Analysis of Chestnut Cellular Tissue during Osmotic Dehydration, Air Drying, and Rehydration Processes

Abstract

The analysis of changes in microstructure is very important in order to understand heat and mass transfer processes in biological systems and to evaluate physical properties and the quality of fresh and processed food materials. In this study, chestnut (Castanea sativa M.) samples were submitted to several processes such as osmotic dehydration by immersion in sucrose solution (60% w/w) at 25 degrees C, drying with hot air at 65 degrees C, and rehydration by contact with water at 25 degrees C. The surface cellular tissue of fresh and processed chestnut at different moisture contents was characterized by optical microscopy by means of size (surface area, perimeter, Feret's diameter) and shape (roundness, compactness, and elongation) parameters. The results indicated that during the osmotic dehydration the changes in microstructure can be considered practically negligible and during drying the size of chestnut cells decreased and shape parameters changed (decreasing roundness and compactness and increasing elongation). Finally, during rehydration the cells recovered their size by swelling rapidly (30min is enough to recover the size of the cells of fresh tissue), achieving at longer times greater sizes than those measured in the fresh chestnut; nevertheless, the shape parameters are not completely recovered (lower compactness and roundness values).