Methyl ester generation associated with flesh browning in ‘Fuji’ apples after long storage under repressed ethylene function

‘Fuji’ apples stored under depressed ethylene by 1-MCP treatment (1-MCP) or in CA storages with 1.5% or 5.0% CO2 (CAL or CAH) were profiled for volatile production related to flesh browning severity after 4, 6 and 8 months of storage. Among the volatiles observed, methyl esters correlated with browning area at the developing stage. This relationship was further demonstrated using apples harvested the following year. Expression levels of genes related to senescence and alcohol synthesis were compared and expression of MdPME2 tended to be higher in injured apples. However, methyl esters increased with MdPME2 levels only in healthy individuals, suggesting that pectin methyl esterase (PME) may regulate methanol liberation from pectin well before visible browning development. Thus, methyl ester generation reflected flesh browning of ‘Fuji’ apples, which may be associated with PME activation that induces methanol liberation and oxidative stress after long storage.