A Melatonin Treatment Delays Postharvest Senescence, Maintains Quality, Reduces Chilling Injury, and Regulates Antioxidant Metabolism in Mango Fruit

Abstract

The effects of an exogenous application of various concentrations and dipping duration of melatonin (MT) treatment on postharvest senescence, quality, chilling tolerance, and antioxidant metabolism of mango fruit cv. “Dashehari” were examined. Fruits were treated with three concentrations of MT (50, 100, or 150 µM), each applied for three times (60, 90, or 120 min), followed by storage at 5 ± 1°C. The MT concentration of 100 µM with a dipping duration of 120 min was efficient in reducing the chilling injury and maintaining the quality of mango fruit for 28 d. Effects of this treatment were due to its effectiveness in reducing metabolic activity, specifically, respiration rate and ethylene production, resulting in higher firmness, titratable acidity, and ascorbic acid content and lower weight loss, total soluble solids, pH, and total soluble solid : acidity ratio. Moreover, it maintained a higher concentration of total phenolics and total flavonoids, as well as antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl and cupric reducing antioxidant power assays), as compared to other treatments. This was further confirmed with higher activities of antioxidant enzymes superoxide dismutase and catalase and membrane stability (according to a lower malondialdehyde content and lipoxygenase activity). Thus, our data show that a 100 µM MT administered for 120 min appears to be the most appropriate treatment to maintain the quality of mango fruits stored at chilling temperatures.

Melatonin Alleviates Chilling Injury Symptom Development in Mango Fruit by Maintaining Intracellular Energy and Cell Wall and Membrane Stability

“…We recently proposed that ethylene is the important factor that regulates CI in mango cultivars with MT treatment ( 7 ). Ethylene biosynthesis arises from higher ACC synthase ( ACS ) and ACC oxidase ( ACO ) gene expressions.…”

“…The sorted fruit was disinfected with 1% (v/v) sodium hypochlorite for 2 min followed by a random division of 300 fruit from each cultivar into six groups, consisting of 50 fruits in each group. The first three groups were immersed in distilled water (control) in three different buckets, and the other three groups were immersed in 100 µM MT (treated) for 2 h at 25 ± 2 • C under the low light conditions in three different buckets (7). After air drying for 2 h at 25 • C, the fruits were placed into storage at 5 ± 1 • C and RH 85-90%.…”

“…Each observation was recorded in triplicates and each replicate consisted of three fruits. For analyses, the fruit epicarp and mesocarp tissues were frozen with liquid nitrogen on the day of observation followed by storage at −80 • C. Besides this, a lot of 45 fruits from each treatment were used for recording CI symptom development at ambient conditions (25 • C, 90-95% RH) after 3 days of shelf life (7).…”

“…The low-temperature storage is the most commonly used technique to extend the shelf life and to assure the nutritional aspect and sensory quality of mangoes. Most Indian mango cultivars cannot tolerate temperatures below 13 • C due to the development of chilling injury (CI); the cultivars 'Langra' and 'Dashehari' are exceptions to some extent, tolerating exposure to 8-9 C. Symptoms of CI include abnormal (uneven) softening and color development, peel darkening and pitting, poor flavor due to lack of aroma, and lenticel prominence (4)(5)(6)(7). Therefore, methods that can alleviate CI may raise global marketing by reducing postharvest degradation and increasing shelf life.…”

“…Recently, postharvest preservation and quality maintenance of fruits and vegetables by MT have gained attention due to strong evidence for their role in delaying senescence and promoting tolerance against fungal decay (17)(18)(19). Furthermore, many studies have provided evidence that MT application demonstrates a prominent efficiency in conferring chilling tolerance in pomegranate (20,21), tomato (22)(23)(24), peach (10,(25)(26)(27), cucumber (28), litchi (29,30), bell pepper (31), plum (32), mango (4-7), and banana (33) fruits by (1) promoting endogenous MT accumulation accompanied by (2) promotion of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme activity and signaling H 2 O 2 accumulation, (3) enhancing ROS protection and scavenging systems activity, (4) preserving membrane unsaturation status by higher expression of fatty acid desaturase (FADs) genes, along with (5) lower expression of phospholipase D (PLD) and lipoxygenase (LOX) genes and enzyme activities, (6) promoting oxidative pentose phosphate, shikimic acid and phenylpropanoid pathways activity, (7) enhancing arginase pathway activity by activating the ZAT2/6/12-CBF1 signaling pathway for triggering endogenous nitric oxide, polyamines, proline, and γ-aminobutyric acid (GABA) accumulation, (8) enhancing intracellular energy adenosine triphosphate (ATP) and reducing power of NADPH supply, and (9) activating GABA shunt pathway activity.…”