A continuous study on qualitative assessment of rehydrated 'Annurca' apple. Influence of process conditions and drying pre-treatment

In a previous paper the effect of chemical pre-treatment on quality attributes of 'Annurca' apple slabs dried at different temperatures was investigated. Herein, we evaluated the effect of the same pre-treatment on the quality attributes of the same dried 'Annurca' apple samples rehydrated at two temperatures. Specifically, slabs were initially pretreated in a dipping solution containing trehalose, sodium chloride, sucrose. Then, they were dried by using a convective dryer at 50°, 55°, 60°, and 65°C, and rehydrated at 30° and 70°C by immersion in water. The combination of pre-treatment, drying at 65°C and rehydration temperature of 30°C enabled to obtain the best preservation of rehydration indices (i.e, water absorption capacity), structure and colour properties. On the contrary, the highest antioxidant activity (EC50) in treated samples was found at the lowest drying temperatures (50° and 55°C) among those investigated and rehydration temperature of 30°C. The PCA provided different behaviours among untreated and treated dried apples when rehydrated at 30° and 70°C, demonstrating that this pre-treatment combined with drying/rehydration temperatures influenced the quality attributes of rehydrated samples.