Effect of microwave and ultrasonic pretreatment of carrot slices before infrared drying

The purpose of this study was to investigate the impacts of microwave pretreatment (MWP) and ultrasonic pretreatment (USP) on drying time, mass transfer rate, and effective water diffusivity (Deff) of carrot slices during drying in an infrared (IR) dryer. MWP was applied for 0, 15, 30, 45, and 60 s before the IR drying of carrot slices. Also, USP was applied in an ultrasonic bath for 0, 5, 10, 15, and 20 minutes. The results demonstrated that the MWP and USP decreased the drying time (higher moisture loss) of carrot slices. Also, the drying time of pretreated samples by 30-60 s microwave and 15-20 min ultrasound was significantly lesser than the untreated carrot slices (p<0.05). The calculated Deff values were varied from 1.80×10-9 to 2.79×10-9 m2s-1, and from 1.53×10-9 to 2.24×10-9 m2s-1, for samples pretreated by microwave and ultrasound, respectively. The experimental data of the drying process are in agreement with the commonly used thin film models, and the Page model with experimental constants (k and n) is suitable for describing the dehydration rate of carrot slices. In general, the use of MWP for about 30 s or USP for about 15 min is promising pretreatment techniques for IR drying of carrot slices with higher mass transfer and shorter drying time.