Ozone fumigation as a postharvest treatment

In a world demanding more from every harvest, ozone fumigation could help South African fruit growers to stay ahead. By Ilyaas Rhoda.

Postharvest treatments are essential for meeting phytosanitary requirements and maintaining fruit quality during storage. However, the fruit industry is under increasing pressure to adopt greener treatments.

Ozone fumigation could offer a science-backed upgrade to existing postharvest treatments. A project funded by Hortgro and the Post-Harvest Innovation Programme and led by Dr Renate Smit is examining the use of ozone fumigation to control specific phytosanitary pests and postharvest pathogens.

Smit manages PHYLA, the pome- and stone-fruit industry’s specialised phytosanitary facility.

Testing ozone at PHYLA

Ozone is a naturally occurring compound consisting of three oxygen atoms. It is highly reactive and commonly used as a disinfectant, as it can destroy microbes, mould spores, and pests.

When used in fumigation, ozone gas is pumped into a sealed chamber or cold room, spreading evenly across the fruit and through the surrounding air. During the disinfection process, ozone is converted to regular oxygen, making it an eco-friendly solution.

“Ozone fumigation is quite new, and people are afraid of using it because it is reactive and potentially dangerous,” says Smit. “However, our system is highly controlled, and we have invested significantly to streamline all processes.”

PHYLA’s high-tech facilities make upscaling easy. Preliminary trials involve modified two-litre containers with three valves and a sampling port. If a treatment works on this, the smallest scale, the next step is a cubic-metre box, followed by a cold room.

Cold-room temperatures and atmosphere are constantly monitored, and Smit can manage the entire system directly from her smartphone. “This sophisticated system takes readings every five minutes to detect any potential issues,” says Smit. “If anything changes, I receive instant alerts and can usually make adjustments remotely.”

Diverse treatments for diverse fruit

Ozone fumigation is not a one-size-fits-all solution. Smit tailors each treatment, considering several factors before deciding on the best approach. For example, fruit characteristics like sugar content and natural wax layers vary across seasons and cultivars, and can affect treatment efficacy.

“These differences need to be carefully considered and could impact how different cultivars react to fumigation,” states Smit. “A treatment may work well for one cultivar but might not be suitable for another.”

The treatment approach depends largely on the target pest or pathogen. Trials have shown that both higher ozone concentrations for shorter periods, such as a 24-hour treatment, and lower concentrations over extended durations can be effective.

In the case of cherries, the main concern is typically pathogens rather than insects. Since cherries are often airfreighted, a high-dose 24-hour ozone treatment is ideal.

In contrast, pears are stored for longer periods, often 8–9 months and are not usually airfreighted. The objective is to preserve fruit quality over time. A lower concentration of ozone applied over a longer period can reduce postharvest decay.

“The aim is to have significantly high insect mortality and spore reduction with no impact on fruit quality,” says Smit. “Ideally, treated fruit should appear nearly identical to when it was harvested.”

The objective is to make ozone fumigation commercially viable. While it may not eliminate all pests and pathogens, reducing decay means more fruit reaches consumers, increasing value for farmers. Smit urges the industry to stay involved, support the research, and help unlock its full potential for the fruit sector.

What does industry say about this research?

“As traditional chemicals face growing restrictions, ozone fumigation is gaining attention as a sustainable, residue-free alternative. It shows promise for pathogen control and sanitising storage environments. Applications range from low-dose ozone during storage for fruit quality and high-dose ozone for empty room sanitisation.

“However, adoption is still limited by high equipment costs and concerns such as lenticel damage, for which ozone may become the scapegoat in cases where the damage may result from other factors. Lenticel damage due to high-dose ozone is a risk and emphasises the need for ultra-sensitive dosage controllers.

“Despite these challenges, ozone offers value as part of an integrated postharvest approach. Industry leaders recognise it might not replace existing postharvest methods overnight. However, it could play a vital role in safeguarding export quality and enabling chemical compliance.”

Braam Mouton. Postharvest Technical Manager at Dutoit Agri.