Lower levels of PPO activity were observed in the samples treated with combined ultrasound and antioxidants (ascorbic acid or GSH) compared to the samples treated only with ultrasound.
The results were in agreement with Jang and Moon (2011), who observed that simultaneous treatment with ultrasound and ascorbic acid had a synergistic inhibitory effect on PPO in fresh-cut apple.
Fig. 1 also shows that the synergistic effect of ascorbic acid withultrasound was more pronounced than that of GSH with ultrasound.