Jul 28, 2011

CA storage has become staple of the fruit industry

In the past 50 years, the use of controlled atmosphere (CA) storage has become a staple of the fruit industry. It is one of the tools that allow growers and packers to extend the available seasons for produce and meet demand with supply.

What is CA storage?

CA storage is a system where fresh, perishable fruits and vegetables are stored under narrowly defined environmental conditions that extend the useful marketing period after harvest, according to David Dilley, a horticulturist with Michigan State University.

The specific conditions being controlled vary according to the commodity being stored. That may include storage at the lowest safe temperature to avoid freezing or chilling injury. It may mean use of the lowest safe oxygen level to attenuate respiration rate and slow ripening. It could mean the highest safe carbon dioxide level to reduce respiration rate and slow ripening and senescence. For some produce, the best method may require the lowest practical ethylene levels to suppress initiation or development of ripening or senescence, or maybe the high humidity levels to minimize moisture loss from the commodity, Dilley said.

Apples, for example, take in oxygen and give off carbon dioxide as starches in the flesh change to sugar. In the sealed rooms of CA storage facilities, this respiratory process reduces the oxygen, thus slowing the ripening process.

“The optimal levels of these atmospheric variables differ according to the commodity and stage of development,” Dilley said. “Moreover, tissue response may vary because of interactions among these variables as influenced by variety and preharvest conditions and climatic factors peculiar to the region where the commodity is grown.”

The objective in using CA storage is to extend the useful marketing period for the produce after it is harvested to keep the market value intact, according to Dilley. Demand for the product in relation to cost, benefit and practicality will ultimately determine the use of CA storage technology for postharvest maintenance of the product.

The history of CA

Franklin Kidd and Cyril West at the Low Temperature Research Station at Cambridge, England, laid the basic groundwork leading to the widespread commercial application of CA storage in the early 20th century. They began a systematic study of fruit respiration and ripening as influenced by temperature, carbon dioxide and oxygen.

The first commercial apple storage to employ the “gas storage” technique in England was constructed in 1929, according to Dilley. In 1930, the commercial value of CA storage was realized, leading to rapid expansion in the use of gas storage technology for apples and pears in the 1930s.
Putting a gas-tight, sheet-metal liner in an existing refrigerated apple storage facility created one of the first commercial CA storage facilities in the United States in the early 1950s. The practice of sealing apple storage rooms provided most of the early expansion in CA storage volume in the United States and Canada. It was not until the mid-1950s, when the practice of using bulk bins and lift trucks was introduced, that new construction of CA storages with high ceilings began. The increased efficiency in fruit handling and labor savings by using bulk bins for harvesting, handling and storing fruit were important factors in the growth of CA storage capacity worldwide since 1950, Dilley said.

“My grandfather actually had one of the first CA storage rooms back in the 1950s at A.J. Schaefer & Sons Orchards in Sparta, Michigan,” said Jim Schaefer, owner of Storage Control Systems, one of the leading producers of CA storage facilities.

The most significant and accelerated expansion of CA storage in the United States began in the 1960s, when Washington state apple storage operators and shippers realized the improvements to be gained in dessert quality and marketability of Red and Golden Delicious apples by storing them under CA, Dilley said. By 1960, the total CA holdings of apples and pears in the United States amounted to more than 4 million bushels. Expansion in CA storage capacity for apples and pears in the United States and Canada and around the world has continued unabated since 1960. By the late 1980s, U.S. CA storage capacity for apples and pears exceeded 100 million bushels.

Eastern Washington, where most of the state’s apples are grown, has enough warehouse storage for 181 million boxes of fruit, according to a 1997 report from the Washington State Department of Agriculture. The report shows that 67 percent of that space – enough for 121 million boxes of apples – is CA storage, according to the Washington Apple Commission (WAC).

What’s next?

CA storage technology is expanding to be more accessible to smaller-scale growers, according to Schaefer. His company is working to refine and make the machinery more user-friendly and efficient. New developments, such as SCS LiveView, a web-based monitoring tool, allow growers and packers to monitor and make changes to storage facilities anywhere they have access to the Internet. This includes smartphone technology.

“The push in the future will be to keep fruit chemical-free,” Schaefer said. “We should see the use of dynamic controlled atmosphere in the U.S., again following the European lead, in the next 20 years. Dynamic atmosphere control is using the fruit respiration effects to determine the minimal oxygen needed to allow that fruit to survive. This delicate balance of low O2 allows for firmness retention and overall quality throughout the eight to nine-month storage season.”

“Michigan growers tend to be slow to advance with new CA technologies and practices, mostly due to financial reasons,” said Randy Beaudry, a professor at Michigan State University. “However, while Michigan growers may be slower to adapt to new CA storage trends, they tend to be more financially secure in the log run.”

Modern technologies in CA storage can be traced back to the early- to mid-20th century, and coincide with the realization that important components of developmental physiology are regulated by oxygen and carbon dioxide, Beaudry said.

CA is a relatively mature technology, comprising important storage strategies for a number of commodities, Beaudry said. It provides for the inhibition of ethylene action, as well as cut surface browning, chlorophyll degradation, decay and disease proliferation. These processes are targeted by recently developed technologies such as solid-state ethylene monitoring, breathable patches on packages, 1-MCP ethylene action inhibition and dynamic controlled atmosphere storage.

“Regarding future innovation, promising research suggests that additional advancement could come soon in the areas of sense-and-respond systems for packages and CA environments, packaging films with new properties, miniature active and passive control devices for packages and, finally, in the very fruit itself,” Beaudry said. “Postharvest innovation, begun over 5,000 years ago with the first modified atmosphere environments, continues and promises improved capabilities and better food for the consumer in the years to come.”

By Derrek Sigler, Assistant Editor