Combined osmotic dehydration-microwave drying of fruits. application to apple cubes

N.L. WAIS; M. E. AGNELLI; R. H. MASCHERONI

Club Mediterranée Rio das Pedras, Brasil

Congreso; ENPROMER 2005, 4th MERCOSUR Congress on Process System Engineering; 2005

simultaneous mass and heat transfer takes place. Hot air drying is mostly used for this purpose, although this method is sometimes slow and energy demanding. The advantage of microwave technology is that allows a higher rate of drying, but it has still a low energy efficiency. Combination of osmotic dehydration (OD) with microwave drying appears as a promising possibility of application. Also, OD introduced as a pre-treatment may lead to obtain higher quality products. Mass transfer evolution in apple cubes treated by osmotic dehydration (OD) in sugar solutions (sucrose) was followed through weight loss and solids gain. After OD, fruits were dried to their final condition in a microwave oven (MWD) at different power conditions. Fruit quality was evaluated after each step, testing for colour and texture changes. Fresh fruit and only MWD fruits were used to compare the possible advantages of OD and OD-MWD and the influence of OD conditions (soluble sugars and contact time). The results show that the use of this combined process allows producing dehydrated apple with highly accepted sensory, colour and texture characteristics, removing all the accessible water in considerably shorter times for MWD than for the process carried out without pretreatment.