Mitigating postharvest chilling injury in Orlando tangelo fruit: potential of melatonin and GABA in enhancing the antioxidant system

Orlando tangelos are highly susceptible to low temperatures, which can cause chilling injury and result in significant peel depressions that make them unsuitable for commercial purposes. Melatonin and gamma-aminobutyric acid (GABA) act as an eco-friendly treatment to improve plant reactions to stress factors. The impact of melatonin, GABA, and their co-application (melatonin + GABA) on chilling tolerance and postharvest quality of Orlando tangelo fruit was investigated throughout the cold storage (90 days at 3 +/- 0.5 degrees C plus 5 days at 20 degrees C, shelf life). The results of the study indicated that the application of treatments significantly enhanced the chilling tolerance of Orlando tangelo fruit as compared to the untreated fruit. Fruits treated with melatonin + GABA did not exhibit indications of chilling until 90 days after storage. At this stage, the chilling injury of the control fruits was approximately 84.3% greater than those treated with melatonin + GABA. In addition, the treated fruits exhibited a reduced weight loss and malondialdehyde (MDA) concentration compared to the control. The study showed that fruits treated with melatonin exhibited a significantly increased (2.09 mg/g) total phenol content compared to the control (1.34 mg/g) fruits. All treatments significantly enhanced the flavonoid, antioxidant capacity, peroxidase (POD), and catalase (CAT) activity of the fruit compared to the control. A co-application of GABA and melatonin had a more significant impact on protecting the quality of the fruit during cold storage compared to using each treatment separately.