Microstructure analysis on pre-treated apple slices and its effect on water release during air drying

Microstructural studies have played an important role in the comprehensive understanding of some food phenomena that occur during drying processes. The aim of this work was to study the effect of four pre-treatments (immersion in boiling water, vacuum impregnation, freezing/thawing, and uni-axial compression) on apple microstructure characterized by cell cavities size parameter and how the changes induced by these pre-treatments can affect the water loss rate during air drying. The quantitative structure analysis showed that freezing/thawing and compression pre-treatments caused more damage on the apple structure, yielding larger cell cavities in comparison to vacuum impregnation and immersion in boiling water and control. Apple slices that were frozen/thawed, compressed and immersed in boiling water displayed the higher drying rates and diffusivity coefficients than the vacuum impregnated and control samples. These results allow concluding that disruption of the cell walls can be considered as a factor that affects the drying rate. (C) 2011 Elsevier Ltd. All rights reserved.