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Controlled Atmosphere Surveys

CRT is able to provide a comprehensive monitoring service for gas and vapour concentrations during the transport of fruit and vegetables. We have the in-house expertise to collect data during transit or at the outturn.

Why do we need to know what the gas concentration in shipment are? The answer to this question is complex. 

Fruit and vegetables are actually alive, their cells are metabolising, consuming oxygen and carbohydrate and producing water vapour and carbon dioxide. Also small amounts of ethylene gas are produced.

Therefore it is not enough to just refrigerate the cargo, a supply of fresh air must also be provided. If insufficient fresh air is supplied several things can happen:

  • Too much carbon dioxide can produce tissue damage, in apples this condition is known as brown heart.

  • Not enough oxygen can result in anaerobic respiration, in this case the metabolic pathway is incomplete and the final product becomes alcohol resulting in alcoholic fruit.

  • Too much water vapour can encourage the development of moulds, rots and fungi. However, not enough is just as bad as it promotes desiccation of fruit and vegetables.

  • Ethylene gas is a ripening hormone, very small quantities building up can promote premature ripening in fruit or degreening in green vegetables.

Controlled Atmosphere Shipments 

It becomes obvious that control of gas concentrations can be used to improve outturn quality. In the 1930's it was discovered that low oxygen and moderate carbon dioxide levels could be used to vastly increase the storage life of apples. This has become the basis of controlled atmosphere which is beginning to be used in some transport applications.

CRT has been involved with shippers and equipment manufacturers for many years. This includes the technical aspects of equipment and the outturn quality of shipments. We have detailed knowledge of ventilation rates and effective gas concentrations for controlled atmosphere shipments.

Controlled Atmosphere Database

One of the problems of using controlled atmosphere is knowing what gas concentrations to use. CRT have a database with over 10,000 entries which has been compiled in association with the University of California at Davis which lists optimum conditions. Access to the database through RTIS membership is of course available. 

Gas Measurement

On the gas concentration measurement front, CRT operates a range of specialised instrumentation.

The key gases of interest are:

  • Carbon dioxide, a product of respiration. For measuring concentrations in the range of 0 - 25%, CRT employ portable battery operated instruments which can be used anywhere. The CRT detectors operate by observing the absorption of infra red light by carbon dioxide

  • Oxygen: a component of respiration. Oxygen concentrations are measured by paramagnetic detectors.

  • Ethylene, a naturally occurring ripening hormone, Measurement of ethylene gas is a relatively complex business because of the extremely low concentrations that need to be measured. For this purpose CRT own and operate a portable gas chromatograph which is capable of measuring ethylene down to ten parts per billion. It works by taking a one millilitre sample and passing it through a column using a carrier gas of extremely pure air. Ethylene is detected by a photo ionisation sensor and the concentration calculated by an on-board computer.

CRT will be pleased to discuss your problem and to quote for the use of any of these instruments. The service is available for measurements in fixed locations and during transport by land, sea and air.

International Institute of Refrigeration Papers 

CRT have presented a papers on CA transport to The International Institute of Refrigeration at a Symposium on Refrigeration in Sea Transport Commission D2/3 to be held at Gdansk, Poland September 1994 and at Montreal 1991. The papers were entitled;

"Controlled atmosphere during transportation, why is every line not using it?"

"Measurement of ethylene gas prior to and during transport"

Copies of the papers are available to RTIS members through the library service.


related information

BS EN standards

american ANSI standards

japanese standards

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