1-methylcyclopropene and storage temperature influence responses of 'Gala' apple fruit to gamma irradiation

'Gala' apple (Malus x domestica Borkh.) fruit pre-treated with 0.5 muL L-1 1-methylcyclopropene (MCP) or air (control) for 12 h at 20 degreesC were exposed to gamma radiation at doses of 0, 0.44, 0.88 or 1.32 kGy at 23 degreesC. The fruit were then stored at 20 degreesC for 3 weeks or at 0 degreesC for 8 weeks plus 7 days at 20 degreesC. Fruit treated with MCP had higher firmness and titratable acidity (TA) than control fruit after storage at either temperature. During the post-irradiation storage at 20 degreesC, irradiation promoted respiration of MCP-treated fruit throughout the 3-week period but had no consistent effect on respiration of control fruit. Fruit firmness and TA decreased with increased radiation dose after 3 weeks storage at 20 degreesC regardless of MCP treatment. Compared to non-irradiated fruit, irradiated fruit had lower TA and similar firmness after storage at 0 degreesC for 8 weeks plus 7 days at 20 degreesC. Some irradiated fruit stored at 20 degreesC for 3 weeks developed internal browning, and MCP-treated fruit had more injury than control fruit. Storage at 0 degreesC after irradiation greatly reduced development of internal browning. Production of volatile esters, alcohols and 6-methyl-5-hepten-2-one by fruit stored at 0 degreesC was reduced. The magnitude of reduction directly increased with radiation dose. It appears that some responses of apple fruit to gamma radiation are influenced by ethylene action and post-irradiation storage temperature. Published by Elsevier Science B.V.