## 3 Results and Discussion
### Enzymatic Activity
#### 3.2.2 Pineapple Core  
As the storage time of 48 h did not differ in comparison with the storage time of 24 h in TPC and antioxidant activity, the enzymatic determination included only the samples with a storage time of 24 h. The shorter storage time would be beneficial at the industrial level, as it speeds up the production process and reduces costs with the refrigeration system. Wounding and storage time did not influence the enzymatic activity of bromelain since the results (10.31-11.92 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) did not show significant differences (Figure 6a). In general, heat treatments maintained or decreased the enzymatic activity of bromelain. The whole pineapple core samples did not show significant differences between the thermal treatments at 30 \({}^{\circ}\)C (7.35 \(\pm\) 0.67 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) and 40 \({}^{\circ}\)C (6.25 \(\pm\) 0.98 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) with a storage time of 24 h, although the samples showed a reduction in the enzymatic activity of bromelain 36% and 46%, respectively, compared (Figure 6a) with the raw material (11.56 \(\pm\) 0.88 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter). The maximum value of enzymatic activity (12.33 \(\pm\) 0.60 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter) was obtained for the sample with heat treatment at 30 \({}^{\circ}\)C, without other abiotic stress (wounding or storage time), although there are no significant differences compared to the raw material (11.56 \(\pm\) 0.88 mg tyrosine\(\cdot\)min\({}^{-1}\) g\({}^{-1}\) dry matter). A study carried out [PERSON] and [PERSON] (2011) [59] with pineapple juice observed that the enzymatic activity of bromelain gradually decreased between 25 and 95 \({}^{\circ}\)C, although it presented activity stable to heating up to 85 \({}^{\circ}\)C. The addition of ethanolic extract of cashew leaves with polyphenols helped stabilizing bromelain activity due to the bromelain-polyphenol complex, that showed good resistance to heat treatment. In the present work, wounding in the pineapple core samples may have released phenolic compounds from the cell compartments, binding with bromelain. This bond may be responsible for the increase in temperature resistance since the stresses did not promote a measurable increase in the enzymatic activity of bromelain. [PERSON] et al. (2000) [60] mentioned that bromelain did not lose activity after 120 min incubated at 37 \({}^{\circ}\)C and maintained 80% of activity when incubated at 45 \({}^{\circ}\)C. Additionally, if the heating is more intense (60 min at 75 \({}^{\circ}\)C), bromelain is almost completely inactivated. [PERSON], [PERSON], and [PERSON] (2007) [61] also found that there was no loss of bromelain enzyme activity when incubated at 37 \({}^{\circ}\)C for 180 min or at 55 \({}^{\circ}\)C for 60 min, but at a higher temperature (60 \({}^{\circ}\)C, 30 min) bromelain still held 80% of its initial activity. In agreement with the results obtained in the above-mentioned studies, in the present work and for the same temperature range the by-products of pineapple core also maintained the initial enzymatic activity, although in some cases there was a decrease (6-32%). Figure 6: Effect of abiotic stresses, heat treatment and wounding, on the enzymatic activity of pineapple core: (**a**) bromelain activity; (**b**) phenylalanine ammonia-lyase activity (PAL); and (**c**) polyphenol oxidase activity (PPO). Error bars stand for \(\pm\) standard deviation (n = 9). Different letters express significant differences between samples.