Catalytic Infrared Dehydration of Onions

Abstract

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.