Sep 6, 2024

Michigan State University Controlled Atmospheric Storage Clinic offered discussion on apple storage disorders, best practices

Postharvest physiology experts from across North America focused on apple storage disorders and best practices during a Michigan State University (MSU) Controlled Atmospheric Storage Clinic.

The day of talks was hosted by Randolph Beaudry, an MSU postharvest physiology professor and Ph.D. The event also included speakers from Cornell University, Washington State University, USDA-ARS and others. The researchers are working together to advance our understanding of how apple biology changes in storage conditions. Their work informs industry best practices and allows for increased storage time with limited reductions in apple quality.

The goals of long-term storage are reducing food waste, increasing grower profits and maintaining a constant supply of apples available on the market. This system has been especially pertinent to Michigan apple growers through the past two years of bumper crops that have required long periods of storage prior to distribution.

Postharvest

Apples are living and “breathing” after harvest. Apple cells continue to respire and use up stored sugars and starches. During storage, by reducing the temperature, we slow ripening and respiration and by reducing oxygen, we can inhibit ripening. Low oxygen levels inhibit the action of ethylene, a phytohormone required for apple ripening.

However, oxygen levels must be tightly controlled. If they dip too low for the given apple lot, the cells will flip to anaerobic respiration and begin fermenting. This is called the Low Oxygen Limit (LOL). Keeping oxygen levels just about the LOL is crucial for long-term storage operations.

Carbon dioxide levels must also be controlled in the controlled atmospheric storage environment to limit senescence or CO2 injury.

Controlled atmospheric storage

Controlled atmospheric storage for apples has become a common industry practice over the 100+ years following its first implementation in England. In this system, apples are stored in sealed rooms at low temperatures, low oxygen levels and low carbon dioxide levels.

This practice is now evolving into dynamic controlled atmospheric (DCA) storage as companies including Gas At Site and Storage Control Systems have developed and commercialized tools that accurately keep a pulse on thousands of apple storage rooms across the world. These tools allow for real-time adjustments to room conditions based on the behavior of the fruit in the storage and inform users on room opening order for product distribution.

Ethylene drives apple ripening and later senescence. The system works as a positive feedback loop in which ripening apples produce ethylene which is sensed by nearby apples that also produce the chemical. Plant growth regulators are used to control ethylene production both before and after harvest.

ReTain, a Valent USA product, is applied prior to the harvest window to prevent ethylene from developing. This allows growers to control harvest windows. Chris Watkins, a Cornell University horticulturist, also spoke about how early ReTain applications (21 days preharvest) were more effective at enhancing firmness and reducing internal browning than applications close to harvest for Gala apples in his recent experiments.

The widely used plant regulator, 1-Methylcyclopropene (1-MCP), binds to the ethylene receptors, thereby limiting ethylene action and further production. Although 1-MCP is a gas, it can be applied preharvest with products like Harvista. 1-MCP is also widely used in storage rooms to reduce ethylene production with multiple different formulations and delivery methods available.

During the discussion, Beaudry noted the delivery of effective dose is critical with different companies having different release kinetics that impact efficacy. He also discussed ongoing work on the impact of 1-MCP on volatile aroma chemicals. Plant growth regulators are an important tool in controlling harvest windows and internal browning in storage. However, timing and application methods are crucial for success. Watkins pointed out that there are no silver bullets; all factors are connected in postharvest physiology.

Disorders

Apple disorders are a key issue for long term storage. These include bitter pit, soft scald, CO2 injury, lenticel breakdown, soggy breakdown, leather blotch and more.

Jennifer DeEll, postharvest physiologist and fresh market quality program lead for the Ontario Ministry of Agriculture, Food and Rural Affairs highlighted maturity at harvest, storage temperature, oxygen levels, carbon dioxide levels and 1-MCP timing as key factors surrounding disorders in Ambrosia apples like internal browning and soft scald. Reducing apple stress in storage with DCA storage systems can also reduce the incidence of disorders, especially browning in Gala, as indicated by work presented by both DeEll and Watkins.

While apple disorders frequently appear in storage, growing conditions are critical for their management. Chayce Griffith, an MSU Department of Horticulture Ph.D. graduate research assistant, discussed his research into the underlying causes of bitter pit. He stressed that xylem dysfunction was a main cause for the disorder.

Bitter pit is linked to calcium deficiency, which is only mobile through the xylem. As apples develop over the course of the season, peripheral xylem becomes gradually dysfunctional and breaks down. Griffith is testing plant growth regulators like NAA and IAA, which can enhance the xylem and reduce incidence of bitter pit. His work highlights the importance of in-season considerations on postharvest conditions.

Postharvest physiology research continues to explore the interactions between field conditions, storage conditions and apple varieties across apple growing regions. Furthering our understanding of these connections can inform and improve industry practices. This meeting was sponsored by Storage Control Systems, AgroFresh, Fine America, Gas At Site, Janssen PMP, Valent USA, MirTech and Lytone.

Join us for the next Controlled Atmospheric Storage Clinic in 2026. Lindsay Brown is a Michigan State University Extension tree fruit integrated pest management educator covering West Michigan and based in Kent County. Randy Beaudry, Ph.D., is a professor in the Department of Horticulture at Michigan State University. His research program is focused on assessing the quality of harvested plant products and the development of technological interventions to improve quality maintenance.

Article written by Lindsay Brown and Randy Beaudry, contributing writers

Lindsay Brown is a Michigan State University Extension tree fruit integrated pest management educator covering West Michigan and based in Kent County.

Randy Beaudry, Ph.D., is a professor in the Department of Horticulture at Michigan State University. His research program is focused on assessing the quality of harvested plant products and the development of technological interventions to improve quality maintenance.