Storing vegetables and fruits

Fruits and vegetables are very valuable food products that contain vital complex of vitamins, enzymes and other bioactive substances required for human health.

Losses in storing such foods are more than 30%. As a result more than 50% of fruits and vegetables are supplied from abroad sources in winter-summer period. Therefore, the country is highly dependable on import in these valuable food products required for supporting human health.

The major reason of such high losses in our country is the application of outdated technology of chill storage. It doesn’t provide long-term product conservation, and in some cases losses reach 40%. Besides, the remaining part of products has low eating quality and bad marketable condition.

Only a technology of storing fruits in controlled atmosphere (CA) helps to preserve the quality with minimal loss. It is worth mentioning that this technology in our country is still called “controlled gas atmosphere”, that is an outdated, improper term with “CGA” abbreviation. “Controlled atmosphere” term is more suitable to the essence of this technology, as the composition of gases similar to atmosphere (N2, O2 and CO2) is supported in the camera. The only difference is their proportion. As opposite to natural atmosphere,, the O2 concentration is lowered from 21 to 1-2.5%, while CO2 concentration is 1-3.5%.

Lowering the concentration of 02 and increasing the part of CO2 in cameras leads to significant slowing of all metabolic processes running in fruits and vegetables. As a result, the storage life is increased by 2-3 months, losses become 2-3 times smaller. Moreover, the taste and nutritional properties are maximally preserved. Apples and pears can be stored up to the next fruit crop. In the countries with developed gardening (Italy, Netherlands, Belgium, Germany, England, USA, etc.) virtually the entire commercial crop of apples and pears intended for eating fresh is stored in CA.

The values of О2 and СО2 concentration depend on the product type, cultivation terms and other factors. The technology is constantly improved. Currently a technology with ultra low oxygen (ULO) is used in other countries. ULO term is used both in our country and abroad.

The implementation of this technology requires refrigerating chambers with proper proofness and corresponding equipment. It includes nitrogen generator, CO2 absorber and automatic equipment system.

Nitrogen generator is intended for primary lowering of O2 concentration in chambers. The absorber provides periodical removal of CO2 emitted by products, and the automatic equipment system periodically chances CO2 and O2 concentration and temperatures and switches on/off the proper hardware for correcting required modes.

Membrane or absorptive gas-separation plants. are used as nitrogen generators for this technology. Membrane plants are based on membranes with selective permeability for O2 and N2. Absorptive plants are based on using molecular gates that selectively absorb one of these gases.

Absorbers of different construction are used for removing СО2. They feature adsorbent that occlude this gas with regeneration by purging with clean atmosphere gas.

Over the last five years the CA technology becomes more and more popular in our country. It is implemented either by building new refrigerators with CA or by reconstruction of existing refrigerators or industrial buildings. Each of these options has its own advantages and disadvantages. Thus, by constructing a new refrigerator it is possible to obtain optimal size of chambers, build packing area with dispatch room and gates, locate all required technological equipment on the technologic floor above the transport one.

Using lightweight metal structures and heat-insulating “sandwich” panels allows speeding up the construction process significantly. Modern panels possess high heat-insulating features, they are durable, flame retardant and healthful. A few native companies produce PUF panels. However, they fall short of quality compared to panels produced abroad. It is much easier to gain the required chamber proofness building panel refrigerators значительно проще добиться требуемой герметичности камер, что необходимо для реализации технологии хранения в регулируемой атмосфере. Как показала уже и отечественная практика, холодильник с РА на 2500–5000 т можно построить за 3–4 месяца. It is required for implementation of storage in controlled atmosphere technology. As the native and worldwide practice has shown, a 2500-5000 T refrigerator with CA can be constructed in 3–4 months.

The reconstruction of an existing building into a CA refrigerator is cheaper, as there are no expenses on earthworks and building envelope. However, in some cases it is impossible to implement the required planning due to the limitations in chambers height.

Specific requirements in supporting high relative humidity (88-93%) in chambers for storing fruits and vegetables should be taken into account during the reconstruction of existing building or construction of a new one for implementing CA storage technology. That is why a correct calculation and choice of refrigerating equipment with proper chilling scheme, refrigeration capacity, air exchange rate, characteristics of air coolers, TEV type, air velocity and other criteria is highly important. Some foreign manufacturers, including Helpman and Goedhard, produce air coolers with construction optimized for long-term fruits and vegetables storage.

The major gases that influence on the product are oxygen, ethylene and carbon dioxide. The storage period of fruits and vegetables depend on their concentration in chambers.

There are a few ways of storage fruits in controlled gas atmosphere:
-Classic — the concentration of carbon dioxide is 5-7%, oxygen - up to 12%
-With lower oxygen (5%) and carbon dioxide (3%) concentration
-Ultra low oxygen technology (ULO) — the concentration of carbon dioxide is only 0-1.5%, oxygen - 2%

The most popular technology is ULO (Ultra Low Oxygen). Besides refrigerating equipment and equipment for supporting proper humidity level, this technology implies the installation of hardware for creating a specific gas environment. Oxygen is removed (remaining in concentration up to 2%), as well as carbon dioxide. Ethylene level is also controlled, as it causes gestation of fruits and vegetables. The main filling gas is nitrogen.

Чаще всего в камерах ULO хранят яблоки и помидоры. Перед их загрузкой плоды сортируют. Отбраковывают мятые, битые, гнилые и т.п. Температура при хранении яблок устанавливается в пределах +1- 4 градуса, а влажность около 95%. Пр таких условиях сильно возрастает чувствительность плодов к углекислому газу. Сохраняемость яблок в значительной степени зависит от времени их созревания и сорта.Apples and tomatoes are mostly stored in ULO cameras. Before loading the fruits and vegetables they are properly sorted. Rumpled, beaten, rotten ones are removed. The temperature for storing apples is +1- 4 degrees with humidity about 95%. In such conditions fruits become much more sensitive to carbon dioxide. The storage qualities of apples highly depend on their sort and gestation time.

Major hardware parts:
-CO2 scrubber (decreases the content of CO2)
-Ethylene converter (removes ethylene)
Nitrogen generator (decreases the oxygen concentration and increases the concentration of nitrogen)
-Control computer

The fruits are loaded right after collection. Then they are discharged upon occurrence – usually in winter. As a rule a range of chambers is constructed, as after opening one chamber its entire content must be used. The repeated load is unacceptable.

It is required to install refrigerating and humidity control equipment besides the gas atmosphere controller.

This type of equipment (ULO) is reasonable to install in close proximity to the source of yield (gardens, fields, etc.), because fruits get the most of damages in transportation and cargo handling. Damaged fruits are sorted out.

In order to get more details about fruits and vegetables storage systems from PRIMEHOLD, please call by these phone numbers: (044) 369-58-19, (044) 227-50-17.