Efficacy of Diphenylamine, Ultra-low Oxygen, and Ethylene Scrubbing on Scald Control in `Delicious' Apples

Incidence of scald in nontreated and DPA (2000 mg·liter -1 )-treated 'Delicious' apples (Malus domestics Borkh.) was assessed after 8.5 months in 1.5% or 0.7% O2 plus 1.5% CO2 at 0.2C, with and without C2H4 scrubbing. Incidence of scald was high in non-DPA fruit held in 1.5% O 2, and DPA treatment reduced scald in fruit held in 1.5% or 0.7% O2. Scald control was better with 0.7% O 2 and no DPA 'treatment than with 1.5% O2 and a DPA dip. Ethylene scrubbing had no effect on scald in fruit held in 0.7% or 1.5% 0 2. Susceptibility of fruit to scald-and flesh browning exhibited seasonal variation, which was related to the differences in fruit maturity and the amount of watercore at harvest, respectively. Chemical name used: diphenylamine (DPA). Control of scald in sensitive apple cultivars, such as 'Deli- cious', is achieved by treating the fruit with DPA or 6-ethoxy- l,2,-dihydro-2,2,4-trimethyl quinoline (ethoxyquin) immedi- ately following harvest (Hardenburg, 1965; Smock, 1955, 1957). Recent concerns about the effects of chemicals on human health and the environment are creating uncertainty over the long-term future use of DPA and ethoxyquin. Therefore, a search for non- chemical control of apple scald is required. One approach has been low O2 (Chen et al., 1985; Little and Taylor, 1981; Pat- terson and Workman, 1962; Roberts et al., 1963), another low C2H4 (Dover, 1985; Knee and Hatfield, 1981; Liu, 1977). British Columbian-grown 'Delicious' could benefit from the use of low O2 for controlling scald because it does not develop much purple-brown skin discoloration in low-O 2 atmospheres (Lau, 1990). 'Delicious' apples stored in 0.5% O 2 plus 1.5% CO2 at 0.5C for 7 months followed by 2 months in air at 0C and 7 days in air at 20C had a skin discoloration incidence of 8% compared to 61% in 'Spartan' and 44% in 'McIntosh'. The purpose of the present study was to determine the effi- cacy and potential problems associated with the use of low-O 2 atmospheres (1.5% or 0.7%), DPA treatment (2000 mg·liter -l