Ph.D. Thesis

"The studies of utilization of infrared and microwave radiation for apples drying"

The purpose of the study was to examine the changes of selected quality indexes of dried apples storied at 4, 25 and 40ºC, obtained using convective, infrared-convective and microwave-convective drying. The quality of the products was evaluated on the basis of fol-lowing properties: general (shrinkage, density and porosity), structural, optical (color and browning potential), reconstitution (water absorption capacity and rehydration kinetic), hy-groscopic (adsorption kinetic and isotherms), mechanical, nutritional (polyphenols content and radical scavenging activity) and by biological respiratory activity and sensory evaluation.  
Drying time of apples was reduced 63% and 30%, compared to convective drying, sup-ported by microwave and infrared radiation, respectively, and obtained dried materials had better quality indexes.
Microwave-convective dried apples had the best physical and chemical properties just after drying. However, the greatest changes occurred in the material during storage, so its properties were less advantageous than two other dried products after one year of storage.
It was found that the process with infrared radiation was better method to obtain dried apples, both in terms of quality, their stability during storage and lower costs resulting from shorter time of drying process.

Key words: microwave-convective drying, infrared-convective drying, convective drying, apples, physical properties, polyphenols, radical scavenging activity, sensory evaluation, shelf-life