Types Of Ca Storage

During the past 60 years, tremendous progress has been made in the technology of CA storage. The commercial application of CA during transit and storage has received considerable attention since 1960, resulting in the development of different methods of establishing and maintaining CA. These include regular CA; short-term, high-C02 treatment; rapid CA; low-oxygen CA; low-ethylene CA; and low-pressure, or hypobaric, storage.

Short-Term High-C02 Treatment

Short-term, high-C02 treatment was originally developed to maintain the firmness of Golden Delicious apples (1). Subsequently, it was found that pears and other fruits and vegetables also benefit from this treatment (2,3). This treatment involves the exposure of fruit to 10-20% C02 for four to seven days prior to adjustment of the atmosphere to regular CA concentrations. Carbon dioxide injury of the fruit skin may occur if moisture has condensed on the surface of the fruit. This high-C02 treatment gives excellent results in maintaining the quality of Golden Delicious apples and Anjou pears (1,2,4).

Rapid CA

Rapid CA is a strategy that shortens the time between harvest and establishment of the desirable CA conditions (5). The faster the CA conditions are attained after harvest, the better the fruit quality can be maintained, providing that the cooling rate in storage is not adversely affected by the rapid loading of the room. To achieve the objectives of rapid CA, the storage room should be filled and sealed within three days or less of harvest.

Low-Oxygen CA

Low-oxygen CA has recently received increased attention; not only because it markedly retards fruit softening, but also because it greatly reduces the development of storage scald and breakdown of apples and pears (6). In regular CA, the recommended 02 concentrations are usually 2% or higher. It has been found that 02 levels between 1 and 1.5% are even more effective in extending the storage life of some fruits and vegetables (7). Careful monitoring to maintain the precise 02 level is essential to avoid damage due to anaerobic respiration.

Low-Ethylene CA

In low-ethylene CA, ethylene is scrubbed from the C A room to improve storage quality of the fruit. Removal of ethylene from the storage atmosphere results in retardation of ripening, retention of flesh firmness, and reduction of the incidence of superficial scald of apples (8). It is generally recognized that the concentration of ethylene should be maintained below 1 ppm to obtain the beneficial effect of low-ethylene CA. Storage life of several apple varieties such as Empire and Bramley's Seedling can be extended by this technique (9,10).

Low-Pressure Hypobaric, Storage

Low-pressure, or hypobaric, storage consists of storing fruits and vegetables at below-normal atmospheric pressure. Enhanced diffusion of gases under reduced-pressure facilitates the loss of C02 and ethylene from the commodity and reduces the 02 gradient between the inside and outside of the commodity. The partial pressures of 02 is directly related to the absolute pressure of air (11). Thus the 02 concentration is equivalent to 0.55% at 20 mm Hg. Ethylene inside the fruit is also reduced proportionally. Therefore, this storage technique combines the advantages of low 02 storage and low-ethylene storage. Ripening can be inhibited and storage life prolonged when fruit are stored under hypobaric conditions.

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