## 3 Results and Discussion
### Total Phenolic Content and Antioxidant Activity
#### 3.1.2 Pineapple Core
Different letters express significant differences between samples. Wound-induced signalling starts by damage, then the signalling migrates to the adjacent undamaged tissue and can change the metabolic activity promoting phenolics production as observed in fresh-cut lettuce (_Latuca sativa_ L) samples [42]. Plant tissue responds to damage by increasing respiration rate and ethylene production [43]. A study carried out with freshly cut carrot samples found that the increase in respiration occurs due to the synthesis of enzymes involved in the respiratory pathway [44]. Phenolic compounds also increase due to wound induction in the enzyme responsible for phenolic biosynthesis, phenylalanine ammonium lyase (EC 4.3.1.5). Phenolic compounds can be oxidized to quinones by another polyphenol oxidase enzyme (EC 1.10.3.1), which polymerizes and produce dark compounds as seen in wound lettuce samples [45]. The values of phenolic content from wounded pineapple core samples do not evidence the effect of damages on changing respiratory activity, metabolic activity, and the synthesis of the new bioactive compounds. The enzymatic activity promoted by the wounds was quantified in order to obtain more information about the phenomena that occurred in the samples of pineapple by-products. The total antioxidant capacity of fruits and vegetables may increase due to wounding, since the wounds induce the synthesis of phenolics and not the increase in antioxidant compounds such as ascorbic acid [46]. Wounding is one of the stresses most applied to freshly processed products. The shape of the cut is of great importance in the quality of freshly cut fruits and vegetables. The trapezoidal cut of melon was considered the best option for the panelists due to the balance between texture and translucency. On the other hand, the melon cylinders were firmer and had greater translucency during 10 days of storage [47]. The slices of papaya (_Carica papaya_ L.) presented 2 more days at 5 \({}^{\circ}\)C and 1 more day at 10 \({}^{\circ}\)C of shelf-life compared to the papaya cubes [48]. Contrary to the results obtained for total phenolic content, in the present work the antioxidant activity of pineapple core samples was favored by the wound, although the longer storage time (48 h) did not show increases in antioxidant activity compared to the shorter storage time (24 h). The phenolic compounds of fruits can be modified by oxidative reactions during processing and storage, namely by the antioxidant activity of phenols and as substrates for oxidative browning reactions. Phenolics can be reactive oxygen species and can act as substrates for polyphenol oxidases and as antioxidants for free radicals, which are the main oxidants in food [49]. Hot water treatment (45 \({}^{\circ}\)C for 10 min and storage at 4 and 25 \({}^{\circ}\)C) applied to kiwis showed advantages at the microbiological level and accumulation of reactive oxygen species. This heat treatment also promoted a significant increase in the activity of antioxidant enzymes and the content of total phenolic content [50]. In the present study, the content of phenolic content in the pineapple core samples was improved with the application of thermal treatments (40 \({}^{\circ}\)C for 10 min, storage during 24 h) alike what was observed for the test performed with kiwi fruit reported above. The antioxidant activity in the pineapple core was maximized by the treatment (30 \({}^{\circ}\)C for 10 min, storage during 24 h), although wounding caused a greater impact on this increase. [PERSON], [PERSON], and [PERSON] (2009) [51] observed polyphenic and antioxidant changes in mangoes after immersion in hot water (46.1 \({}^{\circ}\)C, 70-110 min, 4 days of storage at 25 \({}^{\circ}\)C). The polyphenic gallic acid and gallotannins, as well as total soluble phenolics, decreased due to long treatments in hot water, while the antioxidant capacity was maintained after the treatment. All treatments reduced total soluble phenolics and antioxidant capacity over 4 days of storage, regardless of treatment time.