Coupling Melatonin and Ultrasound Modulates ROS Production, Antioxidant System, and Biochemical Attributes Linked to Oxidative Browning in Litchi Pericarp

Litchi (Litchi chinensis Sonn.) is a non-climacteric fruit with a red pericarp that browns after harvest, reducing market value. Pericarp browning is linked to oxidative stress caused by reactive oxygen species (ROS). This study explored the combined effects of ultrasound (US; 37 ± 3 kHz for 10 min) and melatonin (1 and 2 mM) on litchi pericarp browning during ambient storage. On last day of storage, US combined with 1 and 2 mM melatonin exhibited lowest pericarp browning compared to their individual application with a score of 2.54 and 3.64. The results suggest that, combined treatment of ultrasound and melatonin effectively mitigates oxidative stress with lower ROS accumulation and polyphenol oxidase activity. Additionally, higher levels of anthocyanins, polyphenols, antioxidants, and phenylalanine ammonia lyase activity were maintained. It also preserved fruit quality, including weight, soluble solids, and titratable acidity, while reducing decay suggesting combined treatment of ultrasound and melatonin effectively enhances the postharvest quality of litchi fruit with reduced pericarp browning.