3.2. pH
Table 1a shows the pH values of strawberries with different treatments during storage. Statistical analyses revealed that interactions of three factors (Day*Power*Time) were not
significantly important. However, significant levels of interactions were found between Day*Power (Table 1b) and Power*Time (Table 1c). In contrast to 90 W and CNT treatments, 30 W and 60 W had the lower pH values of 3.56 and 3.61, respectively (Table 1b). From the data in Table 1c, it can be seen that there was a significant difference between 30 W and other treatments for 10 min. A possible explanation for this difference in pH values might be related to high CO2 levels inside 90 W and CNT packages. High CO2 accumulation is an indicator of the high respiration and degrada-tion rates of organic acids ( Almenar et al., 2007; Holcroft & Kader, 1999; Zhao et al., 2007). These findings showed that 30 W and 60 W ultrasound treatments were effective in maintaining pH of strawberries during storage.