Tests carried out by Spanish scientists suggest that ozone treatment is at least 90 per cent as effective sulphur dioxide (SO2) in the protection and preservation of table grapes during cold storage.

Many grape varieties are particularly susceptible to fungal infection during high-humidity cold storage, for which SO2 is the traditional treatment. It is highly effective against decay, but has been shown to cause the machinery used in the preservation process to corrode, as well as induce allergic reactions in some consumers.

Francisco Artés-Hernández and a team of researchers at the Technical University of Cartagena, have compared several existing preservation methods with a new technique that involves exposing macroperforated packages of grapes at 0°C to cycles of 0.1 µll-¹ozone.

Under perfect conditions, ozone treatment compared very well with SO2. In addition, total phenolics - the antioxidant compounds found in many coloured fruits - increased in ozone-treated grapes, up to four-fold under certain conditions.

While this is an interesting consequence, it is not yet known why polyphenol levels increase, but Artés-Hernández said that because these compounds are up-regulated in response to environmental stress in plant cells, it could be that the ozone is perceived as a biochemical insult.

The scientist added that 90 per cent efficiency is already commercially viable, but more work is needed to get the fungal control up to the same level as that conferred by the harsher SO2 treatment.

One issue which may preclude mass use of the ozone treatment is its higher cost, which may see companies using the treatment aim for a niche market - in which people will pay more for a hypoallergenic, polyphenol-rich product.

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