Volatile emissions and chlorophyll fluorescence as indicators of freezing injury in apple fruit

Use of volatile emissions and chlorophyll fluorescence as indicators of fre ezing injury were investigated for apple fruit (Malus xdomestica Borkh.). ' Northern Spy' and 'Delicious' apples were kept at -8.5 degreesC far 0, 6, o r 24 h, and then at 20 degreesC. After 1, 2, 5, and 7 d at 20 degreesC, fru it were analyzed for firmness, skin and flesh browning, soluble solid conte nt, titratable acidity, ethanol, ethyl acetate, ethylene, respiration rate, and chlorophyll fluorescence. Freezing caused skin and flesh browning and a loss of fruit firmness, which was greater in 'Northern Spy' than in 'Deli cious'. In 'Northern Spy' fruit subjected to the freezing treatments, ethan ol and ethyl acetate concentrations mere as much as 37- and 300- fold great er, respectively, than in control fruit. 'Delicious' fruit showed similar p atterns of ethanol and ethyl acetate increase, but of lower magnitude, as a result of freezing. Higher fruit respiratory quotients were associated wit h increased ethanol and ethyl acetate concentrations. Ethylene production a nd chlorophyll fluorescence of fruit were reduced by freezing.