Coffee Bean Heating Uniformity and Quality as Influenced by Radio Frequency Treatments for Postharvest Disinfestations

Abstract

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°C using RF energy by 4.6 min, compared to more than 237 min for samples to reach only 45°C when using forced hot air at 48°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°C in the interior of the sample and 50.6°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°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.

Pasteurization of Salmonella spp. in black fungus (Auricularia auricula) powder by radio frequency heating

“…As for horizontal temperature distribution, results were shown in Figure 4(b) and (c). Edge heating phenomenon was observed in each layer, the center temperature was the lowest Some studies which used cylindrical containers obtained similar results (Ozturk et al, 2018; Pan et al, 2012), and similar heating patterns were also reported for corn flour (Ozturk et al, 2019), coffee bean (Pan et al, 2012), potato starch (Zhu et al, 2017). This is due to that the edge areas absorb more electromagnetic energy (Tiwari et al, 2011), so edges was heated faster than center.…”