Melatonin Treatment to Pomegranate Trees Enhances Fruit Bioactive Compounds and Quality Traits at Harvest and during Postharvest Storage

Abstract

The effect of melatonin pomegranate tree treatments on fruit quality and bioactive compounds with antioxidant activity at harvest and during storage at 10 °C for 60 days was assayed in two consecutive years, 2019 and 2020. In the first year, trees were treated with 0.1, 0.3 and 0.5 mM of melatonin along the developmental fruit growth cycle, and results showed that bioactive compounds (total phenolics and total and individual anthocyanins) and antioxidant activity at harvest were higher in fruits from melatonin-treated trees than in controls. Other fruit quality parameters, such as firmness, total soluble solids and aril red colour, were also increased as a consequence of melatonin treatment. In fruit from control tress, firmness and acidity levels decreased during storage, while increases occurred on total soluble solids, leading to fruit quality reductions. These changes were delayed, and even maintenance of total acidity was observed, in fruit from melatonin-treated trees with respect to controls, resulting in a fruit shelf-life increase. Moreover, concentration of phenolics and anthocyanins and antioxidant activity were maintained at higher levels in treated than in control fruits during the whole storage period. In general, all the mentioned effects were found at the highest level with the 0.1 mM melatonin dose, and then it was selected for repeating the experiment in the second year and results of the first year were confirmed. Thus, 0.1 mM melatonin treatment could be a useful tool to enhance aril content on bioactive compounds with antioxidant activity and health beneficial effects and to improve quality traits of pomegranate fruit, at harvest and during postharvest storage.

Melatonin Pre-harvest Treatments Leads to Maintenance of Sweet Cherry Quality During Storage by Increasing Antioxidant Systems

“…However, melatonin treatment by foliar spray of apricot trees did not affect the on-tree ripening process although positive effects were observed on crop yield and fruit quality parameters at harvest, which were maintained during storage, either at chilling or non-chilling temperatures, as compared with apricots from control trees ( Abd El-Naby et al, 2019 ; Medina-Santamarina et al, 2021 ). Similar effects of melatonin pre-harvest treatments have been reported recently for ‘Mollar de Elche’ pomegranate ( Lorente-Mento et al, 2021 ).…”

“…In this sense, pre-harvest treatments of apricot tree with melatonin increased fruit quality parameters at harvest and these quality traits were maintained during storage ( Medina-Santamarina et al, 2021 ). Higher values of quality parameters, either at harvest or during storage, were observed on pomegranate fruit as a consequence of melatonin tree treatments during on-tree fruit development ( Lorente-Mento et al, 2021 ). In sweet cherry, 0.05, 0.1, and 0.2 mM melatonin applied on tree canopy (3, 2, and 1 weeks before harvest) resulted in fruit with higher TSS and lower TA in the ‘Hongdeng’ cultivar ( Xia et al, 2020 ), but no storage experiment was performed in this research.…”

Effects of Melatonin Treatment on Sweet Cherry Tree Yield and Fruit Quality

“…Postharvest melatonin treatments have shown a general trend on increasing phenolic content, including anthocyanins, and antioxidant activity in a wide range of fruit species, such as 'Santa Rosa' plum [44], strawberry [45], nectarine [46], tomato [17], litchi [47] and pomegranate [48]. Accordingly, preharvest treatment of pomegranate trees led to enhanced concentrations of total phenolics and total and individual anthocyanins as well as of total antioxidant activity in arils at harvest, showing that melatonin treatment stimulated the anthocyanin biosynthesis pathway [16].…”

“…In addition, enhanced apricot quality parameters at harvest and maintenance during storage, at chilling and not-chilling temperatures, have recently been reported in apricot fruits from melatonin-treated trees [15]. Accordingly, melatonin treatment of 'Mollar de Elche' pomegranate trees increased fruit quality traits at harvest, including anthocyanin and phenolic content, and overall fruit quality was maintained during storage at higher levels as compared with fruit from control trees [16].…”

“…Total anthocyanins were extracted by homogenising 5 g of flesh with 15 mL of methanol/formic acid/water (25:1:24, v/v/v). The extracts were centrifuged at 10,000× g for 10 min at 4 • C and the supernatant was used to quantify total anthocyanins by reading absorbance at 520 nm according to previous report [16]. The results were expressed as mg 100 g −1 of cyaniding 3-glucoside equivalent (cyn 3-glu, molar absorption coefficient of 26,900 L cm −1 mol −1 and molecular weight of 449.2 g mol −1 ).…”