Phenylalanine induces mango fruit resistance against chilling injuries during storage at suboptimal temperature.

Cold is the best means of prolonging fruit storage. However, tropical fruit are susceptible to cold storage. The mode of action of mango fruit tolerance to suboptimal cold temperature of 7 or 10 °C after postharvest application of 8 mM phenylalanine was investigated using transcriptomic and metabolomic analyses of mango fruit during suboptimal cold storage. Phenylalanine-treated fruit had less chilling injuries-black spot and pitting electrolyte leakage,-and reduced decay after suboptimal cold storage. Phenylalanine treatment induced genes related to plant-pathogen interactions, plant hormone signal transduction, and the phenylpropanoid pathway, increasing the levels of the flavonoids quercetin and kaempferol glycosides and anthocyanins, and antioxidant content. Reduced oxidation led to lower lipid peroxidation, and a reduction in fatty acid-degradation products, e.g., volatile aldehydes. Treatment with phenylalanine, therefore, enhances chilling tolerance of mango fruit through regulation of metabolic and defense-related pathways, maintaining high levels of flavonoids, and antioxidants enzyme activity, and reducing H2O2 content, lipid peroxidation, and volatile aldehydes.

Preharvest Application of Phenylalanine Induces Red Color in Mango and Apple Fruit's Skin.

Anthocyanins are secondary metabolites responsible for the red coloration of mango and apple. The red color of the peel is essential for the fruit's marketability. Anthocyanins and flavonols are synthesized via the flavonoid pathway initiated from phenylalanine (Phe). Anthocyanins and flavonols have antioxidant, antifungal, and health-promoting properties. To determine if the external treatment of apple and mango trees with Phe can induce the red color of the fruit peel, the orchards were sprayed 1 to 4 weeks before the harvest of mango (cv. Kent, Shelly, and Tommy Atkins) and apple fruit (cv. Cripps pink, Gala and Starking Delicious). Preharvest Phe treatment increased the red coloring intensity and red surface area of both mango and apple fruit that was exposed to sunlight at the orchard. The best application of Phe was 2-4 weeks preharvest at a concentration of 0.12%, while a higher concentration did not have an additive effect. A combination of Phe and the positive control of prohydrojasmon (PDJ) or several applications of Phe did not have a significant added value on the increase in red color. Phe treatment increased total flavonoid, anthocyanin contents, and antioxidant activity in treated fruit compared to control fruits. High Performance Liquid Chromatography analysis of the peel of Phe treated 'Cripps pink' apples showed an increase in total flavonols and anthocyanins with no effect on the compound composition. HPLC analysis of 'Kent' mango fruit peel showed that Phe treatment had almost no effect on total flavonols content while significantly increasing the level of anthocyanins was observed. Thus preharvest application of Phe combined with sunlight exposure offers an eco-friendly, alternative treatment to improve one of the most essential quality traits-fruit color.