Ultrasound treatment on phenolic metabolism and antioxidant capacity of fresh-cut pineapple during cold storage

• Ultrasound treatment stimulated PAL activity of fresh-cut pineapple.
• Hormetic dosage of ultrasound enhanced antioxidant activity of fresh-cut pineapple.
• Induction of PAL was correlated with higher total phenolic content.

Ultrasound treatment at different power output (0, 25 and 29 W) and exposure time (10 and 15 min) was used to investigate its effect on the phenolic metabolism enzymes, total phenolic content and antioxidant capacity of fresh-cut pineapple. Following ultrasound treatment at 25 and 29 W, the activity of phenylalanine ammonia lyase (PAL) was increased significantly (P < 0.05) by 2.0 and 1.9-fold, when compared to control. Meanwhile, both the activity of polyphenol oxidase (PPO) and polyphenol peroxidase (POD) in fresh-cut pineapple was significantly (P < 0.05) lower than control upon subjected to ultrasound treatment. In the present study, induction of PAL was found to significantly (P < 0.001) correlate with higher total phenolic content and thus higher antioxidant capacity in fresh-cut pineapple. Results suggest that hormetic dosage of ultrasound treatment can enhance the activity of PAL and total phenolic content and hence the total antioxidant capacity to encounter with oxidative stress.