Melatonin treatment delays postharvest senescence and maintains the organoleptic quality of ‘Newhall’ navel orange (Citrus sinensis (L.) Osbeck) by inhibiting respiration and enhancing antioxidant capacity

•Melatonin treatment attenuates the rates of postharvest respiration, weight loss, and sensory quality deterioration as indicated by an increase in fruit firmness, total soluble solids, soluble sugar content, titratable acidity, and citrus color index (CCI) in ‘Newhall’ navel orange fruit.•Melatonin treatment inhibits the accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in postharvest orange fruit.•Melatonin enhances antioxidant capacity in ‘Newhall’ navel orange fruit by increasing the activity and expression of anti-oxidative enzymes including catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase further promoting the accumulation of antioxidants including ascorbate, reduced glutathione, and total phenol.•Principal component analysis (PCA) demonstrated that melatonin delayed postharvest senescence of orange fruit and was associated with inhibition of postharvest respiration and stimulation of oxidant-defense system.