## 3 Results and Discussion
### pH, Titratable acidity (TA) and Soluble Solids Content (SSC)  
The pH readings of fresh, SD, OD65\({}^{\circ}\), OD85\({}^{\circ}\), CC and CF samples are listed in Table 2. All the samples, except SD, had a pH value higher than fresh ones (3.82) and there are significant differences between them (\(p\) < 0.000078) (Tables S13 and S14). Titratable acidity is considered amongst the best predictors of sensory attributes, acid taste, overall flavor and apple flavor [34] and it is a quality feature of the fruit, distinguishing sweet from sour apples [35]. For the \"normal acidity\" apple category, TA can range between 0.4 and 1.0% [36], but the sweet taste of an apple perceived during the eating experience depends also on the amount of acids present. [PERSON] and [PERSON] [37] considered that the typical malic acid content for apple fruit is between 0.27 and 1.02%. The TA of fresh and SD samples was 0.8% and the highest percentages were 1.3% in both OD65\({}^{\circ}\) and OD85\({}^{\circ}\). In commercial samples we have registered acidity of 0.4% and 0.7% for CC and CF samples, respectively. There are significant differences between them (\(p\) < 0.000001) (Tables S15 and S16). The increase in TA values is probably due to the organic acids in apples that become more concentrated with the high temperature [38]. The importance of SSC and TA in the prediction of consumers' acceptance of products leads to the development of some indices that show their correlation [39]. The increase in SSC and the reduction in TA result in an increase in the SSC/TA ratio, which is associated with consumer acceptance of the fruits. This index is used to determine the taste [40]. The soluble solids content (SSC) is the best objective predictor of sweetness [41] and in our analysis varies from 14.3 to 33.8 \({}^{\circ}\)Brix (all the values are significantly different), which \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **pH** & **TA (\% Malic Acid)** & **SSC (\({}^{\circ}\) Brix)** & **SSC/TA Ratio** \\ \hline fresh & 3.8 \(\pm\) 0.1 \({}^{\text{b,c}}\) & 0.8 \(\pm\) 0.1 \({}^{\text{b}}\) & 14.3 \(\pm\) 0.6 \({}^{\text{f}}\) & 18.9 \(\pm\) 1.2 \({}^{\text{c}}\) \\ \hline SD & 3.8 \(\pm\) 0.1 \({}^{\text{c}}\) & 0.8 \(\pm\) 0.1 \({}^{\text{b}}\) & 22.1 \(\pm\) 0.1 \({}^{\text{e}}\) & 29.3 \(\pm\) 2.9 \({}^{\text{b}}\) \\ \hline OD65\({}^{\circ}\) & 3.9 \(\pm\) 0.1 \({}^{\text{a,b}}\) & 1.3 \(\pm\) 0.1 \({}^{\text{a}}\) & 28.0 \(\pm\) 0.2 \({}^{\text{c}}\) & 21.6 \(\pm\) 1.2 \({}^{\text{b,c}}\) \\ \hline OD85\({}^{\circ}\) & 3.9 \(\pm\) 0.1 \({}^{\text{a,b}}\) & 1.3 \(\pm\) 0.2 \({}^{\text{a}}\) & 26.7 \(\pm\) 0.3 \({}^{\text{d}}\) & 20.9 \(\pm\) 3.4 \({}^{\text{c}}\) \\ \hline CC & 4.0 \(\pm\) 0.2 \({}^{\text{a}}\) & 0.4 \(\pm\) 0.1 \({}^{\text{c}}\) & 33.8 \(\pm\) 0.1 \({}^{\text{a}}\) & 24.5 \(\pm\) 1.5 \({}^{\text{b,c}}\) \\ \hline CF & 4.0 \(\pm\) 0.1 \({}^{\text{a}}\) & 0.7 \(\pm\) 0.1 \({}^{\text{b}}\) & 31.5 \(\pm\) 0.5 \({}^{\text{b}}\) & 44.3 \(\pm\) 5.4 \({}^{\text{a}}\) \\ \hline \hline \end{tabular} Data are expressed as mean \(\pm\) standard deviation (\(n\) = 3). Values with different lowercase letters in same parameter column are significantly different (\(p\) < 0.05). The samples were used dehydrated before liophilization.  
\end{table} 
Table 2: pH, titratable acidity (TA) and soluble solids content (SSC) 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). Figure 1: Scanning electron microscope images of the surface 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). for fresh samples is in agreement with the literature on the _Royal Gala_ cultivar [42; 43].