## 4 Discussion  
It has been reported in the literature that different pre-treatments could have an influence on the color parameters of the treated products. [PERSON] et al. [24] showed an increase in the luminosity (L*) of kiwifruit samples treated with OD in trehalose solution, while no differences were observed when sucrose was used in the osmotic solution. Similarly, the PEF pre-treatment alone resulted in significant changes in the color parameters of kiwifruit samples [25]. However, in the present work, the effect of the pre-treatment was evaluated only in the combination with the drying process and did not show any statistical differences. The decrease in luminosity observed in the kiwifruit snack samples pre-treated with the combination of OD/PEF and PEF/OD and dried at 50 and 70 \({}^{\circ}\)C could be due to the increased release of enzymes, such as peroxidase (POD) and polyphenoxidase (PPO), and their substrates induced by the electroporation of the cell membrane [26] and by the leaching of pigments during osmotic dehydration [26]. Moreover, those samples also presented lower chroma parameter (C*) values which indicates a loss of color intensity. The drying temperature of 60 \({}^{\circ}\)C seems to be the most suitable for the maintenance of the kiwifruit fresh-like color. However, the color differences between the various samples, although significant in certain cases, do not indicate a negative effect of any of the applied treatments. Fruits and vegetables are good sources of natural antioxidants, containing carotenoids, vitamins, phenolic compounds, folate and flavonoids. One of the reasons why kiwifruit is widely appreciated by consumers is related to its high nutritional quality. Polyphenols are compounds which can influence the characteristics of plant materials, including color, bitterness and antioxidant activity [27]. Raw kiwifruit from the Jintao cultivar is particularly rich in polyphenols and, according to the literature, presents a value of TPC ranging from 139.5 to 143.8 mg GAE/100 g [28]. As previously summarized, both pre-treatments and temperatures applied in this work had a negative effect on TPC except for the kiwifruit chips exposed to the OD treatment and dried at 60 \({}^{\circ}\)C. In particular, it appears that PEF alone and in combination with OD as well as thermal treatment could influence the PPO activity by enhancing its reaction with polyphenols and oxygen, which involves the oxidative degradation of phenolic compounds as explained by [PERSON] et al. [29]. Conversely, higher TPC was observed for dried goji berries pre-treated with the combination of PEF (at different field strengths of 0.9, 1.8 and 2.8 kV/cm) and OD (60 min at 55 \({}^{\circ}\)C in a hypertonic multi-component solution) processes when decreasing the drying time at 60 \({}^{\circ}\)C [15]. [PERSON] et al. [29] reported a loss in TP of around 48.8% for blueberries pre-treated with PEF at 3 kV/cm, with 200 pulses per second, a pulse width of 1 \(\upmu\)s and total treatment time of 5 min subsequently subjected to the OD process (fruit/syrup ratio of 1:2 at 40 \({}^{\circ}\)C), without further drying. Kiwifruit is rich in vitamin C, which represents the prevalent nutritional compound in this type of fruit; indeed, it accounts for about 130 to 170 mg/100 g and 68 to 104 mg/100 g, respectively, in Jintao and Hayward cultivars at the harvest time [30]. Moreover, vitamin C is a compound sensitive to oxidative reactions, which may be triggered by the high temperature and the presence of oxygen, so for this reason, it can be considered as an indicator of the overall quality of this kind of fruit during processing. It is stated from the literature that the increasing drying temperature and time provoke a decrease in vitamin C content in different types of fruit [31; 32; 33].