Drying related properties of apple

Drying related properties of apple are evaluated for various different dryi ng methods (namely, convective, vacuum, microwave, osmotic and freeze dryin g). and their corresponding process conditions. The examined properties are drying kinetics, equilibrium material moisture content, density, porosity, color and viscoelastic characteristics. The effect of various process fact ors on these properties is described through particular mathematical models . The model parameters are estimated by fitting the corresponding model equ ations on a wide range of experimental data. Drying kinetics is greatly aff ected by the characteristic particle size and drying air temperature for co nvective drying, while for the case of microwave drying they are affected b y the vacuum pressure and the emitted radiation power. Equilibrium material moisture content is affected by the temperature and the humidity of the su rrounding air, while the osmotic pretreatment shifts the sorption isotherms to higher water activity levels. The quality properties examined, are sign ificantly affected by the drying method. More specifically, osmotic dehydra tion decreases the porosity of the final product, while it prevents color d eterioration and enchances the viscous nature of dehydrated apple. Freeze-d ried apples develop the highest porosity, have the most elastic structure a nd the lowest rate of color deterioration.