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News Article

Postharvest energy savings


Reducing ethylene levels allows higher storage temperatures for vegetables

Storing and transporting fruit and vegetables in low temperatures reduces postharvest losses, but refrigeration also increases energy costs and environmentally harmful emissions. Decreasing ethylene concentrations in the atmosphere surrounding the produce might be an alternative way for extending postharvest life. However, there have been few comprehensive studies – especially for non-climacteric produce – that quantify the relationship between temperature and ethylene concentration. A recent study investigated how different combinations of low temperatures and reduced levels of ethylene impacted postharvest life in green vegetables and discovered that reducing ethylene concentrations around produce could result in substantial energy savings.

The objective of the study, published in The Journal of Horticultural Science and Biotechnology earlier this year, was to examine the relationship between storage temperature and ethylene concentration on the postharvest life of the non-climacteric vegetables Chinese cabbage, broccoli, mint and green beans. The study also aimed to examine whether lowering ethylene levels could reduce the need for refrigeration in storage and transport.

“Reducing ethylene levels around produce delays the senescence of fruit and vegetables and therefore has the potential to reduce the need for refrigeration during transport and storage, which would result in substantial energy savings,” explained the authors.

Non-climacteric fruit and vegetables – which unlike climacteric species ripen without ethylene and respiration bursts – generate ethylene at relatively low levels, but in storage chambers the levels may still quickly accumulate. Ethylene around produce may also originate from vehicle exhausts and outside air pollution.

Postharvest life was determined by consumer purchase expectations; yellowing in Chinese cabbage and broccoli, leaf abscission in mint, and loss of firmness in green beans were assessed by visual examination to determine the level of decay in these vegetables. The vegetables, excluding mint, were studied in treatments comprising all combinations of four temperature (0, 5, 10 and 20 degrees Celsius) and four ethylene concentrations (1, 0.1, 0.01 and less than 0.001 μL per L). Mint was not exposed to 0 degrees Celsius, so the vegetable was studied in 12 instead of 16 treatments. Finally, the authors conducted a two-way analysis of variance to determine significant differences between treatments, and employed a multivariate regression analysis to describe the postharvest life as a function of storage temperature and ethylene concentration.

According to the results, the postharvest life increased as the temperature and ethylene concentration decreased. “The data indicate, for example, that to achieve a 14-day postharvest life, reducing ethylene to 0.001 μL per L would allow the temperature to be raised to about 10 degrees Celsius for Chinese cabbage, broccoli, and mint, and to about 18 degrees Celsius for bean,” the authors summarised. “These temperatures are well above the recommended temperatures of 0 degrees for Chinese cabbage, broccoli, and mint, and 5 degrees Celsius for bean, and could result in substantial energy savings.”

However, decreasing ethylene levels in this way to manage postharvest life would require some planning; the stakeholders involved in the supply chain would need to know when the produce will be marketed. The authors give some examples. “For broccoli marketed by 21 days, a storage temperature of about 5 degrees Celsius is acceptable if the lower levels of ethylene are maintained, and if marketed by 14 days, 8 degrees Celsius will maintain an acceptable quality at the lower ethylene levels.”

The study is original because it shows that reducing ethylene concentration was consistently beneficial in inhibiting vegetable decay at all temperatures from 0 to 20 degrees Celsius. The authors conclude that optimum storage conditions are at the lowest achievable ethylene concentration and lowest appropriate temperature considering chilling injury susceptibility.

Interested in finding out more about the role of ethylene in storage life? Subscribers to Horticultural Science can use the search string "storage" AND "ethylene" AND "quality" and return over 3,000 results. A selection is given in the further reading below.

Reference

Li Y, Wills RBH, Golding JB (2017) Interaction of ethylene concentration and storage temperature on postharvest life of the green vegetables pak choi, broccoli, mint, and green bean. The Journal of Horticultural Science and Biotechnology, published online. DOI: 10.1080/14620316.2016.1263545