Optimization of drying parameters and color changes of pretreated organic apple slices STELA JOKI * , JASMINA LUKINAC, DARKO VELI, MATE BILI, DAMIR MAGDI, MIRELA PLANINI Department of Process Engineering, Faculty of Food Technology, University J.J. Strossmayer of Osijek, F. Kuhaca 18, P.O. Box 709, 31000 Osijek, Croatia * Corresponding author. Tel.: +385 98 1666629, fax: +385 31 207 115, E-mail address: stela.jokic@ptfos.hr ABSTRACT The aim in this research was to determine the optimal drying parameters for the production of dried apple slices of good texture, good rehydration ability and suitable color. Organic apple samples variety “Florina” were pretreated and dried in laboratory tray drier at different temperatures. Different chemical pretreatments were applied on samples (dipping in 0.5% ascorbic acid solution; 0.3% L–cysteine solution; 0.1% 4–hexyl resorcinol solution and 1% sodium metabisulfite solution). Drying temperatures for nontreated samples were 50, 60, and 70 °C at airflow velocity of 1.5 ms -1 . Color changes were measured by chromameter and digital image analysis. The Page’s mathematical model was used to calculate the drying kinetic parameters. The obtained results showed a good agreement with experimental data. According to drying time, rehydration and color characteristics the optimal drying temperature was found to be 60 °C. The best results were achieved when samples were pretreated with 4–hexyl resorcinol. Keywords: Drying kinetics; Color; Rehydration; Pretreatment; Organic apple; Image analysis ABBREVIATIONS a red-green AK ascorbic acid solution b yellow-blue B blue BL blanching in hot water G green k, n parameters in model (6) L lightness-darkness LC L–cysteine solution