Optimization of Ultrasound-Assisted Osmotic Dehydration of Ber (Ziziphus mauritiana)

Abstract

The effect of ultrasound-assisted osmotic dehydration on drying kinetics of ber (Ziziphus mauritiana L.) was analyzed. Slices of ber samples were pre-treated using KMS and ultrasound-assisted osmotic dehydration (UAOD) and dried in a drying oven. An investigational design was developed to assess the effect of ultrasound time, amplitude, and osmotic solution concentration on the water loss and sugar gain during the drying time. The ultrasonic pre-treatment was carried out for 10,20,30 minutes and at 30,60,90% amplitude at 25°C. Osmotic solution concentration of 40,50,60 °Brix was applied in the treatments, the sample to solution ratio kept is (1:5), and air drying was carried out at 70°C. The effects of drying parameters (ultrasonication time, ultrasonication amplitude, syrup concentration) on the sample's drying kinetics and physicochemical properties were analyzed. Based on these physicochemical properties, the process parameters for osmotic dehydration of ber slices were optimized using response surface methodology. The physicochemical properties analyzed were DPPH (2,2-diphenyl-1-picrylhydrazyl) assay (antioxidant property), total phenolic content, total soluble salts, water activity, and acidity. The cell wall shape and connection between the cells are lost, and tissue breaks down due to osmotic dehydration. Ultrasound creates the formation of microscopic channels in the fruit structure. The changes due to osmotic dehydration and ultrasound reveal the effect on water diffusivity. Ultrasound treatment increases water diffusivity due to the formation of microscopic channels, which also offers lower resistance to water diffusion. In order to achieve the best-operating conditions for maximum WL, drying rate, and solid gain, MC of ber slices, RSM was helpful in optimizing process parameters for osmotic dehydration as pre-treatment of ber slices. The condition optimized for maximum WL, TSS and drying rate minimum MC, acidity and water activity were 90% ultrasonication amplitude, 30 minutes ultrasonication time, 60°Brix syrup concentration in order to get MC 0.84 and drying rate of 0.0046. The condition optimized for DPPH, and TPC, were 60% ultrasonication amplitude, 20 minutes ultrasonication time, 50°Brix syrup concentration. To cut energy costs and preserve the product's authenticity, osmotic dehydration of ber could be used as a pre-treatment prior to air-drying.