The effects of ultrasonication on the phytochemicals, antioxidant, and polyphenol oxidase and peroxidase activities in coffee leaves

•Ultrasound conditions affected alkaloids and phenolics differently in coffee leaves.•Triple-frequency (20/35/50 kHz) ultrasound inhibited phytochemicals and PPO activity.•Single frequency (35 kHz) ultrasound increased phenolics and inhibited POD.•PPO and POD were temporarily inactivated by ultrasound.•The activities of PPO and POD were recovered during the incubation period. In the present study, we investigated the impacts of ultrasonic conditions on the phytochemical profiles, antioxidant activity, and polyphenol oxidase (PPO) and peroxidase (POD) activities in coffee leaves. Ultrasonic frequency, power, and time, pH, and incubation time affected PPO and POD differently, thus resulting in different ABTS scavenging capacity and phenolic content in coffee leaves. Triple-frequency (20/35/50 kHz) ultrasound significantly (P