3.3. Acidity and pH
The effects of storage time on the acidity and pH are presented in Fig. 3 and Fig. 4. Results for acidity showed significant differences at all levels (Table 3). At −12 °C, at any time, acidity of samples showed a significant difference (5%) and at 24 °C, acidity was fixed at the first and last storage period. Study of acidity changes against storage time is important; in this study, acidity, volatile and aromatic acids are computed on the basis of the dominant acid (i.e. citric acid). Average pH showed, significant differences (5%) between 15 days, second and third months (Fig. 4). At −12 °C, in the final storage period, pH was above 3.4 and this could be one of the reasons for anthocyanin decrease at this temperature. At pH above 3.4, anthocyanin is destroyed (Sistrunk et al., 1983). Storage time, enzymatic and microbial changes have many effects on hydrogen ion concentration; therefore, pH is important in assessing the efficiency and quality of performing processing methods.