Synergy of ultrasound and osmotic dehydration in improving drying kinetics and quality of dried sweet potato (Ipomea batatas L.)

The effect of ultrasonic pretreatment and combined ultrasonic-osmotic dehydration using different pretreatment times (10, 20, 30, and 45 min) at 60 degrees C was investigated. The aim of the present work was to shorten the total drying time and to improve the quality of sweet potato slices. The results showed that the moisture effective diffusivity increased when ultrasound was used as pretreatment to reduce the drying time, while the osmotic solution had no effect on moisture diffusivity. Among different ultrasound pretreatment timings, 30 min ultrasonically osmotic dehydrated treatment (US/GC10%-3) proved the best in drying time reduction, which showed that ultrasound has a positive impact on osmotic dehydration. The drying kinetics of sweet potato slices were improved by sonication, which involves an improvement of mass transfer coefficient and drying rate. The logarithmic model showed the best fit to the experimental data for all treatments. For ultrasound treated samples, the parameters including enzyme inactivation, color, microstructure, mass transfer parameter had significant changes in comparison with distilled water treated and osmotically treated samples of sweet potatoes.