## 3 Results and Discussion
### Enzymatic Activity  
#### 3.2.1 Pineapple Shell  
The values obtained for TPC and antioxidant activity in the pineapple shell indicate that the assay should proceed only with whole samples, excluding wound samples in the analysis of enzymatic activity. Bromelain activity (Figure 5a) in pineapple shell was not favorably influenced by heat treatments at 40 \({}^{\circ}\)C (23.70-33.00 mg tyrosine\(\cdot\)min\({}^{-1}\cdot\)g\({}^{-1}\) dry matter). The thermal treatment at 30 \({}^{\circ}\)C showed similar values to the raw material (34.97 \(\pm\) 1.11 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) for a storage time of 0 h (34.90 \(\pm\) 1.23 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) and 48 h (34.64 \(\pm\) 0.79 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter), and showed a significant increase (\(p\) < 0.05) of 7% in the enzymatic activity of bromelain for treatments with a temperature of 30 \({}^{\circ}\)C and storage time of 24 h (37.42 \(\pm\) 0.98 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter). The isolated effect of storage time for 24 h (32.23 \(\pm\) 0.87 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) significantly decreased (8%) bromelain activity, and storage time at 48 h (38.55 \(\pm\) 1.00 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) significantly increased (10%) bromelain activity (\(p\) < 0.05), compared to the raw material (34.97 \(\pm\) 1.11 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter). The enzymatic activity of bromelain was improved by the lower temperature (30 \({}^{\circ}\)C) combined with the shorter (37.42 \(\pm\) 0.98 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) storage time (24 h) or by the longer storage time (48 h) without the effect of heat treatment (38.55 \(\pm\) 1.00 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter). The behaviour of bromelain under the effect of postharvest abiotic stresses needs to be further studied since there are only a few works in this area. One of them concluded that, in order to maintain the beneficial effects of pineapples for health, namely, the activity of bromelain, the treatment temperature that allows obtaining maximum functionality varies between 35 and 50 \({}^{\circ}\)C and the pH between 4.5 to 8.5 [52]. The pineapple shell samples evaluated in the present work showed slight decreases when subjected to thermal treatments with temperatures of 40 \({}^{\circ}\)C and maintained or showed a slight increase with the temperature of 30 \({}^{\circ}\)C. The effect of the storage time seems to be more evident than the heat treatment. Bromelain is very stable at low temperature, with incubation at 40 \({}^{\circ}\)C showing no loss of activity in treatments up to 60 min, while treatments at 50 \({}^{\circ}\)C showed 83% of the initial activity [53]. The results of enzymatic activity obtained in the present work for the pineapple shell agree with those obtained by other authors. The heat treatment at 40 \({}^{\circ}\)C showed enzymatic activity between 68 and 94% when compared to the initial activity. The enzymatic activity (Figure 5b) of phenylalanine ammonia-lyase (PAL) was maintained or was reduced with the application of abiotic stresses at 30 \({}^{\circ}\)C (129.10-137.83 \(\upmu\)mol t-cinnamic\(\cdot\)h\({}^{-1}\) g\({}^{-1}\) dry matter) and 40 \({}^{\circ}\)C (109.17-129.83 \(\upmu\)mol t-cinnamic\(\cdot\)h\({}^{-1}\) g\({}^{-1}\) dry matter), as compared to the raw material (138.77 \(\pm\) 0.97 \(\upmu\)mol t-cinnamic\(\cdot\)h\({}^{-1}\).g\({}^{-1}\) dry matter). The 24 h storage time (169.31 \(\pm\) 2.99 \(\upmu\)mol t-cinnamic\(\cdot\)h\({}^{-1}\) g\({}^{-1}\) dry matter) showed PAL enzyme activity 22% higher (\(p\) < 0.05) than the raw material (138.77 \(\pm\) 0.97 \(\upmu\)mol t-cinnamic\(\cdot\)h\({}^{-1}\) g\({}^{-1}\) dry matter), which suggests that the isolated effect of the storage time has an important effect on PAL enzymatic activity (Figure 5b).