An intermittent microwave convective drying method combined with a real-time computer vision technique
was employed to detect the effect of drying parameters on color properties of apple slices. The experiments
were performed at air temperature of 40 to 80C, air velocities of 1–2 m/s, microwave powers of 200–600 W,
and pulse ratios (PRs) of 2–6. Drying rate and drying time varied from 0.014 to 0.000001 min1 and 27 to
244 min, respectively. The normalized lightness values had ascending and descending parabolic trends with
decrease in product moisture content. With descending dimensionless moisture content, redness, yellowness,
color change, hue angle, and chroma were enlarged. The normalized redness values changed from 4
to 3. Models relating drying parameters with drying time, drying rate, and lightness were obtained and found
to be significant (P<0.01). Results indicated that microwave power and PRs had more influence on lightness
and color change than other parameters.
کلید واژگان :
Apple slices, intermittent microwave convective drying, computer vision system, online monitoring, color properties
