Methyl salicylate pretreatment maintains quality and antioxidant capacity of fresh-cut pitaya fruit by modulating phenylpropanoid metabolism and antioxidant system

The effect of 0.1 mmol L-1 methyl salicylate (MeSA) pretreatment on quality properties of fresh-cut pitaya fruit and their relationships with phenylpropanoid metabolism and antioxidant system were studied. Results revealed that MeSA pretreatment efficiently inhibited flesh browning, respiration rate, ethylene production, electrical conductivity (EC) and malondialdehyde (MDA) content of fresh-cut pitaya fruit compared with the control. Moreover, the contents of total phenolics and flavonoids, antioxidant system, and the major phenolic acids (protocatechuic acid, chlorogenic acid and gallic acid) and flavonoid compounds (phloridin, kaempferol, rutin and epicatechin) were overall higher in MeSA-pretreated group than those in the control. Meanwhile, the gene expressions and activities of key enzymes (phenylalanine ammonia lyase (PAL), 4-coumarate-CoA ligase (4CL), cinnamic acid 4-hydroxylase (C4H)) closely related with phenolic biosynthesis were induced by MeSA, while polyphenoloxidase (PPO) and peroxidase (POD), key enzymes closely related to phenolic oxidation, were suppressed at lower activities in MeSA-pretreated group. In addition, MeSA pretreatment stimulated higher superoxide anion (O-2(center dot-)) generation rate and hydrogen peroxide (H2O2) content at the beginning of storage but led to lower levels of them afterwards. As for the antioxidant enzymes system and ascorbate-glutathione (AsA-GSH) cycle, superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) activities were all increased, while the losses of AsA and GSH were alleviated due to the application of MeSA. These results demonstrated that MeSA pretreatment maintained quality of fresh-cut pitaya fruit through modulating phenylpropanoid metabolism and antioxidant system.