Quarantine treatment of cherries using 915 MHz microwaves: temperature mapping, codling moth mortality and fruit quality

Sweet cherries (Prunus avium L.) were treated by 915 MHz microwaves in a pi lot-scale multimode microwave system with an auxiliary hot air heater to de termine heating characteristics and the effect of treatments on insect mort ality and fruit quality. Quality parameters of the microwave-treated 'Bing' cherries were compared with control fruit and those subjected to methyl br omide fumigation. When heating cherries to average pit temperatures of 45, 50 and 55 degrees C, the cherry pits heated faster than the surface, and la rger cherries heated more quickly than smaller ones. Cherry temperature inc reased linearly with time with heating rates dependent on the microwave pow er, sample weight, cherry size and radial location inside the cherry. With a 2 min holding and 5 min hydrocooling protocol after microwave treatments, adjusted percentage 3rd instar codling moth (Cydia pomonella L.) mortality ranged from 5 to 62% and 39 to 98% without and with 1-2 days cold storage, respectively. A higher mortality rate was obtained for insects in 'Bing' t han 'Rainier' fruit. Firmness, percentage soluble solids content, titratabl e acidity, fruit weight, and objective fruit colour of microwave-treated 'B ing' fruit were comparable with these properties of control fruit and to th ose of cherries fumigated with methyl bromide. Stem greenness colour was re duced after the microwave and dry hot air combined treatments. Microwave en ergy may provide an alternative non-chemical quarantine treatment against c odling moth in export cherries, but further study is needed to optimize the treatment protocol for insect control and fruit quality. (C) 1999 Elsevier Science B.V. All rights reserved.