Antioxidant metabolism in stem and calyx end tissues in relation to flesh browning development during storage of 1-methylcyclopropene treated ‘Empire’ apples

Abstract Development of firm flesh browning, a physiological disorder, in ‘Empire’ apples during long term controlled atmosphere (CA) storage, can be enhanced by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception. The disorder develops earlier in stem-end tissues than in calyx-end tissues. The antioxidant scavenging systems in the tissue zones of fruit stored under CA conditions (2 kPa O 2 /2 kPa CO 2 ) at 3 °C at 6 and 10 months were investigated. Flesh tissue browning as indicated by lightness and hue angle was greater in 1-MCP treated than in untreated fruit, and in stem-end tissues than in calyx-end tissues. 1-MCP treatment decreased superoxide production as indicated by nitroblue tetrazolium (NBT) reducing activity but increased H 2 O 2 concentrations, while treatment effects on malondialdehyde concentrations were inconsistent. Ascorbic acid (AsA) and glutathione (GSH) concentrations declined during storage, regardless of 1-MCP treatment, but were lower in stem-end tissue than in calyx-end tissue. While ascorbate peroxidase (APX) activity was not affected by 1-MCP treatment, its activity in untreated fruit was lower in stem-end tissues than in calyx-end tissues. The activities of superoxide dismutase (SOD) and copper/zinc-superoxide dismutase (Cu/Zn-SOD) increased during storage. The activities of catalase (CAT) and peroxidase (POX) decreased in 1-MCP treated fruit but effects on activities of other enzymes were inconsistent. Overall, higher browning may be associated with lower AsA and GSH concentrations in stem-end tissues, but the enhanced browning resulting from 1-MCP treatment does not appear to be directly related to antioxidant metabolism.