## 3 Results and Discussion
### Enzymatic Activity
#### 3.2.2 Pineapple Core
Whole pineapple core samples with 24 h storage time (124.38 \(\pm\) 3.04 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) showed a significant increase (41%) in PAL enzyme activity while samples crushed with 24 h storage time (131.78 \(\pm\) 2.59 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) showed a significant (_p_ < 0.05) reduction (17%) in PAL enzyme activity, when compared to raw material (88.42 \(\pm\) 3.42 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter). Storage time increased the enzymatic activity of PAL (Figure 6b) in whole (88.42-124.38 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) samples and reduced it in wounded samples (159.56-131.78 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter). The wounded samples (without storage time) showed (159.56 \(\pm\) 2.81 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) an increase significantly (_p_ < 0.05) of 80% in the enzymatic activity of PAL when compared to the raw material (88.42 \(\pm\) 3.42 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter). The wounded samples with a storage time of 24 h (131.78 \(\pm\) 2.59 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) showed an increase of 6% in PAL activity when compared to the whole samples with the same storage time (124.38 \(\pm\) 3.04 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter), thus showing an effect of storage time greater than the effect of abiotic stress caused by the wound (Figure 6b). The heat treatment promoted increases in the enzymatic activity of PAL of 94% and 125% for the temperatures of 40 \({}^{\circ}\)C (171.88 \(\pm\) 1.83 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter) and 30 \({}^{\circ}\)C (198.77 \(\pm\) 3.94 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter), respectively, when compared to the raw material (88.42 \(\pm\) 3.42 umol t-cinnamic h\({}^{-1}\) g\({}^{-1}\) dry matter). The temperature was the abiotic stress applied to the pineapple core that was most efficient in increasing the enzymatic activity of PAL, and this effect surpassed that of the other applied stresses (wounding and storage time). However, the effect of wounding alone also showed very interesting results in the enzymatic activation of PAL (Figure 6b). The increase in the enzymatic activity of PAL did not show a direct relationship with the increase in TPC, contrary to what would be expected and has been observed by other authors. A possible explanation for this occurrence may be the virtual absence of oxygen in the packaging (vacuum-packed pineapple core). Oxygen limitation may have inhibited the oxidation of compounds and reduced the synthesis of phenolic compounds. Stress triggers the rupture of the cell membrane, that in turn causes the oxidation of phenolic compounds due to the combination of phenolics with oxidative enzymes, predominantly PPO, and stimulates the degradation of the antioxidant. A second response is developed to repair the damage caused by the wound and involves the synthesis of monomeric or polymeric phenolics through changes in the activity of PAL, which is the main metabolic enzyme in the phenylpropanol pathway and is responsible for enhancing antioxidant synthesis [34; 62]. Some works have studied the effect of abiotic stresses due to wounding, temperature and storage time in fruits. [PERSON] et al., (2011) [33] demonstrated that the maximum activity of PAL in control carrot pieces occurred after 24 h of storage, that is, enzymatic activation does not happen immediately after the wounding and needs time to occur. This stress caused by the wound in the carrots promotes the accumulation of phenolic compounds. The activation of PAL gene expression induced by wounding in the expression of and the consequent accumulation of phenolic compounds is associated with signalling molecules (reactive oxygen species). In [PERSON] and [PERSON] (2003) [35], wounding caused an initial PAL activity increase of ~73 and 14-fold in the flesh and peel of purple-flesh potatoes, respectively.