Post harvest Management of Horticultural Crops (2+1)

Controlled Atmosphere Storage

Controlled Atmosphere Storage (CA Storage)

The storage of fruits and vegetables in CA Storage is one of the most advanced methods of storage. It was first suggested by W.R. Philips of Canada.
From the construction point of view, controlled atmosphere facilities are similar to refrigeration facilities. However, they should be airtight to allow creation of an atmosphere different from normal. The Oxygen consumption and its replacement by carbon dioxide by respiration, create the atmosphere. When the appropriate combination has been reached, a limited intake of oxygen is required to satisfy the reduced rate of respiration. Accumulation of carbon dioxide is removed by means of different methods.

Physiological basis of CA Storage
Air contains about 20.9% O2 78.1 % N2, 0.003 % CO2 and trace amount of other gases including Ne, He, CH4 and water vapour. In CA storage, oxygen is reduced and CO2 is increased and ripening and respiration rates are slowed down.

Essential features of CA Storage

1. Mechanical refrigeration is used to maintain temperature of -1 to 3°C.
2. The CA storage room is constructed gas tight.
3. Reduction on O2 - Nitrogen gas is introduced into the storage by cylinder to reduce the oxygen level after room is filled and sealed. CO2 is added into storage from CO2 gas cylinder.
4. Excess CO2 is removed by dry hydrated lime, Ethanolamine, Aluminium calcium silicate, Activated carbon, Magnesium oxide, activated carbon are other CO2 scrubbers.
5. Atmospheric composition is crop specific. However, as a general rule the most common combinations are 2-5% oxygen and 3-10% carbon dioxide
6. The storage room atmosphere samples are taken daily for CO2 and O2 monitoring.


Benefits of CA storage

1. Retardation of senescence and associated biochemical and physiological changes
2. Reduction of produce sensitivity to ethylene action at O2 levels below 8% and/ or CO2 levels above 1 %.
3. Useful tool for insect control in some commodities.


Limitations of CA storage

1. Causes certain physiological disorders such as black heart in potatoes, brown stain of lettuce.
2. Irregular ripening of produce such as banana, pear, tomato etc.
3. Development of off flavours and off odours at very low O2 concentrations.
4. Timely non availability of gas
5. Costly and technical knowhow is required



Fig: Blackening due to tissue asphyxia (suffocation) of an artichoke head caused by storing in an inadequate atmosphere