Changes in Structure, Rheology, and Water Mobility of Apple Tissue Induced by Osmotic Dehydration with Glucose or Trehalose

Abstract

The impact of osmotic dehydration to water activity (a w) at 0. 97 or 0. 94 with glucose or trehalose solutions on structure (optical and transmission electronic microscopy observations), rheological properties (small-scale dynamic oscillatory and creep/recovery measurements and large-scale compression force-deformation testing) and water mobility ( 1H-NMR spectra) of parenchymatous apple tissue was investigated. In general, the nature and the concentration of sugar employed significantly affected the material properties and the structure of apple tissue. A dramatic loss in rigidity (E d); an increase in deformation at rupture (ε R R), creep compliances (J 0, J 1, and J 2), and fluidity (1/η 0) and a decrease in storage (G′) and loss (G″) moduli, true rupture stress (σ R R), and proton transverse relaxation times (T 2i) were induced by osmotic treatments. ε R R, C 1, and T 2i parameters allowed to discriminate between the sugars used as osmotic agents while the different a w levels for each sugar resulted in changes in σ R R, W, and T 2i values. Loss of turgor due to plasmolysis or rupture of membranes and desorganization/degradation of walls allowed explaining, at least partially, the changes in material parameters.