A new method for ridding harvested fruits and vegetables of insect pests and microorganisms, without the use of ozone-depleting chemicals like methyl bromide, has been developed by researchers at UC Davis.

The technique, called metabolic stress disinfection and disinfestation, effectively suffocates insects found in harvested produce. Forces produced by alternating vacuum and pressurized carbon dioxide applications cause irreversible changes in cell chemistry and damage to essential respiratory structures. Ethanol gas also is applied briefly to accelerate killing of fungi and bacteria and to damage insect eggs.

The process would be applied to pallets of fruits and vegetables to prevent damage during storage and shipping, and to avoid transporting potentially invasive insects from one country to another. A patent is pending on the technology, which was reported in the July issue of the Journal of the Science of Food and Agriculture.

"All major fruits, including table grapes, citrus, apples, pears, bananas and kiwifruits, as well as vegetables and ornamental flowers, retain their quality when treated with this technology," said Manuel Lagunas-Solar, a research chemist at UC Davis' Crocker Nuclear Laboratory.

The process also has been shown to be effective in controlling spoilage and insect pests in dried fruits, grains and nuts. Soft-tissue fruits, such as raspberries and blackberries, are among the very few commodities that do not withstand the forces used in this method, he noted.

The researchers hope that the new technique will replace the use of post-harvest pesticides and allow for the complete phase-out of methyl bromide. Although originally slated for phase-out in 1997 because it destroys the Earth's ozone layer, the use of methyl bromide by processing companies and farmers has been extended because of a lack of feasible alternatives for fumigation.

An added environmental benefit of the new procedure is that the carbon dioxide and ethanol used during the treatment are recovered and recycled.

Lagunas-Solar is preparing a collaborative research project to test the new method's effectiveness on several insect pests and fruit flies with U.S. Department of Agriculture labs in Cape Cod, Mass., and in Hilo, Hawaii. He anticipates the new technology will receive regulatory clearance, and commercial processing units could be available in two to three years.