Dynamics of water in strawberry and red onion as studied by dielectric spectroscopy

Abstract

We have investigated the microscopic dynamics of strawberry and red onion by means of broadband dielectric spectroscopy. In contrast to most of the previous experiments on carbohydrate-rich biological materials, which have mainly considered the more global dynamics of the "biological matrix," we are here focusing on the microscopic dynamics of mainly the associated water. The results for both strawberry and red onion show that the imaginary part of the permittivity contains one conductivity term and a clear dielectric loss peak, which was found to be similar to the strongest relaxation process of water in carbohydrate solutions. The temperature dependence of the relaxation process was analyzed for different water content. The relaxation process slows down, and its temperature dependence becomes more non-Arrhenius, with decreasing water content. The reason for this is most likely that, on average, the water molecules interact more strongly with carbohydrates and other biological materials at low water content, and the dynamical properties of this biological matrix changes substantially with increasing temperature (from an almost rigid matrix where the water is basically unable to perform long-range diffusion due to confinement effects, to a dynamic matrix with no static confinement effects), which also changes (i.e., reduces) the activation energy of the relaxation process with increasing temperature (i.e., causes a non-Arrhenius temperature dependence). This further changes the conductivity from mainly polarization effects at low temperatures, due to hindered ionic motions, to long-range diffusivity at T>250 K . Thus, around this temperature ions in the carbohydrate solution no longer get stuck in confined cavities, since the motion of the biological matrix "opens up" the cavities and the ions are then able to perform long-range migration.

Secondary relaxations in supercooled and glassy sucrose–borate aqueous solutions

“…The b-relaxation times reported in Table 2 are in good agreement with recent data by Swenson and co-workers 26 for sucrose solutions with 25 and 30 wt % water concentrations. The temperature dependence of the b-relaxation time follows a typical Arrhenius behavior:…”

“…The aim of this study is to generate information pertaining to the dynamics of the b-relaxation in the sub-T g and supercooled regimes, and to compare the behavior of the aqueous sucrose to that of sucrose-borate solutions over the same range of water content and temperature. Our results extend the b-relaxation map obtained by Champion et al 25 and Swenson and co-workers 26,27 for highly concentrated sucrose-water mixtures to water-sucrose-borate mixtures, and help us to rationalize the role of water and borate in such systems.…”

“…15 Several authors 13,14,[16][17][18][19][20][21] have studied the dielectric relaxation of water-rich solutions (water contents higher than 30 wt %) in the high frequency range (above 1 MHz), where the contribution to the relaxation is essentially due to the hydroxylic groups of water and the saccharide. Other measurements have been performed at frequencies lower than 1 MHz 15,[22][23][24][25][26][27] in the saccharide-rich region (water contents lower than 30 wt %).…”

“…Chan et al 15 argued that the motion of water molecules is only partially responsible for the b-relaxation, while Moran et al, 24 based on NMR studies of anhydrous glucose and glucose 75 wt %, 8,24 suggested that the motion of the hydroxymethyl groups should not be used to explain the fast b-relaxation. Recent studies by Swenson and co-workers 26 the b-relaxation in these mixtures is mainly due to hydration water.…”

“…28,29 Its dielectric properties in aqueous solutions have been studied in the past in the water-rich region, 14,17,20 and more recently in the sucrose-rich region. [25][26][27] It is also known 30,31 that the addition of sodium tetraborate (borax) and other oxyanions to aqueous sucrose results in the formation of esters, thereby reducing component mobility and improving protein or cell stability in co-lyophilized oxyanion-disaccharide matrices. [32][33][34] In spite of their technological and biological significance, the dynamics of disaccharide-oxyanion mixtures have not been measured before.…”