Fuji and Delicious apple volatile production during high CO₂ or low O₂ controlled atmosphere storage

Christie L. Lumpkin

Apple fruit [Malus sylvestris var. domestica (Borkh.) Mansf.] contain many diverse biochemical pathways that are differentially regulated according to development and ripening. From these pathways numerous volatiles contributing to apple aroma are produced. Although apple fruit have an extended storage life, improper storage conditions increase the risk of physiological disorder development that decreases fruit quality during and after storage. This study examined the impact of high CO2 or low O2 controlled atmosphere on apple volatile production and disorder development. Volatile production and quality changes were monitored in ‘Fuji’ and ‘Delicious’ apples during long term controlled atmosphere (CA) storage at high CO2 (0.5, 1.5, or 5.0 kPa, 1 kPa O2) or low O2 (0.3, 0.8, 1.6 kPa, 1 kPa CO2), respectively. A regular atmosphere (RA) control was also used for each cultivar. Volatile samples collected onto solid sorbent traps by sampling storage chamber headspace were analyzed using GC-MS. CA storage conditions prolonged storage life, reducing ethylene production, disorder incidence, and losses in firmness, soluble solids, and titratable acidity. Volatile production differed quantitatively by O2 and CO2 concentration and storage duration, and overall production trends from measuring volatiles during storage were similar to those reported from measuring after storage. Differences in volatile production were greatest during the first 2 months of ‘Fuji’ storage and the first 6 months of ‘Delicious’ storage, indicating that monitoring volatile production as an indicator for high CO2 or low O2 stress should occur in the first 2-6 months, depending on the cultivar. CO2 injury incidence was observed at 4 months and was highest in 5.0 kPa CO2 stored ‘Fuji’ apples. Methyl ester production increased with increasing CO2 in ‘Fuji’ apples and may be a potential indicator for CO2 stress injuries. ‘Delicious’ apple fruit stored at 0.3 kPa O2 had higher levels of stem browning, but overall incidence was below 10%. Acetaldehyde, ethyl esters, and ethanol levels increased with decreasing O2 and could be used to monitor low O2 stress. Additionally, one could measure the rate of ethanol accumulation to monitor low O2 stress, as ethanol content also increased with decreasing O2.

Fuji and Delicious apple volatile production during high CO₂ or low O₂ controlled atmosphere storage

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