A new method for ridding harvested fruits and vegetables of insect pests and microorganisms, without the use of ozone-depleting chemicals such as 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. Inside sealed chambers, alternating vacuum forces and pressurized carbon dioxide applications cause irreversible changes in the animals' cell chemistry and respiratory structures. Ethanol gas also is applied briefly to accelerate killing of fungi and bacteria and to damage insect eggs.

In practice, the process would be applied to pallets of fruits and vegetables to prevent insect 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 the developer, Manuel Lagunas-Solar, a research chemist at UC Davis' Crocker Nuclear Laboratory.

The process also controls spoilage and insect pests in dried fruits, grains and nuts. Only a few soft-tissue fruits, such as raspberries and blackberries, do not take the treatment well.

The researchers hope that the new technique will become a permanent substitute for methyl bromide, which destroys the Earth's ozone layer. Although it was scheduled for phase-out in 1997, methyl bromide is still used by processing companies and farmers because of a lack of feasible alternatives.