Volatile Metabolite Changes in ‘Ambrosia’ Apple Fruit Associated with Soft Scald Development

Soft scald is a postharvest storage disorder that affects some cultivars of apples (Malus domestica) and can cause substantial losses during storage. Delayed cooling treatments following harvest that consist of holding fruit at 20C for 4 to 7 days have been shown to be effective in reducing the development of soft scald. However, little is known of the mechanisms underlying the postharvest development of soft scald or its mitigation. Therefore, this study was conducted to explore the impact of delayed cooling on fruit volatile metabolism and its potential relationship with soft scald development. To explore these relationships, ‘Ambrosia’ apple fruit were harvested from 3 commercial orchards in British Columbia, Canada that historically had issues with the expression of soft scald during storage. Fruit from each orchard were either placed directly into cold storage at 0.5C or subjected to a delayed cooling treatment of 20C for 4 days prior to cold storage. Expression of soft scald during 3 months of storage was evaluated on 24-apple samples. In addition, headspace volatile compounds were repeatedly sampled from 6 individual apples from each orchard and treatment after 0, 1, and 3 months of storage using volatile collection tubes. Volatiles were analyzed using gas chromatography-mass spectroscopy on both wax and VF5 analytical columns. Chromatograms were analyzed using an untargeted analysis procedure. Using a hierarchal cluster analysis with group averages based on Euclidian distances, compound groups were identified for each of the analyses. Principle component analysis (PCA) revealed a shift in volatile composition during storage and in response to the delayed cooling treatment. Relationships of fruit volatile metabolism with scald expression and changes in proteins will be discussed.