Development of a saline water immersion technique with RF energy as a postharvest treatment against codling moth in cherries

`Sweetheart' sweet cherries (Prunus avium L.) immersed in 0.15% saline water were treated with radio frequency (RF) energy. The dielectric and ionic conductivity properties of the immersion water and that of fruit were matched to obtain a relatively uniform temperature distribution within and among fruits during RF heating. With immersion in saline water of 0.15% NaCl, the mean temperature of the water and that of the cherries differed by less than or equal to 0.6 degreesC, while the maximum temperature variation within and among fruits determined within 1 min after RF treatment completion was < +/- 1.0 degreesC of the set temperatures of 48 and 50 C. The saline water immersion technique helped overcome the markedly high temperature differential problem within and among fruits; normally associated with treatments in air (without immersion) during RF heating. More than 99% mortality of the 200-400 codling moth larvae or 589-624 eggs was obtained at 50 C when treated for between 7 and 10 min (heating 2-5 min and holding 5 min). Most quality parameters analyzed were better, or are comparable with methyl bromide fumigated fruit. Saline-water-immersion treatment in RF may be used to overcome the problem of slow conventional hot air or water heating, as well as the non-uniformity of temperature associated with electromagnetic heating in air, for developing alternative quarantine treatment for fruits. (C) 2002 Elsevier Science B.V. All rights reserved.