Fruits and vegetables are commonly shipped for long distances from one country to another before they are ripe so they can endure the voyage and remain viable. Upon arrival at their destination, the first order of business is to get them ripe and ready for sale and consumption.
As fruit and vegetables ripen, they release ethylene, a naturally occurring growth hormone. To be profitable and meet demands, commercial fresh produce companies need to speed up the ripening process in a uniform and predictable way, which is achieved by adding more ethylene in a controlled environment. Typically the fresh produce is placed in air-tight ripening rooms and ethylene is introduced at concentrations between 10 and 1,000 ppm depending on the type of produce.
Ethylene is not harmful to humans in the concentrations used in ripening rooms. An extremely high level of ethylene would have to be inhaled in order to have an adverse effect on human health. That being said, ethylene is a very reactive and flammable gas, making the potential for an explosion a safety concern. The LEL for ethylene is 27,000 ppm (2.7%) and a common concentration used in a ripening room is 1,000 ppm (0.1% by volume), with a typical exposure time of 24 hours.
Two common ways to add ethylene to the ripening rooms is by high pressure gas cylinders or ethylene generators. If ethylene is delivered into the rooms by pipes from cylinders, there are areas for potential leaks and the threat of explosion from cylinders of pure ethylene is high. An ethylene gas detector would be highly recommended to continuously monitor the ethylene gas levels in the cylinder storage room.
In the ripening rooms, the primary reason for an ethylene gas detector is not for the safety of humans, but rather for the safety of the perishable goods. Assisted ripening is a complex process and predictions can be made about the remaining shelf life of the perishable goods based on the level of ethylene gas that is present; that the produce gives off. Some types of fruits and vegetables are more sensitive to ethylene than others. Ethylene sensitive produce will spoil if exposed to levels that make them ripen too quickly. Varieties that are more tolerant but don’t get the right amount will not ripen on schedule.
There is also the potential for ethylene to leak from one room into another, especially if the method of delivery is through a network of pipes. This could cause premature ripening or result in damage to the other types of produce in adjacent rooms. Monitoring the concentration levels of the ethylene gas in each room will help ensure the correct amount is being delivered at all times.
As fruit ripens, it releases carbon dioxide. This decreases the oxygen level in the room and delays the effects of the ethylene. CO2 levels in excess of 1% (10,000 ppm) will slow the ripening process, and can cause quality and production problems. When CO2 levels build up, the ripening room should be vented, which could be as simple as opening the door, or turning on a ventilation system. Constant monitoring of the CO2 levels inside the room with a gas detector that can be configured to activate the ventilation system at a predefined concentration would allow for more efficient control and optimization of the ripening process, a higher safety level and better production.
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CHEMAXX INC. “Ethylene Explosion – Banana Ripening.” (2006). Retrieved from http://www.chemaxx.com/explosion17b.htm [accessed 30 September 2015]
Catalytic Generators LLC “All About Ripening.” (2015). Retrieved from http://ripening-fruit.com/ingredients_for_proper_ripening [accessed 30 September 2015]