CONTROLLED ATMOSPHERE STORAGE
Controlled atmosphere storage is a system for holding produce in an atmosphere that differs substantially from normal air in respect to CO2 and O2 levels. Controlled atmosphere storage refers to the constant monitoring and adjustment of the CO2 and O2 levels within gas tight stores or containers. 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.
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.
IMPORTANCE OF CONTROLLED ATMOSPHERE
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 factors as:
- The species of crop
- The cultivars of crop
- The concentration of the gases in the store
- The crop temperature
- The state of maturity of the crop at harvest
- The degree of ripeness of the climacteric fruit
- The growing conditions before harvest
- 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:
- A considerable decrease in respiration rate, with a reduction in climacteric maximum, accompanied by an expansion of both pre-climacteric and post-climacteric periods
- 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
- An extension in storage life, which can even be doubled, in as much as the over ripening is delayed
- A high turgidity is achieved, such that fruits are more juicy and crisp
- A smaller loss of acidity, sugars and vitamin C, so that the nutritional and sensory quality is higher
- A limited degradation of chlorophyll, with a consequent higher stability of colour.
- Some physiological alterations, such as chill injuries, spot, decay, browning, water core and scald are prevented, or greatly limited
- Moulds can be reduced, in particular under low O2, high CO2 atmospheres
- A longer shelf life in the post storage trading, which can even be trebled thanks to the protraction of the effects on respiration and on the other metabolic activities.
FRUITS AND VEGETABLES STORAGE UNDER CA
The storability of fruits and vegetables is strictly related to their respiration rate, which is an expression of metabolic activity. Aerobic respiration requires O2, and results in CO2 and heat release. More than 95% of the energy released is lost as heat. The temperature decrease, in particular if helped by modification of the atmosphere leads to a reduction in respiration rate, and therefore to an increase in storage life in fruits with climacteric respiration. Selection of the most suitable atmosphere depends on cultivars, stage of maturity, environmental and cultivation parameters. No one atmosphere is best for all produce, specific recommendations and cautions must be determined for each crop over the range of storage temperature and periods.