Colour Change and Kinetics of Winter Jujube Slices during Pulsed Air-Jet Impingement Drying

The colour and the characteristics of colour change curves of winter jujube slices at different temperatures (55, 60, 65, 70, and 75 degrees C) by the single factor experiment during pulsed air-jet impingement drying were stidied. The experimental data of colour difference (Delta E*) were fitted and verified by classic colour change model of thin fruit and vegetable. The results showed that L*(whiteness/darkness) and -a* (redness/greenness) of winter jujube slices decreased with the increase of drying time at different drying temperatures, while the change in the early stage was rapid, the latter stage was slow. The b* (yellowness/blueness) increased with the increase of drying time at different drying temperatures. Under different drying temperatures, the colour difference (Delta E*) of winter jujube slices increased with the increase of drying time during the drying process, the change in the early stage was rapid, the latter stage was slow. When the drying temperatures were 55, 60, 65 and 75 degrees C, the first order fractional model of the colour difference (Delta E*) obtained the best fitting results with experimental data. Meanwhile, when the drying temperature was 70 degrees C, the first of the first order mode of the total colour difference (Delta E*) was the best.