A poststorage burst of 6-methyl-5-hepten-2-one (MHO) may be related to superficial scald development in 'Cortland' apples

'Cortland' apples (Malus xdomestica Borkh,), either untreated or treated wi th diphenylamine (DPA), were stored for 120 days in air at 0 degrees C. Pee l samples were taken from these fruit immediately after storage, placed in glass vials and incubated for 48 hours, or were isolated from fruit held 2 to 72 hours at 22 degrees C and incubated in the vials for 2 hours. Emissio n of 3,7,11-trimethyldodeca-1,3(E),6(E),10-tetraene, known as trans,trans-a lpha-farnesene, or simply alpha-farnesene, and its oxidation product, MHO, were measured in the vial headspace, alpha-Farnesene content in the gas pha se of vials with peel samples reached a maximal level 2 hours after vials w ere sealed and was higher in DPA-treated than untreated fruit. The content of alpha-farnesene in the vial headspace remained unchanged for DPA-treated fruit peel during the 2-day holding period, However, alpha-farnesene decli ned rapidly after 10 hours incubation for control samples. Incubating peel samples of control fruit under N-2 atmosphere prevented the decline in alph a-farnesene. The MHO release by the peel of control fruit was rapid during the first 2 hours and continued to increase for 24 hours. In contrast, the MHO released from DPA-treated fruit peels was 8000-fold lower than from pee l samples of control fruit. The increase in vapor phase MHO was concomitant with peel browning in controls, For whole fruit held at 22 degrees C for 2 to 72 hours, cumulative MHO release from fruit peels followed a pattern th at was similar to the pattern of superficial scald development in these fru it.