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.
