Post-harvest treatments for fruits: promising results with ozone

Ozone has a strong interest for fruit preservation due to its strong oxidizing power. However, its use, which is still unregulated* in this sector, may be potentially dangerous. While waiting for the legislative framework to evolve, trials conducted in Switzerland and France are evaluating the interest of this molecule for post-harvest applications.

Since 2015, the Swiss research center, Agroscope, has been conducting experiments in collaboration with DLK Technology on apples and strawberries, with post-harvest ozone treatments, at different doses and frequencies of application. According to the results, these treatments have allowed limiting the development of fungal diseases without completely inhibiting them. They had no negative impact on the physico-chemical properties of fruits (firmness, acidity, and sugar content) or on the sensory qualities of strawberries. However, on apples, lenticular burns could be observed, as well as an increase in greasy appearance, at high doses or frequencies of application. According to Séverine Gabioud Rebeaud, researcher at Agroscope, "ozone must be applied with great precautions" to protect operators, with the need for "good ventilation and precise regulation" in storage cells "to avoid the accumulation of ozone in certain places that could be harmful to fruits."

Finding the right dose and the right frequency of ozone application is a major issue "for each fruit and even each variety of fruit", an excess can induce physiological damage on fruits, while a quantity too low can affect treatment effectiveness. To conclude, "according to our experiences since 2015, ozone is an interesting solution to fight against secondary diseases (Botrytis, Penicillium...) but on orchard diseases like lenticular rot, it's a bit more difficult, because ozone must destroy the epidermis of the fungus."

French trials confirm these results

On the TOAsT platform of PURPAN's engineering school dedicated to ozone research, trials were set up in 2018 in three storage rooms to evaluate the performance of ozone-based conservation on Pink Lady apples for one month. The application of ozone had a beneficial effect on Phytophthora disease, with a significant reduction in the surface fungal population. In terms of sensory quality, no harmful changes were observed. These results were confirmed by results obtained in 2019 with fruits that were not treated before harvesting and stored for 5 months.

Frédéric Violleau, Deputy Director of Research at PURPAN, is now "convinced of the fungistatic effect of ozone" and that it is a "non-remnant solution", with no residue for consumers. "Also, applying ozone in storage rooms under a protective atmosphere is a solution that does not expose operators to ozone concentrations that could be harmful." These results were presented at the CTIFL webinar on February 4, 2021.

* To date, in France, ozone is only authorized for treatment of water intended for human consumption and ready-to-eat salads.