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

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 (?? _R ^R ), creep compliances (J ₀, J ₁, and J ₂), and fluidity (1/?? ₀) and a decrease in storage (G??) and loss (G??) moduli, true rupture stress (?? _R ^R ), and proton transverse relaxation times (T _2i) were induced by osmotic treatments. ?? _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 ?? _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.