Controlled and modified atmosphere (CMA) creation for vegetables and fruits storage implies the provision and maintenance of narrowly defined environmental conditions. To ensure supply of quality products and extend their useful life this complex process should include control of: ambient temperature, relative humidity, Ethylene, Carbon Dioxide and Oxygen.
Regulation of these conditions minimizes the two most important life processes - respiration and transpiration (both should be limited, but not stopped) - which helps to reduce products metabolism, and therefore prolongs storage life.
Ambient temperature (T)
Respiration and transpiration processes are reduced by temperature lowering in storage rooms. This prevents premature vegetables and fruits spoilage and also ensures their high quality.
Additional benefits of low temperatures are:
- reduced sensitivity to ethylene
- suppressed ethylene production
- slow microbial development
For long-term storage, temperatures between 0 and 14 °C are usually used, depending on the vegetable or fruit. Temperature must also be stable, since even minor changes and deviations from the set level by only a few degrees can shorten products storage life or affect their marketable condition.
Relative humidity (RH)
High relative humidity is as important as low temperature for vegetables and fruits storage.
Keeping a high RH level (in the range of 80-100% RH for different vegetables and fruits types) lowers the transpiration process, which prevents water loss and products wilting, and consequently reduction in shelf life and market value decrease. Although relative humidity increases as air cools down, it is still recommended to check if its levels in storage rooms are satisfactory.
It is also necessary to control that RH level is not too high, as this promotes bacteria growth and fruit or vegetables spoilage.
Climacteric fruits and vegetables, which are able to ripen on their own, continue to emit gaseous Ethylene - a natural growth hormone - during storage.
In the case of long-term storage, in contrast to ripening rooms, this factor is undesirable, since just 1 ppm C2H4 in air can trigger the ripening process and shorten produce shelf life. Therefore, it is important to keep the Ethylene concentrations as low as possible and ventilate a room, if necessary.
For controlling and reliable determining C2H4 levels in storage rooms, gas detectors installation is provided. For more accurate measurement in this application E26xx series Evikon MCI gas detectors with electrochemical sensors with detection range of 0-10 ppm are used.
C2H4 detection problems
As mentioned above, high humidity must be maintained at all times in the storage rooms.
All electrochemical sensors are absorbing humidity that lead to significant reduction of sensor´s lifetime. In other words, the device will be broken in a short period of time.
Evikon MCI solves this problem with a special internal heating which prevents high humidity from getting inside and so ensures the correct work of all E26xx series C2H4 gas detectors even in 100% RH atmosphere.
Thanks to that, users can be sure that a product will work for the whole period stated in the data sheets.
Carbon Dioxide (CO2)
In addition to Ethylene, fruits and vegetables also release Carbon Dioxide during respiration, which accumulates in the room. For long-term storage, it is necessary to maintain CO2 concentration at the required level for each product.
Keeping a high Carbon Dioxide level (up to 14%) can stop the Ethylene production and, therefore, slow down the ripening process and prolong shelf life. However, too high CO2 concentrations can negatively affect products appearance, its taste, nutritional value and storage time. Use of Evikon MCI gas detectors (with special detection ranges up to 100% CO2 for this application) helps to control the excess or lack of Carbon Dioxide in storage rooms and keep it at the desired level.
A decrease in Oxygen concentrations reduces respiration rate and Ethylene production, delays ripening and aging, also slows down pathogens growth and therefore prolongs produce shelf life. In storage rooms, Oxygen level is reduced (down to 4% of O2 and below depending on vegetables and fruits types) by replacement with Nitrogen or / and Carbon Dioxide. Once the desired O2 level is reached, fruits itself will continue to lower its concentration during respiration. Care must be taken that the Oxygen level does not fall too low (below 1%), as this can cause irreversible changes in the fruit and affect their quality. Evikon MCI O2 gas detectors with detection range of 0-25% for this application will help maintain required gas levels and extend product shelf life.