The action of ethanol in controlling superficial scald of apples

Studies over 3 seasons with Granny Smith apples suggest that ethanol vapour controls superficial scald by reducing the production of alpha-farnesene and preventing its breakdown to conjugated trienes. Ethanol at 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 bags 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 this treatment was 4.7 mg/mL. The above concentrations occurred early in storage and fell later. The concentrations of alpha-farnesene and conjugated trienes rose in the untreated apples but remained at low levels in the treated apples. There were close and highly significant inverse relationships between the concentration of ethanol in the juice and scald. The severity of scald was directly related to the concentrations of alpha-farnesene and conjugated trienes in the skin. After 4 months 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 amounts of ethanol (2.8 or 5.6 g/kg fruit) at the beginning of storage continued to accumulate alpha-farnesene during the post storage period at 20 degrees C but conjugated trienes did not increase.