## 3 Results and Discussion
### pH, Titratable Acidity and Total Solids Content  
In Figure 3, the \(pH\) values obtained for the samples of fresh and dried apples are illustrated. It can be seen that the samples of fresh apple slices have average values between 4.02 and 4.19, while the \(pH\) values of dried apple chips decreased compared to the fresh samples and ranged from 3.85 to 4.02. [PERSON] [57] obtained, for the same apple cultivars, \(pH\) values between 3.68 and 4.20, while [PERSON] et al. [53] reported \(pH\) values between 5.34 and 5.60 for fresh samples. According to [PERSON] et al. [17] and [PERSON] et al. [58], decreases in \(pH\) values of dried apple samples may be associated with the dissociation of organic acids with temperature. The \(pH\) of dried apple chip samples during storage varies very little compared to the \(pH\) obtained for the freshly dried samples, and on the 21 st day of storage, the mean \(pH\) values were between 3.61 (S2) and 3.80 (F2). Perception of fruit taste is given by the apples' acidity. Moreover, it is considered that sour taste depends on organic acid contents such as malic or citric acids, while soluble solids content is responsible for the sweet taste [59]. According to [PERSON] and [PERSON] [35], the typical malic acid content in apple fruit is between 0.27 and 1.02%. In this study, the values obtained for the _TA_ of fresh apple samples from 'Golden Delicious' and 'Florina' cultivars fall between these values. The higher content of malic acid was registered in apple samples from the 'Golden Delicious' cultivar (0.33 \({}^{\text{a}}\)\(\pm\) 0.03% acid malic) followed by apple samples from the 'Florina' cultivar (0.29 \({}^{\text{b}}\)\(\pm\) 0.01% malic acid) and 'Starkrimson' cultivar (0.17 \({}^{\text{c}}\)\(\pm\) 0.03% acid malic). _TA_ values are close to those obtained by [PERSON] et al. [59]: 0.30% for 'Golden Delicious', 0.20% for 'Florina' and 0.10% for 'Starkrimson'. [PERSON] et al. [6] reported a titratable acidity for other apple cultivars that varied between 0.24 and 0.61%. Titratable acidity values of dried apple chip samples are presented in Table 1. It can be observed that all dried apple chip samples have higher values of _TA_ than fresh samples, regardless of cultivar or type of drying. The _TA_ values of dried apple chips increased compared to the _TA_ of fresh apple samples due to the organic acids in apples that become  
Figure 3: \(pH\) evaluation of fresh and dried apple chips during storage under ambient conditions (S1—apple chips ‘Starkrimson’, oven; S2—apple chips ‘Starkrimson’, dehydrator; G1—apple chips ‘Golden Delicious’, oven; G2—apple chips ‘Golden Delicious’, dehydrator; F1—apple chips ‘Florina’, oven; F2—apple chips ‘Florina’, dehydrator). Notes: 0*—fresh apple samples, 0—dried apple samples. Different lowercase letters (a–d) show significant differences between the groups (\(p<0.05\)). more concentrated as the temperature increases [58]. During storage, _TA_ values increase for all samples. The total solids content of fresh apple slices varies from 15.00 \({}^{\circ}\)Brix ('Golden Delicious's cultivar samples) to 16.46 \({}^{\circ}\)Brix ('Starkrimson' cultivar samples). These values are close to those obtained by [PERSON] [57]: 15.01 and 15.3 \({}^{\circ}\)Brix for 'Golden Delicious' and 'Starkrimson' cultivars available on the market in 2018. In the case of 'Florina' cultivar fresh samples, a mean value of 15.40 \({}^{\circ}\)Brix for _TSS_ (Figure 4) was obtained, a value close to that obtained by [PERSON] et al. [59] (15.00 \({}^{\circ}\)Brix) for apples of the same cultivar. [PERSON] et al. [53] reported _TSS_ values ranging between 13.0 and 15.3 \({}^{\circ}\)Brix for 'Starkrimson' apples, between 10.6 and 14.2 \({}^{\circ}\)Brix for apples from the 'Florina' cultivar and 12.2-15.8 \({}^{\circ}\)Brix for 'Golden Delicious' apples. The total solids content for three apple cultivars determined by [PERSON] et al. [60] varied from 13.78 to 17.61%, while [PERSON] et al.