Ultra Low Oxygen (ULO) technology represents the latest achievement in long term storage of fresh fruit segment. ULO regime in chambers provides the storing of the entire apple crop and offer to the market at any time of the year. ULO (Ultra Low Oxygen) technology enables the apple to maintain unchanged properties for a long period of time without any chemical intervention.

ULO (Ultra Low Oxygen) technology refrigerator is the third generation refrigerator for long term storing of fruit and vegetables. It is used in developed countries of Europe (Germany, Denmark, France, Italy, Holland, etc.) for storing the total of 70% of fruit, and around 50% in the USA. The first generation of refrigerators in the world, Europe and in our country had a simple technology and was based on lowering the temperature in the cooling space and increase of relative humidity of air. In such storage conditions the period of preservation of some products can be up to 3 months. Currently the majority of storages in Serbia and Vojvodina are of the first generation excluding the deep freeze refrigerators. ULO refrigerator technology, especially the one of the third generation, prolongs the season of fruit demand and guarantees the national population fruit and vegetable consumption in fresh state during the entire year, which is of great importance for the preservation of health of the population and large economic use and increase of the GDP of the country.

Second generation of the refrigerators, or refrigerators with controlled atmosphere (CA) bring further progress in the fruit and vegetables storing technology. Low temperature is controlled in these refrigerators with moisture increase in the cooling space, gas participation is controlled, that is, oxygen share is reduced, and carbon oxygen level is increased, which slows the biological process of the fruit, and the storage period is prolonged from previous 3 months (1^st generation) for additional 1 to 3 months, to a period of fruit storing of 6 months.

The third generation of refrigerators or ULO (Ultra Low Oxygen) refrigerators is the result of further research of fruit physiology. Basic principle of ULO refrigerator operation is the temperature control, air moisture, oxygen and carbon dioxide. Plus cooling temperature is reduced in these refrigerators and air moisture is increased depending on the fruit species with simultaneous control of oxygen presence parameters within the limits of 0.8 – 3% and carbon dioxide of 0.7 – 5.0% depending on the species of the fruit, sort and atmosphere area of the storage. This technology differs from refrigerators of the second generation by reducing the intensity of fruit breathing for 30% thus eliminating harmful influence of carbon dioxide, by lowering the oxygen and carbon dioxide share in the cooling chamber atmosphere, which could not have been done in the second generation refrigerators. In such storage conditions, all biological processes in the fruit are slowed down, so certain fruit species like apple can be stored for 12 months and more, without significant loss of quality of fruit from the moment of picking, except for significant reduction or elimination of certain physiological diseases of the fruit appearance