Elevated 6-methyl-5-hepten-2-ol levels in storage room headspace precede superficial scald symptom development on ‘Granny Smith’ apples

Authors: LEE, JENWOOK - Chung-Ang University; LWIN, HNIN PHYU - Washington State University; Leisso, Rachel; MATTHEIS, JAMES - Retired ARS Employee; Rudell Jr, David

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2025
Publication Date: 3/31/2025
Citation: Lee, J., Lwin, H., Leisso, R.S., Mattheis, J.P., Rudell Jr, D.R. 2025. Elevated 6-methyl-5-hepten-2-ol levels in storage room headspace precede superficial scald symptom development on ‘Granny Smith’ apples. Postharvest Biology and Technology. 226. https://doi.org/10.1016/j.postharvbio.2025.113535.
DOI: https://doi.org/10.1016/j.postharvbio.2025.113535

Interpretive Summary: Superficial scald is a disorder that can contribute to significant annual losses of susceptible apple varieties such as ‘Granny Smith’. For conventional production, superficial scald can be controlled by crop protectants. Where crop protectant use is restricted, scald mitigation relies on controlled atmosphere (CA; low oxygen) to reduce symptom development. Atmospheric composition must be established soon after placement in the cold room and must be of adequately low oxygen for the best disorder control. Scald control effectiveness of storage conditions can be assessed by acquiring samples from storage rooms and analyzing peel metabolites associated with scald risk. Other scald-associated metabolites are volatile meaning they can be detected in the air around the apples and, hypothetically, used to assess scald risk without removing fruit from the room. We tested this potential using research CA rooms that scale up from smaller CA chambers typically used in cold chain research. We monitored and compared the headspace in rooms with adequate CA to control scald as well as conditions less likely to control scald such as where atmospheric establishment was delayed for 7 days or apples were stored in air. Using this process, we found one volatile metabolite associated with a storage environment that would later develop scald or a condition known to provide less scald control. With additional work, using this technique to monitor scald risk in commercial sized rooms would indicate to apple producers cold chain conditions that are not adequately controlling scald so that the room may be marketed first, before scald develops, or the storage conditions adjusted accordingly.

Technical Abstract: Metabolic changes in the apple peel occur prior to and during superficial scald symptom development. We expected changes of volatile organic compound (VOC) levels in the storage room headspace associated with these events to precede scald symptom development. To determine this, we compared the headspace over air stored (0.5 °C) ‘Granny Smith’ with that of hypoxic CA (0.5% O2/0.5% CO2; 0.5 °C) established immediately or following a 7 day delay. Apples were harvested at commercial maturity and internal ethylene concentration (IEC), a-farnesene, conjugated trienols (CTOL), headspace VOCs, and superficial scald incidence were evaluated at 0.25, 1, 2, 3, 6, and 9 months. The final scald evaluation followed 9 months’ storage and transfer to 20 °C for 7 days. IEC, CTOL, and superficial scald levels were highest during air storage, compared with the other storage regimes. Increases of 2-propanol and 6-methyl-5-hepten-2-ol (6MHol), but not 6-methyl-5-hepten-2-one (6MHO), levels preceded the appearance of superficial scald symptoms on apples stored in air and were greatest in air storage followed by delayed CA storage. Monitoring headspace concentration of 6MHol may be a means to non-destructively assess superficial scald risk during long-term commercial storage.