STUDIES ON EFFECT OF ULTRASOUND ASSISTED OSMOTIC DEHYDRATION PROCESS ON CONVECTIVE DRYING OF PINEAPPLE SLICES

Abstract

The effect of ultrasound assisted osmotic dehydration (USOD) on convective drying kinetics and the quality characteristics of dried pineapple slices were investigated. A Box-Behnken design of response surface methodology was employed to characterize and optimize the process parameters of USOD process and investigate the effect of independent variables viz., osmotic solution concentration (50, 60 and 70°B), sonication time (20, 30 and 40 min), temperature (10, 20 and 30°C) and type of osmotic agent (Glucose and Fructose) on the water loss (WL), solid gain (SG), osmotic dewatering rate (ODR). Multi-criteria optimization based on maximum values of WL, ODR and minimum value of SG was evaluated. A 50°B osmotic solution concentration, 26.6 min of sonication time, 30°C temperature, using fructose as osmotic agent were found to be optimum process parameters. Osmotic dehydration (OD) without ultrasound assistance was run at optimised conditions and at ambient temperature. Results showed that USOD treatments increased WL, ODR and SG. The samples were then further finish dried employing Hot air (HA) cabinet drier and Infrared (IR) drier at three different temperatures (50, 60 and 70°C) at constant air velocity of 1.5 m/s. USOD treated samples showed a significant decrease in drying time, increased drying rate and effective moisture diffusivity. Experimental data were fitted to four semi-empirical thin layer drying models and the Page model gave the best fit for all the drying conditions. Drying temperature of 60°C was found to be optimum. The USOD treated IR dried samples at 60°C resulted in pineapple slices of better physico-chemical, microbial and sensory quality.