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

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 storag

γ-Aminobutyric acid treatments of pomegranate trees increase crop yield and fruit quality at harvest

γ-Aminobutyric (GABA) is a non-protein amino acid that has been reported to affect different plant developmental processes, including delay of fruit senescence and maintenance of quality when applied as postharvest treatment. In this experiment, GABA treatments (10, 50 and 100 mM) were applied by foliar spray to ‘Mollar de Elche’ pomegranate trees at three key points of fruit development. Results showed that GABA treatments increased crop yield in a dose-dependent way, this effect being due to a higher number of fruit harvested per tree. In addition, GABA treatments led to a deeper red colour of pomegranate skin and arils, the highest effects being observed for 100 mM dose. Total phenolic and total anthocyanin concentrations were also increased by GABA treatment, while other quality parameters such as total soluble solids, total acidity or firmness were not affected by treatments. Then, GABA preharvest treatment, applied at 100 mM, could be a useful tool to increase the economic profit of pomegranate crop, since higher yield and fruit with higher colour were obtained, which is an important quality parameter for this cultivar. In addition, aril total phenolics and anthocyanin content were increased, which would lead to enhance the antioxidant properties and health benefits for consumers