Scientists from New Zealand's Plant & Food Research have been trialling a specially engineered high-pressure washing machine for taro to help reduce the risk of pests entering the country.

Taro is a particularly difficult vegetable to clean as it is covered in fibrous leaf and root matter and its pitted nature can mean soil residues.

The high-pressure washing machine has been tested along with hot water treatments for its ability to eliminate this material and remove or kill microscopic organisms.

The machine, which was designed and built by engineers at Plant & Food Research’s Ruakura site, forms part of a larger biosecurity project by the Ministry for Primary Industries (MPI) to reduce the use of the fumigant methyl bromide, an ozone depleting gas which can damage the vegetable and affect storage quality and shelf life.

"This has necessitated finding new applications in pest management which meet border control requirements while not compromising the quality of the product," Plant & Food Research postharvest science team leader Dr Allan Woolf said.

"A core aim of the project is to radically reduce fumigation rates of methyl bromide from around 80 percent currently to five percent, while ensuring taro corms of significantly higher quality."

Another key goal of the trial is to ensure that organic matter and unwanted organisms are removed without damaging the product itself. Although detailed post-trail data still need to be collected, initial results are said to be positive.

The machine follows a similar design to those manufactured to clean apples and citrus fruit, but with a modified brush bed and high-pressure nozzles which target the taro corms at specific angles as they sit between the rollers.

The testing in Samoa included establishing the movement of the taro through the machine to optimize the rotation speed and efficacy of the brush rollers, establish the ideal pressure and orientation of the water nozzles, and ensure efficiencies around water use and filtration.

The project also involves gaining a better understanding of the organisms associated with taro.

"As well as assessing the tolerance of taro to hot and high-pressure water treatments, it’s important to study the life-cycle of mites and nematodes, and their mortality rates after treatment," the organization's applied entomologist Lisa Jamieson said.

"From this, we may be able to develop a new quarantine export procedure."

The current machine is not intended as a full commercial unit, but further testing may extend to semi-commercial runs in a packhouse setting to better determine taro shelf life and quality post-treatment.

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