Kinetic modeling of phenolic compound degradation during drum-drying of apple peel by-products

• Application of higher temperatures (140 and 130 °C) yields higher drying rates.
• Total phenolic content (TPC) degradation exhibited first-order kinetics.
• Retention of the TPC was higher at lower temperatures and longer times of residence.
• TPC degradation dynamics and their relation with moisture removal are reported.

The apple peel, a by-product of apple processing, has a high total phenolic content (TPC); however, these compounds can be highly thermosensitive and unstable. Therefore, the aim of this study was to determine the degradation kinetics of the TPC in apple peels during drum-drying as a stabilization and recovery method. Apple peels (Granny Smith) were dried at 110, 120, 130 or 140 °C for 250 s with a constant drum clearance (0.2 mm). TPC degradation exhibited first-order kinetics and their retentions at the end of the process were 73.13% at 110 °C, 57.28% at 120 °C, 43.40% at 130 °C and 21.10% at 140 °C. Finally, empirical models were significantly fitted to predict the TPC as the apple peels reached a certain level of dehydration, which may be useful from the processing standpoint and validate the use of drum-drying as a process tool for the recovery of apple industrial wastes.