## 3 Results and Discussion
### Phenolic Compounds  
3.4.1. Total Phenolic Content (TPC)  
Phenolic compounds, naturally present in foods, are good antioxidants and have beneficial effects on health [29; 45]. The impact of different drying processes can be seen in Figure 2.  
In our study, the TPC of fresh apple has the highest value of gallic acid equivalents (GAE)/100 g of dry matter (d.m.), due to the absence of processing that could degrade phenolic compounds. The solar drying process results in the lowest TPC among all treatments. Oven drying at 65 \({}^{\circ}\)C preserves phenolic content significantly better than solar drying. Oven drying at 85 \({}^{\circ}\)C shows even higher retention of phenolic compounds compared to SD and OD65 \({}^{\circ}\)C, potentially due to shorter drying times reducing the degradation. CC samples have a moderate TPC value, which is lower than oven drying samples but higher than solar drying. CF samples retain phenolic content almost as high as the fresh samples. This suggests that commercial chips undergo processing that moderately affects phenolic content, possibly involving heat exposure or additives; however, the characterization of the apple from which these snacks originate is unknown.  
In summary, fresh and OD85\({}^{\circ}\) samples are statistically similar; OD65\({}^{\circ}\) and CF have similar values but differ from fresh and OD85\({}^{\circ}\). SD is significantly lower than all other tested samples, which could be related to the type of dryer, which provokes a higher exposure to oxygen due to the circulation of the air, resulting in greater degradation [46]. The same results were stained by [PERSON] et al. (2019) [25] in cabin-dried samples. In the oven-dried samples, TPC values do not seem to be clearly affected by the temperature diferen  
Figure 2: Total phenolic content (TPC) of fresh apple, samples dried with different methods (SD—solar; OD65\({}^{\circ}\)—oven at 65\({}^{\circ}\); OD85\({}^{\circ}\)—oven at 85\({}^{\circ}\)) and commercial samples (CC—commercial white label; CF—commercial label). Data are expressed as mean \(\pm\) standard deviation (n = 3). Values with the same lowercase letters are not significantly different (\(p<0.05\)).  
According to the bibliography the TPC values can present a high variation [19; 20; 25; 47], which could be related to which part of the apple is utilized, whether the whole apple, with or without peel; the apple peel is more rich in phenolic compounds [19; 47; 48; 49; 50]. It is common for TPC to become concentrated during dehydration, due to the loss of water, although partial degradation of sensitive compounds or conversion into oxidized or modified forms can also occur. Exposure to certain temperatures can promote the loss of phenolic compounds in dried food [45], because they are sensitive to high temperatures [19; 30]. [PERSON] et al. [51] also reported that an increase in drying temperature produced higher degradation of total phenolics with respect to content in fresh apples, but [PERSON] and [PERSON] [52] and [PERSON] et al. [4] showed an increase in TPC in dried apples of the varieties they studied. Thermal treatment can provoke the disruption of cell compartments and enzymatic degradation, denaturation and inactivation [53], which decreases the content and bioactivity of phenolics of a big variety of fruits and vegetables [54] (Tables S21 and S22).