THE ACTION OF ETHANOL IN CONTROLLING SUPERFICIAL SCALD OF APPLES

Studies over 3 seasons with Granny Smith apples suggest that ethanol v apour controls superficial scald by reducing the production of alpha-f arnesene and preventing its breakdown to conjugated trienes. Ethanol a t the rate of 0.35-5.6 g/kg apples was placed in dishes together with 10 or 20 fruit in polyethylene bags (thickness 50 mu m). The bags were sealed and stored at 0 degrees C for 16-36 weeks. The polyethylene ba gs were found to be permeable to ethanol vapour. The levels of ethanol in the headspace of bag for maximum application rate was 11 mg/L with fruit and 86 mg/L without fruit. The maximum level in the juice for t his treatment was 4.7 mg/mL. The above concentrations occurred early i n storage and fell later. The concentrations of alpha-farnesene and co njugated trienes rose in the untreated apples but remained at low leve ls in the treated apples. There were close and highly significant inve rse relationships between the concentration of ethanol in the juice an d scald. The severity of scald was directly related to the concentrati ons of alpha-farnesene and conjugated trienes in the skin. After 4 mon ths of storage at 0 degrees C the alpha-farnesene content of untreated fruit declined during a 2-week period at 20 degrees C and conjugated trienes increased during this period. Fruit treated with higher amount s of ethanol (2.8 or 5.6 g/kg fruit) at the beginning of storage conti nued to accumulate alpha-farnesene during the post storage period at 2 0 degrees C but conjugated trienes did not increase.