Flesh browning development of 'Empire' apple during a shelf life period after 1-methylcyclopropene (1-MCP) treatment and controlled atmosphere storage

Little information is known about metabolism of flesh browning disorders in apples after removal of fruit from cold storage. 'Empire' apples develop a firm flesh browning, a physiological disorder that is assumed to be a chilling injury because it occurs usually at 0.5 degrees C; however, incidence is increased in fruit at warmer storage temperatures (2-3 degrees C) if fruit have been treated with 1-methylcyclopropene (1-MCP). In this study, fruit were untreated or treated with 1-MCP and stored in controlled atmospheres at 0.5 or 3 degrees C for 40 weeks, followed by a 10 d shelf life period at 20 degrees C. The greatest increase of internal ethylene concentration (IEC) and softening occurred in the fruit that had been stored at 3 degrees C without 1-MCP, and the lowest in fruit from 0.5 degrees C plus 1-MCP. Flesh browning was present in 1-MCP treated fruit and in fruit stored at 0.5 C at the time of removal, and low in fruit stored at 3 degrees C. Incidence and severity of the disorder in 1-MCP treated fruit stored at 3 degrees C increased greatly during the shelf life period. Electrolyte leakage was higher in 1-MCP treated fruit stored at 0.5 degrees C than in the other treatments. Polyphenol oxidase (PPO) activity was higher in 1-MCP treated fruit regardless of storage temperature but peroxidase (PDX) activity was higher in fruit that had been stored at 0.5 degrees C regardless of 1-MCP treatment. The highest PDX activity was measured in the fruit that had been stored at 0.5 degrees C without 1-MCP treatment. Overall, browning development during the shelf life is associated with higher PPO activity in 1-MCP treated fruit and higher PDX activity at the lower storage temperature.