The effects of combined infrared-vacuum drying parameters, including infrared power (300-400 W), pressure (5-25 kPa) and time (0-140 min) on the drying kinetics of grapefruit slices were investigated. Both the infrared lamp power and vacuum pressure influenced the drying time of grapefruit slices. The regression results showed that the quadratic model satisfactorily described the drying behavior with highest R and lowest SE values. The effective moisture diffusivity increases as power increases and range between 5.83×10-10 and 2.13×10-9 m2/s. The colour scale parameters including redness (a*), yellowness (b*) and lightness (L*) values of dried grapefruit slices increased during drying. The rise in infrared power has a negative effect on the color change intensity (∆E) and with increasing in infrared radiation power it was increased. Different kinetic models were used to fit the experimental data and the results revealed that the power model was the most suitable to describe the ∆E.
