Influence of some process conditions on the rehydration of apple cubes

Dried fruit and vegetables are widely used as ingredients in many food formulations such as pastries, confectionery products, ice-creams, frozen desserts and yoghurts. The different water content of the dried fruit in respect to that of other ingredients may enhance the mass transfer (water or solutes) with problems of phase separation or loss of textural properties. Nevertheless it is not easy to obtain, only by a drying treatment, fruit pieces with "adjusted" aw values; hence, it could be profitable to have a standard dried fruit rehydrated in water or sugar solutions under appropriate conditions in order to obtain an optimum aw value. In this work, different rehydrating trials have been carried out on air dried apple cubes by varying the rehydration medium concentration (from 0 to 30°Bx), temperature (from 20 to 80°C) and agitation rate (from 0 to 250 r.p.m.). During rehydration, water content, water uptake and solid loss or gain of samples were measured. Results have shown that the rehydration time was the main important parameter for the water uptake and for the solid loss, while the medium concentration influenced only the solid gain of apple cubes.