ABSTRACT
This paper presents the effect of ultrasonic pretreatment on osmotic drying of ash gourd and its associated micro structural changes. The ash gourd cubes of dimensions 15 mm × 15 mm × 15 mm were subjected to ultrasonic (US) waves at a frequency of 30 ±1 kHz for 0, 10, 20, and 30 min. Then, osmotic drying was carried out by immersing the samples in 50, 60 and 70°C Brix sugar solution at various osmotic temperatures of 40°C, 50°C, and 60°C till equilibrium moisture contents are achieved in the samples. The microstructures of pretreated samples were examined using a scanning electron microscope. The results showed that an ultrasound pretreatment performed for more than 10 min had a positive effect on the mass exchange caused by osmotic drying. The creation of microchannels or the increase of tissue porosity in the samples was measured using ImageJ image processing software. Finally, the investigation showed that the ultrasound-assisted osmotic treatment prior to vacuum drying reduced the final drying time in the vacuum dryer by 47–70% and also reduced the total energy consumption by 56–63%.
