## 3 Results and Discussion
### Phenolic Content  
The phenolic content of apples was measured by HPLC-MS/MS analysis, and the content of each detected phenolic is reported in Table 2. The phenolic content of Pink Lady apples was 2.14 mmol kg\({}^{-1}\) f.w. (144 mg kg\({}^{-1}\) f.w. ), which is in agreement with the range that was reported in previous studies [11; 30]. In order to verify whether the DBD plasma treatment carried out in the experimental conditions of this study could have determined a significant decrease of polyphenols, the product was over-treated for 120 (60 + 60) min of processing, whereby a significant decrease (17% ca.) of total phenolic was observed. At the investigated treatment time suitable for fresh-cut apple stabilization [25], the treatment was found to significantly affect the total phenolic content of apples, with a significant increase (21% ca.) after 10 (5 + 5) min of processing, which reduced slightly in the 20 (10 + 10) min treated sample, and after 30 (15 + 15) min, reached values not significantly different from those of raw apples (Table 2). Specifically, the initial phenolic increase after 10 min of processing was mainly due to a significant increase of procyanidin B trimer, flavonoids, hydroxycinnamic acids, and phloretin xylosyl glucoside. The increase of procyanidin B trimer was the most outstanding in relative terms and corresponded, in molar terms, to a reduction of catechin, epicatechin, and dimers B1 and B2, suggesting the occurrence of polymerization reaction. When calculated as a percentage of total procyanidins, the content of trimeric procyanidins increased, while those of dimeric and monomeric procyanidins decreased. According to [PERSON] et al. [31], the formation of procyanidins upon catechins polymerization occurs in apples due to both enzymatic and chemical oxidation reactions; the latter could easily take place during plasma treatment due to the action of radical species and the availability of oxygen in the atmosphere. Procyanidins with high molecular weight (from tetramers to decamers) where not found in this study, while oligomers up to dodecamers have been previously observed in Red Delicious apples. This difference may be due to the different extraction procedure used for the HPLC-MS/MS analysis. Specifically, in the present study, methanol:water was used for the extraction of polyphenols from the freeze-dried samples, while the compounds with higher molecular weight were generally extracted using acetone:water mixtures [32]. The increase of trimer concentration could also have other explanations, since the extraction of procyanidins in apples could be favored by the activity of some carbohydrate-hydrolyzing enzymes, such as pectinase, cellulase, hemicellulose, and glucanase, which help the release of polyphenols complexed with cell walls [33; 34; 35], which are mainly catechin and procyanidins. Indeed, polyphenols, which are mainly located in vacuoles, can form complexes with polysaccharides in the cell wall through non-covalent binding upon decompartmentalization [36]. As 10 min of cold plasma processing in the same experimental conditions of this study were found to slightly affect (12% ca. reduction) the enzymatic activity present in apples [25], it is not clear whether other naturally occurring apple enzymes (e.g., pectinases) are likely to exert their hydrolytic activity within this period of time. In this study, no increase in catechin and dimeric procyanidin was observed