POST HARVEST THE SCIENCE

Ethylene (C₂H₄) is an odourless, colourless gas naturally produced and released by fresh fruits and vegetables as a ripening agent.

Ethylene gas is also an ever-present pollutant resulting from exhaust fumes from internal combustion engines (including propane-powered forklifts), improperly vented greenhouse heaters, industrial waste, and similar sources.

Ripening fruit is well known for producing ethylene. However, other plant tissues also produce this gas and can lead to decay and wilting. Even when cut from the growing plant, fruits, vegetables, and flowers are still alive and respiring. Gaseous respiration products of fruits and vegetables, production by normal healthy flower and plant tissue, chopped or damaged leaf tissue, and diseased leaves and tissues can all be significant sources of ethylene.

Ethylene, also known as the “ripening hormone”, plays a regulatory role in many processes of plant growth, development and senescence.

Fruits, vegetables and flowers contain receptors which serve as bonding sites to absorb ethylene molecules. The common practice of placing a kiwi, avocado or banana in a bag to hasten ripening is an example of the action of ethylene on produce: increased levels of ethylene contained within the bag, released by the produce itself, serve as a stimulant to initiate the production of more ethylene. The overall effect is to hasten ripening, ageing and eventually spoilage.

A refrigerator acts in a similar way: while kept closed to retain the desired temperature, it also enables an increased concentration of built-up ethylene. Any closed environment, such as a truck trailer, reefer container, ship’s hold, or warehouse will have a similar effect.

The effects of ethylene gas damage are: shrinkage of fresh produce and flower bulbs; spotting of leafy vegetables; yellowing; increased odour and sprouting; wilting of vegetables and cut flowers; scald and loss of crunch; and rind breakdown. Controlling ethylene levels preserves freshness.

Within the industry, it is estimated that losses directly related to ethylene run into billions of dollars annually. Removal of ethylene from the storage and shipping environment delays spoilage, reduces loss and increases profit.

Ethylene will penetrate most substances. It will permeate through produce cardboard shipping boxes, wood and even concrete walls.

Ethylene is harmful to many fruits, vegetables, and floral items. While ethylene is invaluable due to its ability to initiate the ripening process in several fruits, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the ageing process and decreasing product quality and shelf life. The degree of damage depends upon the concentration of ethylene, the length of exposure, and product temperature. One of the following methods should be used to ensure that ethylene-sensitive produce is not exposed:

1. Ethylene-producing items (such as apples, avocados, bananas, melons, peaches, pears and tomatoes) should be stored separately from ethylene-sensitive ones (broccoli, cabbage, cauliflower, leafy greens, lettuce and similar). Ethylene is also emitted by engines — propane, diesel and petrol powered engines all produce it in amounts large enough to damage the ethylene-sensitive produce mentioned.
2. Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene.
3. Remove ethylene with ethylene absorbing filters. These have been proven in reducing and maintaining low ethylene levels. If ethylene damage is suspected, a quick and easy way to detect ethylene levels is with hand held sensor tubes. This will indicate whether the above steps should be followed.

Ethylene has been scientifically proven to cause:

• Increase in respiration
• Water loss and weight loss
• Yellowing or spotting
• Production of more ethylene
• Accelerated ripening, ageing and decay
• Reduction in nutrient content, for example loss of vitamin C
• Taste and aroma changes, off-flavours such as bitterness
• Loss of leaves and flowers, sprouting, toughening

The research these pages draw on is published in subscription journals and industry magazines. Rather than host copies, we have summarised the findings — what each study measured, what it concluded, and what it means in a packing shed — with links to the original sources.

1. Postharvest ethylene research: what the studies actually found — three Australian studies on ethylene thresholds, measured levels in real supply chains, and how much shelf life is lost. Wills et al. (1999, 2001) and Warton et al. (2000), Australian Journal of Experimental Agriculture.
2. Ethylene management in postharvest handling — climacteric and non-climacteric crop tables, crop-specific damage symptoms, controlling sources in the shed, and removal methods. Drawn from Sydney Postharvest Laboratory information sheets.
3. How ethylene absorption works: the science behind KMnO₄ scavengers — the oxidation chemistry, and what determines how well a scavenger performs.
4. Postharvest fundamentals: temperature, moisture and the cost of delay — field heat, pre-cooling, why refrigeration itself dries produce out, and cool room air circulation. Drawn from Sydney Postharvest Laboratory information sheets.

Ethylene in your cold room or container?

Biopac supplies KMnO₄ ethylene absorption in two formats — filters for the storage room or reefer, and Fresh Up^® sachets for inside the carton. Which one you need depends on the crop, the load and the length of the chain.

See ethylene filters
Talk to us about your crop