Postharvest Ethylene Research: What the Studies Actually Found
Most postharvest guidance treats 0.1 µL/L as the ethylene level where damage begins. Three Australian studies published between 1999 and 2001 suggest that figure is far too high — and that the ethylene levels found in ordinary supermarkets, distribution centres and wholesale markets are already costing shelf life every day.
Here is what the research found, what it means in a packing shed, and where it stops short.
1. The damage threshold is far lower than the industry assumes
Wills, Ku, Shohet and Kim tested 23 kinds of non-climacteric fruit and vegetables across a range of ethylene concentrations, at both ambient and cold temperatures. They found storage life extended linearly as ethylene concentration fell logarithmically — and that produce held below 0.005 µL/L lasted roughly 60% longer than produce held at 0.1 µL/L.
Their conclusion was that the real threshold for ethylene action sits well below 0.005 µL/L, and that commercial storage never gets near it. Any step that reduces ethylene accumulation around non-climacteric produce will extend its postharvest life.
Wills, R.B.H., Ku, V.V.V., Shohet, D. and Kim, G.H. (1999). Importance of low ethylene levels to delay senescence of non-climacteric fruit and vegetables. Australian Journal of Experimental Agriculture 39(2): 221–224. View at CSIRO Publishing
2. Real supply chains sit well above that threshold
The obvious question is what ethylene levels actually occur in commercial handling. Warton, Wills and Ku answered it directly, taking more than 700 measurements over three years across wholesale markets, distribution centres, supermarket retail stores and domestic refrigerators.
| Environment | Mean ethylene level |
|---|---|
| Supermarket receival, storage and display | 0.017 – 0.035 µL/L |
| Wholesale markets and distribution centres | approx. 0.06 µL/L |
| Domestic refrigerator, no apples present | 0.029 µL/L |
| Domestic refrigerator, apples present | 0.20 µL/L |
From this the authors proposed a working rating scale: at or below 0.015 µL/L, less than 10% of potential postharvest life is lost; at or above 0.1 µL/L, the loss is unacceptable.
Set the two studies side by side and the gap is clear. The best-performing environment measured — a supermarket cold room — still sits several times above the level at which produce reaches its full potential shelf life. A wholesale market or distribution centre sits higher again. The loss is not caused by a fault or a breakdown; it is the normal operating condition of the chain.
Warton, M.A., Wills, R.B.H. and Ku, V.V.V. (2000). Ethylene levels associated with fruit and vegetables during marketing. Australian Journal of Experimental Agriculture 40(3): 465–470. View at CSIRO Publishing
3. It matters most for the most sensitive crops
The third study turned to climacteric fruit — the crops that ripen after harvest. Wills, Warton, Mussa and Chew held mature unripe mango, peach, custard apple, kiwifruit and tomato at 20°C under controlled ethylene concentrations, with kiwifruit and custard apple also tested at 0°C and 14°C respectively.
Time to ripen increased linearly as ethylene fell logarithmically, across the whole range tested. But sensitivity varied considerably between crops:
banana and kiwifruit > custard apple and mango > tomato, avocado and peach
The authors were careful about what follows from this. Because commercial ethylene levels are always above 0.005 µL/L, climacteric fruit cannot be held unripe as long as it theoretically could — but they concluded that active intervention to limit ethylene is warranted mainly for the most sensitive crops, not universally.
That caveat is worth taking seriously. It argues against blanket treatment and in favour of matching the intervention to the crop, the ethylene load and the length of the chain.
Wills, R.B.H., Warton, M.A., Mussa, D.M.D.N. and Chew, L.P. (2001). Ripening of climacteric fruits initiated at low ethylene levels. Australian Journal of Experimental Agriculture 41(1): 89–92. View at CSIRO Publishing
What this means for a packer
Assume ethylene is present. The measurements say it always is. Planning on the basis that a clean, well-run cold chain is a low-ethylene environment is not supported by the data.
Target the sensitive crops first. The 2001 sensitivity ranking is a practical priority list. If budget is limited, the return is highest on the crops at the top of it.
Match the method to the load. A high-ethylene-generating crop in a large carton is a different problem from a low-generating crop in a retail pack, and the same solution will not serve both. Later work by Wills and Warton on potassium permanganate absorbents found removal efficiency declined over time and suggested such absorbents suit lower ethylene-generating produce, with larger packages of high-generating produce requiring impractical quantities of absorbent. Sizing matters.
Consider the barrier as well as the scavenger. Reducing ethylene accumulation and slowing respiration are two different levers. Modified atmosphere packaging addresses the second; ethylene absorption addresses the first. Long chains and sensitive crops often need both.
Further reading
Wills, R.B.H. and Warton, M.A. (2000). A new rating scale for ethylene action on postharvest fruit and vegetables. In Improving Postharvest Technologies of Fruits, Vegetables and Ornamentals, pp. 43–47. Artés, F., Gil, M.I. and Conesa, M.A. (eds). International Institute of Refrigeration, Murcia, Spain.
Wills, R.B.H. and Warton, M.A. (2004). Efficacy of potassium permanganate impregnated into alumina beads to reduce atmospheric ethylene. Journal of the American Society for Horticultural Science 129: 433–438.
Jobling, J. (2002). Postharvest management of fruit and vegetables. Good Fruit and Vegetables Magazine, January 2002. Sydney Postharvest Laboratory Information Sheet.
Sydney Postharvest Laboratory. Postharvest ethylene: a critical factor in quality management. Information Sheet.
Related reading
Not sure which crops in your program are most exposed?
Biopac engineers MAP bags to the respiration rate of each crop and sizes Fresh Up® ethylene absorption to the load and carton. Tell us the crop, the carton and the length of the chain, and we will tell you what the numbers suggest.
