Luis Vargas and Hao Feng

Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign

In ultrasonication treatment, cavitation-induced activities may help to increase the transmembrane flux by changing plane cell membrane permeability and cell wall integrity. Moisture diffusivity is an important parameter for the design of drying process. Changes in the tissue structure caused by ultrasonication pretreatments might change the moisture diffusivity of plant tissues.
This study was undertaken to examine moisture diffusivity of apple tissues pretreated by ultrasonication.
Excised cylinders (0.51 cm diameter) of apple tissues (Red delicious, Golden delicious and Granny smith) were placed in distilled water (DW) with a sample-to-water ratio of 1:30 and agitated for 1 min at 100 rpm and 25°C. Washed cylinders were placed between two ultrasonic plates (10 cm spacing at 25kHz) in a water tank and treated with ultrasound for 0, 10 and 30 min. Treated cylinders were cut and weighed, and drying experiments were immediately conducted. The effective moisture diffusivities (Deff) of apple tissues were determined from drying curves produced with a TA Instruments Q50 thermogravimetric analyzer, using the slope method. The drying experiments were conducted at 70°C for 200 minutes.
Two falling rate periods were observed. The Deff for the three apple varieties and three ultrasonication pretreatment levels ranged from 3.98 x 10-8 to 5.0 x 10-8 m2/s for the first falling rate period and 3.7 x 10-8 to  5.1 x 10-8 m2/s for the second falling rate period.
Ultrasonic pretreated samples exhibited a faster drying than the Control. Significant different Deff values were observed between apple varieties. A significant higher Deff during the second falling rate was achieved in the ultrasound-treated granny smith samples, and no significant differences were observed within red delicious and golden delicious varieties.
Ultrasonic treatment can increase cell membrane permeability or cell wall damage, and may find use in drying enhancement for plant materials.