The industrial preservation with Cold storage for Onion, other vegetables, and fruits is an industrial challenge since each vegetable and fruit has its characteristics. And that requires a specific form of preservation and refrigeration to ensure that they maintain their properties and their active metabolism.
Climate and Non-climate fruits and vegetables:
The fruits are classified into climacteric (they can continue to ripen once they have been separated from the plant) and non-climacteric (they only ripen on the plant, and therefore must remain there until their optimum point of maturation). To determine which type each fruit belongs to, it is observed whether the fruit in question naturally increases its production of ethylene during its ripening process (climacteric) or this level remains almost unchanged during this process (non-climacteric).
As examples of climacteric fruits, we can mention apples, bananas, figs, pears, tomatoes … and as non-climacteric fruits: citrus, raspberry, grapes, pineapple, strawberry, cucumber, pepper …
The cold in the marketing of vegetables and fruits:
There must be an adequate collection, handling, storage, and distribution of fruits and vegetables so that they reach the final consumer in perfect condition.
Refrigeration is the best way to keep these foods fresh and increase their shelf life. Therefore, invest in commercial cold and industrial cold:
- Delays maturation and senescence (aging of tissue cells).
- Avoid the attack of microorganisms.
- Minimize global quantitative and qualitative losses of products.
The cold storage for onion in a controlled atmosphere, being ecological facilities if they use CO2, ammonia, and glycol as a refrigerant. These cold rooms control the temperature, humidity, circulation, and air renewal.
In the case of climacteric fruits, before picking the fruit, the time of collection, transport, storage, and distribution is calculated, so it is collected well before its ripening, which will later be completed in cold rooms that ensure adequate conditions, until the moment of its sale.
For non-climacteric fruits, the time of collection, transport, storage, and distribution is calculated taking into account that the fruit must be on the plant until the optimum moment of maturation, as we have commented.
Therefore, the factors that must be controlled in the refrigeration of fruits and vegetables are temperature, relative humidity, and ventilation (air circulation).
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Refrigerator chamber temperature:
The temperature affects the fruits in different ways, depending on whether they are climacteric, delaying their ripening, or non-climacteric, delaying their deterioration.
A high temperature will damage its tissues and destroy its enzymatic activity, if the temperature rises above 40ºC or 60ºC respectively, causing unpleasant alcoholic flavors and changes in the texture of the fruits.
On the contrary, a low temperature, freezing or close to it, will also cause unpleasant alterations in the taste and breakage of tissues.
In the case of tropical fruits, especially sensitive to cold, they will suffer injuries such as blackening and changes in taste, if they are subjected to temperatures between 5ºC and 14ºC for a certain period.
The temperature control will be carried out with a field of damping thermal probes that give a deviation from the interior conditions, in addition to, in some cases, a witness probe in the product, so its interior evolution can be compared over time.
Relative humidity in fruit refrigeration:
Along with temperature, humidity is another very important factor, since, during ripening, the fruits naturally perspire and lose water. Therefore, to avoid water loss or dehydration and the acceleration of the fruit’s senescence (the fruits and vegetables as a result of dehydration wrinkle and wither while losing weight and vitamins).
The cold rooms in which they are stored must have high relative humidity, being adequate, between 85 and 95%, generally 90 % for fruits and over 95% for vegetables. Although, the appropriate relative humidity for each product will depend on its surface/volume ratio. This value must be adequately controlled since excess humidity could cause the appearance and growth of molds.
The relative humidity is managed using control systems of the conditions of the refrigerant in question (CO2 refrigerant, ammonia, and glycol), inside the evaporator and/or humidification of the premises, with steam or sprayed water.
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Ventilation and industrial atmosphere in its conservation:
The atmosphere must be controlled with proper ventilation, to avoid that, due to the fruit’s respiration, an atmosphere is created whose oxygen level drops below 2%. If this happens, the fruits that need oxygen to change color for ripening will remain green, and fermentation processes will begin, leading to fruit loss.
Therefore, cold storage for onion must control the correct oxygen / CO2 ratios, and these will depend on the specific product in question. Changes in the proportion of these gases will generally be compensated with nitrogen, which does not cause any effect.
At the same time, the ethylene that the fruits naturally give off as a result of their ripening will have to be controlled, eliminating it with adequate ventilation.