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Hot Bath Foils Lychee and Longan Insect Foes

By Marcia Wood
May 4, 2004

Two exotic tropical fruits--lychee and its smaller cousin, longan--have sweet, slightly firm flesh with a pleasing texture that's been likened to that of a fresh, peeled grape. A packinghouse procedure developed by the Agricultural Research Service for preparing these tropical fruits for shipment from Hawaii to mainland U.S. supermarkets doesn't harm that delightful texture or appealing flavor.

At the same time, the process ensures that each lychee (also spelled litchi) or longan is free of live insect pests such as the litchi fruit moth or oriental fruit fly. If these insects were to stow away in shipments, they could pose a threat to crops in other warm-weather states.

ARS entomologist Peter A. Follett and colleagues designed, built and tested a twin-tank system that provides a hot-water bath to kill the insects, followed by a cooling bath to prevent spoilage and protect the fruit's flavor and fragrance. He's with the agency's U.S. Pacific Basin Agricultural Research Center in Hilo, Hawaii.

The unit features submerged, plastic conveyor belts studded with rubber cleats. These tracks take fruit smoothly in and out of the heating and cooling tanks.

The hot-water tank is calibrated precisely to meet federal requirement that the fruit be submerged for 20 minutes in water heated to 120 degree F. The work by Follett's team gives growers a proven, practical way to meet this requirement, which was established in 1997.

Follett worked with Glenn McHam of MMG Manufacturing, Inc., a Fresno, Calif, commercial equipment fabricator; John White, a Fresno designer of agricultural equipment; and Mike Strong, owner of Kahili Farms, Kilauea, Hawaii. One of Hawaii's premier growers and packers of tropical fruit, Kahili Farms is in the final stages of obtaining federal approval for the unit.

Read more about this research in the May issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.