COFFEE BEAN HEATING UNIFORMITY AND QUALITY AS INFLUENCED BY RADIO FREQUENCY TREATMENTS FOR POSTHARVEST DISINFESTATIONS

Developing effective and economically viable treatments that replace chemical phytosanitary and quarantine practices is urgently needed for the coffee bean industry to maintain competitiveness in domestic and international markets. The objective of this study was to determine coffee bean heating uniformity and quality as influenced by radio frequency (RF) treatments for postharvest disinfestations. A pilot-scale, 27 MHz, 6 kW RF unit was used to study RF heating uniformity, develop a treatment protocol, and evaluate quality attributes in treated coffee beans. After comparing three selected electrode gaps, an appropriate gap of 14 cm was obtained to raise the central temperature of 2.75 kg samples to 48 degrees C using RF energy by 4.6 min, compared to more than 237 min for samples to reach only 45 degrees C when using forced hot air at 48 degrees C. RF heating uniformity in bean samples was improved by adding forced hot air and back and forth movements on the conveyor at 0.89 m min(-1). The final temperatures reached 50.4 degrees C in the interior of the sample and 50.6 degrees C on the sample surface, resulting in small uniformity index values of 0.023 to 0.060 for the interior temperature and 0.073 for surface temperature distributions. RF treatments combined with forced hot air at 48 degrees C to hold the target temperature for 10 min followed by forced room air cooling through a 3 cm product layer provided good bean quality. No significant differences in weight loss, moisture content, and color were observed between RF treatments and unheated controls.