Structural, physical, functional and nutraceutical changes of freeze-dried fruit

This review examines the structural, physical, functional and nutraceutical changes of lyophilized fruits. Collapse, porosity, color, glass transition temperature, rehydration capacity, ability to retain water, volatile compounds, phenolic compounds, ascorbic acid, and beta-carotene, were defined, and the causes of changes in these parameters, during freeze-drying, were analyzed. Advantages and limitations of the freeze-drying, were shown, and strategies to reduce the costs associated with its use were proposed. It was concluded that lyophilized fruit retained to a greater proportion characteristics of fresh fruits, compared with other methods of dehydration. The effects of freeze-drying on physical and chemical properties vary in accordance with factors intrinsic to the fruit, and with extrinsic properties inherent to process. Most fruits maintain their color using freeze-drying. The porosity of freeze-dried fruit depends on the freezing speed. The glass transition temperature of dry solid would be an important optimization parameter for the freezing-drying process. The majority of phenolic acids and volatile compounds were conserved in freeze-drying. Freeze-drying increases the rehydration capacity of dried fruits, to a greater extent the hydrophilic groups which are responsible for interaction with water. However, dried fruits by freeze-drying can show structural collapse. The long processing time and energy costs are limiting the application of technology. The researchers recommend using combined to potentiate the benefits of freeze-drying and to lessen their limiting technologies.   Key words: Freeze-drying, fruit, dehydration.