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 wateractivity (a_w) to obtain high moisture fruits with characteristics close to fresh ones. Many mechanisms areinvolved in mass transfer of solutes inside the product with an opposite flux of water, but also complexphysical and structural modifications occur that influence interactions between water andbiomacromolecules, affecting mechanical behaviour of fruits. This study evaluated the effect of twohumectants (maltose or maltose syrup), at two different water activity (a_w) values: 0.94 and 0.97, on therheological behavior at large deformations (compression test) and small deformations (dynamic oscillatoryshear and creep/recovery test), water mobility (spin-spin relaxation times), and micro and ultrastructurestudies (light microscopy, LM, and transmission electron microscopy, TEM) of parenchymatous apple tissuesThe nature of the sugar (maltose or maltose syrup) used as osmotic agent and the level of dehydration (a_w0.97 or 0.94) significantly influenced compression and viscoelastic properties of apple as well as protonrelaxation and water status. A dramatic loss in tissue rigidity; an increase in deformation at rupture, creepcompliances and fluidity, and a decrease in storage and loss moduli and proton transverse relaxation timeswere induced by osmotic treatments. Osmotic dehydration caused loss of cell turgor due to cytoplasmplasmolysis or even ruptures of membranes, and therefore collapse and tissue shrinkage and alteration of cellwalls, more notable at the lowest a_w value.