A far-infrared radiation-assisted heat pump (HP-FIR), which is a novel drying method, was used for drying
chopped garlic and compared with conventional hot-air (HA) drying. The drying characteristics and
the qualities of the dried chopped garlic in terms of the allicin content, volatile oil content and colour
were investigated. HA and heat pump (HP) drying were carried out at a temperature of 50 C. The farinfrared
radiation (FIR) power levels used in combination with HP drying were 250, 350 and 450 W. A
coupled heat and mass transfer model was developed to estimate the effective moisture diffusivity (Deff)
and to predict the evolution of the moisture content and internal temperature of chopped garlic. The
experimental results showed that an increase in the FIR power resulted in a faster decrease in the moisture
content and a shorter drying time. The amounts of allicin in samples dried by HP-FIR at different FIR
powers were not significantly different; their percentage losses were about 20% higher than those
obtained from HA or HP drying. However, the volatile oil contents in all dried samples were similar to
those of fresh samples. HP drying provided garlic powder with the brightest colour as manifested by
the highest values of L and the hue angle. The values of L and the hue angle had a decreasing trend when
the FIR power increased. In addition to quality issues, the developed model could estimate the Deff of
chopped garlic rather well. The Deff value was in the range 0.41–1.43 1010 m2/s at the internal product
temperature range from 50 to 62 C. The predicted moisture content and internal temperature of chopped
garlic agreed quite well with the experimental data.
A far-infrared radiation-assisted heat pump (HP-FIR), which is a novel drying method, was used for dryingchopped garlic and compared with conventional hot-air (HA) drying. The drying characteristics andthe qualities of the dried chopped garlic in terms of the allicin content, volatile oil content and colourwere investigated. HA and heat pump (HP) drying were carried out at a temperature of 50 C. The farinfraredradiation (FIR) power levels used in combination with HP drying were 250, 350 and 450 W. Acoupled heat and mass transfer model was developed to estimate the effective moisture diffusivity (Deff)and to predict the evolution of the moisture content and internal temperature of chopped garlic. Theexperimental results showed that an increase in the FIR power resulted in a faster decrease in the moisturecontent and a shorter drying time. The amounts of allicin in samples dried by HP-FIR at different FIRpowers were not significantly different; their percentage losses were about 20% higher than thoseobtained from HA or HP drying. However, the volatile oil contents in all dried samples were similar tothose of fresh samples. HP drying provided garlic powder with the brightest colour as manifested bythe highest values of L and the hue angle. The values of L and the hue angle had a decreasing trend whenthe FIR power increased. In addition to quality issues, the developed model could estimate the Deff ofchopped garlic rather well. The Deff value was in the range 0.41–1.43 1010 m2/s at the internal producttemperature range from 50 to 62 C. The predicted moisture content and internal temperature of choppedgarlic agreed quite well with the experimental data.
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