Relationship between O2 levels, 1-Methylcyclopropene (1-MCP), coniugated trienes (CTs) and superficial scald in "Granny Smith" apples

Granny Smith apples were stored for 180 days at 0°C in 0.3%, 0.6%, 0.9%, 1.2%, 2.0% and 21%O2 (air) plus 0.01% CO2; some lots were postharvest treated with 625 ppb 1-methylcyclopropene (1-MCP). The influence of these treatments on conjugated trienes (CTs) and superficial scald as well as on ethanol content in the fruit tissue was evaluated. At harvest the CTs content in the peel, expressed as optical density (OD268), was 0.20 OD268. During storage, the OD remained substantially unchanged in apples exposed to 0.3% O2 (<0.35 OD268), and increased moderately in apples exposed to 0.6%, 0.9% and 1.2% O2 up to 1.42, 1.73 and 1.94 OD268 for 180 days. In apples stored in 2.0% O2 and in air (21% O2), the CTs contents had the highest increase and reached 4.6 and 11.5 OD268 respectively. In apples treated with 625 ppb 1-MCP the CT content in the peel was 0.66 OD268 at the end of storage. The first symptoms of superficial scald appeared after 60 days in air and after 120 days in 2% O2. At the end of the storage period no symptom was detected on the apples treated with 1-MCP and with 0.3%, 0.6% O2, whilst from 3 to 7% of the fruit kept in 0.9% and 1.2% was affected. Low O2 conditions induced the accumulation of ethanol in the tissue, the rate being considerably more marked in the 0.3% to 0.6% range and was linearly correlated to the time in storage. After 60 and 120 days of storage in 0.3% O2, the apples showed symptoms of hypoxic injuries and off-flavour while at higher values they were undamaged.