CA warehouse
CA storage (controlled atmosphere) is an agricultural storage technology , especially, but not only, for storing pome fruit , especially for apples , and more rarely for vegetables and meat (e.g. ham). In a CA warehouse, the aging of perishable goods is slowed down.
functionality
CA stands for Controlled Atmosphere , a controlled atmosphere , and describes a storage technique that delays the ripening of climacteric fruits . In CA warehouses, temperature , humidity , oxygen and carbon dioxide content are monitored using measurement and control technology and kept at the desired level.
Thanks to CA storage, certain types of fruit and vegetables are available all year round, regardless of the harvest time. Compared to traditional cold storage , the costs of CA storage are significantly higher. In addition, it is not suitable for all types of fruit and vegetables.
The following conditions exist in CA warehouses:
- low temperature (−1 to 6 ° C, depending on the fruit and variety)
- high humidity (mostly 92%)
- low oxygen content (usually 2 to 3%)
- increased carbon dioxide content (2 to 5%, depending on the fruit and variety)
The metabolism of the stored goods and thus the breakdown of valuable ingredients should be reduced as much as possible. This is done on the one hand by lowering the temperature by cooling and dissipating respiratory heat. On the other hand, the fruits are stored in storage cells, which enable the gas exchange to be controlled. By breathing and dosed subsequent delivery, the oxygen content in the storage cells is reduced to such an extent that breathing and thus the metabolism are greatly reduced. However, a decrease in the O 2 concentration to 0% must be prevented, as ethanol and musty fermentation aromas are formed under anaerobic conditions . At the same time, the resulting CO 2 should be absorbed by so-called scrubbers , as it can cause metabolic damage from a concentration of 5%. Constantly high humidity ensures that the fruits do not dry out.
In special CA stores, the natural “ripening gas” ( phytohormone ) ethene is also removed or its formation is inhibited. Another possibility is to block the ethene receptor, e.g. B. with 1-methylcyclopropene .
backgrounds
Fruits have a metabolism . They also consume oxygen after the harvest, generating heat , carbon dioxide , water vapor and aromatic compounds . This ripening is dependent on the oxidation of the carbohydrates , sugars and acids in the tissue of the fruit.
There is a relationship between the respiration of fruits and vegetables and their shelf life. Onions can be kept refrigerated for up to 250 days and produce around 3 mg of carbon dioxide per kilogram and hour. Strawberries, on the other hand, only last 8 days in the fridge, but produce ("breathe") around 65 mg of carbon dioxide per kilogram and hour. The more a fruit breathes, the faster it ages.
Less oxygen and more carbon dioxide slow down ripening in the storage room. Vitamins and acids are broken down more slowly, less ethene is produced in the fruit, less chlorophyll is broken down (and thus the core tan ), and the pulp does not soften as quickly.
If the oxygen content is particularly low, damage can occur to the fruits. Large fruits from trees with low yields are more susceptible to storage diseases.
History and creation
In 1821 , Jacques Étienne Bérard , a researcher in plant physiology , discovered that fruits and vegetables had a reduced metabolism when stored at low oxygen levels. At the beginning of the 20th century, the term CA was given a precise scientific definition by researchers Franklin Kidd and Cyril West . The real economic introduction of CA began simultaneously in the USA and Europe, but only at the end of the 1950s.
Further developments
A variant of the CA bearings are the so-called ULO bearings ( Ultra Low Oxygen ), which contain extremely little oxygen (<1%); With a relative humidity of around 92% and temperatures between 1 ° C and 4 ° C, the apples stay fresh well into the next year.
See also
- Protective atmosphere
- CA cell
- Maturing bananas at a controlled temperature and with ethene , artificially added or derived from ripening apples .
literature
- Robert Smock and the diffusion of controlled atmosphere technology in the US apple industry, 1940-1960 (Cornell agricultural economics staff paper) Dept. of Agricultural Economics, Cornell University Agricultural Experiment Station, New York State College of Agriculture and Life Sciences, Cornell University, 1988
- CA cold storage with the Braeburn apple variety as tiered storage with the lowest (ULO) oxygen conditions , in: Revue Suisse Vitic. Arboric. Hortic. Vol. 34 (6), 357-364, 2002 JEAN-PIERRE SIEGRIST AND PIERRE-YVES COTTER, Agroscope - RAC