Peroxidase and polyphenoloxidase activities in relation to flesh browning of stem-end and calyx-end tissues of ‘Empire’ apples during controlled atmosphere storage

• 1-MCP treatment increase flesh browning of ‘Empire’ apples.
• Browning begins first at stem end of fruit.
• PPO and POX activities, and total phenolic concentration (TPC), were measured.
• Changes of enzyme activities and TPC in stem and calyx end tissues are inconsistent.
• Browning is not closely related with enzyme activities or TPC.

Incidence of a physiological disorder expressed as flesh browning of ‘Empire’ apples (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) during controlled atmosphere storage can be increased by treatment of fruit with 1-methylcyclopropene (1-MCP). Flesh browning incidence develops earlier in the stem-end than calyx-end region of the fruit. In this study, the color, activities of polyphenol oxidase (PPO) and peroxidase (POX), and the total phenolic concentrations in the two tissue zones of fruit stored under CA conditions for 36 weeks have been investigated in fruit from two harvests (H1 and H2), two weeks apart. Flesh browning incidence was similar in fruit from both harvests after storage. At harvest, PPO activity was higher in calyx- than stem-end tissues while POX activity was higher in calyx- than stem-end tissues only at H1. During storage, the average PPO and POX activities were higher overall in fruit from H2 than H1, and PPO activity was higher in calyx-end than stem-end tissues. However, inconsistent patterns of change of PPO and POX activities were found in response to 1-MCP treatment and storage time. Total phenolic concentrations at harvest were higher in H2 than H1 fruit but during storage increased in H1 to higher concentrations than in H2 fruit. Overall, no evidence for close involvement of phenolics and/or PPO and POX activity in the development of flesh browning disorders was detected in this study.