Every vegetable undergoes metabolism. That means that every fruit is alive and breathes, consuming oxygen, not only while growing, but also after harvest. The breathing cycle is about demolishing and oxydating carbohydrates such as starch, sugar and acids stored inside the vegetable tissues.
The final outcome of the breathing cycle is composed of: heat, carbon dioxide, water vapour and some aromatic compounds. The more intense is the breathing activity of fruit, the faster is its senescence and deterioration and therefore the shorter is its storage period. The use of cold has been for a long time the only method of storage of fresh fruit products.
It was 1821 when a plants' physiology scholar, Berard, found out that fruits stored at lower oxygen levels had a reduced methabolism. At the beginning of the 20th century, thanks to the researchers Kidd and West, the concept of C.A. (Controlled Atmosphere) found a precise scientific definition, but it was only at the end of the '50s that a real commercial application of C.A. took place both in Europe and in the U.S.A.
The combined action of a lower concentration of oxygen and a higher concentration of carbon dioxide in the storage room considerably reduces respiratory activity.
The C.A., together with temperature reduction, acts deeper on the vegetables metabolism, for example, reducing ethylene production typical of fruits, blocking the chlorophyll degradation (green color), delaying pectin hydrolysis (pulp firmness), slowing the breakdown of vitamins and acids.
Controlled atmosphere techniques: "Rapid CA" and "U.L.O."
From the product point of view the consequence is not only the organoleptic quality maintenance, but also the reduction of losses caused by pathogens (fungal diseases) and known physiopathologies such as senescence scalding, aging and chilling injuries in general. These clear advantages become even stronger with some new improved techniques of C.A. introduced for the first time in Italy by Isolcell S.p.a. These are the "Rapid CA" and "U.L.O." techniques.
The first technique achieves a fast oxygen reduction inside the storage (from 21% to 5% in 36 hours). The U.L.O. (Ultra Low Oxygen) atmosphere, on the other hand, is about product storage at approximate 1% oxygen level. The choice of technique depends on the produce (species, varieties) and its physiological condition at the time of harvesting.
The advantages of U.L.O. compared to traditional C.A. are an additional decrease (30%) of the respiration and metabolism but more importantly, for apples and pears, the control of a few important physiological disorders such as scald, internal breakdown and browning.
These achievements, together with a better maintenance of fruits' flesh firmness, makes the product shelf-life much longer.
In the last few years a new storage technique named "dynamic" has been developing, with a further oxygen reduction of the storage atmosphere, until the tolerance oxygen level of the fruit is reached. In order to reach such extreme atmosphere conditions, Isolcell S.p.a. has already developed sophisticated new generation products such as the (IS) Intelligent Carbon Dioxide Scrubber.
CONTROLLED ATMOSPHERE STORAGE ROOMS
Numerous, specific and sectoral studies allowed the realisation of highly innovative controlled atmosphere storage systems. A great advantage and plus point for the fruits and vegetables sector.
The reduction of the amount of oxygen in a storage room, brings, as a consequence, the slowing down of the natural, metabolic process of every fruit and vegetable, which translates in an increase of the shelf life for every single product.
One of the advantges of controlled atmosphere storages is the almost complete absence of chemicals in the process. The creation of a controlled atmosphere environment links a lower temperature level to the reduction of the oxygen percentage in the air. This reduction is achieved by using specific machines which are able to absorb oxygen which is normally at a 20% level at standard atmosphere conditions.
Research evolution has allowed to apply this technique, whose scientific definition goes back to the 1900, also to larger storage rooms.
This is why it became possible to build very large controlled atmosphere storages, allowing produce companies to stock larger amounts of products, and easily distribute them throughout the year.