Risk assessment candidates for carbon dioxide-related internal browning of apple during controlled atmosphere storage

Authors: MCTAVISH, CHRISTINE - Us Forest Service (FS); Klarer, Emmi; MILNE, SHAE - University Of Wyoming; Valdez, Natalie; MATTHEIS, JAMES - Retired ARS Employee; LEISSO, RACHEL - Former ARS Employee; Rudell Jr, David

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2025
Publication Date: 8/20/2025
Citation: McTavish, C., Klarer, E.R., Milne, S., Valdez, N.C., Mattheis, J., Leisso, R., Rudell, Jr., D.R. 2025. Risk assessment candidates for carbon dioxide-related internal browning of apple during controlled atmosphere storage. Postharvest Biology and Technology. 230. Article 113840. https://doi.org/10.1016/j.postharvbio.2025.113840.
DOI: https://doi.org/10.1016/j.postharvbio.2025.113840

Interpretive Summary: Flesh browning of apple is most widely attributed to elevated levels of respiration and accumulation of carbon dioxide around apples during low oxygen controlled atmosphere storage. This disorder contributes to significant annual losses during the cold chain of many economically important apple varieties produced in the U.S. In this project, we determined changes in levels of natural chemicals produced in apple flesh associated with the risk of developing internal browning. First, symptomatic flesh was compared to asymptomatic flesh of 5 apple varieties to determine chemical changes that reflect symptomatic tissue. Next, changes in levels was examined prior to and during symptom development in a sixth apple variety. Using this approach, we determined changes in multiple natural chemicals associated with disorder risk during the pre-symptomatic stage. Monitoring levels of these chemicals or related gene expression, with further development, may provide a basis sensing when apple are compromised by storage conditions and adjusting those storage conditions to reduce further likelihood of developing internal browning.

Technical Abstract: Internal browning of apple (Malus domestica Borkh.) associated with high respiration and pCO2 continues to contribute to annual losses of many economically important cultivars in most growing regions worldwide. This effort sought to determine metabolites that change with storage conditions factors and, consequently, infer relative risk. To accomplish this, internal browning was triggered in 5 cultivars using high pCO2 and ultra-low pO2 conditions, coupled with diphenylamine drenching to verify if elevated pCO2 was a contributing factor. From this, the metabolic fingerprints of symptomatic and asymptomatic cortex were compared on all 5 cultivars. Levels of metabolites altered by symptom development in multiple cultivars were then monitored in ‘Fuji’ asymptomatic cortex prior to and during symptom development in apples stored in a range of pCO2 revealing a number of metabolites that were associated with high-risk storage conditions and symptom development. These included elevated levels of lipids such as acylated steryl glycosides, free fatty acids, sphingolipids, diglycerides, and unknowns likely produced from ''-tocopherol. Metabolite levels that diminished with risk included steryl esters and select amino acids. Relationships between candidate metabolite levels and risk conditions are expected to remain robust with the tested cultivars and, potentially, other susceptible cultivars. Whether other production variables impacting risk of internal browning are represented by the same metabolic changes is the subject of continued investigations with the goal of developing tests indicative of compromised fruit before symptoms appear.