Optimization of hot air drying temperature combined with pre-treatment to improve physico-chemical and nutritional quality of 'Annurca' apple

'Annurca' apple, a southern Italian cultivar, is known for its reddening, taste and flavour among the other types of apples, and also for health promoting effects. The aim of this study is to evaluate the effect of a novel pre-treatment, by dipping in a solution containing trehalose, sodium chloride, sucrose, and of drying process conditions (temperature and time) on drying kinetics and quality attributes of dried apple slabs. Drying experiments were carried out by convective drying at temperatures of 50, 55, 60 and 65 degrees C at a constant air velocity of 2.3 m/s. Pre-treatment provided an increment of moisture loss, and a reduction of drying time and shrinkage at all temperatures. The combination of pre-treatment and drying at 65 degrees C assured the lowest colour changes, the best preservation of structure, as well as the less shrinkage, the higher rehydration capacity and the highest score for sensorial overall acceptability. On the contrary, the used pre-treatment combined with lower drying temperatures (50 and 55 degrees C) better preserve the antioxidant activity of apple slabs. In conclusion, the proposed solution enabled to reduce the processing time and better retain the quality attributes (i.e. physical, chemical, nutritional, sensorial) of dried apples slabs for their commercialization as snacks. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.