Phenylalanine Alleviates Postharvest Chilling Injury of Plum Fruit by Modulating Antioxidant System and Enhancing the Accumulation of Phenolic Compound

Abstract

Research background. Low temperature storage causes chilling injury (CI) in plum (Prunus domestica L.) fruits. Consequently, any treatments with beneficial effects on these symptoms would achieve attention. For this purpose, phenylalanine treatments were applied on ‘Stanley’ plum fruits. The main purpose of the present study was to investigate the influence of the exogenous application of phenylalanine on fruit quality, chilling tolerance, and antioxidant capacity of ‘Stanley’ plums during cold storage. Experimental approach. Phenylalanine at different concentrations were applied on ‘Stanley’ plums. Following phenylalanine application, plums were cold stored. Chilling injury, antioxidant capacity, electrolyte leakage, malondialdehyde, proline, and internal contents of anthocyanin, flavonoids, phenols, ascorbic acid, and some antioxidant enzymes were assessed. Results and conclusions. Phenylalanine treatment significantly alleviated chilling injury in plum fruits by enhancing antioxidant capacity and increasing the activity of phenylalanine ammonia lyase enzyme (PAL). Phenylalanine-treated fruits had higher levels of ascorbic acid, anthocyanin, flavonoids, and phenols, as well as a higher total antioxidant activity, than the control fruits during low temperature storage. Phenylalanine at 7.5 mM was the most effective treatment in enhancing the activity of PAL and the accumulation of phenolic compounds and in reducing the severity of chilling injury. Treatments delayed mass loss and maintained fruit firmness. In addition, the application of 7.5 mM phenylalanine improved the activities of antioxidant enzymes (superoxide dismutase, catalase, and ascorbate peroxidase), decreased the accumulation of hydrogen peroxide, and increased the endogenous content of proline. Moreover, phenylalanine maintained membrane integrity, manifested by a reduced electrolyte leakage and malondialdehyde accumulation. Novelty and scientific contribution. In the current study, chilling injury had a positive correlation with the activities of PAL and antioxidant enzymes. However, negative correlations were observed between chilling injury and ascorbic acid content and antioxidant capacity. Considering the results, phenylalanine treatment could be spotted as an encouraging approach to alleviate the severity of chilling injury and thus preserve nutritional quality of plums during low temperature storage.