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The importance of ethylene in the fruit ripening process

Ethylene has been used for decades in the degreening and ripening of fruit, as it is a naturally occurring gaseous plant growth substance, which is involved in many aspects of growth, development and senescence.  It has a profound effect on colour and flavour.

In nature, the release of small amounts of ethylene is triggered by temperature increase or invasion of the fruit by pests and pathogens. Ethylene release will in turn initiate the ripening process in neighbouring fruit. Ripening/degreening utilises the natural process under controlled conditions, to give the best results, at the right time.

In fruit like bananas, the starch turns to sugar and aroma develops during ethylene treatment and ripening takes place.  Citrus fruits do not ripen after harvesting, and the ethylene breaks down the green colour of the chlorophyll in the skin, to reveal the orange colour (degreening).It is important that the fruit is picked at the right time, still firm but not too green.

The degreening / ripening room design and operation need to take a range of factors into account.  Different types of fruit require different conditions.  The correct ethylene concentration, temperature, air flow, humidity and time will ensure an attractive even colour. CO2 and organic volatiles have to be removed. The fruit has to be stacked correctly to expose the surface to the circulating gas.

The Afrox branded gas mixture with ethylene as an active ingredient is Ripegas, which also contributes significantly to lower losses with regard to spoilage of fruit during transport. The fruit is transported before ripening, and undergoes the treatment after it has reached the destination from where it will be distributed to the market. 

Afrox recommends the use of a 5% ethylene in nitrogen for this purpose. Ripegas 5 ethylene is an explosive gas if mixed with air and can cause excessive damage if an ignition occurs through static electric discharge. Using Ripegas 5 will eliminate this as a risk and lower the cost of the ripening room, as no explosion proof electrical equipment is necessary. Some fruit is better suited for ripening with ethylene than others. Fruit like bananas, avocados and mangoes work very well.