The effects of modified atmosphere packaging on core browning and the expression patterns of PPO and PAL genes in ‘Yali’ pears during cold storage

• MAP was applied to regulate the core browning of ‘Yali’ pear stored at 0 °C.
• MAP (10 μm thickness) reduced core browning.
• Phenolic content and PPO activity were significantly influenced by MAP.
• PAL1, PAL2 and PbPPO1 played an important role on core browning.

Pear fruits often experience core browning when exposed to excessive CO2 during storage. Therefore, it is critical to understand the mechanism of this process to optimize atmospheric conditions during postharvest pear storage. In the present study, the browning process, phenolic content, polyphenol oxidase (PPO) activity and expression profiles of phenylalanine ammonia-lyase (PAL) and PPO genes in the core tissue of ‘Yali’ pears (Pyrus bretschneideri Rehd cv. Yali) were investigated under modified atmosphere packaging (MAP). The results showed that MAP1 (with a thickness of 10 μm) reduced core browning, retarded the peak appearance of PPO activity and phenolic content, and inhibited the expression of PbPAL1, PbPAL2, and PbPPO1 genes in core tissue relative to the control (which had no packaging), but MAP2 (with a thickness of 30 μm) exerted the opposite effects during cold storage (0 °C). There was no significant relation between PbPPO4, PbPPO5 and PbPPO6 expression in core tissue and core browning. These results suggested that MAP1 was suitable for cold storage and that the PbPAL1, PbPAL2 and PbPPO1 genes might be involved in core browning under modified atmosphere storage in ‘Yali’ pears.