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Microwave convective drying of plant foods is a promising process due to the shorter drying time and better product quality. High microwave power decreases the drying time but causes charring of the product. In this work, microwave drying under constant and variable microwave power were compared. Temperature-sensitive products, such as plant foods, are especially affected by microwave power during the final drying period. Therefore, drying at variable microwave power was found to be a more suitable drying process. Air (temperature and velocity) has an important role during microwave drying, not only as carrier of evaporated moisture but also as it contributes to a more homogeneous and faster drying.

This work reports on the mass transfers and retention of phenolic compounds (RPH), condensed tannins (RT) and antioxidant activity (RA) of banana slices submitted to osmotic dehydration (OD). The slices were osmotically dehydrated according to a 2 2 full factorial design with three repetitions at the central point. The independent variables were temperature (30, 40 and 50C) and sucrose solution concentration (45, 55 and 65% w/w). The analyses of banana slices were performed after 60 and 180 min of process. There was an increase in the water loss and reductions in parameters L*, RPH and RA with increasing temperature of the solution. An increase in the osmotic solution concentration boosted the gain of solids. The RA of the osmotically dehydrated fruit was greater than 97%, leading to the conclusion that OD reduces the moisture of fruits maintaining the antioxidant activity of their bioactivities compounds with an intensification of fruits color.

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