropanol metabolism and quality attributes depending on the effect of wounding, storage temperature and time. The activation of PAL and the resulting synthesis of phenolic compounds was influenced by the intensity of the wound, with an increase of 22% additional phenolicscontent in quartered strawberries than in whole stored strawberries (2 \({}^{\circ}\)C for 15 days). The enzymatic activity of PAL in strawberries increased with the intensity of the wounding, the intensity of the damage being proportional to the activity of the PAL and the content of phenolic compounds. [PERSON] et al. (2014) [55] have also reported comparable results where wounding of lemon samples improved the phenolic content, possibly due to PAL activity. Phenolics' changes during the processing and storage of mandarin samples were also described. Wounded lettuce leaves showed an increase in PAL activity of around eight times and a maximum activity 24 h after damaging [63]. In agreement with these studies, in the present work the pineapple core samples' wounding alone, and wounding combined with the 24 h storage time promoted considerable increases in PAL activity of 80% and 49%, respectively. [PERSON] et al. (2012) [64] showed that the stresses caused by heat treatments also affect the enzymatic activity of PAL in peaches. Hot water treatments (40 \({}^{\circ}\)C for 5 and 10 min) were applied to peach fruits and there was an accumulation of reactive oxygen species and induction of the expression of defense-related genes, with greater enzymatic activity, namely in terms of PAL. In the present work, the pineapple core samples that showed higher values of PAL activity were the heat treated (30 \({}^{\circ}\)C and 40 \({}^{\circ}\)C) whole samples without storage time (0 h). The effect of the abiotic stress caused by wounding maintained or reduced the enzymatic activity of PPO (Figure 6c). The samples wounded with heat treatment at 40 \({}^{\circ}\)C and storage time 24 h (8.77 \(\pm\) 1.27 U\(\cdot\)g\({}^{-1}\) dry matter) showed a significant increase (\(p<\) 0.05) of 54%, compared to the raw material (5.69 \(\pm\) 0.82 U\(\cdot\)g\({}^{-1}\) dry matter). This change seems to be promoted by heat treatment and storage time, without interference from wounding. The storage time (24 h) had a positive influence (\(p<\) 0.05) in PPO activity (18.39 \(\pm\) 0.54 U\(\cdot\)g\({}^{-1}\) dry matter), which registered a 223% increase when compared to the raw material (5.69 \(\pm\) 0.82 U\(\cdot\)g\({}^{-1}\) dry matter). The synergy between storage time (24 h) and the thermal treatments (30 \({}^{\circ}\)C-20.89 \(\pm\) 0.59 U\(\cdot\)g\({}^{-1}\) dry matter and 40 \({}^{\circ}\)C-28.97 \(\pm\) 0.78 U\(\cdot\)g\({}^{-1}\) dry matter) resulted in higher values of enzymatic activity of PPO than the ones registered for samples treated with storage time alone (18.39 \(\pm\) 0.54 U\(\cdot\)g\({}^{-1}\) dry matter). The pineapple core samples with 24 h storage time and heat treatment showed significant increases (\(p<\) 0.05) in PPO activity of 14% and 58%, respectively, for the temperatures of 30 \({}^{\circ}\)C (20.89 \(\pm\) 0.59 U\(\cdot\)g\({}^{-1}\) dry matter) and 40 \({}^{\circ}\)C (28.97 \(\pm\) 0.78 U\(\cdot\)g\({}^{-1}\) dry matter), when compared to samples subjected to the abiotic stress of storage time for 24 h alone (18.39 \(\pm\) 0.54 U\(\cdot\)g\({}^{-1}\) dry matter). The heat treatment thus promoted an increase in the enzymatic activity of PPO.