Recent developments in osmotic dehydration.
Osmotic dehydration is an operation used for partial removal of water from foods such as fruits and vegetables. In this process, foods are placed in hypertonic (osmotic) solution. Three different mass transfer mechanisms occur in the osmotic dehydration; (i) water migration from food to the solution, (ii) solute migration from solution to food, and (iii) solute concerning product extracted to solution. Osmotically dehydrated fruits and vegetables are generally dried by hot air flow. In recent years, osmotic dehydration has been combined with various methods such as the high hydrostatic pressure, high electrical field pulses, gamma irradiation, ultrasound, vacuum and centrifugal force. These new combination methods increase mass transfer and drying rate and foods by increasing the cell membrane permeability. The operation time in the combined methods is shorter than that in traditional osmotic dehydration, causing further energy saving. In this study, recent advances in osmotic dehydration will be reviewed.
Enhanced Mass Transfer During Osmotic Dehydration of High Pressure Treated Pineapple
High pressure pretreatment (100–700 MPa) was applied to 
enhance mass transfer rates during osmotic dehydration of 
pineapples and accelerate the process. Experimentally determined 
diffusivity values, based on a Fickian model, increased 
fourfold for water and twofold for sugar. Diffusivity 
values were correlated with pretreatment pressure by an 
equation of the form D�A exp(�B/P), which suggests that 
diffusivity would level after an initial increase in pressure. 
The increase was attributed to breaking-up of cells walls 
which facilitated the transport of water. Evidence for the extent 
of cell wall break-up with applied pressure was based 
on differential interference contrast microscopic examination 
of tissue. Preliminary experiments on rehydration characteristics 
showed high pressure pretreated samples did not 
absorb as much water as controls.
Osmotic Dehydration Behavior of Red Paprika (Capsicum Annuum L.)
Osmotic dehydration of red paprika was studied using a combined sucrose (5 to 45 g/100 g) and sodium chloride (0 to 15 g/100g) solution. The effective diffusion coefficients for water and solute were determined using the slope method based on the Fickian diffusion model. The effects of concentration of sucrose, sodium chloride and their complex interaction on water and solute diffusion coefficients as well as on equilibrium moisture and solid contents were studied using central composite rotatable design of experiments. The graphical optimization showed that at optimum conditions (sucrose concentration and sodium chloride concentration were 21.86 g/100 g and 2.02 g/100 g, respectively), the following criteria were achieved: water diffusion coefficient (D cw ) ≥ 0.80 x 10 -9 m 2 /s, solid diffusion coefficient (D) ≥ 0.82 x 10 -9 m 2 /s, equilibrium moisture content (m∞) ≤ 6.85 kg/kg, and equilibrium solid content (s∞) ≤ 2.00 kg/kg.