Alleviating Effect and Mechanism of Cold Shock Pretreatment on Browning of Fresh-Cut Pitaya Fruit

The alleviating effect and mechanism of cold shock pretreatment (-2 ℃ cold air for 3 h) on flesh browning in fresh-cut pitaya fruit was explored by evaluating its effect on the phenylpropanoid pathway and antioxidant system during storage. Results revealed that cold shock pretreatment efficiently inhibited the increase in electrical conductivity and malondialdehyde (MDA) content compared with the control. Cold shock pretreatment promoted the gene expression and activities of key enzymes (phenylalanine ammonia lyase, cinnamic acid 4-hydroxylase, and 4-coumarate-CoA ligase) related to phenylpropane biosynthesis, and improved the accumulation of total phenolics and flavonoids, as well as most individual phenolic compounds, which led to enhanced antioxidant capacity. The activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were increased by cold shock pretreatment. In addition, cold shock pretreatment accelerated the production of superoxide anion and H₂O₂ at the early stage of storage, but had no effect on their peaks and led to lower levels of superoxide anion and H₂O₂ afterwards, alleviating flesh browning in fresh-cut pitaya fruit. These results indicated that cold shock pretreatment can effectively alleviate wound-induced oxidative stress by modulating the phenylpropanoid pathway and reactive oxygen species (ROS) metabolism, thus inhibiting flesh browning in fresh-cut pitaya fruit.