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

Abstract

Sweet cherries (Prunus avium L.) were treated by 915 MHz microwaves in a pilot-scale multimode microwave system with an auxiliary hot air heater to determine heating characteristics and the effect of treatments on insect mortality and fruit quality. Quality parameters of the microwave-treated ‘Bing’ cherries were compared with control fruit and those subjected to methyl bromide fumigation. When heating cherries to average pit temperatures of 45, 50 and 55°C, the cherry pits heated faster than the surface, and larger cherries heated more quickly than smaller ones. Cherry temperature increased linearly with time with heating rates dependent on the microwave power, 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’ than ‘Rainier’ fruit. Firmness, percentage soluble solids content, titratable acidity, fruit weight, and objective fruit colour of microwave-treated ‘Bing’ fruit were comparable with these properties of control fruit and to those of cherries fumigated with methyl bromide. Stem greenness colour was reduced after the microwave and dry hot air combined treatments. Microwave energy may provide an alternative non-chemical quarantine treatment against codling moth in export cherries, but further study is needed to optimize the treatment protocol for insect control and fruit quality.