Volatile Emissions and Chlorophyll Fluorescence as Indicators of Freezing Injury in Apple Fruit

Use of volatile emissions and chlorophyll fluorescence as indicators of freezing injury were investigated for apple fruit ( Malus × domestica Borkh.). 'Northern Spy' and 'Delicious' apples were kept at -8.5 °C for 0, 6, or 24 h, and then at 20 °C. After 1, 2, 5, and 7 d at 20 °C, fruit were analyzed for firmness, skin and flesh browning, soluble solid content, titratable acidity, ethanol, ethyl acetate, ethylene, respiration rate, and chloro- phyll fluorescence. Freezing caused skin and flesh browning and a loss of fruit firmness, which was greater in 'Northern Spy' than in 'Delicious'. In 'Northern Spy' fruit subjected to the freezing treatments, ethanol and ethyl acetate concentrations were as much as 37- and 300- fold greater, respectively, than in control fruit. 'Delicious' fruit showed similar patterns of ethanol and ethyl acetate increase, but of lower magnitude, as a result of freezing. Higher fruit respiratory quotients were associated with increased ethanol and ethyl acetate concentrations. Ethylene production and chlorophyll fluores- cence of fruit were reduced by freezing.