Catalytic Infrared Dehydration of Onions

Abstract

Dehydrated onions are commonly dried with convection heating, which is inefficient and costly. This study compared the drying and quality characteristics of onion dried with catalytic infrared (CIR) heating and forced air convection (FAC) heating. Sliced high‐solids onions were dehydrated under 9 conditions: CIR heating with and without air recirculation, and FAC each operated at 60, 70, and 80 °C. In general, CIR both with and without air recirculation had higher maximum drying rates, shorter drying times, and greater drying constants than FAC at moisture contents greater than 50% (d.b.). Dried onion quality, measured as pungency degradation, was similar for both the drying methods at 60 and 70 °C. The color analysis showed better product color (whiter and less yellow) at lower temperatures for CIR and higher temperatures for FAC. The browning could have been caused by the higher surface heat flux of the CIR heating and longer process times of FAC drying. Aerobic plate counts and coliform counts were not significantly different for either product from the CIR or FAC drying. However, samples dried by the CIR had significantly lower yeast and mold counts than those dried by the FAC. It is recommended that CIR be used in the early stages of onion drying.

Processing and quality characteristics of apple slices processed under simultaneous infrared dry-blanching and dehydration with intermittent heating

“…The dramatic drop in drying rate after reaching the peak was mainly because following moisture removal in the surface layer, the speed of further drying is limited to the rate of moisture diffusion from the interior of the slice to the surface layer. This did not show a constant drying rate period, which agreed with many other infrared drying studies such as the infrared drying of onions and strawberries (Gabel et al, 2006;Shih et al, 2008). In general, thin slices showed higher drying rates than thick slices.…”

“…An empirical Page model was chosen to fit the drying curves in this study due to its simplicity and good performance of describing drying thin-layer fruits and vegetables in many reported works (Togrul, 2005(Togrul, , 2006Gabel et al, 2006;Kumar et al, 2006;Sacilik and Elicin, 2006). The model was stated as:…”

“…Platinum catalyst inside the CIR emitter oxidizes natural or propane gas, resulting in medium-and farinfrared radiation with peak wavelengths between 3 to 6 lm which match reasonably well with the three infrared absorption peaks of water in the wavelength range. Therefore, rapid heating of high-moisture foods has led to the successful demonstrations of blanching and/or dehydration of many fruits and vegetables including pears, carrots, and sweet corn kernels (Pan and McHugh, 2004), onions (Gabel et al, 2006), bananas and strawberries Shih et al, 2008), blueberries (Shi et al, 2008a,b), and apples (Zhu and Pan, 2009). SIRDBD can be operated in two heating modes, continuous and intermittent heating.…”

Processing and quality characteristics of apple slices under simultaneous infrared dry-blanching and dehydration with continuous heating

“…Catalytic IR (CIR) emitter is powered by natural gas or propane to produce thermal radiant energy through a catalytic reaction with a mesh catalyst pad built into CIR emitters. The radiation energy that is generated has a peak wavelength in the range of medium-and far-IR which matches reasonably well with three of the absorption peaks of water, resulting in rapid heating and moisture removal from high-moisture foods (Pan and McHugh, 2004;Gabel et al, 2006). Continuous IR heating mode, in this study, is achieved by maintaining constant radiation intensity through continuous supply of natural gas to CIR emitters.…”

“…Simple empirical drying model, page model, was used to fit the drying curves in this study based on reported works on drying thin-layer fruits and vegetables (Togrul, 2005;Gabel et al, 2006;Kumar et al, 2006;Sacilik and Elicin, 2006;Togrul, 2006).…”