Background: Plum fruits constitute a good source of natural antioxidant substances. Particularly, plums contain large amounts of phenolic compounds and flavonoids that have natural antioxidant activity which is useful to human health. The study aimed to evaluate the effects of foliar sprays with salicylic acid (SA), putrescine (PUT) and moringa leaf extract (MLE) on the fruit quality attributes and bioactive compounds of 'Golden Japan' plums under cold storage conditions. Plum trees were sprayed twice; at fruit set stage and one month later during seasons 2018 and 2019 by combinations from SA (3 and 4 mmol/L), PUT (3 and 4 mmol/L) and MLE (5 and 10%), as well as distilled water (control). Fruits were harvested at maturity stage and stored at 0°C with relative humidity 85-90% for eight weeks.
Results: With advance storage period, fruit weight loss, total soluble solids (TSS), total carotenoids content (TCC) and total phenolics content (TPC) increased significantly while the fruit firmness, lightness (L*), hue angle (h°) of colour, titratable acidity (TA), total flavonoids content (TFC) and antioxidant activity (AA) decreased significantly (P < 0.05). Statistically significant differences were observed between different treatments in maintenance on all measured parameters when compared to control. At the same time, a combined SA at 3mmol/ L, PUT at 4 3mmol/ L and MLE at 10% treatment was found to be more effective than other treatments in decreasing the weight loss, softening and maintaining titratable acidity, total carotenoids, total phenolics, total flavonoids and antioxidant activity in plum fruits during storage at 0 °C.
Conclusion: It was concluded that preharvest treatment of plum fruits with salicylic acid, putrescine and moringa leaf extract was effective in delaying the ripening processes and can be used commercially to extend the storage life of postharvest plum fruits with acceptable fruit quality.