Effect of maltose and maltose syrup on rheological characteristics at high and small deformations, water mobility and structure of osmotically dehydrated apple tissue

摘要

Osmotic dehydration (OD) with aqueous sugar solutions is a common operation used to slightly reduce water activity (a_w) to obtain high moisture fruits with characteristics close to fresh ones. Many mechanisms are involved in mass transfer of solutes inside the product with an opposite flux of water, but also complex physical and structural modifications occur that influence interactions between water and biomacromolecules, affecting mechanical behaviour of fruits. This study evaluated the effect of two humectants (maltose or maltose syrup), at two different water activity (a_w) values: 0.94 and 0.97, on the rheological behavior at large deformations (compression test) and small deformations (dynamic oscillatory shear and creep/recovery test), water mobility (spin-spin relaxation times), and micro and ultrastructure studies (light microscopy, LM, and transmission electron microscopy, TEM) of parenchymatous apple tissues The nature of the sugar (maltose or maltose syrup) used as osmotic agent and the level of dehydration (a_w 0.97 or 0.94) significantly influenced compression and viscoelastic properties of apple as well as proton relaxation and water status. A dramatic loss in tissue rigidity; an increase in deformation at rupture, creep compliances and fluidity, and a decrease in storage and loss moduli and proton transverse relaxation times were induced by osmotic treatments. Osmotic dehydration caused loss of cell turgor due to cytoplasm plasmolysis or even ruptures of membranes, and therefore collapse and tissue shrinkage and alteration of cell walls, more notable at the lowest a_w value.