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what is CA storage?
||WHAT IS CONTROLLED ATMOSPHERIC STORAGE?
Eating crisp, juicy apples year-round is possible due to controlled atmosphere storage. Known simply as "CA" in the industry, controlled atmosphere storage involves careful control of temperature, oxygen, carbon dioxide and humidity.
CA storage got its start in England before World War II when farmers discovered their produce kept longer if stored in an airtight room. It was up to scientists to unravel the reasons for longer storage.
Apples take in oxygen and give off carbon dioxide as starches in the flesh change to sugar. In the sealed rooms, this respiratory process reduced the oxygen, thus slowing the ripening process.
CA storage has come a long way since then, and researchers in Washington state have been among the leaders in this technology. CA was first used in the United States in the 1960s and Washington now has the largest capacity of CA storage of any growing region in the world.
The large, airtight CA rooms vary in size from 10,000 boxes to 100,000 boxes, depending on the volume of apples produced by the apple shipper and his marketing strategies.
CA is a process in which: Oxygen levels in the sealed rooms are reduced, usually by the infusion of nitrogen gas, from the approximate 21 percent in the air we breathe to 1 percent or 2 percent. Temperatures are kept at a constant 32 to 36 degrees Fahrenheit. Humidity is maintained at 95 percent and carbon dioxide levels are also controlled. Exact conditions in the rooms are set according to the apple variety. Researchers develop specific regimens for each variety to achieve the best quality. Computers help keep conditions constant.(In a general CA storage)
Timing of harvest is critical to good storage results. Apples picked too early will not store well in CA nor will those that are past the proper maturity.
In mid-August, apple growers start testing the maturity of their apples to accurately predict when to harvest their crop to put in CA rooms so the apples are mature, but not too ripe. Firmness, skin color, seed color, sugar level and flesh chlorophyll are tested.
When the proper growing and harvesting techniques are used, many varieties of apples can store for 12 months or longer in CA. Most of these apples are shipped to market between January and September. Regular refrigerated storage is used for much of the fruit marketed in the fall and early winter months.
WHAT ELSE CAN BE STORED IN ‘CA’ STORAGE?
Two major classes of commodity can be stored in controlled atmosphere:
1. Dry commodities such as grains, legumes and oilseed. In these commodities the primary aim of the atmosphere is usually to control insect pests. Most insects cannot exist indefinitely without oxygen or in conditions of raised (greater than approximately 30%) carbon dioxide. Controlled atmosphere treatments of grains can be a fairly slow process taking up to several weeks at lower temperatures (less than 15°C). A typical schedule for complete disinfestations of dry grain (<13% moisture content) at about 25°C, with carbon dioxide, is a concentration above 35%(v/v) carbon dioxide (in air) for at least 15 days. These atmospheres can be created either by:
o adding pure gases carbon dioxide or nitrogen or the low oxygen exhaust of hydrocarbon combustion, or
o using the natural effects of respiration (grain, moulds or insects) to reduce oxygen and increase carbon dioxide Hermetic storage
2. Fresh fruits, most commonly apples and pears, where the combination of altered atmospheric conditions and reduced temperature allow prolonged storage with only a slow loss of quality.
The gas mixture will constantly change due to metabolic activity of the respiring fruits and vegetables in the store and leakage of gases through doors and walls. The gases are therefore measured periodically and adjusted to the predetermined level by the introduction of fresh air or nitrogen or passing the store atmosphere through a chemical to remove CO2.
WHAT ARE DIFFERENT TYPES OF ‘CA’?
There are different types of controlled atmosphere storage depending mainly on the method or degree of control of the gases. Some researchers prefer to use the terms “static controlled atmosphere storage” and “flushed controlled atmosphere storage” to define the two most commonly used systems. “Static” is where the product generates the atmosphere and “flushed” is where the atmosphere is supplied from a flowing gas stream, which purges the store continuously. Systems may be designed which utilize flushing initially to reduce the O2 content then either injecting CO2 or allowing it to build up through respiration, and then
Maintenance of this atmosphere by ventilation and scrubbing.
WHAT IS THE IMPORTANCE OF CONTROLLED ATMOSPHERE STORAGE?
CA storage has been the subject of an enormous number of biochemical, physiological and technological studies, in spite of which it is still not known precisely why it works. The actual effects that varying the levels of O 2 and CO2 in the atmosphere have on crops varies with such
a. The species of crop
b. The cultivars of crop
c. The concentration of the gases in the store
d. The crop temperature
e. The state of maturity of the crop at harvest
f. The degree of ripeness of the climacteric fruit
g. The growing conditions before harvest
h. The presence of ethylene in the store
There are also interactive effects of the two gases, so that the effects of the CO2 and O2 in extending the storage life of a crop may be increased when they are combined. The practical
Advantages of storage under CA can be summarized as follows:
1. A considerable decrease in respiration rate, with a reduction in climacteric maximum, accompanied by an expansion of both pre-climacteric and post-climacteric periods.
2. A reduction in the effect of ethylene on metabolism due to the interaction of O2 with
ethylene, with a consequent delay of appearance of senescence symptoms
3. An extension in storage life, which can even be doubled, in as much as the over ripening is delayed
4. The preservation of an excellent firmness of flesh, due to effect of CO2 concentration on the enzymes acting on cellular membranes.
5. A high turgidity is achieved, such that fruits are more juicy and crisp
6. A smaller loss of acidity, sugars and vitamin C, so that the nutritional and sensory quality is higher
7. A limited degradation of chlorophyll, with a consequent higher stability of colour