Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2019
Publication Date: 11/18/2019
Citation: Poirier, B.C., Mattheis, J.P., Rudell Jr, D.R. 2019. Extending ‘Granny Smith’ apple superficial scald control following long-term ultra-low oxygen controlled atmosphere storage. Postharvest Biology and Technology. 161. Article 111062. https://doi.org/10.1016/j.postharvbio.2019.111062.
Interpretive Summary: Superficial scald is a postharvest peel browning disorder that contributes to annual losses of susceptible apple cultivars. Previously, the consensus of reports indicated that scald control treatments were only effective if applied during the first few weeks of cold storage, after which the completion of scald induction rendered treatments ineffective. Our results indicate that controlled atmosphere (CA) storage delays scald induction, lengthening the window of time available to employ conventional scald control strategies (postharvest crop protectants) as well as treatments that may be used where crop protectants are restricted (hot water immersion). Our results also demonstrate that changes in peel metabolism can be used to monitor the extent of scald induction after CA storage and assess the potential effectiveness of post-CA treatments. This work contributes to the understanding of superficial scald physiology and provides apple producers with novel and necessary options for scald management throughout storage.
Technical Abstract: Superficial scald is an apple postharvest peel browning disorder that contributes to annual losses of susceptible cultivars, principally where crop protectants that control the disorder are restricted. Controlled atmosphere (CA) storage reduces or eliminates superficial scald while apples remain in storage, especially when pO2 is maintained below 1 kPa. However, symptoms often develop during the post-storage cold chain, which can last beyond a month. Diphenylamine (DPA) or 1-methylcyclopropene (1-MCP) treatment can be used to control scald, but application is required within the first weeks of cold air storage following harvest. After this time, treatments are no longer effective due to irreversible physiological changes, hereby referred to as ‘scald induction’. As a recent report indicates, apple flesh softening can be reduced by 1-MCP treatment following ultra-low oxygen CA (ULO-CA) storage (pO2 = 1.0 kPa). Here, we sought to determine if ULO-CA would also preserve the capacity to control scald with post-CA treatments. To determine this, ‘Granny Smith’ were treated with hot water and 1-MCP at harvest and following long-term (>3 months) in-house and commercial ULO-CA for two consecutive years. Different CA storage environments (2.0 kPa and 1.0 kPa O2) and delays in ULO-CA establishment were used in combinations with delayed DPA and 1-MCP treatments to determine how different storage practices may impact the effectiveness of post-CA scald control measures. Taken together, results indicate that scald induction is effectively delayed during ULO-CA storage and resumes upon return to air storage. 1-MCP and hot water treatments applied after four months of ULO-CA storage were equally effective at controlling scald during subsequent air storage as treatments applied at harvest. However, the efficacy of post-storage treatments relied on the rapid establishment and maintenance of ULO conditions and immediate treatment upon removal from ULO-CA storage. Scald induction resulted from cumulative oxygen exposure occurring prior to, during (pO2) and after CA storage. Conjugated trienol and acylated steryl glycoside levels at the end of ULO-CA storage provided an accurate estimate of how much scald induction had occurred and, likewise, the efficacy of post-storage scald mitigation treatments.