The time required for the gas composition to stabilize to quasi steady state is an important factor in MA storage. The stabilization period is a function of the designed gas composition, commodity respiration, relative stacking volume, and airtightness of the system. The time required to reach the stable gas levels may be in the order of days to weeks. If the stabilization period is too long, the product may deteriorate more than desired. In this situation, it may be advantageous to use a rapid O2 pull-down method for the initial modification of the atmosphere.MA storage systems are widely used in European countries, whereas they are only beginning to be popular in North America (45). Several silicone membrane-based systems have been conceived since the early 1970s, the most popular of which is the Marcellin system. This system consists of a series of silicone rubber bags that are connected in parallel (Fig. 16). Air from the storage room is circulated through the exchanger, resulting in an exchange of gases as they diffuse through the silicone rubber bags. The amount of diffusion taking place can be changed by changing the number of bags that are being used. The maintenance of 5% CO2 and 3% O2 requires 50 m2 of silicone membrane for every 100 tons of fruit at a bulk density of 200 to 250 kg.m-3 (41). A modified version of the Marcellin system uses a diffusion unit that functions similarly to a plate heat exchanger. Within an airtight box, a number of gas diffusion panels made by using square framing hold the semipermeable silicone membrane in place. Air from the storage room is passed through the diffusion unit by a blower, and in the same manner outside air is passed through the diffusion unit. A silicone membrane separates the two types of air flowing through the system and allows the diffusion of gas from one side of the membrane to the other (45). The air from the storage room picks up some O2 and releases some CO2 as it contacts the silicone membrane. The outside air passing through the diffusion unit absorbs the excess CO2 and releases O2.
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