Hypobaric storage removes scald-related volatiles during the low temperature induction of superficial scald of apples

'Law Rome' and 'Granny Smith' apples were stored hypobarically in air at 5 kPa total pressure and also in air or controlled atmosphere (CA) at 1.5 or 3% O-2 with 0 or 3% CO2, for 8 months at 1 degrees C. Fruit were placed under hypobaric storage immediately after harvest or after 0.5, 1, 2, 3, 4, 5 or 6 months storage in air at 1 degrees C to determine the effects of delaying imposition of hypobaric storage on ripening and scald development and on the production of alpha-farnesene and its oxidation product 6-methyl-5-hepten-2-one (MHO). If fruit were placed under hypobaric conditions within 1 month after harvest, scald did not develop. After a 3-month delay, scald development was similar to that for fruit stored continuously in air. Both cvs. produced MHO which accumulated in their epicuticular wax when fruit were placed under hypobaric storage after a 1-month or more delay in air. MHO which had partitioned in the epicuticular wax of fruit stored hypobarically after 2 or more months delay was released upon transfer of fruit to atmospheric pressure of 20 degrees C; MHO accumulated and/or was produced in direct proportion to the delay prior to hypobaric storage. In another experiment with five apple cvs., the production rates of alpha-farnesene and MHO were low during hypobaric storage, but upon removal of fruit from storage after 7 months, the rates increased over a 7 day period in air at 20 degrees C and then sharply decreased afterward. After storage, a-farnesene and MHO production rates were similar and high for 'Law Rome','Mutsu','Red Delicious' and 'Golden Delicious' apples and were the lowest for 'Granny Smith'. Scald did not develop on any hypobarically stored fruit whereas it did on all cvs. except 'Golden Delicious' stored in air. It was proposed that hypobaric ventilation removes a scald-related volatile substance that otherwise accumulates and partitions into the epicuticular wax of fruit stored in air at atmospheric pressure. (C) 2000 Elsevier Science B.V. All rights reserved.