Postharvest Handling Solutions

What is 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 level. Controlled atmosphere storage refers to the constant monitoring and regulating of the CO2 and O2 level within gas-tight store rooms or containers. The gas mixture will constantly change due to metabolic activity of the respiring fruits and vegetables in the store room and leakage of gases through doors and walls. Therefore, gases in the storage room are measured periodically and regulated to the predetermined level by introducing fresh air or nitrogen in, or removing CO2 using chemicals.

There are different types of controlled atmosphere storage systems depending mainly on the method or control degree over 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 stored product generates the atmosphere while "flushed" is where the atmosphere is supplied by a flowing gas stream, which purges the store room continuously. Systems may be designed using flushing initially to reduce the O2 level, next either injecting CO2 or allowing it to build up through respiration. Finally, the proper atmosphere will be maintained by ventilation and scrubbing.

Importance of Controlled Atmosphere
CA storage has aroused the interests of many researchers. The actual effects CA storage has on crops vary with the following factors:
1. Species of crop
2. Cultivars of crop
3. Concentration of the gases in the store room
4. Crop temperature
5. State of maturity of the crop at harvest
6. Ripeness degree of the climacteric fruit
7. Growing conditions of crop before harvest
8. Presence of ethylene in the store room

Advantages of CA Storage
Since there are interactive effects between the two sorts of gases, effects of CO2 and O2 on extending the storage life of produce may be increased when they are combined together. The practical advantages of CA storage can be summarized as follows:
1. CA storage may cause a considerable decrease in respiration rate of crops, with a reduction in climacteric maximum, accompanied by an expansion of both pre-climacteric and post-climacteric periods.

2. Under CA storage, effect of ethylene on fruits metabolism is reduced due to the interaction between O2 and ethylene. Therefore, the appearance of senescence symptoms of the fruits is delayed.

3. Storage life of fruit or vegetable can be extended or even doubled since over ripening is delayed.

4. CA storage can keep meat fresh due to the effect of CO2 concentration on the enzymes acting on cellular membranes.

5. A high turgidity is achieved, so that fruits are more juicy and crisp.

6. CA storage guarantees a smaller loss of acidity, sugar and vitamin C, so that the nutritional and sensory quality of fruits or vegetables is higher.

7. Some physiological changes, such as chill injuries, spot, decay, browning, water core and scald are prevented, or greatly reduced.

8. Moulds can be reduced, in particular under low O2, high CO2 atmosphere.

9. Longer shelf life of produce in the post storage trading is possible. Produce’s life can even be trebled thanks to the CA effects on respiration and the other metabolic activities.

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