## 3 Results and Discussion
### Enzymatic Activity of Polyphenoloxidase, Peroxidase and Browning Index  
The presence of PPO and POD enzymes in the Deglet-Nour date has been already confirmed via the demonstration and the determination of their catalytic activity within this fruit [4; 5]. A significant decrease in PPO activity of 6 kJ m\({}^{-2}\) irradiated samples was noted throughout the whole storage period (Figure 3); it was affected by UV-C treatment. It may be that the expression of PPO gene was inhibited; indeed, the decrease in PPO activity in certain tissues of _Agaricus bisports_ has been correlated with the inhibition of expression of the PPO gene in these tissues [28]. The actual results are in agreement with those of [PERSON] et al. [29]. By applying doses of 0.25, 0.5 and 0.75 kJ m\({}^{-2}\) to strawberry fruit, these authors observed a decrease in PPO activity, and they obtained the lowest activity after 5 d of storage at 10 \({}^{\circ}\)C using 0.75 kJ m\({}^{-2}\). Indeed, irradiation has been used to control the adverse browning phenomenon by inhibition of PPO activity [30]. Figure 3: _Cont._  
The obtained results showed, for kJ m\({}^{-2}\), a decrease in POD activity versus control from the second month until the end of storage (Figure 3). However, 1 kJ m\({}^{-2}\) and 3 kJ m\({}^{-2}\) induced a slowdown of POD activity for the last three months of storage. POD activity increased in irradiated samples during the first month, as generally peroxidase activity is stimulated by the readily available phenolic substrates, wounding and physiological stress, which were induced in this case by radiation and manipulation of samples. No statistical significance was observed between the browning index values of treated and control dates during the first three months of storage, although the indexes of irradiated samples appeared to be lower (Figure 3). It was only in the fourth month that this difference was more significant in favor of a considerable reduction in browning indexes of irradiated samples, irrespective of the dose, in comparison with the control. Noting that, the analysis of results showed increased values of the browning index of all samples during storage, compared with the results of D\({}_{0}\) as initial analysis. However, this increase was more pronounced in the case of control samples, proving that UV-C slowed browning of Deglet-Nour dates, which resulted in a longer shelf-life during storage. Indeed, ascorbic acid is a highly effective inhibitor of enzymatic browning, especially since generally, its rate increases within stored Deglet-Nour dates following its exposure to abiotic stress such as storage under modified atmospheres [4]. The result is consistent with that of [PERSON] et al. [31], who found that browning was significantly reduced during 21 d of storage at 5 \({}^{\circ}\)C of peaches (_Prunus persica_ cv. [PERSON]) following exposure to 3, 5 and 10 min to UV-C radiation. Another study using comparable doses of UV-C reported the effectiveness of the low dose (0.5 kJ m\({}^{-2}\)) to preserve grapefruit from decay development, while the untreated control sample was marked by severe rind browning and necrotic peel [30]. It is also interesting to underline that the combination of UV-A and UV-C rays could exert a noticeable inactivation effect on PPO activity in apple juice, and the reduction in this enzyme activity was estimated at 32.58% [32]. A study conducted on coconut water revealed the effectiveness of UV-C irradiation to reduce the activity of PPO and POD enzymes in the exposed samples by 94 and 93%, respectively [27]. The exposition of potato slices to a combination composed of ascorbic acid, calcium chloride and UV-C significantly reduced the activities of PPO and POD [33].